大氣成分和大氣化學(xué)研究進展

1 大氣成分及相關(guān)特性變化的觀測研究

1.1 2016年12月紅色預(yù)警的北京冬季重污染事件中邊界層內(nèi)氣象要素對PM2.5爆發(fā)性增長的相對作用

2016年12月至2017年1月PM2.5重污染事件（HPEs）頻發(fā)，但其中PM2.5質(zhì)量濃度爆發(fā)性增長的成因仍不確定。本研究利用地面PM2.5質(zhì)量濃度以及風(fēng)、溫、濕等垂直分布的氣象要素及ECMWF再分析資料，著重分析邊界層內(nèi)氣象要素對此爆發(fā)性增長的相對作用。北京HPEs 前期以輸送為主，后期以累積為主。輸送階段 （TS） 地面高壓位于北京以南，較強偏南風(fēng)將北京南部的污染物輸送至北京促使污染形成。累積階段 （CS） 中以弱偏南風(fēng)為主，以小風(fēng)靜風(fēng)、異常逆溫和近地層水汽聚集為特征的穩(wěn)定層結(jié)觸發(fā)了PM2.5爆發(fā)性增長 （質(zhì)量濃度在幾至十幾小時內(nèi)加倍）。累積階段弱南風(fēng)抑制污染物水平擴散,有利于輸送而來的污染物累積。較高濃度的PM2.5會使更多的太陽輻射反-散射回空間，使到達地面的輻射減少，近地面溫度降低，進而引起異常逆溫。逆溫抑制垂直方向的湍流擴散，降低邊界層高度，進而使得污染物和水汽進一步累積；同時近地面冷卻會降低飽和水汽壓，使得相對濕度大幅增加。近地面水汽聚集加強了氣溶膠的吸濕性增長并加速其液相反應(yīng)和非均相化學(xué)反應(yīng)，其中未完全量化的反應(yīng)過程需要進一步研究。以上氣象要素的正反饋過程對PM2.5累積階段中的爆發(fā)性增長過程的貢獻超過80%。（張小曵）

1.2 北京春節(jié)及國慶假期期間氣溶膠光學(xué)特性觀測及其與氣象和排放條件的關(guān)系

國慶期間減少的城區(qū)車流量和春節(jié)期間燃放的煙花爆竹為研究北京地區(qū)人為因素對氣溶膠光學(xué)特性的影響提供了一個獨特的機會。將2014、2015年的國慶假期和2015年、2016年的春節(jié)假期選為研究時期，發(fā)現(xiàn)在2015年國慶期間和2015、2016年春節(jié)期間，440 nm波段的氣溶膠光學(xué)厚度呈現(xiàn)出增長的趨勢，并且分別超過了背景水平的81%、21%和36%，而2014年國慶假期間的氣溶膠光學(xué)厚度可能由于降水的原因而相對較低。440 nm波段的吸收性光學(xué)厚度與光學(xué)厚度變化較為一致，分別超過了背景水平的75%、19%和23%。春節(jié)期間的單次散射反照率較背景水平偏高，而國慶期間可能由于主城區(qū)機動車流量減少而偏低。在假期間的污染過程中，細(xì)模態(tài)和粗模態(tài)粒子的體積濃度較背景水平分別高出了0.04～0.25 μm3和0.03～0.15 μm3。潛在源區(qū)分析和濃度權(quán)重分析發(fā)現(xiàn)北京以南區(qū)域?qū)Ρ本┑貐^(qū)偏高濃度的PM2.5有著極大貢獻。這些發(fā)現(xiàn)有利于深入了解北京地區(qū)人為活動對氣溶膠光學(xué)特性的影響并且有助于區(qū)域空氣質(zhì)量的提高。（車慧正）

1.3 2014—2015年中國主要城市大氣污染特征及其與氣象條件的關(guān)系

2013年1月開始，環(huán)境監(jiān)測總站向公眾發(fā)布全國主要城市實時的6項污染物（CO、NO2、O3、PM10、PM2.5和SO2）小時濃度，該數(shù)據(jù)為研究我國大氣污染時空變化特征提供了基礎(chǔ)數(shù)據(jù)。盡管少量研究分析了我國大氣污染的時空變化特征，但多尺度氣象條件與我國大氣污染的關(guān)系及空間差異依然認(rèn)識不清。本文利用2014—2015年全國31個省會城市空氣質(zhì)量觀測數(shù)據(jù)，分析了我國大氣污染的時空變化特征以及多尺度氣象條件對大氣污染的影響。2014年，31個省會城市6項污染物（CO、NO2、O3、PM10、PM2.5和SO2）年均濃度分別是1.2、42.4、49.0、109.8、63.7和32.6 μg/m3。2015年CO、NO2、PM10、PM2.5和SO2年均濃度分別下降了5.3%、4.9%、11.4%、12.0%和21.5%，O3年均濃度上升了7.4%。首要污染物比率最高的是PM2.5，其次依次為PM10、O3、NO2、SO2和CO。氣象條件是決定污染物濃度逐日變化的首要因子，其解釋方差超過了70%。與2014年相比，2015年氣象條件更加不利，間接說明排放管控措施取得顯著成效。（何建軍）

1.4 云凝結(jié)核（CCN）數(shù)濃度的分粒徑預(yù)報及其活化特征的長期觀測

大氣氣溶膠粒子可作為云凝結(jié)核影響大氣水循環(huán)和氣候變化。為了提高對云凝結(jié)活化特征的理解并準(zhǔn)確預(yù)報其濃度，在中國長三角地區(qū)開展了長期野外觀測試驗。結(jié)果表明，云凝結(jié)核在受到污染的農(nóng)村站點比在清潔站點（如亞馬遜地區(qū)）和多塵站點（如春季的坎布爾）更容易活化，但在污染較嚴(yán)重的地區(qū)（如北京）更難以活化。使用包括最大活化率和異質(zhì)程度2個額外參數(shù)的新方法被提出以便精準(zhǔn)預(yù)報CCN的分粒徑濃度。評估了這些參數(shù)的取值范圍以及預(yù)測不確定。在內(nèi)混的假設(shè)下，使用該新方法并結(jié)合分粒徑的氣溶膠化學(xué)組分，預(yù)報的CCN與長期野外觀測具有較好的一致性。（張小曵）

1.5 中國5個大氣本底站鹵代化合物的濃度特征

2011年1月至2012年12月對中國5個本底站大氣中的3種含氯氟烴（CFCs）、3種氫氟氯碳化合物（HCFCs）、6種氫氟碳化合物（HFCs）、3種氟碳化合物（PFCs）以及六氟化硫（SF6）開展了高精度的觀測。CFC-11、CFC-12、CFC-113、HCFC-22、HCFC-141b、HCFC-142b、HFC-125、HFC-134a、HFC-143a、HFC-152a、HFC-23、HFC-32、PFC-116、PFC-218、PFC-318以及SF6在5站的平均濃度分別為（239.5±0.69）×10-12、（536.5±1.49）×10-12、（74.66±0.09）×10-12、（232.1±4.77）×10-12、（23.78±0.29）×10-12、（22.92±0.42）×10-12、（11.75±0.43）×10-12、（71.32±1.35）×10-12、（13.62±0.43）×10-12、（9.10±1.26）×10-12、（25.45±0.1）×10-12、（7.28±0.48）×10-12、（4.32±0.03）×10-12、（0.63±0.04）×10-12、（1.36±0.01）×10-12、（7.67±0.03）×10-12，這些濃度和北半球2個AGAGE本底站：愛爾蘭MHD站和美國加利福利亞THD站相近。與前期在北京上甸子的在線觀測結(jié)果對比可知大氣CFCs濃度在下降而HCFCs、HFCs、PFCs和SF6均呈上升趨勢。觀測到的CFCs、HCFCs和HFCs污染事件占總觀測數(shù)的比例呈現(xiàn)出臨安站＞上甸子站＞龍鳳山站＞香格里拉站＞瓦里關(guān)站的特征；濃度抬升值呈現(xiàn)出HCFCs（（40.7 ～ 175.4）×10-12）＞HFCs（（15.8 ～ 66.3）×10-12）＞CFCs（（15.8 ～ 33.8）×10-12）＞PFCs（（0.1～0.9）×10-12）的趨勢，其中HCFC-22的抬升范圍為36.9×10-12到138.2×10-12。經(jīng)分子量換算后，本研究的結(jié)果表明，HCFCs的排放量在上述站點的區(qū)域排放量最大，HFCs和CFCs次之，PFCs最小，這與我國逐漸以HCFCs替代CFCs的特點相吻合。此外，在我國長三角地區(qū)這些鹵代化合物的相對排放強度由強到弱依次為： HCFC-22＞HCFC-141b＞HFC-134a＞HCFC-142b，而在華北地區(qū)則為HCFC-22＞HCFC-142b＞HCFC-141b≈HFC-134a。（張根）

1.6 中國蘭州城市環(huán)境下顆粒物數(shù)濃度粒徑分布和新粒子生成事件特征

利用掃描電遷移粒徑譜儀從2014年8月14日到11月18日，在我國西北地區(qū)蘭州開展顆粒物數(shù)濃度變化特征以及新粒子生成事件特征研究工作，研究顆粒物粒徑范圍在14.6 nm 到661.2 nm之間。研究表明，研究時段顆粒物核模態(tài)、愛根模態(tài)、積聚模態(tài)和全模態(tài)平均數(shù)濃度分別為2833、12898、6210、21940/cm3。平均數(shù)濃度粒徑分布呈現(xiàn)明顯單峰模式，峰值粒徑在60 nm左右，粒子數(shù)濃度的日變化特征主要受新粒子生成事件的影響。愛根模態(tài)、積聚模態(tài)和全模態(tài)的日變化規(guī)律均表現(xiàn)出了早晚2個時段的峰值，這2個峰值與交通和餐館排放有關(guān)。由于人為活動的增強，數(shù)濃度和質(zhì)量濃度在工作日的濃度水平均高于非工作日的濃度水平，數(shù)濃度水平白天高于夜間。亞微米氣溶膠以及硫酸鹽、硝酸鹽和銨鹽的質(zhì)量濃度白天高于夜間。而有機物濃度夜間高于白天，主要是由于夜間取暖和晚高峰排放疊加所致。觀測期間，新粒子生成事件發(fā)生頻率為34%，核模態(tài)粒子生成和增長速率分別為1.71/（cm3/s）and 6.10 nm/h，典型的新粒子生成事件有2級增長，并對粒子增長和演變過程起到了至關(guān)重要的作用。后徑向軌跡分析結(jié)果顯示，來自西部的氣團顆粒物的數(shù)濃度和質(zhì)量濃度均偏高，主要受西部局地工業(yè)排放的影響，而來自北部和西北部的氣團代表著相對潔凈的空氣。（張養(yǎng)梅）

1.7 2015年秋冬季北京北部地區(qū)氣溶膠重污染事件中化學(xué)組分的特征及氣象要素的作用

重污染事件通常起于深秋，進入冬季后在北京及周邊地區(qū)更為嚴(yán)重。本文著眼于北京及周邊地區(qū)北部的重污染事件形成和變化的原因。其中主要關(guān)注2015年秋冬季重污染事件中，PM1的分粒徑化學(xué)組分及氣象條件變化。研究表明，區(qū)域氣團穩(wěn)定和與弱南風(fēng)相關(guān)的較高的大氣凝結(jié)過程導(dǎo)致了重污染事件形成。重污染事件開始后，細(xì)顆粒物濃度在數(shù)小時內(nèi)增加超過2倍。其中80%的PM爆發(fā)性增長被認(rèn)為由來源于更穩(wěn)定大氣和更高水汽凝結(jié)率的氣象因子正反饋引起，這源于形成的污染與邊界層內(nèi)氣象條件的相互作用。硝酸鹽是秋季PM1的最大組成部分，也是相對于秋冬季清潔階段的重污染過程中增長最為顯著的部分。在秋季有機氣溶膠的比例與硝酸鹽類似，但是重污染事件中上升幅度要小很多，這主要因為清潔階段有機氣溶膠濃度較高。與增長幅度最大的硝酸鹽相比，銨鹽也出現(xiàn)相似的上升，表明大量銨鹽主要與硝酸根結(jié)合生成，而不是硫酸根。除了弱偏南風(fēng)輸送北京及周邊地區(qū)南部的污染物外，偏西風(fēng)也輸送內(nèi)蒙古中部和山西北部由于燃煤引起的污染物，導(dǎo)致冬季北京及周邊地區(qū)北部的重污染形成，并引起較高濃度的硫酸鹽、硝酸鹽和有機氣溶膠（張小曵）

1.8 長三角背景地區(qū)夏季PM2.5化學(xué)組成特征

隨著城市化和工業(yè)化的進程加快，長三角地區(qū)大氣化學(xué)的研究越來越受到關(guān)注。本研究對長三角背景地區(qū)臨安大氣本底站夏季PM2.5進行連續(xù)采集，并對其進行OC、EC、左旋葡聚糖和硫酸鹽、硝酸鹽和氨鹽等水溶性離子測試分析。臨安夏季PM2.5平均濃度為30.19±8.86 μg/m3，低于以前的研究報告，說明通過逐步排放控制措施，中國的空氣污染得到了一定的改善。硫酸鹽、硝酸鹽和銨鹽之間的關(guān)系研究表明，主要以的形式存在，而則可能是以NaNO3和KNO3的形式存在?；诜肿邮聚?，天氣數(shù)據(jù)以及氣團軌跡分析，發(fā)現(xiàn)靜穩(wěn)天氣和區(qū)域傳輸都可以影響臨安地區(qū)PM2.5的化學(xué)組成特征。通過對臨安霾和清潔天氣PM2.5化學(xué)組成特征比較發(fā)現(xiàn)，二次有機氣溶膠和二次無機氣溶膠呈現(xiàn)了不同的變化特征：二次有機氣溶膠在潔凈晴朗天氣時更為重要，而二次無機氣溶膠則是在霾污染天氣更容易生成，從而變得更重要。（梁林林）

1.9 利用氣溶膠質(zhì)譜儀對我國西北城市冬季亞微米氣溶膠化學(xué)特征的研究

2014年10月27日到12月3日期間利用氣溶膠質(zhì)譜儀測量了蘭州城區(qū)亞微米氣溶膠主要化學(xué)組分質(zhì)量譜。觀測期間，冬季亞微米氣溶膠PM1平均質(zhì)量濃度為37.3 μg/m3（從2.9 變化到128.2 μg/m3），其中主要化學(xué)組分有機物（48.4%）、硫酸鹽（17.8%）、硝酸鹽（14.6%）、銨鹽（13.7%）和氯化物（5.7%）是主要成分。利用正交矩陣因子分析法（PMF）和多線性工程（ME-2）手段，解析出了6類有機氣溶膠，分別為與機動車排放有關(guān)的有機氣溶膠（HOA）、燃煤排放類有機氣溶膠（CCOA）、餐館排放類有機氣溶膠（COA）、生物質(zhì)燃燒排放類有機氣溶膠（BBOA）和2種氧化類有機氣溶膠（OOAI和OOAII）分別占有機氣溶膠的8.5%、20.2%、18.6%、12.4%、17.8%和22.5%。一次排放的有機氣溶膠在細(xì)顆粒物中占有相當(dāng)大的比重，而且在蘭州冬季重污染事件中起著非常重要的作用。后徑向軌跡分析結(jié)果表明，來自西部區(qū)域傳輸過程載帶的污染氣團是導(dǎo)致蘭州冬季亞微米氣溶膠污染的主要來源。（張養(yǎng)梅）

