王占祥,郭久久,穆 熙,李繼祥,高 宏*,黃 韜,馬建民

寧東基地大氣PAHs污染特征及呼吸暴露風(fēng)險(xiǎn)

王占祥1,郭久久2,穆 熙1,李繼祥1,高 宏1*,黃 韜1,馬建民3

(1.蘭州大學(xué)資源環(huán)境學(xué)院,甘肅省環(huán)境污染預(yù)警與控制重點(diǎn)實(shí)驗(yàn)室,甘肅 蘭州 730000；2.中國(guó)電建集團(tuán)國(guó)際工程有限公司,北京 100036；3.北京大學(xué)城市與環(huán)境學(xué)院,北京 100871)

利用主動(dòng)觀測(cè)技術(shù)對(duì)寧東能源化工基地大氣PM2.5、PM1.0和氣相中的PAHs濃度水平、族譜特征、時(shí)空分布及來源進(jìn)行研究,并基于該觀測(cè)數(shù)據(jù)對(duì)居民呼吸暴露健康風(fēng)險(xiǎn)進(jìn)行評(píng)估.結(jié)果表明,寧東基地大氣PM2.5、PM1.0及氣相中∑16PAHs濃度范圍分別為:17.95~325.12ng/m3、12.66~311.96ng/m3和26.33~97.88ng/m3,年均濃度分別為(99.42±117.48)ng/m3、(78.88±100.58)ng/m3和(57.89±47.39) ng/m3.寶豐基地冬夏季大氣PM2.5、PM1.0和氣相中∑16PAHs濃度水平均明顯高于英力特;寶豐和英力特基地冬季大氣PM2.5、PM1.0中∑16PAHs濃度水平均明顯高于夏季濃度.寧東基地大氣中∑16PAHs的濃度水平要高于國(guó)內(nèi)外其他城市,大氣PAHs污染較為嚴(yán)重.源解析表明夏季寧東基地PAHs的主要排放源是工業(yè)煤燃燒和機(jī)動(dòng)車尾氣,冬季則主要來自工業(yè)煤燃燒和木材、薪柴等生物質(zhì)燃燒排放.寧東基地人群暴露于大氣PAHs 可能會(huì)造成平均冬季每百萬人中約有33~2628人罹患癌癥,夏季每百萬人中約有11~834人罹患癌癥的風(fēng)險(xiǎn).

寧東能源化工基地；多環(huán)芳烴；大氣濃度水平；來源解析；呼吸暴露風(fēng)險(xiǎn)

多環(huán)芳烴(PAHs)是含有兩個(gè)及以上稠合芳環(huán)的化學(xué)物質(zhì),主要來源于含碳有機(jī)物的不完全燃燒排放[1].因其對(duì)生物具有強(qiáng)烈的致畸、致癌、致突變作用,并且在環(huán)境中具有持久性、半揮發(fā)性、生物蓄積性及高毒性而受到廣泛關(guān)注[2-6].PAHs的主要來源包括自然源和人為源.火山爆發(fā)和森林火災(zāi)是PAHs的主要自然排放源[7].人為源主要包括化石燃料燃燒、煉焦、原鋁生產(chǎn)、垃圾焚燒、生物質(zhì)燃燒、石油及石油產(chǎn)品的釋放等[4,8-9].進(jìn)入大氣中的PAHs主要以氣相和顆粒相2種形式存在,經(jīng)由大氣進(jìn)行長(zhǎng)距離遷移、擴(kuò)散,最終主要通過干濕沉降等過程去除,而沉降于植物葉片表面的PAHs則會(huì)通過生物轉(zhuǎn)化發(fā)生降解[10].環(huán)境中未被清除的PAHs通過呼吸、飲食、皮膚等途徑被人體直接或間接攝取或吸收,對(duì)人體健康構(gòu)成一定威脅.

