張 婷，曹軍驥,，劉隨心

1.中國(guó)科學(xué)院地球環(huán)境研究所 中國(guó)科學(xué)院氣溶膠化學(xué)與物理重點(diǎn)實(shí)驗(yàn)室，西安 710061

2.中國(guó)科學(xué)院地球環(huán)境研究所 黃土與第四紀(jì)地質(zhì)國(guó)家重點(diǎn)實(shí)驗(yàn)室，西安 710061

3.西安交通大學(xué) 環(huán)境科學(xué)與工程系，西安 710049

寶雞市PM2.5中水溶性離子組分污染特征及來(lái)源分析

張 婷1,2，曹軍驥1,2,3，劉隨心1,2

1.中國(guó)科學(xué)院地球環(huán)境研究所 中國(guó)科學(xué)院氣溶膠化學(xué)與物理重點(diǎn)實(shí)驗(yàn)室，西安 710061

2.中國(guó)科學(xué)院地球環(huán)境研究所 黃土與第四紀(jì)地質(zhì)國(guó)家重點(diǎn)實(shí)驗(yàn)室，西安 710061

3.西安交通大學(xué) 環(huán)境科學(xué)與工程系，西安 710049

本文通過(guò)對(duì)2012年3月至2013年3月寶雞市大氣PM2.5中各個(gè)水溶性無(wú)機(jī)離子組分的質(zhì)量濃度進(jìn)行研究，獲得了水溶性離子的時(shí)間變化特征，并結(jié)合主成分分析方法討論了不同離子的來(lái)源。結(jié)果顯示，寶雞市PM2.5中水溶性離子主要由組成，分別占總水溶性離子質(zhì)量濃度的40.47%、30.75%和15.07%；PM2.5整體偏酸性。比值隨API指數(shù)的升高而增大，當(dāng)空氣質(zhì)量較好時(shí)PM2.5中硫酸鹽居多，而隨著空氣污染發(fā)生硝酸鹽逐漸增多并占優(yōu)勢(shì)。主成分分析結(jié)果表明PM2.5中水溶性離子的主要來(lái)源有二次氣溶膠、生物質(zhì)燃燒和土壤塵。

寶雞；PM2.5；水溶性離子；來(lái)源

大氣氣溶膠是由大氣與懸浮在其中的固體和液體微粒共同組成的多相體系，其中空氣動(dòng)力學(xué)等效直徑＜2.5 μm的顆粒物定義為PM2.5。大氣PM2.5顆粒由于其粒徑小、比表面積大、富含大量有毒有害物質(zhì)、輸送距離遠(yuǎn)，因而對(duì)氣候、人體健康、空氣質(zhì)量及能見(jiàn)度均有重要影響（曹軍驥，2012）。水溶性無(wú)機(jī)離子是PM2.5的重要組分之一，其控制顆粒物的酸堿性從而影響氣溶膠的形成機(jī)制、在大氣中的生命周期以及健康效應(yīng)（Hu et al，2014）。因此研究PM2.5中水溶離子的組成及來(lái)源等對(duì)于有效控制大氣細(xì)粒子污染具有重要意義（Chow et al，2012）。

寶雞是關(guān)中城市群的重要城市之一，是西北乃至西部地區(qū)的比較優(yōu)勢(shì)區(qū)域。近年來(lái)隨著區(qū)域經(jīng)濟(jì)的快速發(fā)展，寶雞市空氣污染事件時(shí)有發(fā)生，給大氣環(huán)境、群眾健康、交通安全等帶來(lái)了嚴(yán)重影響，因此大氣氣溶膠研究及污染治理刻不容緩。然而目前對(duì)寶雞市大氣污染狀況的研究相對(duì)較少且主要集中在顆粒物的質(zhì)量濃度方面（胡淑圓等，2010；張紅芳等，2014；黃戰(zhàn)勝和范鎧，2015；薛平等，2015），而對(duì)顆粒物中主要化學(xué)組分污染特征的研究比較匱乏。