1.10 北京大氣顆粒物中真菌孢子對有機碳貢獻

真菌孢子是大氣氣溶膠的重要組成部分，也是氣溶膠中有機碳（organic carbon，OC） 的主要貢獻者。本研究在北京城區(qū)連續(xù)一整年每天同時采集PM10和PM2.5，并在晚春和夏季在北京郊區(qū)進行PM10樣品對比采集。研究結(jié)果發(fā)現(xiàn)，在北京市區(qū)PM2.5和PM10中，真菌孢子OC質(zhì)量濃度的年均值分別為0.3±0.2μg C/m3和0.8±0.7 μg C/m3，其對氣溶膠中OC的貢獻分別為（1.2±0.7）%和（3.5±3.7）%。在PM2.5和PM10中，真菌孢子對OC的貢獻呈現(xiàn)相似的季節(jié)變化規(guī)律，從高到低的順序為夏、秋、冬、春。在夏季北京市區(qū)和郊區(qū)的對比采樣中，發(fā)現(xiàn)北京市區(qū)和郊區(qū)真菌孢子對OC的貢獻均處于較高水平，分別達到了（7.3±3.3）%和（14.1±10.5）%，說明即使在北京城市地區(qū)，真菌也是碳質(zhì)氣溶膠中不可忽略的重要組分。因此，需要更多的研究來關(guān)注真菌氣溶膠對OC貢獻的時空變化特征和粒徑分布特征。（梁林林）

1.11 遞減的中國東部午后局地降水頻次：氣溶膠污染的可能影響

利用中國東部高密度（500余個）雨量站長時間序列（1970—2010年）的小時降水?dāng)?shù)據(jù)，針對夏季午后熱對流空間覆蓋小、與氣溶膠效應(yīng)關(guān)系密切等特點，定義了“午后局地尺度降水（LSP）”這一新概念。在此基礎(chǔ)之上，發(fā)現(xiàn)中國東部LSP事件發(fā)生頻次呈顯著下降趨勢，降水強度呈顯著增加。同期的氣溶膠污染排放也呈增加趨勢，二者的相關(guān)性分析進一步揭示了氣溶膠可能是導(dǎo)致這種局地降水事件減少、夏季午后極端降水強度增加的主因。由于本研究既在空間上給這些降水事件做了約束（局地尺度），時間上也僅限午后到傍晚，而非以往研究所采用的日降水這一統(tǒng)計尺度，因此，本成果修正了以往基于日累計降水的“氣溶膠減少毛毛雨，增強強降水”觀點。（郭建平）

1.12 氣溶膠-邊界層相互作用及其對空氣質(zhì)量影響

空氣質(zhì)量關(guān)系到氣態(tài)和液／固相的大氣污染物。后者被認(rèn)為是氣溶膠顆粒，也是通過多種機制影響空氣質(zhì)量好壞、天氣和氣候的重要介質(zhì)。與氣態(tài)污染物相比，在邊界層內(nèi)存在強烈的氣溶膠—氣象條件相互作用。作為氣溶膠排放和存在的主要場所，邊界層的發(fā)展易受氣溶膠輻射效應(yīng)影響。氣溶膠的散射和吸收可有效減少到達地面的輻射，進而減少驅(qū)動邊界層日變化的主要因子—感熱通量。此外，氣溶膠通過散射和吸收太陽輻射導(dǎo)致低層大氣出現(xiàn)逆溫層結(jié)，進而增加大氣穩(wěn)定度。這種穩(wěn)定的大氣層結(jié)將有效抑制污染物的擴散，反過來進一步促進污染物濃度的累積和升高。這種氣溶膠—邊界層之間的正反饋機制在重污染期間尤其明顯。因此，人們對邊界層過程的準(zhǔn)確理解對于深刻理解氣溶膠—氣象條件相互作用機制具有重要意義。其中，一個非常關(guān)鍵的因素是氣溶膠如何影響邊界層，尤其是垂直方向上的的日變化過程以及空氣質(zhì)量的影響。本文主要綜述了氣溶膠觀測新技術(shù)、邊界層物理化學(xué)過程及其相互作用，特別對他們之間存在的復(fù)雜反饋機制進行全面闡述，并對未來氣溶膠—邊界層相互作用這一領(lǐng)域的發(fā)展，分別從觀測和模式模擬的角度展開了全面系統(tǒng)的討論。（郭建平）

1.13 中國環(huán)境中PM2.5對健康的影響

中國大部分人都暴露在高濃度的PM2.5中，造成較高的健康風(fēng)險。利用2014—2016年全國367個城市共計1382個監(jiān)測點的PM2.5濃度觀測數(shù)據(jù)，評估了我國PM2.5的健康分擔(dān)率。利用一種暴露—響應(yīng)模式評估各種疾病和死亡率的健康風(fēng)險，根據(jù)國家死亡率基線調(diào)整各省疾病和死亡率基線。研究發(fā)現(xiàn)，2015年因PM2.5污染成腦死亡比率占腦死亡總數(shù)的40.3%，下呼吸道感染死亡比率是33.1%，缺血性心臟病死亡比率是26.8%，肺癌死亡比率是23.9%，肺慢性阻塞性疾病死亡比率是18.7%，占總死亡人數(shù)比率是15.5%?？紤]10年滯后期影響，PM2.5污染造成的死亡率要增加12%。人口權(quán)重平均PM2.5濃度滿足WHO IT-1、IT-2、IT-3和AQG標(biāo)準(zhǔn)時，PM2.5污染導(dǎo)致的死亡人口占現(xiàn)狀的24.0%、44.8%、70.8%和85.2%。（何建軍）

1.14 華北農(nóng)村饒陽站低對流層O3和氣溶膠分布

隨著數(shù)十年的經(jīng)濟快速增長，華北平原已經(jīng)成為我國最大的污染區(qū)域。在華北平原的城市和農(nóng)村站點都觀測到了高濃度O3和氣溶膠。但是大多數(shù)空氣污染物的現(xiàn)場觀測都局限于近地面，因此對O3和氣溶膠的垂直分布的了解很不充分。本項研究于2014年夏天在華北平原一個農(nóng)村站點上空利用攜帶微型設(shè)備的無人飛機開展了2.5 km以下O3和分粒徑氣溶膠數(shù)濃度的觀測，此外還借助激光雷達和系留汽艇手段分別測量了低對流層氣溶膠散射特性的垂直分布和1 km以下的O3垂直分布。根據(jù)激光雷達測量的粒子消光和無人飛機測量的氣溶膠數(shù)譜垂直梯度定出了混合層和夜間殘留層厚度，獲得了每次無人機飛行中混合層及殘留層的O3濃度和氣溶膠數(shù)濃度平均值。結(jié)果表明，大多數(shù)飛行過程中混合層頂以上的O3濃度均高于混合層內(nèi)的濃度。這種上高下低的O3垂直分布特征使殘留層成為混合層O3的重要來源，尤其是在早晨混合層頂迅速抬升的時段。與O3分布相反，氣溶膠數(shù)濃度在混合層內(nèi)通常高于殘留層，特別是在清晨時段。氣溶膠粒子基本都分布在1 μm以下，混合層和殘留層的譜分布只有微小差異。本次觀測證實華北平原農(nóng)村的低對流層已很大程度上受到當(dāng)?shù)厝藶榕欧藕统鞘械貐^(qū)輸送的影響。將本次夏季觀測的O3垂直分布與來自MOZAIC民航飛機項目在北京及周邊取得的O3垂直分布?xì)v史數(shù)據(jù)進行了比較，發(fā)現(xiàn)2004—2014年間2.5 km以下所有高度層的夏季O3濃度均增大了許多，其中最大增幅為41.6×10-9。這表明，華北平原北部地區(qū)經(jīng)歷了迅速的光化學(xué)污染加重的過程。未來應(yīng)該更多關(guān)注這種光化學(xué)污染加重態(tài)勢。（徐曉斌）

1.15 2016年12月一次華北平原重度霧霾期間氣溶膠光學(xué)與輻射特性的綜合分析

為了深入了解2016年12月15—22日華北平原重度霧霾期間的氣溶膠光學(xué)與輻射特性，通過地面觀測并結(jié)合衛(wèi)星資料、氣象觀測資料和大氣環(huán)境監(jiān)測數(shù)據(jù)，在北京、石家莊和焦作開展多源綜合分析。主要結(jié)論為，當(dāng)霧霾污染發(fā)生時，3個觀測站點的500 nm 波段氣溶膠光學(xué)厚度從0.30以下突增至1.4以上。波長指數(shù)在霧霾污染期間幾乎都大于0.80。單次散射反照率的日均值在霧霾污染較為嚴(yán)重的階段都大于0.85，個別時期甚至超過了0.97。霧霾污染期間的細(xì)、粗模態(tài)粒子體積濃度分別較無霾時期增大0.05～0.21 μm3和 0.01～0.43 μm3。北京、石家莊和焦作的吸收性氣溶膠光學(xué)厚度日均值變化分別為0.01～0.11、0.01～0.13和0.01～0.04。霧霾污染期間的吸收性波長指數(shù)在0.6～2.0的范圍內(nèi)波動。這3個站點的氣溶膠對地面輻射強迫分別為-23～-227 W/m2，-34～-199 W/m2和-29～-191 W/m2；對大氣層頂?shù)妮椛鋸娖确謩e為-4～-98 W/m2，-10～-51 W/m2和-21～-143 W/m2。衛(wèi)星資料顯示，在霧霾污染階段邊界層內(nèi)主要存在以煙塵、污染沙塵氣溶膠和污染大陸型氣溶膠所組成的混合氣溶膠。通過潛在源貢獻分析及濃度權(quán)重軌跡分析得出局地排放和上游地區(qū)輸送所造成的PM2.5濃度貢獻值分別為190 ～ 450 μg/m3和100 ～ 410 μg/m3。（車慧正）

1.16 北京城區(qū)夏季大氣氨特征及對銨鹽氣溶膠的影響

為提高對北京城區(qū)大氣氨變化特征的了解，對2009年夏季高分辨率NH3數(shù)據(jù)進行了分析。研究表明，與其他一次污染氣體不同，降雨后NH3分鐘平均濃度總體呈上升趨勢。這主要由于降雨增加了植物和土壤中微生物反應(yīng)過程從而釋放氨，導(dǎo)致大氣中NH3濃度明顯增加。NH3和NOx分鐘平均數(shù)據(jù)在8月存在弱但顯著的線性相關(guān)關(guān)系，說明夏季NH3濃度與交通流量有關(guān)。NH3濃度在早晨出現(xiàn)峰值與汽車流量早高峰相對應(yīng)也支持了這一發(fā)現(xiàn)。NH3日均濃度與PM2.5中的濃度呈現(xiàn)弱相關(guān)，說明在形成過程中NH3起到了重要的前體物作用。NH3/NHx質(zhì)量比平均值為0.76±0.13，表明夏季NHx主要受當(dāng)?shù)嘏欧旁吹挠绊?，NH3干沉降有助于NHx的沉積。夏季高溫、高濕和高氧化能力增強了大氣光化學(xué)反應(yīng)和液相過程，對SO2向轉(zhuǎn)化以及NH3向轉(zhuǎn)化有促進作用。后向軌跡分析顯示，來自華北地區(qū)的氣團輸送對北京城區(qū)大氣NH3和的濃度變化有重要的影響。（孟昭陽）

1.17 我國臨安和龍鳳山區(qū)域大氣本底站黑碳濃度變化特征以及源區(qū)識別

黑碳（BC）是大氣中細(xì)粒子成分之一，與氣候、天氣、空氣質(zhì)量以及人類健康密切相關(guān)。但是，中國本底站長時間序列大氣BC濃度的變化特征和潛在源區(qū)的研究是非常有限的。對2年中國大氣本底站臨安和龍鳳山的BC觀測數(shù)據(jù)的分析結(jié)果表明，臨安站BC濃度的日變化有2個明顯的峰值，但是龍鳳山站日變化特征與其不同，可能是由于不同排放源的貢獻差異。臨安站和龍鳳山站BC月中值濃度的季節(jié)變化分別呈雙峰和單峰分布。2站的2010年年均濃度相對于2009年分別下降1.63 g/m3和0.26 g/m3。臨安站年均背景濃度高于龍鳳山站相應(yīng)濃度的2倍以上。臨安和龍鳳山兩站的主要排放源分別是工業(yè)和民用排放。通過后向7天的傳輸計算，臨安站和龍鳳山站分別對東南到西北的帶狀區(qū)域和近似圓形區(qū)域的表面BC排放敏感。敏感區(qū)域會隨著大氣環(huán)流而變化，主要受夏季風(fēng)或者我國西北部陸地冷氣流的影響。另外，通過BC觀測數(shù)據(jù)和FLEXPART模式模擬計算的排放靈敏度進行了BC源區(qū)的統(tǒng)計分析。夏季，BC源區(qū)主要分布在臨安站的西北部和南部、龍鳳山站的西南部。低BC濃度與來自海上的氣團密切相關(guān)。冬季，BC源區(qū)集中在臨安站的西部和南部以及龍鳳山站印痕stot分布區(qū)域的東北部。西北部的冷氣流對凈化大氣中BC具有重要作用。在年尺度上，BC源區(qū)大約是臨安站西北和東南的5個省以及龍鳳山的西部。這些研究結(jié)果對于BC減排和空氣污染控制具有重要作用。（程巳陽）

1.18 霧霾期間中國東北城市群顆粒物質(zhì)量濃度與能見度及混合層厚度的相關(guān)性

分析了2009—2012年我國東北遼寧中部主要工業(yè)城市沈陽、鞍山、本溪、撫順地區(qū)大氣能見度、顆粒物質(zhì)量濃度和混合層高度（MLH）之間的相關(guān)性及其對該地區(qū)大氣污染的潛在影響。結(jié)果表明，沈陽、鞍山、本溪和撫順地區(qū)的年平均能見度分別為13.7±7.8、13.5±6.5、12.8±6.1、11.5±6.8 km。污染物負(fù)荷量 （PM× MLH） 指出鞍山地區(qū)污染物的垂直擴散較弱，近地面污染物質(zhì)量濃度較高。較高質(zhì)量濃度的氣溶膠細(xì)顆粒物部分來源于9月開始的我國東北區(qū)域遼寧及周邊地區(qū)的生物質(zhì)燃燒排放，以及在混合層高度較低條件下，冬季采暖的燃煤排放。非霧霾天氣條件下，水平能見度大約是霧霾天氣條件下能見度的2.5～3.0倍。在霧霾期間，PM2.5和PM1細(xì)顆粒物質(zhì)量濃度分別約是非霧霾期間的1.8～1.9和1.5倍。與霾污染相比，在霧發(fā)生期間混合層厚度降低的更快。本研究結(jié)果有助于更好地認(rèn)識我國東北地區(qū)遼寧中部城市群污染物垂直擴散對該地區(qū)空氣質(zhì)量的影響。（車慧正）

