李孟林,朱 喬,曹禮明,魏 靜,黃曉鋒

深圳秋季大氣有機(jī)氣溶膠來源與揮發(fā)性研究

李孟林,朱 喬*,曹禮明,魏 靜,黃曉鋒

(北京大學(xué)深圳研究生院,環(huán)境與能源學(xué)院,城市人居環(huán)境科學(xué)與技術(shù)重點(diǎn)實(shí)驗(yàn)室,廣東 深圳 518055)

使用熱擴(kuò)散管與長飛行時(shí)間氣溶膠質(zhì)譜聯(lián)用系統(tǒng)對(duì)2020年深圳市秋季亞微米級(jí)氣溶膠進(jìn)行在線測量,獲取和分析了氣溶膠的化學(xué)組成及揮發(fā)性特征,并利用正矩陣因子分析法(PMF)對(duì)有機(jī)氣溶膠進(jìn)行了來源解析.結(jié)果顯示:觀測期間,氣溶膠平均質(zhì)量濃度為(28.3±11.1)μg/m3(9.5～76.8μg/m3),其中,有機(jī)物占比最高,為57.9%,其次為硫酸鹽(24.7%).PMF對(duì)有機(jī)氣溶膠解析結(jié)果得到四類源,分別為烴類有機(jī)氣溶膠(HOA)、餐飲源有關(guān)的有機(jī)氣溶膠(COA)、低氧化性的氧化有機(jī)氣溶膠(LO-OOA)和高氧化性的氧化有機(jī)氣溶膠(MO-OOA).HOA、COA、LO-OOA和MO-OOA平均分別占到總有機(jī)物的9.1%、27.2%、31.8%和31.9%.進(jìn)一步采用NO+/NO2+比值法和PMF方法估算有機(jī)硝酸酯(ON)濃度,兩種方法估算結(jié)果相關(guān)性良好,ON的平均濃度為0.17～0.25μg/m3,占總有機(jī)氣溶膠質(zhì)量的1.5%～9.7%,說明其對(duì)深圳大氣氣溶膠貢獻(xiàn)顯著.ON與各有機(jī)氣溶膠因子的相關(guān)性比對(duì)發(fā)現(xiàn),其與LO-OOA相關(guān)性最高(R=0.80),說明其可能來源于新鮮的二次生成反應(yīng).揮發(fā)性研究結(jié)果得出,深圳市氣溶膠主要化學(xué)組分揮發(fā)性順序?yàn)槁塞}≈無機(jī)硝酸鹽>銨鹽>有機(jī)物>有機(jī)硝酸酯>硫酸鹽,對(duì)于有機(jī)氣溶膠因子,其揮發(fā)性排序?yàn)長O-OOA> HOA> COA> MO-OOA,除了LO-OOA,其余因子揮發(fā)性與其氧化態(tài)排序一致,而LO-OOA從50～70℃組分下降最多,說明其所含組分揮發(fā)性差異最為明顯.

氣溶膠揮發(fā)性；有機(jī)氣溶膠；TD-AMS；有機(jī)硝酸酯

近年來,我國在空氣污染治理上取得顯著成效,但在重點(diǎn)城市群地區(qū)大氣氣溶膠污染事件仍頻繁發(fā)生,特別是在秋冬季節(jié)[1].大氣氣溶膠化學(xué)組分復(fù)雜,由多種無機(jī)和有機(jī)化合物組成[2].盡管現(xiàn)有的研究已經(jīng)可以較好地理解氣溶膠無機(jī)部分的來源和形成機(jī)制,但依然缺乏對(duì)有機(jī)組成的全面理解[3].有機(jī)組成約占?xì)馊苣z的20%～90%[4],按照來源可以大致分為直接排放的一次有機(jī)氣溶膠(POA)和由揮發(fā)性有機(jī)化合物(VOCs)氧化反應(yīng)生成的二次有機(jī)氣溶膠(SOA).半揮發(fā)性是大氣氣溶膠的重要物理性質(zhì),可以表征氣相與顆粒相中不同化學(xué)組分的密切關(guān)系.氣溶膠揮發(fā)性也可反映大氣演化過程,對(duì)研究二次氣溶膠的形成機(jī)制有一定的參考作用[5-6],且不同地區(qū)揮發(fā)性特征有著明顯差異[7-8].常用的測量氣溶膠揮發(fā)性的方法有:揮發(fā)性串聯(lián)差分遷移率分析儀[8]、稀釋取樣器[9]和熱擴(kuò)散管與氣溶膠質(zhì)譜聯(lián)用(TD-AMS)[10].其中,TD-AMS由于能在線高時(shí)間分辨率獲取氣溶膠不同組分的揮發(fā)性特征,而被廣泛應(yīng)用于外場觀測[6-7,11]和實(shí)驗(yàn)室模擬中[12-13].