本文通過(guò)對(duì)陜西省寶雞市2012年3月— 2013年3月大氣PM2.5中水溶性離子組分的觀測(cè)研究，深入分析了不同水溶性離子的濃度水平及污染特征，并對(duì)其來(lái)源進(jìn)行探討，為寶雞市未來(lái)解決日益嚴(yán)重的灰霾污染問(wèn)題提供了數(shù)據(jù)支持和治理方向。

1 樣品的采集與分析

1.1 PM2.5樣品采集

寶雞（33°35′ — 35°06′ N，106°18′ — 108°03′ E）地處關(guān)中盆地的西端，東西長(zhǎng)156.6 km，南北寬160.6 km，總面積1.8×104km2，總?cè)丝?75萬(wàn)（2014年）。寶雞屬于暖溫帶半濕潤(rùn)氣候，全年氣候變化受東亞季風(fēng)控制，年平均氣溫12—14℃，年平均降水量在590 — 900 mm，是關(guān)中盆地降水量較多的地區(qū)之一。

2012年3月15日至2013年3月14日，使用便攜式氣溶膠采樣儀（Mini volume portable sampler，Airmetrics，Oregon，USA）每6天采集一個(gè)PM2.5樣品，采樣時(shí)間為24小時(shí)，流量為5 L · min?1。使用直徑為47 mm石英濾紙（QM/A，Whatman Inc.，U.K.），采樣前在780℃馬弗爐中焙燒3小時(shí)，以去除可能的污染物。采樣點(diǎn)位于寶雞市環(huán)境監(jiān)測(cè)站內(nèi)，距地面高度約為15 m。

1.2 水溶性離子分析

截取1/4的采樣濾紙加入10 mL去離子水（R＞18.2 MΩ），超聲、震蕩各1小時(shí)后采用0.45 μm的水系過(guò)濾器過(guò)濾待分析。水溶性離子的定量分析采用Dionex-600型離子色譜儀（包括Ion Pac-AS23型分析柱、Ion Pac-AG23型保護(hù)柱、AERS自身再生抑制器、Ion Pac-CS12A型分析柱、Ion Pac-CG12A型保護(hù)柱、CERS自身再生抑制器、ED50電導(dǎo)檢測(cè)器和GP40梯度泵）進(jìn)行檢測(cè)，用Chromeleon軟件進(jìn)行譜圖分析，得到10種水溶性離子組分（F?、Cl?、、 K+、Mg2+、Ca2+）的質(zhì)量濃度。本方法的詳細(xì)介紹及質(zhì)量控制參見(jiàn)Zhang et al（2011）。

1.3 氣象數(shù)據(jù)及API值的獲取

觀測(cè)期內(nèi)氣象數(shù)據(jù)從寶雞氣象信息網(wǎng)（http:// www.bjqx.gov.cn/）獲得。API指數(shù)從寶雞市環(huán)境保護(hù)局（http://www.baojihb.gov.cn/）獲得。

API（Air pollution index）空氣污染指數(shù)是將常規(guī)監(jiān)測(cè)的幾種空氣污染物（SO2、NO2和PM10）濃度簡(jiǎn)化成單一的概念性指數(shù)數(shù)值形式。各污染物污染分指數(shù)中的最大值即為該區(qū)域或城市的空氣污染指數(shù)。API指數(shù)可以用來(lái)反映和評(píng)價(jià)空氣污染程度和空氣質(zhì)量狀況。