1.19 中國地區(qū)大氣含水量變化趨勢及其與氣溶膠變化的潛在聯(lián)系

利用探空數(shù)據(jù)、地面氣象站數(shù)據(jù)和多源衛(wèi)星數(shù)據(jù)分析了1979—2015年中國地區(qū)大氣含水量（PWV）和地表溫度年和季節(jié)長期演變趨勢及大氣含水量與地表溫度、氣溶膠變化之間的潛在聯(lián)系。結(jié)果表明，1979—1999年期間，中國地區(qū)大氣含水量呈現(xiàn)明顯上升趨勢；相反，2000—2015年期間，呈現(xiàn)明顯的下降趨勢。3種類型站點在不同時間段內(nèi)（1979—1999年和2000—2015年）大氣含水量多年平均變化率均表現(xiàn)為，主要城市站點＞省會城市站點＞郊區(qū)站點，分別反映出受到不同強度人為活動的影響。2005—2015年期間，中國大部分地區(qū)吸收性氣溶膠光學(xué)厚度（AAOD）呈現(xiàn)明顯的增長趨勢。運用空間相關(guān)系數(shù)分析方法發(fā)現(xiàn)，中國大部分地區(qū)MODIS大氣含水量與地表溫度之間存在著高的相關(guān)性，年平均相關(guān)系數(shù)達到了0.596。此外，MODIS大氣含水量與AAOD空間相關(guān)系數(shù)呈明顯的負(fù)相關(guān)，在中國中東部和中國西北地區(qū)相關(guān)系數(shù)達到最大，分別為-0.76和-0.71，表明2000年以后AAOD的增加可能是造成中國大部分區(qū)域PWV減少的原因之一。（車慧正）

1.20 不同季節(jié)氣象條件對北京城區(qū)高黑碳濃度變化的影響

利用2013—2015年北京城區(qū)黑碳?xì)馊苣z（BC）和PM2.5觀測資料，結(jié)合地面氣象觀測資料、ECMWF邊界層高度再分析資料和FNL/NCEP不同高度風(fēng)速再分析資料，討論了BC質(zhì)量濃度及其在PM2.5質(zhì)量濃度中所占比例（下文統(tǒng)稱“黑碳占比”）的季節(jié)、月、日變化特征，并通過計算北京城區(qū)BC濃度與不同高度風(fēng)速的相關(guān)矢量，分析了氣象條件和外來輸送對北京城區(qū)BC濃度變化的影響。結(jié)果發(fā)現(xiàn)，研究時段內(nèi)北京城區(qū)BC濃度平均值為4.77±4.49 ug/m3；黑碳占比為（8.23±5.47）%。BC濃度和黑碳占比在春、夏季低，秋、冬季高，其日變化特征在4個季節(jié)均為“白天低夜間高”的單峰型特征。隨著PM2.5濃度的升高，BC濃度增大，黑碳占比減小。當(dāng)北京地區(qū)風(fēng)向為東北、東北偏東、東南和西南偏西（主風(fēng)向）時，BC濃度與風(fēng)速和邊界層高度均呈反向變化，即隨風(fēng)速和邊界層高度的增大而減小。另外，不同季節(jié)BC濃度隨風(fēng)速變化的臨界值及其變化速率不同。冬季高BC濃度時段，北京城區(qū)BC濃度在低層大氣的關(guān)鍵影響區(qū)分別位于河北南部與山東交界地區(qū)以及河北西北部與山西內(nèi)蒙交界地區(qū)；高空關(guān)鍵影響區(qū)主要位于北京以西的河北西部、山西北部和內(nèi)蒙古地區(qū)。（程興宏）

1.21 秋冬季節(jié)華北背景地區(qū)PM1污染特征及來源解析

利用高分辨率飛行時間氣溶膠質(zhì)譜儀（HR-ToF-AMS）在華北背景地區(qū)上甸子區(qū)域大氣本底站開展亞微米氣溶膠（NR-PM1）化學(xué)組分及粒徑分布的連續(xù)觀測試驗，觀測時段為2015年10月17日至2016年1月27日，涵蓋了秋、冬2季。結(jié)果表明，整個觀測期間NR-PM1平均質(zhì)量濃度為25.2 μg/m3，PM1中有機物占絕對優(yōu)勢，硝酸鹽占的比例高于硫酸鹽。各化學(xué)組分平均粒徑分布以積聚模態(tài)為主，其中有機物峰形最寬，峰值粒徑最小，硝酸鹽峰值粒徑最大，表明有機物在顆粒物形成、增長初期及老化階段均有貢獻，硝酸鹽在氣溶膠粒子老化過程中更易于增長為大粒子。有機物種元素特性分析結(jié)果顯示，秋、冬季有機氣溶膠平均氧碳比（O/C）和氫碳比（H/C）為0.58和1.58，OM/OC達1.91，有機氣溶膠的氧化程度高于城市站點平均水平。在華北地區(qū)污染環(huán)境下，有機氣溶膠演變途徑Van krevelen 擬合曲線斜率為-0.21，其老化潛質(zhì)和速率較珠三角地區(qū)和歐美地區(qū)城市要慢。對比污染時段和清潔時段化學(xué)組成特征發(fā)現(xiàn)，在污染時段硝酸鹽質(zhì)量濃度及其對PM1的貢獻率超過硫酸鹽，有機物氧化程度明顯高于清潔時段。后徑向軌跡氣團分析結(jié)果顯示，污染時段氣團來向較為復(fù)雜，來自西部、南部以及東北部氣團均有貢獻，清潔時段主要受來自西伯利亞潔凈空氣的影響，對站點污染物擴散作用明顯。（張養(yǎng)梅）

1.22 雄安新區(qū)大氣污染的氣象特征分析

通過分析雄安新區(qū)2016年5月24日至2017年4月30日的空氣質(zhì)量數(shù)據(jù)和氣象數(shù)據(jù)，對該地區(qū)的大氣污染現(xiàn)狀進行了研究，并揭示其與氣象條件的關(guān)系，旨在為雄安新區(qū)的合理規(guī)劃提供科學(xué)依據(jù)。研究發(fā)現(xiàn)，雄安新區(qū)的主要大氣污染物為PM2.5和PM10，其重污染過程主要出現(xiàn)在秋、冬2季，污染程度與相對濕度呈正相關(guān)，與風(fēng)速和溫度呈負(fù)相關(guān)。盡管雄安新區(qū)目前的開發(fā)程度較低，但受本地排放和周邊污染物輸送的共同影響，大氣污染問題不容忽視。在雄安新區(qū)的規(guī)劃和建設(shè)過程中，需要考慮周邊地區(qū)的協(xié)調(diào)發(fā)展,共同治理大氣環(huán)境。（繆育聰）

1.23 表面羥基對NO2在TiO2上吸附反應(yīng)的影響

羥基（OH）在氧化物表面反應(yīng)過程中具有重要作用。本研究結(jié)合實驗室原位紅外光譜研究與密度泛函理論計算模擬，研究了室溫、模擬空氣氣氛下NO2氣體在不同晶型TiO2樣品表面的反應(yīng)特性。研究發(fā)現(xiàn)，NO2表面反應(yīng)通道與TiO2表面羥基（OH）的種類密切相關(guān)。OH的存在將導(dǎo)致表面HNO3的生成，HNO3即可作為最終產(chǎn)物在無定形TiO2表面存在，又可作為銳鈦礦TiO2上硝酸鹽生成的中間體。已有研究中廣泛認(rèn)為亞硝酸是硝酸鹽生成的重要中間體，本研究工作進一步提出了在具有豐富OH的表面上，HNO3也可能是硝酸鹽生成的重要中間產(chǎn)物。（劉暢）

1.24 運用地基GPS遙感觀測對比評估中國地區(qū)多源大氣含水量產(chǎn)品

水汽是大氣中最重要的溫室氣體之一，也是影響全球水循環(huán)、氣溶膠微物理特性、氣溶膠-云相互作用、氣候變化和地氣系統(tǒng)能量的一個關(guān)鍵因子。本文首先基于MODIS水汽產(chǎn)品分析了中國地區(qū)大氣含水量的時刻分布特征，然后基于2011—2013年中國地區(qū)6個典型城市站點GPS、探空、MODIS和AERONET太陽光度計反演大氣含水量數(shù)據(jù)，評估了4種產(chǎn)品的數(shù)據(jù)質(zhì)量和精度。時空分布分析表明，中國地區(qū)大氣含水量分布具有明顯的地理差異，基本呈現(xiàn)由東南沿海向西北內(nèi)陸逐漸遞減的分布特征。受夏季風(fēng)的影響，中國區(qū)域PWV分布具有明顯的季節(jié)性差異，其中在夏季最多，在秋季和春季次之，而在冬季最小。評估結(jié)果表明：GPS與探空水汽含量之間的相關(guān)系數(shù)在白天（R2=0.98）比晚上 （R2=0.97）更高，白天平均的偏差（Bias）、標(biāo)準(zhǔn)差（STD）和均方根誤差（RMSE）分別為 -0.03、2.36和2.60 mm，而晚上三者分別為 -0.23、2.76和2.95 mm，說明GPS水汽較探空水汽輕微偏低，晚上更為明顯。MODIS水汽含量與GPS和探空水汽含量呈現(xiàn)了同樣的相關(guān)性（R2=0.88）。此外，MODIS近紅外水汽含量較GPS和探空水汽含量均偏高，MODIS近紅外水汽含量與GPS水汽含量之間的偏差（Bias=1.50 mm，RMSE=5.76 mm）比MODIS近紅外水汽含量與探空水汽含量之間的偏差更大（Bias=0.75 mm，RMSE=5.31 mm）。AERONET水汽含量與GPS、探空和MODIS水汽含量之間均呈現(xiàn)了高相關(guān)性，三者相關(guān)系數(shù)（R2）分別為0.970、0.963和0.923，RMSE分別為2.53、3.67和4.39 mm。在北京地區(qū)，AERONET水汽含量與探空、GPS和MODIS水汽含量之間的Bias分別為-0.09、-1.82和-1.54 mm，表明AERONET水汽含量在北京地區(qū)都較其他3種PWV產(chǎn)品偏低。（車慧正）

1.25 日變化及氣象條件對PM2.5與大氣光學(xué)厚度相關(guān)性的影響以及對PM2.5衛(wèi)星遙感的影響

當(dāng)前從衛(wèi)星觀測得到的大氣光學(xué)厚度（AOD）數(shù)據(jù)，通過建立數(shù)學(xué)模型的方式來反演地面PM2.5濃度仍是一個巨大挑戰(zhàn)。本文根據(jù)中國氣象局大氣觀測站網(wǎng)已有的226個大氣成分站2013年1月至2015年12月逐小時的PM2.5觀測數(shù)據(jù)，結(jié)合10 km×10 km分辨率的MODIS/Aqua AOD產(chǎn)品，首先研究了中國地區(qū)的PM2.5濃度的日變化情況。結(jié)果顯示，大約50%站點PM2.5濃度峰值出現(xiàn)在上午，PM2.5濃度峰值出現(xiàn)在下午的概率僅為5%，這可能與下午地表接收到更強的太陽輻射能量以及下午更加劇烈的大氣湍流和對流活動有關(guān)。華北平原PM2.5峰值一般出現(xiàn)在凌晨時分，其濃度是珠三角地區(qū)的2～3倍；長三角地區(qū)PM2.5濃度峰值介于華北平原和珠三角地區(qū)之間。為了研究PM2.5日變化對二者相關(guān)性的可能影響，采用衛(wèi)星過境時刻前后1、3、5、24 h的 PM2.5平均值，分別與MODIS AOD進行匹配。統(tǒng)計結(jié)果顯示，氣溶膠日變化對PM2.5和AOD的相關(guān)性具有顯著影響。其次，不同區(qū)域和季節(jié)，PM2.5與AOD的相關(guān)系數(shù)存在顯著差異。本文還研究了云和相對濕度對二者相關(guān)性的影響，結(jié)果表明高云量和高濕環(huán)境易使華北平原、長三角和珠三角地區(qū)PM2.5和MODIS/Aqua AOD之間的相關(guān)系數(shù)降低，可見在利用MODIS AOD反演地面PM2.5濃度過程中，氣象條件在PM2.5衛(wèi)星遙感反演過程中起到了重要作用。（郭建平）

2 大氣成分模式的發(fā)展應(yīng)用及大氣成分的影響

2.1 我國瓦里關(guān)站大氣CO2：氣團傳輸特征、時間變化以及源匯區(qū)域代表性

為了探究影響瓦里關(guān)站CO2本底濃度的源匯區(qū)域，提出了一種統(tǒng)計計算方法。該方法的關(guān)鍵是找到最優(yōu)印痕閾值。研究過程分成4個步驟：（1）氣團傳輸特征通過FLEXPART模式模擬計算在后向7天時間尺度下瓦里關(guān)站的月總印痕表示。結(jié)果顯示，歐亞大陸地區(qū)的CO2排放頻繁傳輸?shù)酵呃镪P(guān)站，瓦里關(guān)站主要受到冬季西風(fēng)帶影響，也受到東南亞夏季風(fēng)的控制。（2）利用CT2015模式模擬的CO2濃度，經(jīng)過嚴(yán)格的數(shù)據(jù)質(zhì)量控制、篩分?jǐn)M合處理并與觀測濃度進行了比較。瓦里關(guān)全球大氣本底站CO2濃度有明顯的季節(jié)變化，最大最小值分別出現(xiàn)在4月和8月。觀測和模擬之間的擬合本底濃度相關(guān)性為R2=0.91。瓦里關(guān)站CO2時間序列變化特征主要與生物圈和大氣的碳交換、人類活動以及氣團傳輸有關(guān)。（3）對于CT2015的月均CO2擬合本底濃度，結(jié)合潛在源區(qū)（印痕）分布和CO2排放數(shù)據(jù)，通過相關(guān)性分析和數(shù)值迭代方法確定最優(yōu)印痕閾值。印痕值大于該最優(yōu)閾值的網(wǎng)格單元就是最優(yōu)閾值區(qū)域，即影響本底濃度的源匯區(qū)域。4月CO2濃度最大值代表的源匯區(qū)域主要位于青海省，但是8月CO2濃度最小值受到更大范圍區(qū)域排放的影響。（4）統(tǒng)計分析了最優(yōu)閾值區(qū)域內(nèi)CO2源匯特征。由于較少的人類活動以及高海拔地區(qū)植被、氣候影響，影響瓦里關(guān)站CO2本底濃度的源匯區(qū)域表現(xiàn)為碳匯，并且各源匯強度均相對較弱。夏季瓦里關(guān)站CO2濃度更多受到人類活動影響，因為此時傳輸?shù)綔y站的氣團經(jīng)過許多城市區(qū)。因此，利用印痕和排放數(shù)據(jù)能夠評價CO2本底濃度源匯區(qū)域代表性。（程巳陽）