有機(jī)硝酸酯(ON)是指含有硝酸基團(tuán)的酯類化合物及其衍生物的總稱.顆粒態(tài)ON的源?匯過程對(duì)氮氧化物循環(huán)和臭氧生成有著顯著影響[14-16],而當(dāng)前對(duì)于顆粒態(tài)ON的來源和生成途徑依然缺乏全面認(rèn)識(shí).Rollins等[17]基于熱離解—激光誘導(dǎo)熒光方法搭建的儀器,首次測量報(bào)道了環(huán)境大氣中顆粒態(tài)ON的濃度.近年來一些學(xué)者針對(duì)AMS測量的氣溶膠,提出了間接估算定量ON的方法[18-20],并在歐美地區(qū)開展了一系列相關(guān)研究[17,21-25].在我國地區(qū),利用AMS開展的ON研究相對(duì)較少[26-28].目前的研究結(jié)果發(fā)現(xiàn),ON的來源和生成途徑可能與歐美地區(qū)存在差異,如歐美地區(qū)研究普遍認(rèn)為生物排放的BVOCs被夜間NO3-自由基氧化的過程是ON生成的主要途徑[21,29],但是我國地區(qū)ON的生成前體物可能還包括認(rèn)為人排放的芳香烴類VOCs,且可能與生物質(zhì)燃燒的一次排放過程有關(guān)[26,28].除了ON來源生成機(jī)制,目前對(duì)于ON其它重要性質(zhì),如揮發(fā)性等的認(rèn)識(shí)還非常有限,特別是對(duì)于環(huán)境大氣中直接監(jiān)測分析的有關(guān)研究仍十分缺乏.

綜上,為了更好的理解有機(jī)氣溶膠的來源和揮發(fā)性特征,及其重要組分—ON的相關(guān)特性,本研究利用TD-AMS 聯(lián)用系統(tǒng),選取2020年秋季典型月份,對(duì)深圳市亞微米級(jí)氣溶膠化學(xué)組分進(jìn)行了高分辨率在線測量,估算了ON的濃度水平,評(píng)估了加熱條件下化學(xué)組成特征及氣溶膠半揮發(fā)性特征,以此更好地理解有機(jī)氣溶膠的污染狀況和成因,為改善深圳地區(qū)空氣質(zhì)量提供數(shù)據(jù)支撐和參考.

1 儀器與方法

1.1 觀測地點(diǎn)和時(shí)間

選擇北京大學(xué)深圳研究生院(PKUSZ)大氣污染觀測超級(jí)站作為觀測點(diǎn)位.根據(jù)深圳市生態(tài)環(huán)境局的數(shù)據(jù),深圳市大氣污染呈現(xiàn)“西高東低”的分布特征,大鵬新區(qū)和鹽田等地區(qū)污染程度相對(duì)最輕,坪山、羅湖以及南山南部和龍崗南部地區(qū)次之,而光明新區(qū)及龍華區(qū)部分地區(qū)污染較重.PKUSZ點(diǎn)位位于深圳市南山區(qū),在全市屬中度污染水平,能夠很好的代表深圳的平均污染水平.觀測點(diǎn)位周圍以水庫?高爾夫球場和療養(yǎng)基地為主,植被覆蓋率高,無明顯局部污染源.監(jiān)測儀器架設(shè)在研究生院C棟教學(xué)樓頂層(距地面約20m),采樣管架設(shè)在4樓樓頂,切割頭離樓頂約1.5m.根據(jù)深圳市氣象局的氣候概況和四季劃分,本研究選取了秋季的典型時(shí)段(2020年10月1日～11月2日)作為觀測時(shí)間.