2 結(jié)果與討論

2.1 PM2.5中水溶性離子濃度分布特征

如表1所示，2012年3月— 2013年3月寶雞市PM2.5中總水溶性離子的平均質(zhì)量濃度為51.62 μg · m?3，變化范圍在10.54 — 207.00 μg · m?3。其中4月總水溶性離子的平均值最小，為22.1 μg · m?3，2013年2月的平均值最大，為92.33 μg · m?3。總水溶性離子的質(zhì)量濃度在春季較低，夏季整體濃度值較低但有個(gè)別濃度約100 μg · m?3的污染天，秋季總水溶性離子濃度略有升高，冬季顯著升高，是全年當(dāng)中污染最嚴(yán)重的季節(jié)（見(jiàn)圖1）。寶雞市PM2.5中總水溶性離子質(zhì)量濃度的季節(jié)變化趨勢(shì)與我國(guó)大多數(shù)北方城市相似，冬季最高，夏季次之，春秋季較低。冬季寶雞市總水溶性離子濃度平均為76.72 μg · m?3，主要是由于冬季居民燃煤取暖造成排放增加以及氣象條件不利于污染物的擴(kuò)散等因素導(dǎo)致。春季易發(fā)生沙塵暴、揚(yáng)沙及浮塵天氣，這可能會(huì)造成某些水溶性離子發(fā)生事件性的升高。夏季由于關(guān)中平原秸稈焚燒現(xiàn)象增多，高溫高濕的氣象條件有利于二次氣溶膠的形成，所以氣溶膠的濃度可能出現(xiàn)事件性的升高。秋季由于雨水較多，氣象狀況有利于氣溶膠的濕沉降，因此水溶性離子濃度相對(duì)夏季略有下降。

表1 寶雞市PM2.5中水溶性離子的濃度水平（單位：μg · m?3）Tab.1 Concentrations of water-soluble ions in PM2.5 in Baoji (unit:μg · m?3)

圖1 氣象參數(shù)、API指數(shù)及水溶性離子濃度時(shí)間序列Fig.1 Temporal variations of temperature,API and water-soluble ions mass concentrations

API指數(shù)能粗略地反映空氣污染程度，API＜100表示空氣質(zhì)量狀況在良以上。2012年3月—2013年3月寶雞市空氣污染API指數(shù)的年平均值為73.9，變化范圍是40 — 169。從API指數(shù)看寶雞市空氣污染狀況可知，API大部分都小于100，只有冬季一些天的API指數(shù)較高，污染較嚴(yán)重（見(jiàn)圖1）。

2.2 各水溶性離子組分的時(shí)間變化規(guī)律

PM2.5中主要水溶性離子組分的時(shí)間變化規(guī)律如圖1所示，可以看到的時(shí)間變化規(guī)律基本一致，由于冬季人為排放的增加及氣象條件不利于顆粒物的清除和擴(kuò)散，三種主要離子組分均在冬季濃度最高。而夏季濃度僅次于冬季，比春季和秋季高，這主要與夏季溫、濕度的升高有利于人為排放的氣態(tài)污染物（如SO2和NOx）等經(jīng)過(guò)大氣化學(xué)反應(yīng)生成二次氣溶膠有關(guān)。但是溫度的升高會(huì)促使硝酸鹽揮發(fā)至氣相，所以冬季的濃度相當(dāng)甚至高于，而夏季的濃度則遠(yuǎn)高于。

一次來(lái)源的氣溶膠粒子組分中Cl?、Ca2+和K+的質(zhì)量濃度在總水溶性無(wú)機(jī)離子中所占比重相對(duì)較小，分別為4.55%、3.73%和1.73%。這些離子的季節(jié)變化主要反映了排放源的變化特征，如氯離子（Cl?）與燃燒活動(dòng)（燃煤以及秸稈焚燒等）密切相關(guān)，鉀離子（K+）可用于示蹤生物質(zhì)燃燒排放以及煙花燃放活動(dòng)（Duan et al，2004；徐紅梅等，2012），而鈣離子（Ca2+）主要來(lái)自于地殼源，是土壤塵的指示物。如圖1所示，冬季K+的濃度遠(yuǎn)高于其他季節(jié)，表明寶雞冬季生物質(zhì)燃燒對(duì)氣溶膠的貢獻(xiàn)較大，并且伴有中國(guó)傳統(tǒng)節(jié)日春節(jié)時(shí)的燃放煙花爆竹的影響。Ca2+在干旱少雨的冬春季濃度均較高，除了受遠(yuǎn)源傳輸?shù)纳硥m氣溶膠影響之外，本地?fù)P塵也是其主要貢獻(xiàn)之一。Cl?表現(xiàn)出冬季顯著高于其他季節(jié)的時(shí)間變化特征，也與排放源的變化規(guī)律一致。