寧東能源化工基地(以下簡(jiǎn)稱寧東基地)是國(guó)務(wù)院批準(zhǔn)的國(guó)家重點(diǎn)開發(fā)區(qū)和西部重要的能源基地.其主要以煤炭、電力、煤化工三大產(chǎn)業(yè)為支撐[11].智靜等[12]研究表明,火力發(fā)電是寧東基地最主要的大氣污染物排放源,其污染物排放量占大氣污染物排放總量的82.98%.2015 年寧東基地PM10年均濃度為108μg/m3[13],超過國(guó)家《環(huán)境空氣質(zhì)量標(biāo)準(zhǔn)》[14]二級(jí)標(biāo)準(zhǔn)0.54倍;PM2.5年均濃度為42μg/m3,超過大氣二級(jí)標(biāo)準(zhǔn)0.2倍.而煤和石油等燃料的高溫裂解以及生物質(zhì)的不完全燃燒是PAHs的主要貢獻(xiàn)源[15].本文擬以寧東基地為研究區(qū),利用大氣主動(dòng)采樣技術(shù)對(duì)研究區(qū)大氣中美國(guó)環(huán)保局(USEPA)優(yōu)先控制的16種PAHs進(jìn)行觀測(cè)研究,闡明大氣PAHs的濃度水平的時(shí)空分布、粒徑分布及族譜特征,了解寧東基地大氣中PAHs的主要污染來源及其對(duì)當(dāng)?shù)鼐用竦慕】碉L(fēng)險(xiǎn)影響,為寧東基地大氣PAHs污染治理提供科學(xué)的依據(jù).

1 材料與方法

1.1 樣品采集

選用配置PM2.5和PM1.0切割頭的主動(dòng)采樣器采集大氣細(xì)顆粒物PM2.5、PM1.0及氣相樣品,其中PM1.0夏季樣品采集時(shí)使用中流量采樣器(武漢天虹儀表有限責(zé)任公司),冬季使用大流量采樣器(廣州銘野環(huán)?？萍加邢薰?,PM2.5均為大流量采樣器(廣州銘野環(huán)保科技有限公司).其中顆粒相和氣相樣品的采集介質(zhì)分別為石英纖維濾膜(QFF)和聚氨酯泡沫(PUF).本研究中2個(gè)采樣點(diǎn)分別布設(shè)于寧東基地的寶豐工業(yè)基地(以下簡(jiǎn)稱:寶豐基地)和英力特工業(yè)基地(以下簡(jiǎn)稱英力特基地)(圖1).寶豐基地產(chǎn)業(yè)類型較多,重點(diǎn)包括煤炭深加工及轉(zhuǎn)化、以煤化工產(chǎn)品為中間體的深加工等項(xiàng)目,且緊鄰G20青銀高速和103省道.英力特基地位于長(zhǎng)城石化工業(yè)區(qū)內(nèi),毗鄰寧東工業(yè)園煤化工基地,主要發(fā)展大型或特大型的煤氣化、煤制油及配套和深加工等項(xiàng)目產(chǎn)業(yè)[16].采樣點(diǎn)離地面3~5m,距基礎(chǔ)面1.5m,周圍無遮擋建筑物,能較好地反映研究區(qū)大氣平均污染狀況.本研究采樣時(shí)間分為冬季采暖期和夏季非采暖期,具體采樣時(shí)間為2016年7月3日~9日(非采暖期,23h)、7月24日~30日(非采暖期,晝夜各11h)、2016年12月30~2017年1月5日(采暖期,23h)、2017年1月10日~16日(采暖期,晝夜各11h).采樣前,PUF用二氯甲烷、正己烷和丙酮索氏提取48h以除去目標(biāo)物;QFF采樣前在鋁箔中置于450℃的馬弗爐中灼燒5h、平衡24h稱重.