1.2 TD-AMS儀器原理及數(shù)據(jù)分析方法

采用的熱擴(kuò)散管(TD)及高分辨率飛行時(shí)間氣溶膠質(zhì)譜儀(L-ToF-AMS)均由美國Aerodyne公司研發(fā).L-ToF-AMS是更新版本的顆粒物在線監(jiān)測儀器,相比之前研究所用的高分辨氣溶膠質(zhì)譜儀(HR-AMS),該L-ToF-AMS具有更高分辨率特性、更低的檢測限和更快的響應(yīng)特性,最高質(zhì)量高分辨率可達(dá)8000M/ΔM,響應(yīng)速度可達(dá)100Hz.因此,L-ToF-AMS的測量結(jié)果能更好的區(qū)分不同組分碎片,有利于大氣氣溶膠的精準(zhǔn)定性定量分析.

TD-AMS的簡易原理如圖1所示:氣溶膠首先經(jīng)TD,TD 內(nèi)流量為0.45L/min,加熱管中停留時(shí)間約為27.9s.TD 由加熱管和擴(kuò)散管組成,切換閥可在加熱氣路(TD)和旁路(BP)中交替,實(shí)驗(yàn)選擇的加熱溫度為50和70℃.這2個(gè)溫度分別對(duì)應(yīng)了實(shí)驗(yàn)室純硝酸銨和氯化銨完全揮發(fā)的溫度臨界值[30],可以較好的用來研究環(huán)境大氣中各組分揮發(fā)性特征,且最新相關(guān)研究發(fā)現(xiàn),加熱超過100℃可能導(dǎo)致有機(jī)物組成發(fā)生變化[30],因此本研究選擇50和70℃來探究氣溶膠的揮發(fā)性差異.加熱氣路在50,70℃2個(gè)溫度梯度中循環(huán)變化,每個(gè)升溫周期約為25min.顆粒物在TD加熱管停留約28s后進(jìn)入常溫?cái)U(kuò)散層,其中揮發(fā)組分在擴(kuò)散層被活性炭吸附,吸附效率接近100%.剩余組分進(jìn)入L-ToF-AMS,其進(jìn)樣流量為0.08L/ min.L-ToF-AMS在線測量真空動(dòng)力學(xué)粒徑小于1μm的非難熔亞微米級(jí)顆粒物(NR- PM1),包括有機(jī)物(OA)、硫酸鹽(SO42-)、硝酸鹽(NO3-)、銨鹽(NH4+)和氯化物(Cl-)等.在觀測開始前,進(jìn)行電離效率(IE)標(biāo)定、粒徑標(biāo)定和流量標(biāo)定,以確定IE、粒徑和流量的校正擬合參數(shù).電離效率的標(biāo)定方法是,先配置濃度適宜的純硝酸銨溶液,由氣溶膠發(fā)生器(型號(hào)3076,美國TSI公司)產(chǎn)生純硝酸銨顆粒,經(jīng)由硅膠管干燥后,連接盡量短的黑碳管后,將硝酸銨氣溶膠通入AMS中,由電遷移率分析儀(DMA,3081,美國TSI公司)篩選出300nm的單分散硝酸銨顆粒后,同時(shí)由顆粒物凝結(jié)計(jì)數(shù)儀(CPC,3775,美國TSI公司)和AMS測量數(shù)濃度和質(zhì)量濃度,根據(jù)硝酸銨的密度,按照測得的數(shù)濃度,計(jì)算質(zhì)量濃度,并與AMS所測結(jié)果進(jìn)行擬合,計(jì)算AMS的電離效率,本研究中IE為6.4×10-8.對(duì)于監(jiān)測的其它組分,相對(duì)電離效率(RIE)分別為:銨鹽3.8,硝酸鹽1.1,硫酸鹽0.8,有機(jī)物1.4,氯鹽1.3.此外,本研究中還利用標(biāo)準(zhǔn)AMS觀測條件下(濕度小于30%)的采集效率(CE)對(duì)數(shù)據(jù)進(jìn)行校正.CE校正中采用Middlebrook等[31]基于化學(xué)成分的CE估算方法進(jìn)行,觀測期間平均CE在0.5左右.氣溶膠各組分的揮發(fā)性特征以加熱氣路與旁路質(zhì)量濃度之比的質(zhì)量剩余分?jǐn)?shù)(MFR)進(jìn)行半定量描述,MFR 越高,揮發(fā)性越低.