2.3 陰陽(yáng)離子平衡及中和因子分析

根據(jù)以下公式（1）和（2），使用主要陰、陽(yáng)離子組分做離子平衡分析：

如圖2，可以看出2012年3月—2013年3月寶雞市大氣中PM2.5整體偏酸性。陰陽(yáng)離子的相關(guān)性很好（R2＞ 0.95），樣品測(cè)試數(shù)據(jù)有效，所分析的離子能夠代表PM2.5中主要的水溶性組分。分別對(duì)不同季節(jié)的樣品進(jìn)行陰陽(yáng)離子平衡分析，可以看出夏、冬季比春、秋季擬合曲線的斜率更大，指示了夏、冬季寶雞市大氣中PM2.5的酸性更強(qiáng)，這可能與夏、冬季形成更多的二次硫酸鹽和硝酸鹽有關(guān)。而春季擬合曲線的相關(guān)性（R2= 0.86）對(duì)比其他季節(jié)略低，可能是受到了春季沙塵樣品中碳酸鹽的影響。

圖2 陰陽(yáng)離子平衡Fig.2 Ion balance in PM2.5

為研究PM2.5中各個(gè)陰、陽(yáng)離子之間的中和反應(yīng)，使用以下公式（3）、（4）和（5）來(lái)計(jì)算不同陽(yáng)離子的中和因子（Neutralization factor,NF）（Kulshrestha et al，1995；Shen et al，2012）：

圖3 鈣離子、銨根離子和鎂離子中和因子的三角圖Fig.3 Triangular diagrams of NF for Ca2+,and Mg2+

表2 PM2.5中水溶性離子相關(guān)系數(shù)矩陣Tab.2 The correlation coef fi cients of water-soluble ions in PM2.5

圖4 與及摩爾濃度的相關(guān)性Fig.4 Relationship betweenmole concentration and amp;mole concentration

2.6 來(lái)源分析

本研究使用主成分分析法（PCA，SPSS 17.0， SPSS Inc.1988）識(shí)別水溶性無(wú)機(jī)離子的主要來(lái)源，并半定量判別各來(lái)源的大致貢獻(xiàn)。主成分分析法是一種廣泛使用的多元統(tǒng)計(jì)方法，可以很好地按照多變量之間的相關(guān)性密切程度來(lái)分類從而簡(jiǎn)化和解釋數(shù)據(jù)。使用主成分分析可以從大量的質(zhì)量濃度數(shù)據(jù)中提取出少數(shù)幾個(gè)潛在因子（主成分）以便于解釋被測(cè)變量之間的關(guān)系（Han et al，2006）。該組數(shù)據(jù)KMO統(tǒng)計(jì)量＞0.5表明適用主成分分析，并且設(shè)定特征值＞1作為需滿足的條件得到兩個(gè)主成分（Kaiser，1960）。表3為寶雞市大氣PM2.5中主要水溶性離子組分經(jīng)主成分分析得到的旋轉(zhuǎn)后因子載荷矩陣。如表3所示，主成分1因子載荷較大的離子組分為和K+，代表了二次氣溶膠來(lái)源以及和它們相關(guān)性較好的生物質(zhì)燃燒來(lái)源；主成分2因子載荷較大的離子組分為F?、Cl?、Mg2+和Ca2+，代表了一次土壤塵排放源。主成分1和2的累計(jì)貢獻(xiàn)率達(dá)80.0%。

表3 PM2.5中水溶性離子的旋轉(zhuǎn)后因子載荷矩陣Tab.3 Rotated component matrix for water-soluble ions in PM2.5