圖1 寧東基地2個(gè)大氣采樣點(diǎn)分布

1.2 樣品前處理

采用Liu等[17]的方法處理PUF、PM1.0和 PM2.5濾膜樣品.(1)索氏提取:將PUF(包裹在預(yù)先處理好的箔片中)和稱重后的QFF樣品裝入索提裝置中,燒瓶中加入二氯甲烷溶液150mL, 5組分氘代PAHs(PAHs回收率指示物)1000ng,適量銅片,提取24h.(2)旋轉(zhuǎn)蒸發(fā)濃縮:利用旋轉(zhuǎn)蒸發(fā)儀將以上燒瓶中提取液旋轉(zhuǎn)蒸發(fā)至2mL,再用正己烷置換后,濃縮至約1mL.(3)分離凈化:首先用正己烷淋洗柱子,然后加入樣品溶液,再用二氯甲烷和正己烷混合物(:=1:1)淋洗.(4)氮吹濃縮:利用氮吹儀,通過氮?dú)鉂饪s淋洗液,轉(zhuǎn)至樣品瓶.將目標(biāo)液用樣品瓶的內(nèi)套管定容至100μL,加入200ng六甲基苯(內(nèi)標(biāo)物)保存待測(cè).

1.3 樣品分析

1.4 質(zhì)量控制與質(zhì)量保證

為確保分析數(shù)據(jù)的準(zhǔn)確性,在樣品采集階段設(shè)置野外空白,在實(shí)驗(yàn)室分析階段設(shè)置實(shí)驗(yàn)室空白.使用GC-MS測(cè)樣時(shí),首先檢測(cè)標(biāo)準(zhǔn)品以檢查儀器的穩(wěn)定程度,確保儀器偏差不超過±10%.在樣品前處理時(shí)加入氘代PAHs作為PAHs組分的回收率指示物.目標(biāo)化合物PAHs樣品5組分氘代PAHs回收率結(jié)果如下:目標(biāo)化合物的回收率均能控制在70%~ 110%,低環(huán)NapD8(回收率40%~94.87%),其他回收率為72.35%~109.80%,標(biāo)準(zhǔn)偏差在20%以內(nèi).樣品定量校正曲線除Nap外各組分標(biāo)準(zhǔn)曲線2均大于0.999.

1.5 大氣PAHs來源解析

不同排放源排放的PAHs其各組分之間的構(gòu)成比例不同,同時(shí)不同的PAHs也可作為不同類型污染源的排放特征指示.PAHs特征比值法源解析是基于不同污染源排放的特征化合物的濃度差異,通過特征化合物的比值確定排放源,可鑒別石油源、液體石化燃料燃燒源以及煤炭和生物質(zhì)燃燒源的排放.Pio等[18]研究表明IP/(IP+BghiP)和Flua/(Flua+Pyr)在交通、燃煤以及生物質(zhì)燃燒排放源的鑒別中具有重要的作用.

同時(shí),Yunker等[19]總結(jié)了Ant/(Ant+Phe)、Flua/ (Flua+Pyr)、BaA/(BaA+Chry)、以及IP/(IP+BghiP)在PAHs排放源判斷上的特征比值(表1).

表1 PAHs來源解析的特征化合物比值

1.6 大氣PAHs呼吸暴露健康風(fēng)險(xiǎn)評(píng)估方法

大氣中的PAHs可通過呼吸途徑進(jìn)入人體內(nèi),對(duì)人類健康造成一定威脅.本研究利用終身致癌風(fēng)險(xiǎn)(ECR)來定量評(píng)估研究區(qū)人群通過呼吸暴露PAHs的致癌風(fēng)險(xiǎn).首先根據(jù)16種PAHs的毒性當(dāng)量因子(TEF)來計(jì)算PAHs的等效苯并(a)芘BaP 濃度(BaPeq),具體計(jì)算公式如下:

式中:C為大氣第種PAH濃度,ng/m3;TEF為第種PAH的毒性當(dāng)量因子.Nisbet等[20]根據(jù)實(shí)驗(yàn)小鼠致癌毒性,通過比較不同單體PAHs和BaP的差異,估算TEF值.表2中列出本研究中USEPA16種PAHs的TEF值,如下:

表2 　16種PAHs的TEF值

基于研究區(qū)大氣中16種PAHs的BaPeq劑量水平,利用終身致癌風(fēng)險(xiǎn)ECR定量評(píng)估研究區(qū)人群通過呼吸暴露PAHs的致癌風(fēng)險(xiǎn).具體公式如下:

式中:URBaP為單位暴露風(fēng)險(xiǎn)值,即暴露于單位濃度(ng/m3)BaP的人類患癌癥的概率.世界衛(wèi)生組織(WHO)規(guī)定URBaP為8.7×10-5per ng/m3,即假定人均壽命為70a,吸入1ng/m3的BaP每10萬人中大約有8.7個(gè)人可能會(huì)患有癌癥[21].美國(guó)加州環(huán)境保護(hù)署(CalEPA)規(guī)定URBaP為1.1×10-6per ng/m3[22].URBaP為8.7×10-5per ng/m3是根據(jù)對(duì)焦?fàn)t工人進(jìn)行流行病學(xué)研究而得;而URBaP為1.1×10-6per ng/m3是通過倉鼠對(duì)吸入PAHs而導(dǎo)致呼吸道腫瘤的動(dòng)物試驗(yàn)而得.目前這兩個(gè)BaP單位暴露風(fēng)險(xiǎn)值已在很多研究中被應(yīng)用[3,7,23].本研究中同時(shí)采用這兩個(gè)URBaP設(shè)定值進(jìn)行對(duì)照研究,估算寧東基地當(dāng)?shù)鼐用裢ㄟ^呼吸暴露大氣中的PAHs導(dǎo)致的致癌風(fēng)險(xiǎn).

1.7 數(shù)據(jù)處理

利用Excel 2007與Origin 2017進(jìn)行數(shù)據(jù)基本處理,采用SPSS 25.0進(jìn)行主成分等統(tǒng)計(jì)學(xué)分析.

2 結(jié)果與討論

2.1 PAHs濃度水平

由圖2可見,寶豐基地大氣PM2.5、PM1.0及氣相中∑16PAHs的濃度范圍分別為30.27~472.21, 20.45~ 430.89,41.65~169.46ng/m3,年均濃度分別為(149.51± 127.50),(117.83±112.06),(94.08±36.15)ng/m3;英力特基地濃度范圍分別為5.61~94.00,4.87~79.04, 5.39~ 43.82ng/m3,其年均濃度分別為(33.28±27.44), (26.67±22.72),(18.96±10.19)ng/m3.寶豐基地大氣PM2.5、PM1.0及氣相中∑16PAHs的年均濃度均高于英力特基地,分別是其4.26、4.10和4.87倍.基于該2個(gè)采樣點(diǎn),寧東基地PM2.5、PM1.0及氣相中∑16PAH年均濃度范圍分別為17.95~325.12,12.66~311.96, 26.33~97.88ng/m3,平均濃度分別為(99.42±117.48), (78.88±100.58),(57.89±47.39)ng/m3.