2.2 北京夏季“污染型”大氣環(huán)流的識別和邊界層結(jié)構(gòu)

近幾十年以來，北京地區(qū)經(jīng)濟和城市化的迅速發(fā)展，帶來嚴(yán)重的資源環(huán)境問題，尤其是空氣污染問題。目前，北京是我國北方大氣污染最為嚴(yán)重的城市之一，其污染的發(fā)生不僅與污染物的大量排放有關(guān)，還與不利的氣象條件有關(guān)。為了厘清北京地區(qū)與污染有關(guān)的大尺度環(huán)流特征和局地邊界層結(jié)構(gòu)，本文利用再分析資料、夏季午后的探空觀測、近地面氣溶膠濃度觀測和數(shù)值模式進行了較為系統(tǒng)的分析和研究。通過主成分分析，發(fā)現(xiàn)北京地區(qū)夏季“污染型”的大氣環(huán)流（925 hPa氣壓場）主要有3種：（1）在渤海和黃海上存在較強的高壓系統(tǒng)；（2）河北北部和內(nèi)蒙地區(qū)受低壓系統(tǒng)控制，且黃海上有弱高壓；（3）華北平原受東南至西北方向的氣壓梯度的影響。在上述大氣環(huán)流的作用下，北京地區(qū)邊界層的結(jié)構(gòu)會受到高低空冷暖平流、云量以及邊界層內(nèi)的氣溶膠顆粒物的影響。（繆育聰）

2.3 東亞夏季風(fēng)對散射和吸收性氣溶膠強迫的快響應(yīng)和慢響應(yīng)

利用地球系統(tǒng)模式CESM1研究了東亞夏季風(fēng)系統(tǒng)對散射性（硫酸鹽）和吸收性（黑碳）氣溶膠強迫的總響應(yīng)中快響應(yīng)和慢響應(yīng)的作用。結(jié)果表明，東亞夏季風(fēng)對氣溶膠強迫的快響應(yīng)和慢響應(yīng)的機制明顯不同。氣溶膠引起的海表溫度變化造成的慢響應(yīng)在驅(qū)動季風(fēng)變化中起到了關(guān)鍵作用。硫酸鹽強迫的快響應(yīng)主要通過減弱海陸表面熱力對比減弱東亞夏季風(fēng)；而慢響應(yīng)則通過改變對流層熱力和動力結(jié)構(gòu)更強地減弱了東亞夏季風(fēng)。最終，硫酸鹽強迫的總響應(yīng)造成東亞夏季風(fēng)環(huán)流明顯減弱，降水減少。黑碳強迫的快響應(yīng)導(dǎo)致東亞夏季海陸表面熱力性質(zhì)對比增加和東亞副熱帶急流北移，表現(xiàn)為增強東亞夏季風(fēng)。但是，黑碳強迫的慢響應(yīng)通過對大氣溫度和環(huán)流的影響減弱了東亞夏季風(fēng)。最終，黑碳強迫的總響應(yīng)造成東亞夏季風(fēng)略微增強，特別是30°N以北區(qū)域。黑碳強迫的總響應(yīng)和慢響應(yīng)造成東亞夏季降水變化的分布方式基本一致。該研究強調(diào)了海洋對氣溶膠強迫的反饋在氣溶膠強迫驅(qū)動?xùn)|亞夏季風(fēng)變化中的重要性。（王志立）

2.4 東亞夏季風(fēng)對不同類型人為氣溶膠強迫的平衡態(tài)響應(yīng)

利用一個耦合了混合層海洋模式的氣溶膠-氣候在線耦合模式BCC_AGCM2.0.1_CUACE/Aero研究了東亞夏季風(fēng)系統(tǒng)對1850—2000年不同類型人為氣溶膠（硫酸鹽、黑碳和有機碳）排放增加的平衡態(tài)響應(yīng)。結(jié)果表明，不同類型人為氣溶膠通過改變局地海陸表面熱力對比和大氣環(huán)流對東亞夏季風(fēng)產(chǎn)生顯著不同的影響。硫酸鹽氣溶膠排放增加造成海陸之間表面溫壓差減小和東亞副熱帶急流南移，中國東部及其周圍海域出現(xiàn)明顯的北風(fēng)距平，明顯減弱了東亞夏季風(fēng)。然而，有機碳?xì)馊苣z增加造成30°N以北的洋面上明顯降溫，形成一個高壓距平中心，導(dǎo)致海陸之間表面熱力性質(zhì)差異略有增加，且高壓西部出現(xiàn)明顯的南風(fēng)距平，從而增強了東亞北部夏季風(fēng)；而中國南部海陸之間表面熱力性質(zhì)差異減小并出現(xiàn)北風(fēng)距平，從而東亞南部夏季風(fēng)減弱。黑碳?xì)馊苣z增加對東亞夏季850 hPa風(fēng)場和降水影響的分布和有機碳?xì)馊苣z的影響大體一致。黑碳?xì)馊苣z增加造成35°N以北東亞夏季風(fēng)增強，而在35°N以南區(qū)域東亞夏季風(fēng)略有減弱。同時還發(fā)現(xiàn)，顯著增加黑碳?xì)馊苣z的排放并不改變模擬的東亞夏季風(fēng)對黑碳?xì)馊苣z的響應(yīng)，僅增強了其對季風(fēng)影響信號的強度?？傮w來說，硫酸鹽氣溶膠的增加對東亞夏季風(fēng)系統(tǒng)的減弱起了主要作用，而有機碳和黑碳?xì)馊苣z的增加在一定程度上減緩了東亞北部夏季風(fēng)的減弱程度。（王志立）

2.5 全球、東亞和非東亞人為氣溶膠排放變化對東亞夏季風(fēng)系統(tǒng)的影響

利用一個氣溶膠—氣候在線模式BCC_AGCM2.0.1_CUACE/Aero定量研究了全球、東亞和非東亞人為氣溶膠排放變化對東亞夏季風(fēng)系統(tǒng)的影響。結(jié)果顯示，1850—2000年人為氣溶膠排放增加造成東亞季風(fēng)區(qū)夏季大氣頂和地表全天平均凈短波輻射通量分別減少了4.8 W/m2和5.0 W/m2。輻射通量的變化及其引起的熱傳輸、水汽傳輸、云量等的變化共同造成了東亞季風(fēng)區(qū)夏季地表冷卻?？偟娜藶闅馊苣z排放增加造成東亞季風(fēng)區(qū)夏季平均地表氣溫降低了2.1 K，表面氣壓升高了0.4 hPa，其中東亞之外的氣溶膠排放變化對二者變化的貢獻更大。陸地上表面氣溫和氣壓的變化明顯高于海洋上，從而減弱了海陸溫壓差對比，造成夏季中國東部、南部以及周圍海域出現(xiàn)明顯的北風(fēng)和東北風(fēng)距平，進而減弱了東亞夏季風(fēng)，造成東亞季風(fēng)區(qū)夏季平均降水減少12%。東亞外氣溶膠排放變化在造成東亞局地氣溫和氣壓變化中起了更為重要的作用，因此明顯加劇了局地氣溶膠變化對東亞夏季風(fēng)的減弱。二者對季風(fēng)環(huán)流減弱的貢獻程度相當(dāng)，個別區(qū)域貢獻甚至更大。局地和非局地氣溶膠變化對洋面上降水減少的貢獻相當(dāng)，但卻造成了中國東部降水相反的變化。本文的結(jié)果強調(diào)了非局地氣溶膠變化在人為氣溶膠變化對東亞季風(fēng)系統(tǒng)影響中的重要性。（王志立）

2.6 陸面資料不確定性對近地面氣溫和降水模擬的影響

本文利用WRF模式降尺度模擬2006年中國區(qū)域高分辨率（10 km）氣象場，近地面氣溫和降水站點觀測資料評估WRF模擬結(jié)果。將高分辨率的陸面資料（包括SRTM地形資料、MODIS土地利用和覆被資料、HWSD土壤類型資料）應(yīng)用到WRF模式中，并通過敏感性試驗?zāi)M研究了高分辨率陸面資料對模擬結(jié)果的影響。WRF模式較好地模擬了近地面氣溫和降水的時空變化特征，模擬性能存在顯著的區(qū)域和季節(jié)差異。在云貴高原、青藏高原、東北、東南沿海地區(qū)，WRF模式模擬近地面氣溫偏低；在華北、黃土高原、四川盆地、新疆西部等地區(qū)，WRF模式模擬近地面氣溫偏高。在大部分濕潤地區(qū)，WRF模式模擬降水偏多，在大部分干旱區(qū)，WRF模擬降水偏少。從季節(jié)來看，夏季W(wǎng)RF模式模擬降水偏多，冬季模擬降水偏少。采用高分辨率的陸面資料后，WRF模擬氣溫和降水的均值和極值都有所改進，日均氣溫和日累積降水的RMSE分別減小了7%和2.3%。從統(tǒng)計上來看，氣溫模擬改進效果顯著，但降水模擬改進效果不顯著。陸面信息不確定對氣溫的影響比降水的影響顯著。這些發(fā)現(xiàn)對天氣預(yù)報以及東亞氣候變化研究具有重要的意義。（何建軍）

2.7 北京顆粒物污染區(qū)域輸送數(shù)值模擬研究

區(qū)域大氣污染頻繁發(fā)生，給大氣污染防治工作帶來嚴(yán)峻挑戰(zhàn)。利用空氣質(zhì)量數(shù)值模式CUACE和大氣擴散模式FLEXPART，本文研究了北京不同季節(jié)顆粒物的區(qū)域輸送、潛在源區(qū)以及輸送路徑。通過排放源敏感性試驗得出2013年夏季（7月）和冬季（12月）北京近地面PM2.5區(qū)域輸送比率分別為53.4%和36.1%，PM10區(qū)域輸送比率分別為51.8%和 35.1%。夏季北京顆粒物區(qū)域輸送較冬季更顯著，氣象條件季節(jié)差異和排放空間分布特征是造成區(qū)域輸送季節(jié)差異兩大主要因子。敏感性試驗結(jié)果還顯示二次氣溶膠受區(qū)域輸送影響更顯著。北京區(qū)域輸送的顆粒物主要來源于河北和天津。基于后向軌跡分析，北京夏季氣團來源方向非常復(fù)雜，冬季氣團來源主要是西北方向。大氣污染水平、污染物區(qū)域輸送比率與輸送路徑和輸送距離緊密相關(guān)。（何建軍）

2.8 多尺度環(huán)流“接力輸送”對京津冀地區(qū)氣溶膠污染的影響

本研究結(jié)合風(fēng)廓線雷達資料、MODIS數(shù)據(jù)、WRF-Chem模式，以及近地面氣象和氣溶膠觀測，對京津冀地區(qū)2013年6月的一次氣溶膠污染過程進行了研究。結(jié)果發(fā)現(xiàn)，當(dāng)黃海上存在較強的高壓系統(tǒng)時，江蘇和山東等地的污染物會被輸送到渤海地區(qū)；隨后，隨著渤海地區(qū)海風(fēng)的發(fā)生和發(fā)展，海上的大氣污染物會被輸送到北京地區(qū)，造成空氣質(zhì)量的惡化。此外，本研究首次利用逐小時的近地面氣象觀測資料，證實了渤海地區(qū)的海風(fēng)可以影響到北京地區(qū)。（繆育聰）

2.9 1.5 ℃和2 ℃全球變暖下極端氣候變化的情景依賴性

2015年《巴黎協(xié)定》的目標(biāo)是較工業(yè)化前水平把全球平均表面氣溫升高控制在2 ℃之內(nèi)，并努力把升溫控制在1.5 ℃之內(nèi)。決策者們需要關(guān)于這些變暖水平造成的影響的可靠信息來制定氣候減緩和可適性政策。本文利用3組全球氣候模式的集合模擬試驗研究了1.5 ～2 ℃全球變暖下氣候極端（往往與經(jīng)濟損失和人員傷亡緊密聯(lián)系）的變化以及其情景依賴性。結(jié)果顯示，額外的0.5 ℃增暖（1.5～2 ℃）導(dǎo)致大部分區(qū)域極端溫度和極端降水的顯著增加。但是，預(yù)估的這些變暖水平下氣候極端的變化強烈地依賴排放情景的路徑，即情景中有不同的溫室氣體和氣溶膠強迫比值或者溫室氣體濃度水平。在一些重污染區(qū)域，不同的情景造成的額外的0.5 ℃（1.5 ～2 ℃）增暖導(dǎo)致的極端降水變化的差異可高達幾倍。本研究結(jié)果闡明當(dāng)評估1.5 ～2 ℃全球變暖的影響時，不僅僅需考慮總的輻射強迫及其導(dǎo)致的變暖水平，也必須考慮排放情景中的化學(xué)組成。（王志立）

2.10 2013年1月重霾污染過程中國地區(qū)氣溶膠短期輻射影響及其地區(qū)差異

采用WRF-CMAQ-SES2離線耦合模式系統(tǒng)模擬了2013年1月重霾污染過程中國地區(qū)氣溶膠對地面輻射的短期影響效應(yīng)及其地區(qū)差異。首先采用WRF-CMAQ模式模擬了全國PM10和PM2.5濃度，并采用自適應(yīng)偏最小二乘回歸法和153個環(huán)境監(jiān)測站的實測濃度對PM10和PM2.5模擬濃度以及氣溶膠各主要組分的垂直廓線進行了訂正；然后設(shè)計2種模擬試驗方案，采用澳大利亞氣象局輻射傳輸模式SES2以及訂正后的氣溶膠濃度垂直廓線、WRF模擬的云和水汽等氣象要素垂直分布，分別模擬了2013年1月考慮和未考慮氣溶膠影響的地面總輻射和直接輻射通量；最后采用全國78個輻射觀測站資料評估了上述模擬結(jié)果，并分析了氣溶膠對總輻射和直接輻射的短期影響效應(yīng)及其地區(qū)差異。結(jié)果表明：（1）經(jīng)過地面實測PM10和PM2.5濃度訂正后，氣溶膠模擬濃度較接近于實測值，顯著減小了氣溶膠模擬的不確定性；（2）采用上述不確定性較小的氣溶膠垂直廓線資料模擬的總輻射和直接輻射更接近于實測輻射值；（3）2013年1月重污染過程氣溶膠對總輻射的削減值介于100～500 W/m，其短期影響可達氣溶膠長期氣候效應(yīng)的2個量級；（4）由于氣溶膠化學(xué)組成及其垂直分布特征的地區(qū)差異導(dǎo)致氣溶膠的短期輻射影響程度自北向南呈減小趨勢，其中霾污染較重的京津冀地區(qū)氣溶膠對輻射的影響最大，長三角地區(qū)次之，珠三角地區(qū)削減較?。唬?）在地面相同的PM10和PM2.5濃度下，氣溶膠對總輻射的影響亦存在顯著的南北差異，其主要原因是不同地區(qū)高空氣溶膠濃度的垂直分布差異較大。（程興宏）