正矩陣因子分析(PMF)是解決雙線性解混合問題的一種數(shù)學(xué)方法,并已廣泛應(yīng)用于氣溶膠源解析領(lǐng)域[32-33].AMS-PMF方法的基本原理如下:

=GF+(1)

X=Spgf+e(2)

圖1 TD-AMS觀測系統(tǒng)結(jié)構(gòu)[6]

1.3 黑碳測量方法

黑碳儀(Aethalometer,AE-31,Magee ScientificInc,美國)用主動(dòng)方式將空氣中的顆粒物收集在石英纖維濾帶上,然后測定透過的激光強(qiáng)度的衰減,換算出空氣中黑碳(BC)的質(zhì)量濃度,單位一般為μg/m3或ng/m3.

1.4 ON污染分析方法

由于AMS直接測量的是氣溶膠碎片信息,而在以往的大多數(shù)相關(guān)研究中,將NO3-碎片(NO3, total)全部認(rèn)為來源于無機(jī)硝酸鹽的估算方法是不準(zhǔn)確的,因?yàn)镺N的“-ONO2”官能團(tuán)也是NO3-碎片的重要來源.因此,可根據(jù)以下兩種方法,從NO3, total中估算來源于ON(NO3,org)部分的方法.

1.4.1 比值法 在AMS質(zhì)譜中,NO3-的相關(guān)碎片主要集中在NO+和NO2+中,基于NO+/NO2+在ON中的比值(ON)和純硝酸銨物質(zhì)的比值(NH4NO3)存在明顯差別的這一特征,可以估算ON中NO+和NO2+的質(zhì)量濃度.

Farmer等[18]發(fā)現(xiàn)ON的值在不同測量方法以及測量物種中存在較大差異,總結(jié)文獻(xiàn)中實(shí)驗(yàn)室測量結(jié)果,得到ON/NH4NO3在2.08～3.99之間,據(jù)此可以分析估算ON的上下限.具體公式如下:

NOorg=ON′NO2,org(4)

式中:sample表示環(huán)境樣品中的NO+/NO2+;NH4NO3是通過標(biāo)定過程中純硝酸銨的比值得到,在實(shí)際觀測中會(huì)在觀測開始和結(jié)束期間進(jìn)行2次標(biāo)定來確定NH4NO3值.

1.4.2 PMF方法 PMF解析法與常規(guī)OA因子解析相似,輸入數(shù)據(jù)為AMS測量得到的有機(jī)物碎片和NO+與NO2+碎片矩陣,解析結(jié)果包含一個(gè)主要由NO+和NO2+碎片貢獻(xiàn)的因子,將其定義為無機(jī)硝酸鹽因子,其余因子中的NO+和NO2+相關(guān)碎片則可以認(rèn)為是來源于ON,具體的相關(guān)碎片計(jì)算方式如下[21]:

NOorg=S[OA factor]′(NO)(5)

NO2,org=S[OA factor]′(NO2,i)(6)

式中:[OA factor]表示為第個(gè)OA因子的質(zhì)量濃度;(NO)和(NO2,i)分別表示OA因子中NO+和NO2+離子所占比例.而一旦得出了ON中NO3-碎片的值,可以進(jìn)一步通過總監(jiān)測的硝酸鹽減去ON來計(jì)算出無機(jī)硝酸鹽中的NO3-碎片濃度.