圖2　寧東基地采樣點(diǎn)大氣PM2.5、PM1.0及氣相中Σ16PAHs的年均濃度

寧東基地為寶豐和英力特年均濃度的平均值

表3　研究區(qū)寧東基地與國(guó)內(nèi)外部分城市地區(qū)大氣PM2.5、PM1.0及氣相中PAHs 濃度對(duì)比

由表3可見,寧東基地大氣PM2.5中∑16PAHs年均濃度略高于太原[24]和北京[25],與2012年重慶市(84.18ng/m3)[26]大氣PM2.5中∑16PAHs年均濃度相當(dāng),遠(yuǎn)高于合肥(29.19ng/m3)[27]、深圳(38.75ng/m3)[28]、廣州(33.89ng/m3)[29]和浙北地區(qū)[30]等城市,約為其的3倍.這表明寧東基地大氣PAHs污染比較嚴(yán)重,在國(guó)內(nèi)處于較高濃度水平,推測(cè)主要原因是寧東基地以煤炭、焦炭和煤化工為工業(yè)主體,這些行業(yè)均存在較高的PAHs排放.此外,為保證工業(yè)基地的交通運(yùn)輸,研究區(qū)域存在較多的大型貨車和卡車,柴油和汽油車尾氣的排放也是大氣PAHs的一個(gè)主要貢獻(xiàn)源.另一方面寧東作為典型的北方城市,冬季因供暖燃煤大幅增加,導(dǎo)致冬季PAHs排放加大.目前,國(guó)內(nèi)關(guān)于大氣PM1.0中PAHs的相關(guān)研究相對(duì)較少,寧東基地PM1.0中PAHs濃度水平略低于石家莊(56.55~272.35ng/m3)[31].與國(guó)外城市相比,寧東基地大氣PM1.0中∑16PAHs年均濃度要遠(yuǎn)高于巴西城市Canoas和Sapucaia do Sul[32]大氣PM1.0中PAHs濃度,分別是其47倍和34倍左右.此外,寧東基地大氣PM1.0中PAHs濃度水平是捷克城市Brno和Slapanice[33]的2倍左右.寧東基地大氣氣相中∑16PAHs的濃度水平和烏魯木齊[34](40.97~ 468.21ng/m3)、哈爾濱[35](46.47~132.41ng/m3)和北京[36](492ng/m3)相比較低,略低于蘭州(96~ 101ng/m3)[23],但高于加拿大Toronto地區(qū)濃度(3.53~ 61.4ng/m3)[37].

2.2 時(shí)空分布特征

由圖3可見,在空間上寶豐基地大氣PM2.5、PM1.0和氣相中∑16PAHs濃度水平均明顯高于英力特基地.這可能與寶豐基地重點(diǎn)以煤炭深加工及轉(zhuǎn)化、煤化工產(chǎn)品的深加工等項(xiàng)目產(chǎn)業(yè)為主,煤炭消耗量較大密切相關(guān).此外寶豐基地緊鄰G20青銀高速和103省道,汽車尾氣交通源的貢獻(xiàn)也是一個(gè)主要原因.季節(jié)特征表現(xiàn)為寶豐和英力特基地冬季大氣PM2.5、PM1.0中∑16PAHs的濃度水平均明顯高于夏季.寶豐基地冬季大氣PM2.5、PM1.0中∑16PAHs的平均濃度分別256.67ng/m3和212.32ng/m3,明顯高于夏季的濃度.但冬季采暖期氣相中∑16PAHs的平均濃度為93.35ng/m3,低于夏季的濃度(100.23ng/m3),其主要原因可能是夏季溫度較高,部分中高環(huán)PAHs從顆粒相到氣相的揮發(fā)增加,致使氣相濃度增加[37].英力特基地冬季PM2.5和PM1.0中∑16PAHs平均濃度分別為60.32,48.65ng/m3,均明顯高于夏季的濃度10.10, 7.84ng/m3,而不同季節(jié)氣相中PAHs濃度水平相當(dāng),冬季和夏季的平均濃度分別為26.14,12.81ng/m3.