2.11 春季東亞沙塵氣溶膠跨太平洋輸送：觀測與中尺度模式模擬研究

借助星地同步觀測，系統(tǒng)揭示了發(fā)生于2015年3月12—22日的一次典型的起源于中國西北地區(qū)塔克拉瑪干沙漠和隔壁的沙塵跨太平洋輸送事件。CALIPSO衛(wèi)星結(jié)果顯示，在沙塵源區(qū)，沙塵分布的高度在1～7 km，其在向東傳輸過程中，經(jīng)過中國華北平原和東北地區(qū)沙塵氣溶膠發(fā)生了一系列混合，老化等過程，變成污染性沙塵氣溶膠。受太平洋上空（其氣溶膠分布高度范圍介于2～9 km）的阿留申低壓系統(tǒng)影響，此污染沙塵帶分叉為2支，一支往北到達阿拉斯加地區(qū)，另一支繼續(xù)往東到達加拿大西海岸。中尺度模式WRF模擬的云水含量結(jié)果表明，（污染）沙塵氣溶膠傳輸過程易受云雨的濕沉降過程影響。本研究從觀測和模式的角度，從沙塵源區(qū)的大氣廓線觀測、沙塵氣溶膠立體分布及其傳輸過程中的云降水濕沉降影響等方面，系統(tǒng)闡述了氣溶膠遠(yuǎn)距離輸送的物理機制。（郭建平）

2.12 基于CMAQ源同化反演方法的京津冀局地污染源動態(tài)變化特征模擬研究

利用“Nudging”源同化技術(shù)反演了京津冀地區(qū)2014年1、3、7、11月SO2、NOx的局地動態(tài)污染源，分析其排放源強、特征及地理分布，對比其與初始源的差異，同時檢驗反演源的模擬效果。結(jié)果表明，SO2、NOx污染源存在明顯的季節(jié)變化，冬季或采暖期排放強度最大。由唐山、北京、天津、廊坊、保定、石家莊、邢臺、邯鄲構(gòu)成東北-西南走向的帶狀污染物高排放區(qū)，最高排放中心主要集中在太行山、燕山山前區(qū)域，且排放具有典型的“城市化”特征，即各個城市市區(qū)及附近強度最大，周邊郊縣稍弱。與初始源模擬結(jié)果相比，采用反演源更能反映出污染物的時空變化特征，模擬值與實測值較接近，而且對于重污染過程亦具有較好的模擬效果。（程興宏）

Progress in Atmospheric Composition and Atmospheric Chemistry Research

1 Observational studies of atmospheric composition and related properties

1.1 Relative contributions of boundary-layer meteorological factors to the explosive growth of PM2.5 during the red-alert aerosol heavy pollution episode in Beijing in December 2016

Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm (PM2.5)in diameter, ground meteorological data, vertical measurements of meteorological factors, including winds,temperature and relative humidity (RH), and the ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer (BL) during the heavy aerosol pollution episodes(HPEs) that occurred in winter 2016 in the urban Beijing area were analyzed.Beijing HPEs can generally be divided into two stages: the transport stage (TS) under prevailing southerly winds and the period of PM2.5explosion growth and pollution accumulation characterized by temperature inversion with lower winds and higher RH in the lower BL, known as the cumulative stage (CS).During the TS, a surface high lies south of Beijing, and pollutants transported from the south of Beijing are a particularly striking feature.Subsequently,a stable BL characterized by weak winds, temperature inversion and moisture congregation occurs, which corresponds to the CS.Stable atmospheric stratification, which is characterized by light or calm winds,anomalous inversion, and accumulated moisture (RH > 80%) below 250 meters at the beginning of the CS,might be closely associated with the inversion, strengthened by the considerable decrease in near-surface air temperature attributable to the interaction between aerosols and radiation after aerosol pollution occurs.This association is suggested by a significant increase in the PLAM index after pollution formation, which primarily reflects the stability of the air mass and the condensation rate of water vapor on aerosol particles and is linearly correlated with the PM mass change.The difference in the growth rate between the PM2.5mass and the PLAM value during the first 10 hours of the CS indicates that the feedback effects from the more stable BL contribute to 84% of the explosive growth of PM2.5mass in a range of 73%–93%.Additional accumulated near-surface moisture (RH > 80%) caused by the ground-temperature decrease, weaker turbulent diffusion,lower BL height and inhibited vertical mixing of water vapor are conducive to the secondary aerosol formation in chemical reactions, including liquid-phase and heterogeneous reactions, and further increase PM2.5levels.The contribution of these reaction mechanisms to the explosive growth of PM2.5mass during the early CS and subsequent pollution accumulation needs further investigation.(Zhang Xiaoye)

1.2 Aerosol optical properties: observation and its relationship with meteorological conditions and emission during the Chinese National Day and Spring Festival holiday in Beijing

The reduction of traffic flow in downtown areas during the Chinese National Day holiday and the fireworks during the Spring Festival provides a unique opportunity for investigating the impact of urban anthropogenic activities on aerosol optical properties during these important Chinese festivals in Beijing.The National Day in 2014 and 2015 and Spring Festival in 2015 and 2016 were selected as study periods.The aerosol optical depth (AOD) at 440 nm increased over all the holiday periods and the average AODs during the 2015 National Day, 2015 Spring Festival and 2016 Spring Festival were about 81%, 21% and 36% higher than the background levels, respectively.The average AOD in 2014 National Day holiday was lower than the background level partly influenced by a precipitation event.The absorption AOD (AAOD) at 440 nm showed consistent variations with the AOD and the average AAODs during the 2015 National Day, 2015 Spring Festival and 2016 Spring Festival holidays were about 75%, 19% and 23% higher than the background level,respectively.The mean values of single scattering albedo were greater than the background level during the Spring Festival holidays, whereas the values during the National Day holiday in 2015 were lower partly due to the reduction of vehicular emissions in downtown areas.Fine- and coarse-mode particle volumes during pollution periods in holidays were 0.04–0.25 μm3and 0.03–0.15 μm3larger than the background levels,respectively.The results of potential source contribution function and concentration-weighted trajectory analyses identified the areas south of Beijing as the main source regions of PM2.5and were responsible for the extremely high PM2.5concentrations in Beijing during the holiday periods.The findings of this study may aid in understanding the effects of human activities on aerosol optical properties in the Beijing area and contribute to improving regional air quality.(Che Huizheng)

1.3 Air pollution characteristics and their relationship to meteorological conditions during 2014–2015 in major cities in China

In January 2013, the real-time hourly average concentrations of six pollutants (CO, NO2, O3, PM10, PM2.5and SO2) based on data from air quality monitoring stations in major cities in China were released to the public.That report provided a good opportunity to publicize the nationwide temporal and spatial pollution characteristics.Although several studies have systematically investigated the temporal and spatial trends of pollutant concentrations, the relationship between air pollution and multi-scale meteorological conditions and their spatial variations on a nationwide scale remains unclear.This study has analyzed the air pollution characteristics and their relationship with multi-scale meteorological conditions during 2014–2015 in 31 provincial capital cities in China.The annual average concentrations of six pollutants for 31 provincial capital cities were 1.2 mg m–3, 42.4 μg m–3, 49.0 μg m–3, 109.8 μg m–3, 63.7 μg m–3, and 32.6 μg m–3, respectively, in 2014.The annual average concentrations decreased by 5.3%, 4.9%, 11.4%, 12.0% and 21.5% for CO, NO2,PM10, PM2.5and SO2, respectively, but increased by 7.4% for O3in 2015.The highest rate of a major pollutant over China was PM2.5followed by PM10, O3, NO2, SO2and CO.Meteorological conditions were the primary factor determining day-to-day variations in pollutant concentrations, explaining more than 70% of the variance of daily average pollutant concentrations over China.Meteorological conditions in 2015 were more adverse for pollutant dispersion than in 2014, indicating that the improvement in air quality was caused by emission controls.(He Jianjun)

1.4 Prediction of size-resolved number concentration of cloud condensation nuclei and long-term measurements of their activation characteristics

Atmospheric aerosol particles acting as cloud condensation nuclei (CCN) are key elements in the hydrological cycle and climate.To improve our understanding of the activation characteristics of CCN and to obtain accurate predictions of their concentrations, a long-term field campaign was carried out in the Yangtze River Delta, China.The results indicated that the CCN were easier to activate in this rural but still poluted regional station, than in clean (e.g., the Amazon region) or dusty (e.g., Kanpur-spring)locations, but were harder to activate than in more polluted areas (e.g., Beijing).A new method that uses two additional parameters—the maximum activation fraction and the degree of heterogeneity is proposed to predict the accurate, size-resolved concentration of CCN.The value ranges and prediction uncertainties of these parameters were evaluated.The CCN predicted using this new method with size-resolved chemical compositions under an assumption of internal mixing showed the best agreement with the long-term field measurements.(Zhang Xiaoye)

1.5 Ambient mixing ratios of atmospheric halogenated compounds at five background stations in China

High precision measurements of three chlorofluorocarbons (CFCs), three hydrochlorofluorocarbons(HCFCs), six hydrofluorocarbons (HFCs), three perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) were made at five Chinese background stations from January 2011 to December 2012.Their station means in the background air were 239.5 ± 0.69 parts-per-trillion dry-air mole fraction mixing ratios (×10–12) for CFC-11, (536.5 ± 1.49) for CFC-12, (74.66 ± 0.09) for CFC-113, (232.1 ± 4.77) for HCFC-22, (23.78 ± 0.29) for HCFC-141b, (22.92 ± 0.42) for HCFC-142b, (11.75 ± 0.43) for HFC-125, (71.32 ± 1.35) for HFC-134a, (13.62± 0.43) for HFC-143a, (9.10 ± 1.26) for HFC-152a, (25.45 ± 0.1) for HFC-23, (7.28 ± 0.48) for HFC-32,(4.32 ± 0.03) for PFC-116, (0.63 ± 0.04) for PFC-218, (1.36 ± 0.01) for PFC-318, and (7.67 ± 0.03) for SF6,respectively, which were comparable with those measured at the two Northern Hemisphere (NH) AGAGE stations: Mace Head, Ireland (MHD) and Trinidad Head, California, USA (THD).Compared with our results for earlier years from in-situ measurement at SDZ, background-air mixing ratios of CFCs are now declining,while those for HCFCs, HFCs, PFCs, and SF6 are still increasing.The ratios of the number of sampling events in which measured mixing ratios were elevated above background (pollution events) relative to the total sample frequency (POL/SUM) for CFCs, HCFCs, and HFCs were found to be station dependent, generally LAN ＞SDZ ＞ LFS ＞ XGL＞ WLG.The enhancement (Δ, polluted mixing ratios minus background mixing ratios)generally showed distinct patterns, with HCFCs ((40.7–175.4)×10–12) ＞ HFCs ((15.8–66.3)×10–12> CFCs((15.8–33.8)×10–12) ＞ PFCs ((0.1–0.9)×10–12) at five stations, especially for HCFC-22 ranging from 36.9×10–12to 138.2×10–12.Combining with the molecular weights, our findings imply the biggest emissions of HCFCs in the regions around these Chinese sites compared to HFCs and CFCs, while the smallest of PFCs, consistent with CFCs being phased out and replaced with HCFCs in China.In addition, relative emission strengths(emission was expressed by mole fractions) of these halocarbons in China were inferred as HCFC-22 ＞ HCFC-141b ＞ HFC-134a ＞ HCFC-142b for the Yangtze River Delta (YRD) and as HCFC-22 ＞ HCFC-142b ＞ HCFC-141b ≈ HFC-134a in the North China Plain (NCP).(Zhang Gen)

1.6 Characterization of particle number size distribution and new particle formation in an urban environment in Lanzhou, China

A scanning mobility particle sizer was utilized for the real-time measurement of particles in the size range of 14.6 to 661.2 nm from August 14 to November 18, 2014 to characterize the evolution of particle number size distribution and new particle formation (NPF) events in Lanzhou, China.The mean number concentrations of nucleation mode, Aitken mode, accumulation mode, and total particles were 2833, 12,898, 6210, and 21,940 cm?3, respectively.The mean number size distribution was obviously unimodal, with a peak at around 60 nm.The diurnal variation of nucleation mode particles was mainly influenced by NPF events.Two peaks at traffic rush hours were observed for Aitken mode, accumulation mode, and total particles; the peaks were related to traffic and cooking soot emissions.The particle number and mass concentrations were all higher on workdays than on weekends mainly because of the enhancement in human activities and traffic density.Daytime also had higher values of number concentrations than nighttime.The mass concentrations of total submicron particles,sulfate, nitrate, and ammonium had much higher values at daytime than at nighttime, however, organics had slightly higher mass concentrations at nighttime mainly because of heating activities at night and intensified evening peaks.During the measurement period, the frequency of NPF events was calculated to be 34%.The average apparent formation and growth rates of nucleation mode particles were 1.71 cm?3s?1and 6.10 nm h?1, respectively.A typical NPF event with two-stage particle growth was selected and analyzed to provide insight into the evolution of particle number size distributions.Back trajectory clustering analysis indicated that air masses that originated from the west had high values of both particle number and mass concentrations associated closely with local source emissions.Air masses from the north and northwest represented the relatively clean air mass arriving in Lanzhou.(Zhang Yangmei)

1.7 Characteristics of chemical composition and role of meteorological factors during heavy aerosol pollution episodes in northern Beijing area in autumn and winter of 2015

Heavy aerosol pollution episodes (HPEs) usually start from late autumn and become more serious in winter in Beijing and its vicinity (BIV).In this study, we examined the reasons for the formation and change of HPEs in the areas of northern BIV.The size-resolved chemical components of PM1and meteorological conditions were investigated during HPEs in autumn and winter of 2015.Stable regional atmosphere and higher atmospheric condensation processes associated with southerly and lower speed wind led to the formation of HPEs.After the start of these HPEs, the concentration of fine particles increased more than twice in several hours.80% of the “explosive” growth in PM mass can be considered as a positive feedback of meteorological factors that come from even more stable atmosphere and larger condensation rate of water vapor, which was derived from the interaction between formed aerosol pollution and the meteorological factors in the boundary layer.Nitrate was the largest fraction of PM1in autumn, and the most significantly increased component during HPEs relative to clean period during both autumn and winter.The proportion of organic aerosol (OA) was similar to that of nitrate in autumn, but its rise in HPE was much smaller, mainly because the high concentration of OA existed during clean periods.Compared with the largest increase of nitrate, the similar uplift was found for ammonium production, showing that a large amount of ammonium mainly formed by the combination ofin HPEs, rather than.In addition to the lower southerly wind carrying pollutants from southern part of BIV, westerly wind from central Inner Mongolia and north Shanxi can also bring air pollutants originating from coal combustion, contributing to the heavy pollution in the northern BIV area in winter, and resulting in higher sulfate, nitrate and organic aerosol masses.(Zhang Xiaoye)