3 結(jié)論

本研究通過(guò)對(duì)寶雞市2012年3月至2013年3月PM2.5中水溶性無(wú)機(jī)離子組分的研究，得到以下結(jié)論：

（1）2012年3月— 2013年3月寶雞市大氣PM2.5中的總水溶性離子平均質(zhì)量濃度為51.62 μg · m?3，其主要組分是，分別占總水溶性離子的40.47%、30.75%和15.07%，它們的年平均質(zhì)量濃度分別為20.89 μg · m?3、15.88 μg · m?3和7.78 μg · m?3。

（2）研究期間，陰陽(yáng)離子的相關(guān)性很好（R2＞ 0.95），PM2.5整體偏酸性。寶雞市大氣PM2.5中Ca2+和起主要的中和作用。

（3）研究期間，當(dāng)寶雞市空氣質(zhì)量較好時(shí)PM2.5中硫酸鹽居多，而隨著空氣污染發(fā)生硝酸鹽逐漸增多并占優(yōu)勢(shì)。

（4）主成分分析結(jié)果顯示，寶雞市PM2.5中水溶性離子的主要來(lái)源有二次氣溶膠，生物質(zhì)燃燒和土壤塵。

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Pollution characteristics and sources of water-soluble ions in PM2.5in Baoji

ZHANG Ting1,2,CAO Junji1,2,3,LIU Suixin1,2
1.Key Laboratory of Aerosol Chemistry amp; Physics,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an 710061,China
2.State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an 710061,China
3.Department of Environmental Science and Technology,Xi’an Jiaotong University,Xi’an 710049,China