圖3　不同季節(jié)寧東基地大氣PM2.5、PM1.0和氣相中Σ16PAHs的濃度水平

2.3 族譜特征

由圖4可見,寶豐和英力特基地大氣PM2.5、PM1.0和氣相中PAHs的族譜特征呈現(xiàn)出較高的相似性.在冬季采暖期,寧東基地PM2.5中濃度水平相對(duì)較高的PAHs依次是Flua、Pyr、BbF、Phe和Chr,分別約占17.7%、13.6%、10.4%、10.1%和9.5%;而在夏季非采暖期,占比最高依次為BkF、BbF、BghiP和IP,分別約占13.9%、12.1%、10.8%和10.4%.Simcik等[39]研究表明Flua的排放與煤炭燃燒源有關(guān).研究表明BkF和BbF是中國(guó)工業(yè)煤燃燒排放的特征化合物[40-41].寶豐基地主要以煉焦和煤化工業(yè)為主,英力特基地主要以煤制油工業(yè)為主,因此研究區(qū)域內(nèi)較多的工業(yè)煤燃燒源可能是貢獻(xiàn)Flua、BkF和BbF等較高占比的主要原因.

采暖期寧東基地大氣PM1.0中PAHs的濃度水平占比最高的分別是Flua、Pyr、BkF、Chr和BbF,分別約占17.2%、14.1%、10.4%和10.3%;而在夏季占比最高依次為BkF、BbF、IP和BghiP,分別約占15.5%、14.2%、12.3%和12.3%.除工業(yè)能源燃燒源,機(jī)動(dòng)車尾氣是PM1.0中PAHs的另一主要貢獻(xiàn)源.有研究表明,Phe、IP、BbF、BkF和BghiP等是汽車尾氣中最主要的幾種PAHs[39,42-45],而有文獻(xiàn)指出PM1.0占機(jī)動(dòng)車尾氣排放顆粒物的90%以上[46].采暖期寧東基地大氣氣相中濃度占比相對(duì)較高的PAHs依次是Phe、Flu和Nap,分別約占30.7%、16.8%和16.4%;而在非采暖期,占比最高依次為Phe、Flua和Pyr,分別約占37.8%、21.9%和17.0%.

對(duì)不同季節(jié)寶豐和英力特基地大氣PM2.5、PM1.0及氣相中PAHs不同環(huán)數(shù)分配特征進(jìn)行研究,結(jié)果如圖5,冬季采暖期寶豐和英力特基地大氣PM2.5和PM1.0中PAHs均以4環(huán)比例最高,3環(huán)次之;而在夏季非采暖期大氣PM2.5、PM1.0中PAHs環(huán)數(shù)亦均以4環(huán)占比最高,5環(huán)次之.4環(huán)PAHs為煤燃燒的主要排放物,5、6環(huán)主要是柴油機(jī)和汽油機(jī)排放源的特征[39,47],3環(huán)PAHs是木材、薪柴等生物質(zhì)燃燒排放的特征化合物[40].由此推測(cè),采暖期大氣PM2.5、PM1.0中PAHs的主要貢獻(xiàn)源為煤燃燒,其次為生物質(zhì)燃燒源;非采暖期煤炭燃燒為大氣PM2.5、PM1.0中PAHs主要貢獻(xiàn)源,機(jī)動(dòng)車的柴油和汽油燃燒為次要貢獻(xiàn)源.此外冬季顆粒相中碳黑的存在為吸附與固定PAHs 提供很好的基質(zhì),使得顆粒相中的中低環(huán)PAHs在大氣中殘留時(shí)間較長(zhǎng)[48].

2環(huán):Nap、Acey、Ace、Flu;3環(huán):Phe、Ant、Flua;4環(huán):Pyr、BaA、Chr、BbF、BkF;5環(huán):BaP、IP、DiB;6環(huán):BghiP