1.8 Chemical characteristics of PM2.5 during summer at a background site of the Yangtze River Delta in China

With rapid economic development and urbanization, particular attention has been paid to atmospheric chemical studies in the Yangtze River Delta in China.PM2.5samples were collected by a MiniVol? air sampler in summer time at a background site of the Yangtze River Delta in China.Carbonaceous components, i.e.,OC and EC, levoglucosan and water-soluble inorganic ions, including sulfate, nitrate, ammonium, etc., were quantified.The average concentration of PM2.5in summer at Lin’an was (30.19±8.86) μg m–3, lower than that previous studies reported, confirming that air pollution in China is improving, e.g., by emission control measures and subsequent reduction in PM emissions in China.Examination of the relationship among sulfate,nitrate and ammonium showed thatexisted aswhilemight have been present as NaNO3and KNO3.Based on molecular tracer, synoptic data as well as air mass back trajectory analysis, it was revealed that regional transport and stable synoptic conditions both played important roles in controlling the variations of aerosol chemical components.The comparison of aerosol chemical components between clean and hazy days showed that secondary organic and inorganic aerosols have different production processes.Secondary organic carbon (SOC) was much more important during clean days, while secondary inorganic aerosol species were readily produced and consequently became more important during polluted periods in Lin’an during summer time.(Liang Linlin)

1.9 Chemical characterization of submicron aerosol particles during wintertime in a northwest city of China using an Aerodyne aerosol mass spectrometry

An Aerodyne quadrupole aerosol mass spectrometry (Q-AMS) was utilized to measure the size-resolved chemical composition of non-refractory submicron particles (NR-PM1) from October 27 to December 3,2014 at an urban site in Lanzhou, Northwest China.The average NR-PM1mass concentration was 37.3 μg m–3(ranging from 2.9 to 128.2 μg m–3) under an AMS collection efficiency of unity and was composed of organics (48.4%), sulfate (17.8%), nitrate (14.6%), ammonium (13.7%), and chloride (5.7%).Positive matrix factorization (PMF) with the multi-linear engine (ME-2) solver identified six organic aerosol (OA) factors,including hydrocarbon-like OA (HOA), coal combustion OA (CCOA), cooking-related OA (COA), biomass burning OA (BBOA) and two oxygenated OA (OOA1 and OOA2), which accounted for 8.5%, 20.2%, 18.6%,12.4%, 17.8% and 22.5% of the total organics mass on average, respectively.Primary emissions were the major sources of fine particulate matter (PM) and played an important role in causing high chemically resolved PM pollution during wintertime in Lanzhou.Back trajectory analysis indicated that the long-range regional transport air mass from the westerly was the key factor that led to severe submicron aerosol pollution during wintertime in Lanzhou.(Zhang Yangmei)

1.10 Contribution of fungal spores to organic carbon in ambient aerosols in Beijing, China

Fungal spores are ubiquitous components of atmospheric aerosols and contributors to the organic carbon(OC) component in ambient aerosols.Daily PM10and PM2.5samples were collected concurrently at an urban site during an entire year, while PM10sampling was conducted at a rural site during late spring and summer.The annual average concentrations of spore-OC in PM2.5and PM10at the THU site were 0.3 ± 0.2 μg C m–3and 0.8 ± 0.7 μg C m–3, while the respective contributions of spore-OC to organic carbon were (1.2 ± 0.7)%and (3.5 ± 3.7)%, respectively.The contributions of fungal spores to OC in the two size fractions had the following seasonal trend (from highest to lowest levels): summer, autumn, winter and spring.During the summer sampling season, the contribution of fungal spores to OC was observed at a higher level at the rural site compared to the urban site, (14.1 ± 10.5)% and (7.3 ± 3.3)%, respectively.It can be concluded that fungi are a non-negligible source of carbonaceous aerosol even at urban locations such as Beijing, China.Thus, more studies are needed to better understand the spatial, temporal and size distributions of fungal OC contributions to atmospheric aerosols.(Liang Linlin)

1.11 Declining frequency of summertime local-scale precipitation over eastern China from 1970 to 2010 and its potential link to aerosols

Summer precipitation plays critical roles in the energy balance and the availability of fresh water over eastern China.However, little is known regarding the trend in local-scale precipitation (LSP).Here we developed a novel method to determine LSP events in the summer afternoon throughout eastern China from 1970 to 2010 based on hourly gauge measurements.The LSP occurrence hours decrease at an annual rate of 0.25%, which varies considerably by region, ranging from 0.14% over the Yangtze River Delta to 0.56% over the Pearl River Delta.This declining frequency of LSP is generally accompanied by an increase in rain rate of LSP but a decrease in visibility, whose linkage to LSP events was investigated.In particular, more LSP events tended to form when the atmosphere was slightly polluted.Afterward, LSP was suppressed.These findings have important implications for improving our understanding of the climatology of daytime precipitation at local scales.( Guo Jianping)

1.12 Aerosol and boundary-layer interactions and impact on air quality

Air quality is concerned with pollutants in both the gas phase and solid or liquid phases.The later are referred to as aerosols, which are multifaceted agents affecting air quality, weather and climate through many mechanisms.Unlike gas pollutants, aerosols interact strongly with meteorological variables with the strongest interactions taking place in the planetary boundary layer (PBL).The PBL hosting the bulk of aerosols in the lower atmosphere is affected by aerosol radiative effects.Both aerosol scattering and absorption reduce the amount of solar radiation reaching the ground and thus reduce the sensible heat fluxes that drive the diurnal evolution of the PBL.Moreover, aerosols can increase atmospheric stability by inducing a temperature inversion as a result of both scattering and absorption of solar radiation, which suppresses dispersion of pollutants and leads to further increases in aerosol concentration.Such positive feedback is especially strong during severe pollution events.Knowledge of the PBL is thus crucial for understanding the interactions between air pollution and meteorology.A key question is how the diurnal evolution of the PBL interacts with aerosols, especially in vertical directions, and affects air quality.We review the major advances in aerosol measurements, PBL processes and their interactions with each other through complex feedback mechanisms and highlight the priorities for future studies.(Guo Jianping)

1.13 Health burden attributable to ambient PM2.5 in China

In China, over 1.3 billion people have high health risks associated with exposure to ambient fine particulate matter (PM2.5) that exceeds the World Health Organization (WHO) Air Quality Guidelines (AQG).The PM2.5mass concentrations from 1382 national air quality monitoring stations in 367 cities, between January 2014 and December 2016, were analyzed to estimate the health burden attributable to ambient PM2.5across China.The integrated exposure-response model was applied to estimate the relative risks of diseasespecific mortality.Disease-specific mortality baselines in province-level administrative units were adjusted by the national mortality baseline to better reveal the spatial inequality of the health burden associated with PM2.5.Our study suggested that PM2.5in 2015 contributed as much as 40.3% to total stroke deaths, 33.1%to acute lower respiratory infection (ALRI, ＜ 5 years) deaths, 26.8% to ischemic heart disease (IHD) deaths,23.9% to lung cancer (LC) deaths, 18.7% to chronic obstructive pulmonary disease (COPD) deaths, 30.2%to total deaths combining IHD, stroke, COPD, and LC, 15.5% to all cause deaths.The population weighted average (PWA) attributable mortality rates (10-5yr-1) were 112.0 in current year analysis, and 124.3 in 10-year time lag analysis.The mortality attributable to PM2.5in 10-year time lag analysis (1.7 million) was 12% higher than the current year analysis (1.5 million).Our study also estimated site-specific annual PM2.5concentrations in scenarios of achieving WHO interim targets (ITs) and AQG.The mortality benef i ts will be 24.0%, 44.8%,70.8%, and 85.2% of the total current mortalities (1.5 million) when the PWA PM2.5concentrations in China meet the WHO IT-1, IT-2, IT-3, and AQG, respectively.We expect air quality modeling and cost-benefits analysis of emission reduction scenarios and corresponding health benef i ts in meeting the site-specific annual PM2.5concentrations (WHO IT-1, IT-2, IT-3, and AQG) this study raised.(He Jianjun)

1.14 Lower tropospheric distributions of O3 and aerosol over Raoyang, a rural site in the North China Plain

The North China Plain (NCP) has become one of the most polluted regions in China, with the rapidly increasing economic growth in the past decades.High concentrations of ambient O3and aerosol have been observed at urban as well as rural sites in the NCP.Most of the in-situ observations of air pollutants have been conducted near the ground so that current knowledge about the vertical distributions of tropospheric O3and aerosol over the NCP region is still limited.In this study, vertical profiles of O3and size-resolved aerosol concentrations below 2.5 km were measured in summer 2014 over a rural site in the NCP, using an unmanned aerial vehicle (UAV) equipped with miniature analyzers.In addition, vertical profiles of aerosol scattering property in the lower troposphere and vertical profiles of O3below 1 km were also observed at the site using a lidar and tethered balloon, respectively.The depths of the mixed layer and residual layer were determined according to the vertical gradients of lidar particle extinction and aerosol number concentration.Average O3and size-resolved aerosol number concentration in both the mixed and residual layer were obtained from the data observed in seven UAV fl ights.The results show that during most of the fl ights the O3levels above the top of the mixed layer were higher than those below.Such a positive gradient in the vertical distribution of O3makes the residual layer an important source of O3in the mixed layer, particularly in the morning when the top of the mixed layer is rapidly elevated.In contrast to O3, aerosol number concentration was normally higher in the mixed layer than in the residual layer, particularly in the early morning.Aerosol particles were overwhelmingly distributed in the size range ＜ 1 μm, showing slight differences between the mixed and residual layers.Our measurements confirm that the lower troposphere over the rural area of the NCP is largely impacted by anthropogenic pollutants locally emitted or transported from urban areas.Compared with the historic O3vertical profiles over Beijing from the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC), a strong increase in O3can be found at all heights below 2.5 km in the decade from 2004 to 2014, with the largest enhancement of about 41.6×10?9.This indicates that the lower troposphere over the northern part of the NCP has experienced rapidly worsening photochemical pollution.This worsening trend in photochemical pollution deserves more attention in the future.(Xu Xiaobin)

1.15 Optical and radiative properties of aerosols during a severe haze episode over the North China Plain in December 2016

The optical and radiative properties of aerosols during a severe haze episode from 15 to 22 December 2016 over Beijing, Shijiazhuang, and Jiaozuo in the North China Plain were analyzed based on the groundbased and satellite data, meteorological observations, and atmospheric environmental monitoring data.The aerosol optical depth at 500 nm was ＜ 0.30 and increased to ＞1.4 as the haze pollution developed.The ?ngstr?m exponent was ＞ 0.80 for most of the study period.The daily single-scattering albedo was ＞ 0.85 over all of the North China Plain on the most polluted days and was ＞ 0.97 on some particular days.The volumes of fine and coarse mode particles during the haze event were approximately 0.05–0.21 and 0.01–0.43 μm3,respectively—that is, larger than those in the time without haze.The daily absorption aerosol optical depth was about 0.01–0.11 in Beijing, 0.01–0.13 in Shijiazhuang, and 0.01–0.04 in Jiaozuo, and the average absorption ?ngstr?m exponent varied between 0.6 and 2.0.The aerosol radiative forcing at the bottom of the atmosphere varied from –23 to –227, –34 to –199, and –29 to –191 W m–2for the whole haze period, while the aerosol radiative forcing at the top of the atmosphere varied from –4 to –98, –10 to –51, and –21 to –143 W m–2in Beijing, Shijiazhuang, and Jiaozuo, respectively.Satellite observations showed that smoke, polluted dust, and polluted continental components of aerosols may aggravate air pollution during haze episodes.The analysis of the potential source contribution function and concentration-weighted trajectory showed that the contribution from local emissions and pollutants transport from upstream areas were 190–450 and 100–410 μg m–3,respectively.(Che Huizheng)

1.16 Summertime ambient ammonia and its effects on ammonium aerosol in urban Beijing, China

To improve the understanding of NH3variation in urban Beijing, high temporal resolution (1-min averaged) NH3data derived during the summer of 2009 were analyzed.Results indicated that after rain there was generally an increase in NH3concentration.The analysis of the 1-min data revealed that a weak but significant linear correlation existed between NH3and NOxin August, indicating a connection between NH3concentrations and traffic levels during summer.This was further supported by peak NH3levels approximately coinciding with morning rush hours.The daily NH3concentrations were weakly correlated withconcentrations, suggesting that NH3played an important precursor role inin PM2.5formation.The mean mass ratio of NH3/NHxwas 0.76±0.13.This revealed that NHxwas influenced by local sources during the summer and that NH3dry deposition could contribute substantially to NHxdeposition.A high temperature, relative humidity, and degree of oxidization could increase photochemical reactions and aqueous processing, having the important effect of SO2toand NH3toconversion in summer.The back trajectory analysis indicated that the transport of air masses from the North China Plain region contributed to the atmospheric NH3andaerosol variations in Beijing.(Meng Zhaoyang)

1.17 Temporal variation and source identification of black carbon at Lin’an and Longfengshan regional background stations in China

Black carbon (BC) is a component of fine particulate matter (PM2.5), associated with climate, weather,air quality, and human’s health.However, studies on temporal variation of atmospheric BC concentration at background stations in China and its source area identification are lacking.Here we used 2-yr BC observations from two background stations, Lin’an (LAN) and Longfengshan (LFS), to perform an investigation.Results show that the mean diurnal variation of BC has two significant peaks at LAN while different characteristics are found in the BC variation at LFS, which are probably caused by the difference in emission source contributions.Seasonal variation of monthly BC shows double peaks at LAN but a single peak at LFS.The annual mean concentrations of BC at LAN and LFS decrease by 1.63 and 0.26 μg m–3from 2009 to 2010,respectively.The annual background concentration of BC at LAN is twice higher than that at LFS.The major source of the LAN BC is industrial emission while the source of the LFS BC is residential emission.Based on transport climatology on a 7-day timescale, LAN and LFS stations are sensitive to surface emissions respectively in belt or approximately circular area, which are dominated by summer monsoon or colder land air flows in Northwest China.In addition, we statistically analyzed the BC source regions by using BC observation and FLEXible PARTicle dispersion model (FLEXPART) simulation.In summer, the source regions of BC are distributed in the northwest and south of LAN and the southwest of LFS.Low BC concentration is closely related to air mass from the sea.In winter, the source regions of BC are concentrated in the west and south of LAN and the northeast of the threshold areastotat LFS.The cold air mass in the northwest plays an important role in the purification of atmospheric BC.On a yearly scale, sources of BC are approximately from five provinces in the northwest/southeast of LAN and the west of LFS.These findings are helpful in reducing BC emission and controlling air pollution.(Cheng Siyang)

1.18 The relationship of PM variation with visibility and mixing-layer height under hazy/foggy conditions in the multi-cities of Northeast China

The variations of visibility, PM-mass concentration and mixing-layer height (MLH) in four major urban/industry regions (Shenyang, Anshan, Benxi and Fushun) of central Liaoning in Northeast China are evaluated from 2009 to 2012 to characterize their dynamic effect on air pollution.The annual mean visibilities are about 13.7 ± 7.8, 13.5 ± 6.5, 12.8 ± 6.1 and 11.5 ± 6.8 km in Shenyang, Anshan, Benxi and Fushun, respectively.The pollution load (PM× MLH) shows a weaker vertical diffusion in Anshan, with a higher PM concentration near the surface.High concentrations of fine-mode particles may be partially attributed to the biomass-burning emissions from September in Liaoning Province and surrounding regions in Northeast China as well as the coal burning during the heating period with lower MLH in winter.The visibility on non-hazy fog days is about 2.5–3.0 times higher than that on hazy and foggy days.The fine-particle concentrations of PM2.5and PM1on hazy and foggy days are 1.8–1.9 times and 1.5 times higher than those on non-hazy and non-foggy days.The MLH declined more severely during fog pollution than in haze pollution.The results of this study can provide useful information to better recognize the effects of vertical pollutant diffusion on air quality in the multi-cities of central Liaoning Province in Northeast China.(Che Huizheng)