2 結(jié)果與討論

2.1 環(huán)境氣溶膠濃度水平及化學(xué)組成特征

圖2(a)顯示廣東省深圳市西麗大學(xué)城點(diǎn)位的PM1(此處表示NR-PM1與黑碳的總和)平均濃度為(28.3±11.11)μg/m3(9.5～76.8μg/m3),各化學(xué)組分占比及質(zhì)量濃度如圖所示,有機(jī)物貢獻(xiàn)最大,占PM1總質(zhì)量濃度的57.9%.硫酸鹽的貢獻(xiàn)排列第二,占比為24.7%.近年來,深圳局地的SO2減排成效較為明顯,然而區(qū)域尺度上的SO2及硫酸鹽污染依然需要進(jìn)一步控制.與在同點(diǎn)位氣溶膠化學(xué)組成在線監(jiān)測儀(ACSM)觀測到的PM1平均質(zhì)量濃度((26.1± 8.9)μg/m3)結(jié)果相近,且ACSM所測各化學(xué)組成時(shí)間序列與L-Tof-AMS結(jié)果比對(duì)相關(guān)性良好(2=0.83～0.97).由圖2(c)可知,隨著PM1總濃度的增加,有機(jī)物和硝酸鹽所占比例逐漸增加,硫酸鹽占比減少.

圖2(d)為PM1各組分的日變化趨勢圖.其中,BC在早晚高峰時(shí)段出現(xiàn)了濃度的抬升;硫酸鹽的日變化相對(duì)較為平緩,這與其區(qū)域傳輸特征相符.有機(jī)物由于所含組分復(fù)雜且性質(zhì)差異大,將在下文進(jìn)行源解析后再對(duì)具體因子進(jìn)行詳述.總體來說,有機(jī)物在白天的午間(11:00～14:00)和晚間(20:00～22:00)濃度有所抬升,主要對(duì)應(yīng)了光化學(xué)生成以及夜間的餐飲貢獻(xiàn)和邊界層變化影響.如前文所述,本研究從AMS采樣的總NO3-中區(qū)分了無機(jī)硝酸鹽和有機(jī)硝酸酯(比值法和PMF法),兩者的日變化趨勢差異顯著,說明識(shí)別效果良好.無機(jī)硝酸鹽的日變化在午間(11:00～14:00)和夜間(21:00～23:00)出現(xiàn)峰值,可能是由于白天的光化學(xué)反應(yīng)生成以及夜間溫度較低促使氣相/顆粒相分配向顆粒相轉(zhuǎn)化.ON的高值則主要出現(xiàn)在夜間(19:00～次日7:00),這與本研究小組以往觀測的趨勢相符[34].銨鹽的日變化趨勢綜合了硝酸鹽和硫酸鹽的變化趨勢.氯化物的日變化特征為夜間高白天低,近來的研究顯示其主要來源于一次燃燒排放[35].

圖2 環(huán)境氣溶膠濃度水平及化學(xué)特征

2.2 環(huán)境有機(jī)氣溶膠源解析結(jié)果

依據(jù)前文所述的關(guān)鍵參數(shù)診斷和評(píng)判準(zhǔn)則,最終確定有機(jī)氣溶膠因子個(gè)數(shù)為4個(gè),分別是烴類有機(jī)氣溶膠(HOA),餐飲源有關(guān)的有機(jī)氣溶膠(COA),低氧化性的氧化有機(jī)氣溶膠(LO-OOA)和高氧化性的氧化有機(jī)氣溶膠(More-oxidized oxygenated OA, MO-OOA).其中,HOA和COA屬于POA,LO-OOA和MO-OOA屬于SOA.

圖3(a)為各OA因子的特征質(zhì)譜圖.為了便于識(shí)別來源特征,將AMS測定的離子碎片分為5類: CH+是還原性的烷基離子碎片;CHO+是氧化性的含氧基團(tuán),一般來自于有機(jī)物中的羧酸或者醛類; CHN+是含N元素的烷基碎片;CHON+是氧化性有機(jī)氮離子碎片;OH+是水和羧酸打碎的離子碎片,與CO2+(/44)離子碎片成一定線性關(guān)系.5類離子碎片在質(zhì)譜圖中用不同的顏色分別被標(biāo)識(shí)出來.每個(gè)因子的質(zhì)譜差異明顯,HOA的質(zhì)譜圖含有較多CH+碎片,O:C比例最低,為0.29.特征質(zhì)譜在/55和/57通道中,除了烷基碎片C4H7+和C4H9+外,還有相當(dāng)比例的含氧碎片C3H3O+和C3H5O+,而這些碎片主要來源于食物油中的油酸和亞油酸,其O:C比略高于HOA,為0.43.LO-OOA和MO-OOA譜圖具有大量CHO+碎片,O:C比率較高,分別為0.70和1.0,表明其二次老化特征[36-37].HOA、COA、LO- OOA和MO-OOA平均分別占總有機(jī)物的9.1%、27.2%、31.8%和31.9%(圖3(c)),由此可看出,深圳秋季大氣有機(jī)氣溶膠中以SOA貢獻(xiàn)為主.