冬季采暖期寶豐基地大氣氣相中PAHs環(huán)數(shù)占比最高為3環(huán)(45%),2環(huán)次之(44%);而英力特基地占比最高為2環(huán)(48%),3環(huán)次之(43%).夏季非采暖期寶豐和英力特基地大氣氣相中PAHs環(huán)數(shù)占比最高均為3環(huán)最高(66%,63%),4環(huán)次之(26%,26%).對(duì)兩個(gè)觀測(cè)點(diǎn)冬夏季氣相中PAH濃度所占比例進(jìn)行比較,冬季低環(huán)PAHs所占比例相比夏季較高,而中高環(huán)PAHs所占比例較低.其主要原因可能是冬季城市集中供暖燃煤和無組織排放源如家庭木材、薪柴等生物質(zhì)燃燒增加,使得低環(huán) PAHs的排放增加.劉書臻等[40]研究表明Nap、Flu等2環(huán)PAHs是中國(guó)木材、柴薪等生物質(zhì)燃燒排放的指示化合物.英力特基地2環(huán)PAHs所占比例最高的主要原因推測(cè)是其臨近寧東鎮(zhèn),人口密度大,生活排放源更大.此外,Khalili等[49]也提出NAP可以作為焦?fàn)t煉鋼等工業(yè)排放源的特征化合物.冬季北方地區(qū)因供暖能源需求增加,寧東基地作為國(guó)家主要的“西電東輸”的火電基地和寧夏能源供給地,工業(yè)生產(chǎn)活動(dòng)也會(huì)大幅增加.另一方面冬季溫度較低,低環(huán)PAHs相對(duì)比較穩(wěn)定不易揮發(fā),易于在樣品中保存.毛瀟萱[50]研究表明在非采暖期環(huán)境溫度較高,PAHs由于較高的溫度使得其在氣相中的濃度高于顆粒相,而在采暖期環(huán)境溫度降低,PAHs揮發(fā)減弱,使得其在大氣中的平衡狀態(tài)向顆粒相偏移.此外,Zhang等[38]對(duì)大氣PAHs的氣粒分配模擬研究表明,在夏季受溫度影響中高環(huán)PAHs在氣相中所占比例相比冬季較高.

2.4 氣粒分配

為探究不同季節(jié)大氣不同形態(tài)PAHs的族譜特征差異成因,本研究對(duì)不同季節(jié)寶豐和英力特基地大氣環(huán)境中PAHs單體的氣粒分配(圖6)進(jìn)行研究.結(jié)果表明,冬季采暖期高分子量的PAHs主要分布在顆粒相,而低環(huán)分子量小的PAHs主要分布在氣相中,且PAHs在氣相中所占比例隨環(huán)數(shù)及分子質(zhì)量增加而減少.而在夏季非采暖期,3環(huán)以上PAHs和采暖期呈現(xiàn)相同的氣粒分配趨勢(shì),但氣相中2環(huán)PAHs所占比例明顯低于冬季,其在顆粒相PM2.5和PM1.0中所占比例增加,究其主要原因可能是如上所述冬季寧東鎮(zhèn)集中供暖燃煤和家庭木材、薪柴等生物質(zhì)燃燒增加,低環(huán)PAHs的排放增加導(dǎo)致.另一方面冬季溫度較低,2環(huán)PAHs相對(duì)比較穩(wěn)定,易于在空氣中滯留.而夏季太陽輻射較強(qiáng),氣相中的低環(huán)PAHs易與大氣中的羥基自由基、硝基自由基等活性自由基發(fā)生反應(yīng)被降解[51-52],導(dǎo)致氣相中PAHs濃度降低.古孜扎爾等[34]對(duì)烏魯木齊南部冬季空氣中氣相PAHs的監(jiān)測(cè)研究也顯示溫度越低,PAHs的濃度越高,而其中2環(huán)PAHs占比最大.此外與冬季相比,夏季環(huán)境溫度較高,低環(huán)PAHs不穩(wěn)定[53],不易在樣品中長(zhǎng)時(shí)間保存,可能是氣相中低環(huán)PAHs濃度占比降低的一個(gè)原 因.