1.19 Water vapor variation and the effect of aerosols in China

This study analyzed the annual and seasonal trends in precipitable water vapor (PWV) and surface temperature (Ts) over China from 1979 to 2015, and the relationships between PWV andTsand between PWV and aerosol absorption optical depth (AAOD), using data from radiosonde stations, weather stations,and multiple satellite observations.Results revealed a positive PWV trend from 1979 to 1999, and a negative PWV trend from 2000 to 2015.Analysis of the differences in the PWV trend among different station types showed that the magnitudes of the trends were in the order main urban stations ＞ provincial capital stations ＞suburb stations, suggesting that anthropogenic activities have a strong influence on the PWV trend.The AAOD exhibited a significant positive trend in most regions of China from 2005 to 2015 (at the conf i dence level 95%).Using spatial correlation analysis, we showed that PWV trend derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations is correlated withTs, with an annual correlation coefficient of 0.596.In addition, the spatial correlation between PWV and AAOD showed a negative correlation, with the highest correlation coefficients of –0.76 and –0.71 observed in mid-eastern China and central northwest China,respectively, suggesting that the increase in AAOD in recent years may be one of the reasons for the decrease in PWV since the 2000s in China.(Che Huizheng)

1.20 The influence of different seasonal weather conditions for high concentrations of black carbon in Beijing downtown

Based on the black carbon aerosol (BC) and PM2.5observational data in Beijing downtown from 2013 to 2015, according to the ground-based meteorological observational data, ECMWF boundary layer height reanalysis data and FNL/NCEP different heights of wind speed reanalysis data, the seasonal, lunar, diurnal changes of BC mass concentration and the ratio of BC in PM2.5were discussed, and the related vector of BC concentration in Beijing downtown and different heights of wind speed were studied, and the influence of meteorological conditions and remote transport for the change of BC concentration in Beijing downtown were analyzed.It was found that the average of Beijing downtown BC concentration is 4.77±4.49 ug m–3; the ratio of BC in PM2.5is (8.23±5.47)%.BC concentration and the ratio of BC in PM2.5in autumn and winter is higher than in spring and summer, the diurnal change of BC concentration and the ratio of BC in PM2.5in all season showed that they were lower in daytime than in night.When the concentration of PM2.5increased,BC concentration increased and the ratio of BC in PM2.5decreased.When NE, ENE, SE and WSW were the main wind direction over Beijing, BC concentration decreased with the increase of wind speed and boundary layer height.In different seasons, there were different critical values and change rates of BC concentration changing with wind speed.In winter, during the period of high BC concentration, the key influence area of BC concentration in Beijing downtown for low heights was located in two zones, one was the border region of southern Hebei and Shandong, another was the border region of northwestern Hebei, northern Shanxi and lnner Mongolia; the key influence area of BC concentration in Beijing downtown for high heights was located in western Hebei, northern Shanxi and lnner Mongolia.(Cheng Xinghong)

1.21 Sources and characteristics of regional background PM1 in North China during the autumn and winter polluted period

The campaign of investigating the chemical compositions and particle size distributions of NR-PM1(nonrefractory PM1) was conducted by using a high resolution time of fl ight aerosol mass spectrometer (HR-TOF-AMS) at the Shangdianzi (SDZ) regional atmospheric background site (117.07°E, 40.39°N), northeast of Beijing, from October 17, 2015 to January 26, 2016.Results showed that organics was the main component of PM1, and the proportion of nitrate was higher than sulfate in autumn and winter.The mean mass-resolved size distributions for the main components displayed accumulation mode.The wider organic peak shape and larger nitrate peak size indicated that the organics contributed to both small and large particles at the beginning of the particle formation, growth and aging processes, while most of nitrate particles preferred to grow into large particles during the aging process.The ratios of elements between OM and OC, O/C and H/C were calculated as 1.91, 0.58 and 1.58, respectively.The oxidation state of organic aerosols was higher than that of other city sites.Nitrate was the major contributor of NR-PM1during the polluted period, while organics was significantly higher than that during clean period.The results of back trajectories analysis demonstrated that the air masses were complex during the pollution episode.The northwesterly wind from central Inner Mongolia and Siberia dominated the clean episodes, which was conducive to the spread of pollutants.(Zhang Yangmei)

1.22 Meteorological characteristics associated with air pollution in Xiong’an, China

In April 2017, the central government of China announced that it would establish the Xiong’an New Area in Hebei Province, as part of measures to advance the coordinated development of the Beijing-Tianjin-Hebei(BTH) region.The area is expected to become an innovative, market-driven green city; thus, it is urgent to address its environmental issues before urban construction begins.This study involved a systematic analysis of atmospheric pollutants PM2.5, PM10, CO, SO2, NO2, and O3, and their relationships with meteorological parameters in the Xiong’an area for a continuous period from May 2016 to April 2017.The study used observations of 2 m temperature, 2 m relative humidity, and 10 m wind speed along with measurements of the concentration of the six criteria pollutants in Anxin, Rongcheng, and Xiongxian taken on an hourly basis.Results revealed that the Xiong’an area experienced severe air pollution, with heavy aerosol loadings.The annual averaged concentrations of PM2.5and PM10were 101.3 and 144.2 μg m–3, respectively, significantly exceeding the Grade II standard of the Chinese Ambient Air Quality Standards.The maximum 24 h average concentrations of PM2.5and PM10were 540.1 and 642.1 μg m–3, respectively.Distinct seasonal trends were observed for PM2.5and PM10, with the maximum concentrations occurring in winter and the minimum in summer.Other trace gaseous pollutants, including CO, SO2, and NO2demonstrated similar seasonal variations.Contrarily, O3showed a reversed seasonal trend, with concentration peaking in summer, decreasing in spring and fall, and at its lowest in winter.Seasonal variations of atmospheric pollutants were modulated by the seasonal variations in pollutant emissions, but they were also strongly related to meteorological conditions.The relatively cool thermal conditions and low wind speeds in fall and winter can limit the development of the planetary boundary layer and the horizontal transport of pollutants.Such conditions may be partially responsible for the higher concentrations of the primary pollutants during these seasons.On the contrary,secondary pollutant O3exhibited positive correlations with temperature.(Miao Yucong)

1.23 Structure-activity relationship between surface hydroxyl groups during NO2 adsorption and transformation on TiO2 nanoparticles

The role of hydroxyl groups (OH) in understanding the surface reactions on oxides is important.Here we combined spectroscopic experiments and theoretical calculations to reveal the role of OH in the heterogeneous reactions of NO2on TiO2nanoparticles with various crystal structures.The interaction between OH and NO2was determined to be a critical step, giving rise to the formation of surface HNO3.HNO3was found to be either a stable product on amorphous TiO2, or an important intermediate of nitrate on anatase due to further reaction with nearby OH.Lack of surface OH on rutile limited its reactivity toward NO2.This study presents clear evidence that the reactivity of TiO2toward NO2greatly depends on the surface OH as well as the crystalline form.Considering the ubiquitous presence of TiO2nanoparticles in catalysts and in natural environments,our results could provide insights helpful to future research both in environmental catalysis and atmospheric chemistry.(Liu Chang)

1.24 Equilibrium climate response of the East Asian summer evaluation of radiosonde, MODIS-NIRClear, and AERONET precipitable water vapor using IGS ground-based GPS measurements over China

Water vapor is one of the major greenhouse gases in the atmosphere and also the key parameter affecting the hydrological cycle, aerosol properties, aerosol-cloud interactions, the energy budget, and the climate.This study analyzed the temporal and spatial distribution of precipitable water vapor (PWV) in China using MODerate resolution Imaging Spectroradiometer near-infrared (MODIS-NIR)-Clear PWV products from 2011 to 2013.We then compared the four PWV products (Global Positioning System PWV (GPS-PWV), radiosonde PWV (RS-PWV), MODIS-NIR-Clear PWV, and Aerosol Robotic Network sunphotometer PWV (AERONETPWV)) at six typical sites in China from 2011 to 2013.The analysis of the temporal and spatial distribution showed that the PWV distribution in China has clear geographical differences, and its basic distribution characteristics gradually changed from the coast in the southeast to inland in the northwest.Affected by the East Asian monsoon, the PWV over China showed clear seasonal distribution features, with highest values in summer, followed by autumn and spring, and the lowest values in winter.Intercomparison results showed that GPS-PWV and RS-PWV had a slightly higher correlation (R2=0.98) at 00:00 UTC than at 12:00 UTC(R2=0.97).The mean values of Bias, SD, and RMSE between GPS-PWV and RS-PWV (GPS-RS) were –0.03 mm, 2.36 mm, and 2.60 mm at 0000 UTC, and –0.23 mm, 2.76 mm, and 2.95 mm at 1200 UTC, respectively.This showed that GPS-PWV was slightly lower than RS-PWV, and this difference was more obvious during the nighttime.The MODIS-NIR-Clear PWV product showed a similar correlation coefficient (R2=0.88) with GPS-PWV to that with RS-PWV.In addition, MODIS-NIR-Clear PWV was greater than GPS-PWV and RSPWV.The MODIS-NIR-Clear PWV showed a larger deviation from GPS-PWV (MODIS-GPS Bias=1.50 mm,RMSE=5.76 mm) compared with RS PWV (MODIS-RS Bias =0.75 mm, RMSE=5.31 mm).The correlation coefficients between AERONET-PWV and the PWV from GPS, RS, and MODIS-NIR-Clear were 0.970, 0.963,and 0.923 (with RMSE of 2.53 mm, 3.67 mm, and 4.39 mm), respectively.In the Beijing area, the overall mean biases of the AERONET-PWV product with GPS-PWV, RS-PWV and MODIS-NIR-Clear PWV were –0.09 mm, –1.82 mm, and –1.54 mm, respectively, indicating that the AERONET-PWV product was lower than the other three PWV products.(Che Huizheng)

1.25 Impacts of diurnal variability and meteorological factors on the PM2.5-AOD relationship:Implications for PM2.5 remote sensing

PM2.5retrieval from space is still challenging due to the elusive relationship between PM2.5and aerosol optical depth (AOD), which is further complicated by meteorological factors.In this work, we investigated the diurnal cycle of PM2.5in China, using ground-based PM measurements obtained at 226 sites of China Atmosphere Watch Network during the period of January 2013 to December 2015.Results showed that nearly half of the sites witnessed a PM2.5maximum in the morning, in contrast to the least frequent occurrence (5%)in the afternoon when strong solar radiation received at the surface, resulting in rapid vertical diffusion of aerosols and thus lower mass concentration.PM2.5tends to peak equally in the morning and evening in North China Plain (NCP) with an amplitude of nearly twice or three times that in the Pearl River Delta (PRD),whereas the morning PM2.5peak dominated in Yangtze River Delta (YRD) with a magnitude lying between those of NCP and PRD.The gridded correlation maps revealed varying correlations around each PM2.5site,depending on the locations and seasons.Concerning the impact of aerosol diurnal variation on the correlation,the averaging schemes of PM2.5using 3 h, 5 h, and 24 h time windows tended to have largerRbiases,compared with the scheme of 1 h time window, indicating that diurnal variation of aerosols played a significant role in the establishment of explicit correlation between PM2.5and AOD.In addition, high cloud fraction and relative humidity tended to weaken the correlation, regardless of geographical location.Therefore, the impact of meteorological factors could be one of the most plausible alternatives in explaining the varyingRvalues observed, due to its non-negligible effect on MODIS AOD retrievals.Our findings have implications for PM2.5remote sensing, as long as the aerosol diurnal cycle, along with meteorology, are explicitly considered in the future.(Guo Jianping)

2 Model development and implementation, the impacts of atmospheric compositions on climate, weather, and human health

2.1 Atmospheric CO2 at Waliguan station in China: Transport climatology, temporal patterns and source-sink region representativeness

In order to explore where the source and sink have the greatest impact on CO2background concentration at Waliguan (WLG) station, here a statistical method is proposed to calculate the representative source-sink region.The key to this method is to find the best footprint threshold, and the study is carried out in four parts.Firstly, transport climatology, expressed by total monthly footprint, was simulated by FLEXPART on a 7-day time scale.Surface CO2emissions in Eurasia frequently transported to WLG station.WLG station was mainly influenced by the westerlies in winter and partly controlled by the Southeast Asian monsoon in summer.Secondly, CO2concentrations, simulated by CT2015, were processed and analyzed through data quality control, screening, fi tting and comparing.CO2concentrations displayed obvious seasonal variation, with the maximum and minimum concentrations appearing in April and August, respectively.The correlation of CO2fitting background concentrations wasR2=0.91 between simulation and observation.The temporal patterns were mainly correlated with CO2exchange of biosphere-atmosphere, human activities and air transport.Thirdly, for the monthly CO2fi tting background concentrations from CT2015, a best footprint threshold was found based on correlation analysis and numerical iteration using the data of footprints and emissions.The grid cells where monthly footprints were greater than the best footprint threshold were the best threshold area corresponding to representative source-sink region.The representative source-sink region of maximum CO2concentration in April was primarily located in Qinghai Province, but the minimum CO2concentration in August was mainly influenced by emissions in a wider region.Finally, we brief l y presented the CO2sourcesink characteristics in the best threshold area.Generally, the best threshold area was a carbon sink.The major source and sink were relatively weak owing to less human activities and vegetation types in this high altitude area.CO2concentrations were more influenced by human activities when air mass passed through many urban areas in summer.Therefore, the combination of footprints and emissions is an effective approach for assessing the source-sink region representativeness of CO2background concentration.(Cheng Siyang)

2.2 Classification of summertime synoptic patterns in Beijing and their associations with the boundary layer structure affecting aerosol pollution

Meteorological conditions within the planetary boundary layer (PBL) are closely governed by largescale synoptic patterns and play important roles in air quality by directly and indirectly affecting the emission,transport, formation, and deposition of air pollutants.Partly due to the lack of long-term fine-resolution observations of the PBL, the relationships between synoptic patterns, PBL structure, and aerosol pollution in Beijing have not been well understood.This study applied the obliquely rotated principal component analysis in T-mode to classify the summertime synoptic conditions over Beijing using the National Centers for Environmental Prediction reanalysis from 2011 to 2014, and investigated their relationships with the PBL structure and aerosol pollution by combining numerical simulations, measurements of surface meteorological variables, fine-resolution soundings, the concentration of particles with diameters less than or equal to 2.5 μm, total cloud cover (CLD), and reanalysis data.Among the seven identified synoptic patterns, three types accounted for 67% of the total number of cases studied and were associated with heavy aerosol pollution events.These particular synoptic patterns were characterized by high-pressure systems located east or southeast of Beijing at the 925 hPa level, which blocked the air flow seaward, and southerly PBL winds that brought in polluted air from the southern industrial zone.The horizontal transport of pollutants induced by the synoptic forcings may be the most important factor affecting the air quality of Beijing in summer.In the vertical dimension, these three synoptic patterns featured a relatively low boundary layer height (BLH) in the afternoon, accompanied by high CLD and southerly cold advection from the seas within the PBL.The high CLD reduced the solar radiation reaching the surface, and suppressed the thermal turbulence, leading to lower BLH.Besides, the numerical sensitivity experiments show that cold advection induced by the large-scale synoptic forcing may have cooled the PBL, leading to an increase in near-surface stability and a decrease in the BLH in the afternoon.Moreover, when warm advection appeared simultaneously above the top level of the PBL, the thermal inversion layer capping the PBL may have been strengthened, resulting in further suppression of the PBL and thus the deterioration of aerosol pollution levels.This study has important implications for understanding the crucial roles that meteorological factors (at both synoptic and local scales) play important roles in modulating and forecasting aerosol pollution in Beijing and its surrounding area.(Miao Yucong)