OA因子的日變化如圖3(b)所示. HOA在早上7:00和晚上20:00有2個(gè)明顯的高峰,對(duì)應(yīng)早晚交通排放高峰.與餐飲源有關(guān)的COA因子峰值出現(xiàn)在用餐時(shí)間12:00和20:00.LO-OOA和MO-OOA具有相似的變化模式,從9:00開始增加,在20:00時(shí)開始減少濃度下降,這主要可能由白天的光化學(xué)氧化積累引起.

2.3 秋季ON污染特征

根據(jù)比值法和PMF方法估算ON的結(jié)果如表1所示.NO3,org的濃度和NO3,org占總的NO3+的質(zhì)量分?jǐn)?shù).采用比值法計(jì)算得到對(duì)應(yīng)ON/NH4NO3上限和下限值的ON占比為17.6%～26.3%.進(jìn)一步使用PMF方法估算NO3,org,得出的NO3,org占總的NO3的質(zhì)量分?jǐn)?shù)為24.21%.且比值法與PMF方法估算得出的結(jié)果時(shí)間序列相關(guān)性高(=0.75),說明估算結(jié)果的可靠性.進(jìn)一步假設(shè)ON的平均分子量為200～300g/mol[18],計(jì)算得出ON占總OA的3.67%～ 8.63%,說明ON是秋季深圳大氣有機(jī)氣溶膠的重要組成部分.

表2分析了ON與各OA因子的相關(guān)性,結(jié)果顯示:ON與LO-OOA的相關(guān)性=0.8,顯著高于其它因子.說明深圳市秋季ON的來源途徑可能與新鮮二次生成過程密切.進(jìn)一步結(jié)合圖2(d)給出的ON日變化趨勢可得出,ON在夜間一直處于較高濃度水平,這與Yu 等[38]研究深圳地區(qū)推測的ON夜間二次生成反應(yīng)活躍的結(jié)論相符.

2.4 環(huán)境氣溶膠揮發(fā)性特征

圖4給出了TD升溫加熱在50和70℃兩種溫度下大氣顆粒物主要成分MFR值.對(duì)于AMS直接測到的常規(guī)組分(圖4(a)),50℃時(shí)揮發(fā)物質(zhì)以無機(jī)硝酸鹽和氯鹽為主導(dǎo).在50℃時(shí),無機(jī)硝酸鹽和氯鹽中約有15%的組分揮發(fā).而硫酸鹽的揮發(fā)性最低,在50和70℃時(shí),仍有96%的質(zhì)量剩余.ON的揮發(fā)性顯著低于無機(jī)硝酸鹽,在50℃時(shí)的MFR為0.93.一般認(rèn)為,50℃時(shí)的MFR排序可以基本代表物種的揮發(fā)性大小[38-39],因此對(duì)于常規(guī)AMS監(jiān)測物種,揮發(fā)性增加順序?yàn)?氯鹽≈無機(jī)硝酸鹽>銨鹽>有機(jī)物>有機(jī)硝酸酯>硫酸鹽.

圖4(b)進(jìn)一步展示了PMF解析出的OA各因子的MFR值以及各自的氧化態(tài)(OSC≈2O:C-H:C).對(duì)于4個(gè)OA因子,其在50℃時(shí)的揮發(fā)性排序?yàn)?LO- OOA>HOA>COA>MO-OOA,值得注意的是,除了LO-OOA,其余因子的揮發(fā)性高低與其氧化態(tài)高低成正比.揮發(fā)性與氧化態(tài)排序不一致的情況在文獻(xiàn)[40-41]報(bào)道過.而從50～70℃,OA因子中只有LO- OOA的MFR出現(xiàn)了明顯下降,降幅為18%,說明LO- OOA中所含組分復(fù)雜,揮發(fā)性性質(zhì)差異明顯.