Background,aim,and scopeFine particulate matter (PM2.5) causes air quality problems in urban areas,especially visibility reduction and health problems,such as asthma and even mortality.Water-soluble inorganic ions are major components of the atmospheric aerosols,especially PM2.5.They can compose up to 60% — 70% of the total mass of suspended particulate matter.Therefore,observations on the chemical composition of watersoluble fine aerosols would be valuable for understanding their physical/chemical characteristics,sources,and behavior and formation mechanism.Baoji (33°35′ — 35°06′N,106°18′—108°03′E) is an inland city situated in the mid-west part of China.Due to the rapid increase of motor vehicles and the growth in energy consumption over the past few decades,Baoji is facing serious air quality problems,mainly due to the high aerosol loadings in the region.However there has been no much attention paid for the problem in these mid-scale cities.In the current study,we collected the water-soluble ions in PM2.5samples at urban site of Baoji and to investigate the temporal variations and possible sources for these species.This study can provide useful information for establishingcontrol strategies of aerosol pollution.Materials and methodsWater-soluble inorganic ions in PM2.5were collected in Baoji from March 2012 to March 2013.The sampling site was located in Baoji Environmental Monitoring Station that is surrounded by a big residential area.Aerosols were collected by mini-volume samplers equipped with pre-baked quartz fi ber fi lters.A total of 10 water-soluble ions (Na+,,K+,Mg2+,Ca2+,F?,Cl?,,,and) were analyzed by Ion Chromatograph in the aqueous extracts of the air filters.ResultsThe 24-hr average mass concentrations of total water-soluble ions in PM2.5varied from 10.54 μg · m?3to 207.00 μg · m?3,with an overall average of 51.62 μg · m?3.Monthly average concentrations of total water-soluble ions were highest during February (92.33 μg · m?3) and lowest during April (22.1 μg · m?3).In anion,the concentrations of the most abundant ionic species followed the order of＞＞Cl?＞F?,while in cation were＞Ca2+＞Na+＞K+＞Mg2+.Overall,,andwere dominant ionic species in PM2.5,the annual average concentrations were 20.89 μg · m?3,15.88 μg · m?3and 7.78 μg · m?3,respectively.A strong correlation (R2＞0.95) between cation and anion equivalents for all samples indicates that the five cations and five anions were the major ions extracted from the fi lters.The slope (anion/cation) of the linear regression was close to 1.25 in summer and winter,1.08 in spring and autumn.The annual volume-weighted mean values of NF for Ca2+,and Mg2+were 0.23,0.50 and 0.04,respectively,indicating that Ca2+andwere the major neutralizers in PM2.5in Baoji.The seasonal variation of/was shown winter(0.85) ＞ autumn(0.83) ＞ spring(0.66) ＞ summer(0.36).DiscussionThe seasonal variations of secondary components,,and,were similar,i.e.high concentrations in winter and low concentrations in spring and autumn.The seasonal variation trend may be ascribed to (1) the increase of emission sources (i.e.,residential and commercial coal combustion); (2) meteorological conditions during winter were characterized by stagnation with a low inversion layer,which intensify secondary components levels through accumulation of air pollutants.Ion balance calculations are useful for studying the acid base balance of aerosol particles.This result implies that the aerosol particles from summer and winter are more acidic.The buffering of acidity in spring is likely due to the high dust loadings.The neutralization factor (NF) of Ca2+,and Mg2+were calculated using their equivalent concentrations that can be used to describe the interaction between cations and anions.The NF forwas higher in four seasons and NF for Ca2+was higher in spring and autumn,suggesting that Ca2+played a dominant role in the spring and autumn acid neutralization whilehad a stronger buffering ability in the whole year.It showed clearly in correlation coefficients between major ions thatmainly existed as (NH4)2SO4and NH4HSO4,whileas NH4NO3.The mass ratio of/was not suitable for indicator of mobile vs.stationary sources of sulfur and nitrogen in the atmosphere in Baoji./ratio was relatively high with increasing API,it means sulfate decreasing and nitrate increasing while poor air quality.A preliminary source identi fi cation study of the ws-ions was carried out by principal component analysis.The two factor PCA model for the ws-ions in the PM2.5aerosol samples accounted for ～80.0% of the total variance in the concentration data.Factor 1 account for ～49.9% of the total variance,and it was strongly loaded with,,and K+,suggesting likely origins from secondary aerosol and biomass burning.Factor 2 is dominated by F?,Cl?,Mg2+and Ca2+,and it accounted for ～30.1% of the total variance,suggesting their concentrations are affected by primary soil dust.ConclusionsThe annual average concentration of total water-soluble ions in PM2.5was 51.62 μg · m?3in Baoji from March 2012 to March 2013.Water-soluble ions were mainly composed of,and,accounting for 40.47%,30.75% and 15.07% in total water-soluble ions,respectively.PM2.5was generally acidic./ratio was relatively high with increasing API,it means sulfate decreasing and nitrate increasing while poor air quality.The PCA results indicated that secondary aerosol,biomass burning and soil dust were mainly sources of water-soluble ion in PM2.5.Recommendations and perspectivesThe search provide a signi fi cant scienti fi c basis for understanding the pollution characteristics of water-soluble ion in PM2.5at Baoji.To alleviate the PM2.5pollution,reducing coal burning,biomass burning and controlling soil dust should be performed.

National Natural Science Foundation of China (41503123)

ZHANG Ting,E-mail:zhangting@ieecas.cn

Baoji; PM2.5; water soluble ion; source

2016-11-22；錄用日期2017-01-09

Received Date:2016-11-22;Accepted Date2017-01-09

國(guó)家自然科學(xué)基金項(xiàng)目（41503123）

張 婷，E-mail:zhangting@ieecas.cn

張 婷,曹軍驥,劉隨心.2017.寶雞市PM2.5中水溶性離子組分污染特征及來(lái)源分析 [J].地球環(huán)境學(xué)報(bào),8(1):46 – 54.

: Zhang T,Cao J J,Liu S X.2017.Pollution characteristics and sources of water-soluble ions in PM2.5in Baoji [J].Journal of Earth Environment,8(1):46 – 54.

10.7515/JEE201701006