2.3 Disentangling fast and slow responses of the East Asian summer monsoon to reflecting and absorbing aerosol forcings

We examined the roles of fast and slow responses in shaping the total equilibrium response of the East Asian summer monsoon (EASM) to reflecting (sulfate, SO4) and absorbing (black carbon, BC) aerosol forcings over the industrial era using the Community Earth System Model version 1 (CESM1).Our results show that there is a clear distinction between fast and slow responses of the EASM to aerosol forcings and the slow climate response due to aerosol-induced change in sea surface temperature plays an important role in the impacts of aerosols on the EASM.The EASM is weakened by a decrease in land-sea surface thermal contrast in the fast response (FR) component to SO4forcing, whereas the weakening is more intensive due to the changes in tropospheric thermodynamic and dynamic structures in the slow response (SR) component to SO4.The total climate adjustment caused by SO4is a significant weakening of the EASM and a decrease in precipitation.The BC-induced fast adjustment strengthens the EASM both by increasing the local surface landsea thermal contrast and by shifting the East Asian subtropical jet northwards.The BC-induced slow climate adjustment, however, weakens the EASM through altering the atmospheric temperature and circulation.Consequently, the EASM is slightly enhanced, especially in north of 30°N, in the total response (TR) to BC.The spatial patterns of precipitation change over East Asia due to BC are similar in the total response and slow response.This study highlights the importance of ocean response to aerosol forcings in driving the changes of the EASM.(Wang Zhili)

2.4 East Asian summer monsoon response to forcing of anthropogenic aerosol species

We used an online aerosol-climate model to study the equilibrium climate response of the East Asian summer monsoon (EASM) to increases in anthropogenic emissions of sulfate, organic carbon, and black carbon aerosols from 1850 to 2000.Our results show that each of these aerosol species has a different effect on the EASM as a result of changes in the local sea-land thermal contrast and atmospheric circulation.The increased emission of sulfate aerosol leads to a decrease in the thermal contrast between the land and ocean,a southward shift of the East Asian subtropical jet, and significant northerly wind anomalies at 850 hPa over eastern China and the ambient oceans, markedly dampening the EASM.An increase in organic carbon aerosol results in pronounced surface cooling and the formation of an anomalous anticyclone over the oceans north of 30°N.These effects cause a slight increase in the sea-land thermal contrast and southerly flow anomalies to the west of the anticyclonic center, strengthening the northern EASM.An increase in organic carbon emission decreases the sea-land thermal contrast over southern China, which weakens the southern EASM.The response of the summer 850 hPa winds and rainfall over the East Asian monsoon region to an increase in black carbon emission is generally consistent with the response to an increase in organic carbon.The increase in black carbon emission leads to a strengthening of the northern EASM north of 35°N and a slight weakening of the southern EASM south of 35°N.The simulated response of the EASM to the increase in black carbon emission is unchanged when the emission of black carbon is scaled up by five times its year 2000 levels, although the intensities of the response is enhanced.The increase in sulfate emission primarily weakens the EASM, whereas the increases in black carbon and organic carbon emissions mitigate weakening of the northern EASM.(Wang Zhili)

2.5 Impact of anthropogenic aerosols from global, East Asian, and non-East Asian sources on East Asian summer monsoon system

The impact of anthropogenic aerosols from global, East Asian, and non-East Asian sources on East Asian summer monsoon (EASM) system is studied using an aerosol-climate online model BCC_AGCM2.0.1_CUACE/Aero.The results show that the summer mean net all-sky shortwave fluxes averaged over East Asian monsoon region (EAMR) at the top of the atmosphere (TOA) and surface are reduced by 4.8 and 5.0 W m?2,respectively, due to the increases of global aerosol emissions in 2000 relative to 1850.Changes in radiations and their resulting changes in heat and water vapor transport and cloud fraction together contribute to the surface cooling over EAMR in summer.The increases in global anthropogenic aerosols lead to a decrease of 2.1 K in summer mean surface temperature and an increase of 0.4 hPa in summer mean surface pressure averaged over EAMR, respectively.It is shown that the changes in surface temperature and pressure are significantly larger over land than over ocean, thus reducing the contrast of land-sea surface temperature and pressure.This results in the marked anomalies of northward and northeastward winds over eastern and southern China and the surrounding oceans in summer, thereby weakening the EASM.The summer mean precipitation averaged over the EAMR is reduced by 12%.The changes in non-East Asian aerosol emissions play a more important role in inducing the changes of local temperature and pressure, and thus significantly exacerbate the weakening of the EASM circulation due to local aerosol changes.The weakening of circulation due to the sources is comparable,and the effect of nonlocal aerosols is even larger in individual regions.The changes of local and non-local aerosols contribute comparably to the reductions in precipitation over oceans, whereas cause opposite changes over eastern China.Our results highlight the importance of aerosol changes outside East Asia to the impact of the anthropogenic aerosol changes on the EASM.(Wang Zhili)

2.6 Impacts of uncertainty in land surface information on simulated surface temperature and precipitation over China

This study mainly focuses on the effects of uncertainty in land surface information on mesoscale numerical simulations.The Weather Research and Forecasting (WRF) model was used to simulate meteorological fields over China at a spatial resolution of 10 km during 2006.Near-surface air temperature and precipitation simulated in WRF were evaluated using site observations.The effects of accurate and updated land surface information, including Shuttle Radar Topography Mission (SRTM) data, Moderate resolution imaging spectroradiometer (MODIS) land use data, vegetation fraction derived from MODIS normalized difference vegetation index (NDVI) and Harmonized World Soil Database (HWSD) data (LAST simulation),on WRF’s performance were investigated by a comparison with the simulation using the default land surface information (BASE simulation).WRF reproduced the temporal and spatial variations of near-surface air temperature and precipitation over China quite well, although its performance varied significantly season by region.WRF underestimated near-surface air temperatures in most areas of the Yunnan-Guizhou Plateau, the Tibetan Plateau, the Northeast Plain, and the southeastern coastal regions, but temperatures were overestimated in most areas of the North China Plain, the Loess Plateau, Sichuan Basin, and western Xinjiang.WRF overestimated (underestimated) precipitation in most humid (arid) areas.A positive (negative) bias in simulated precipitation is found in summer (winter).With updated land surface information, WRF’s performance in terms of both daily average values and extremes is improved, and the root mean square error values for daily mean temperature and daily accumulated precipitation decreased by 7% and 2.3%, respectively.These improvements are significant for temperature, but not significant for precipitation.Therefore, the uncertainty in land surface information has a greater influence on temperature than on precipitation.These findings are very important for weather forecasting and studies involving climatological analyses over East Asia.(He Jianjun)

2.7 Investigation of particulate matter regional transport in Beijing based on numerical simulations

Based on source sensitivity research performed with the Chinese Unified Atmospheric Chemistry Environment (CUACE) model and dispersion simulations performed with the Flexible Particle dispersion model (FLEXPART), the regional transport of particulate matter (PM), potential source regions, and transport pathways were investigated for Beijing in summer (July) and winter (December) 2013.The mean near-surface trans-boundary contribution ratio (TBCR) of PM2.5in Beijing was 53.4% and 36.1% in summer and winter 2013, respectively, and 51.8% and 35.1% for PM10.Regional transport in summer was more significant than that in winter.Seasonal difference of meteorological condition combined with the distribution of emission was responsible for the seasonal difference of TBCR.The secondary aerosol was mostly contributed by regional transport.The transport of PM was mostly from Hebei Province and Tianjin municipality.Based on backward trajectories analysis, the air mass source occurred from different directions in summer, while occurred from northwest in winter.The pollution level and the TBCR were closely related to the transport pathways and distance, especially in summer.(He Jianjun)

2.8 Relay transport of aerosols to Beijing-Tianjin-Hebei region by multiscale atmospheric circulations

The Beijing-Tianjin-Hebei (BTH) region experiences heavy aerosol pollution, which is found to have close relationships with the synoptic- and local-scale atmospheric circulations.However, how and to what extent these multi-scale circulations interplay to modulate aerosol transport have not been fully understood.To this end, this study comprehensively investigated the impacts of these circulations on aerosol transport in BTH,focusing on an episode occurred on 1 June 2013, through combining both observations and three-dimensional numerical simulations.It was found that during this episode, the Bohai Sea acted as a transfer station, and the high-pressure system over the Yellow Sea and sea-breeze in BTH turned to affect the transport of aerosols.In the morning, influenced by the high-pressure system, lots of aerosols emitted from Shandong and Jiangsu provinces were first transported to the Bohai Sea.These aerosols were then brought to the BTH region in the afternoon through the inland penetration of sea-breeze, significantly exacerbating the air quality in BTH.The inland penetration of sea-breeze could be identified by the sharp changes in ground-based observed temperature, humidity, and wind when the sea-breeze front (SBF) passed by.Combining observations with model outputs, the SBF was found to be able to advance inland more than 150 km, reaching Beijing.This study has important implications for better understanding the aerosol transport in BTH and improving the forecast of such aerosol pollution.(Miao Yucong)

2.9 Scenario dependence of future changes in climate extremes under 1.5 °C and 2 °C global warming

The 2015 Paris Agreement aims to limit global warming below 2 °C and pursue efforts to even limit it to 1.5 °C relative to pre-industrial levels.Decision makers need reliable information on the impacts caused by these warming levels for climate mitigation and adaptation measures.We explore the changes in climate extremes, which are closely tied to economic losses and casualties, under 1.5 °C and 2 °C global warming and their scenario dependence using three sets of ensemble global climate model simulations.A warming of 0.5 °C(from 1.5 °C to 2 °C) leads to significant increases in temperature and precipitation extremes in most regions.However, the projected changes in climate extremes under both warming levels highly depend on the pathways of emissions scenarios, with different greenhouse gas (GHG)/aerosol forcing ratio and GHG levels.Moreover,there are multifold differences in several heavily polluted regions, among the scenarios, in the changes in precipitation extremes due to an additional 0.5 °C warming from 1.5 °C to 2 °C.Our results demonstrate that the chemical compositions of emissions scenarios, not just the total radiative forcing and resultant warming level, must be considered when assessing the impacts of global 1.5/2 °C warming.(Wang Zhili)

2.10 Short-term aerosol radiative effects and their regional difference during heavy haze episodes in January 2013 in China

Short-term direct effects of aerosols on surface shortwave radiation and its regional difference during heavy haze episodes in January 2013 in China were investigated using the offline Weather Research and Forecasting (WRF) the Community Multiscale Air Quality (CMAQ)- second Sun-Edward-Slingo radiative transfer (SES2) model system.The aerosol concentrations were first generated using the WRF-CMAQ model simulations and then corrected based on the observed concentrations of PM10and PM2.5.The atmospheric profile data produced by the WRF model and the corrected aerosol concentrations were used as inputs to the SES2 model to calculate the global horizontal irradiance (GHI) and direct solar irradiance (DIR) at the surface for a period of heavy haze episodes in January 2013 in China.The effects of aerosol on the GHI and DIR at the surface were then analyzed.The modeled radiation was evaluated against the observations first.The results show some improvement due to the correction for the aerosol concentrations.The aerosol shortwave radiative effects were determined by the difference between the model calculations with and without the inclusion of aerosols.It was found that the short-term aerosol radiative impacts during heavy haze days were very large,ranging between 100 and 500 W m–2.The aerosol concentrations had a large spatial variation with the highest concentration occurring in the areas of Beijing-Tianjin-Hebei, which caused a large difference in the radiative effect nationwide.In addition to the total concentration, the aerosol vertical distributions also varied from the north to the south in China and this led to a significant difference in radiative effect even when the PM10concentration was similar in the three regions.(Cheng Xinghong)

2.11 Trans-Pacific transport of dust aerosols from East Asia: Insights gained from multiple observations and modeling

East Asia is one of the world’s largest sources of dust and anthropogenic pollution.Dust particles originating from East Asia have been recognized to travel across the Pacific to North America and beyond,thereby affecting the radiation incident on the surface as well as clouds aloft in the atmosphere.In this study,integrated analyses were performed with the focus on one trans-Pacific dust episode during 12–22 March 2015, based on space-borne, ground-based observations, reanalysis data combined with Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT), and the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem).From the perspective of synoptic patterns, the location and strength of Aleutian low pressure system largely determined the eastward transport of dust plumes towards western North America.Multi-sensor satellite observations revealed that dust aerosols in this episode was originated from the Taklimakan and Gobi Deserts.Moreover, the satellite observations suggested that the dust particles could be transformed to polluted particles over the East Asian regions after encountering high concentration of anthropogenic pollutants.In terms of the vertical distribution of polluted dust particles, at the very beginning they were mainly located in the altitudes ranging from 1 km to 7 km over the source region, then ascended to 2–9 km over the Pacific Ocean.The simulations confirmed that these elevated dust particles in the lower free troposphere were largely transported along the prevailing westerly jet stream.Overall, observations and modeling demonstrated how a typical springtime dust episode developed and how the dust particles traveled over the North Pacific Ocean all the way to North America.(Guo Jianping)

2.12 Study on spatial-temporal variations of pollutant emission sources inversed by adaptive nudging scheme over the Beijing-Tianjin-Hebei region based on the CMAQ model

The pollutant source assimilation of nudging inversion method was applied to simulate the local sources of SO2and NOxin the Beijing-Tianjin-Hebei region during January, March, July and November in 2014.We then analyzed the strengths, patterns, geographical distribution of SO2and NOxsources by comparing their difference from the original sources and evaluating the inversed-source-based modeling performances.The results showed that the sources of SO2and NOxpresented the obvious seasonal variation, the strongest in winter or heating period.A high pollutant emission zone in the northeast-southwest direction consisted of Tangshan, Beijing, Tianjin, Langfang, Baoding, Shijiazhuang, Xingtai and Handan with a serious center in the front of the Taihang and Yan mountains.The pollutant emissions exhibited a typical “urbanization” effect,that is, the sources of SO2and NOxwere high in the urban area and its surroundings and weak in the rural area.Compared with the initial-emission-based modeling, the inversed-emission-based simulation could better capture the spatial-temporal variations of air pollutants against the observation, especially during high pollution periods.(Cheng Xinghong)