表1 2020年深圳秋季觀測期間ON估算結(jié)果

表2 ON與OA因子的相關(guān)系數(shù)

3 結(jié)論

3.1 深圳秋季PM1平均濃度為(28.3±11.11)μg/m3,其中有機(jī)物和硫酸鹽貢獻(xiàn)比例最高.進(jìn)一步對(duì)有機(jī)物利用PMF方法進(jìn)行源解析得到四類因子,其中二次因子所占比例更高,證明有機(jī)氣溶膠二次污染更加嚴(yán)重.

3.2 采用NO+/NO2+比值法和PMF方法估算有機(jī)硝酸酯(ON)濃度得出, ON是深圳秋季大氣有機(jī)氣溶膠的重要組成.ON的日變化趨勢呈現(xiàn)日間低夜間高趨勢,與以往深圳研究結(jié)果得出的ON夜間生成反應(yīng)活躍相符.

3.3 對(duì)氣溶膠不同組分的揮發(fā)性分析,得出NR- PM1的主要組分中,揮發(fā)性增加順序是氯鹽≈無機(jī)硝酸鹽>銨鹽>有機(jī)物>有機(jī)硝酸酯>硫酸鹽.進(jìn)一步分析有機(jī)物各因子揮發(fā)性,發(fā)現(xiàn)除了LO-OOA因子外,其余因子的揮發(fā)性排序與氧化態(tài)一致.

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Source identification and volatility characteristics of ambient organic aerosols in Shenzhen in autumn.

LI Meng-lin, ZHU Qiao*, CAO Li-ming, WEI Jing, HUANG Xiao-feng

(School of Environment and Energy, Shenzhen Graduate School, Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University, Shenzhen 518055, China),, 2021,41(9)：4009～4015

Using a thermodenuder coupled with a long-time-of-flight aerosol mass spectrometry system, we conducted online measurements of submicron aerosols in Shenzhen in the fall of 2020. In addition to obtaining chemical compositions of PM1and analyzing their volatility characteristics, we used positive matrix factorization (PMF) method to apportion sources for organic aerosols (OA). The results showed that during the sampling period, the average mass concentration of aerosol was (28.3±11.11)μg/m3(9.5～76.8μg/m3). Among the chemical compositions, organics contributed most to PM1(57.9%), sulfate was the secondary dominant composition, which accounted for 24.7% in total PM1. PMF analysis for OA resolved four OA factors: hydrocarbon-like OA (HOA), cooking-related OA(COA), less-oxidized oxygenated OA(LO-OOA), and more-oxidized oxygenated OA(MO-OOA). The mass fractions of HOA, COA, LO-OOA and MO-OOA were 9.1%, 27.2%, 31.8% and 31.9%, respectively. Furthermore, we used two methods including NO+/NO2+ratio and PMF methods to estimate organonitrates (ON). The average concentration of ON was 0.17～0.25μgm-3, accounting for 1.5%～9.7% of OA, indicating ON made a substantial contribution to aerosols in Shenzhen. Correlation analysis shows that ON were correlated bestwith LO-OOA(=0.80), suggesting ON maybe formed via localsecondary formation. The volatility analysis revealed that the volatility sequence of the main chemical components was chloride≈inorganic nitrate>ammonium>organic matte>ON>sulfate, and the volatility sequence of the OA factors was LO-OOA> HOA> COA> MO-OOA. Except LO-OOA, the volatility sequence of other OA factors was consistent with their oxidation states. LO-OOA evaporated most from 50℃to 70℃, suggesting the significant difference of volatility existed among its compositions.

aerosol volatility；organic aerosol；TD-AMS；organonitrates

X511

A

1000-6923(2021)09-4009-07

李孟林(1997-)女,四川達(dá)州人,碩士,主要從事大氣氣溶膠方面研究.發(fā)表論文1篇.

2021-05-24

國家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2017YFC0210004);深圳科技計(jì)劃項(xiàng)目(JCYJ20200109120401943);中國博士后科學(xué)基金資助項(xiàng)目(8206300271)

* 責(zé)任作者, 博士, zhuqiao2013@pku.edu.cn