圖6 不同季節(jié)寧東基地大氣各PAH單體氣粒分配

2.5 PAHs特征化合物比值及來源解析

由圖7可知,在非采暖期,寶豐和英力特基地PM1.0中PAHs特征比值A(chǔ)nt/(Ant+Phe)大于0.1, IP/ (IP+BghiP)也大于0.5,說明2個(gè)采樣點(diǎn)PM1.0中PAHs的主要貢獻(xiàn)源均為煤炭和生物質(zhì)燃燒;2個(gè)采樣點(diǎn)PM2.5中的Ant/(Ant+Phe)大于0.1而IP/(IP+BghiP)之比小于0.5,表明液態(tài)化石燃料燃燒、汽車尾氣對(duì)其貢獻(xiàn)較大.對(duì)氣相,寶豐基地Ant/(Ant+Phe)之比大于0.1,IP/(IP+BghiP)之比大于0.5;而英力特基地Ant/ (Ant+Phe)之比小于0.1, IP/(IP+BghiP)之比小于0.5.此結(jié)果表明,寶豐基地氣相中PAHs的主要貢獻(xiàn)源為石油源和煤炭、生物質(zhì)燃燒源,而英力特為石油源和液態(tài)化石燃料燃燒的混合排放源.

在采暖期,寶豐和英力特基地大氣PM2.5和PM1.0中PAHs的特征比值寶豐IP/(IP+BghiP)均大于0.5,但寶豐BaA/(BaA+Chry)大于0.35而英力特小于0.35.此結(jié)果表明寶豐基地采暖期大氣PM2.5和PM1.0中的PAHs主要來源于煤炭、生物質(zhì)燃燒源的排放;而英力特除煤炭、生物質(zhì)燃燒源的排放,還包括石油源的排放,這可能主要是因?yàn)橛⒘μ鼗匾灾攸c(diǎn)發(fā)展大型或特大型的煤氣化、煤制油及配套和深加工產(chǎn)業(yè).對(duì)氣相,寶豐基地的特征比值A(chǔ)nt/(Ant+Phe)大于0.1, IP/(IP+BghiP)小于0.5,而英力特基地特征比值A(chǔ)nt/(Ant+Phe)小于0.1,表明冬季寶豐基地氣相中PAHs的主要來源為液態(tài)化石燃料燃燒和汽車尾氣,而英力特基地為石油源或燃燒源.

圖7 寧東基地大氣PAHs特征化合物比值來源解析

a. Ant/(Ant+Phe)和BaA/(BaA+Chry),b. Flua/(Flua+Pyr)和IP/(IP+BghiP),1、2分別代表夏季和冬季

2.6 大氣PAHs呼吸暴露風(fēng)險(xiǎn)評(píng)估

中國(guó)《環(huán)境空氣質(zhì)量標(biāo)準(zhǔn)》(GB3095—2012)規(guī)定的大氣BaP濃度限值為2.5ng/m3[54].寶豐和英力特基地大氣PM2.5和PM1.0中的∑16BaPeq的年均濃度水平均超過了該標(biāo)準(zhǔn)限值,在冬季寶豐基地∑16BaPeq值最高是限定值的18倍,而英力特基地是限定值的5.6倍;在夏季寶豐基地∑16BaPeq值是限定值的6.1倍,而英力特基地為限定值的1.5倍.寧東基地冬季∑16BaPeq值是國(guó)家限定值的12.1倍,而夏季是其的3.8倍.表明研究區(qū)大氣PAHs 污染對(duì)人體具有潛在的健康風(fēng)險(xiǎn).圖8為使用不同的URBaP值計(jì)算得到的寧東基地夏季和冬季大氣∑16PAHs的超額致癌風(fēng)險(xiǎn)ECR值.如圖8所示,采用WHO(URBaP=8.7×10-5per ng/m3)的標(biāo)準(zhǔn)得到研究區(qū)PAHs的暴露可造成平均冬季每百萬人中大約會(huì)產(chǎn)生2628人的癌癥病例,夏季每百萬人中大約會(huì)產(chǎn)生834人的癌癥病例.采用CalEPA (URBaP=1.1×10-6per ng/m3)的標(biāo)準(zhǔn)得到研究區(qū)PAHs的暴露可造成平均冬季每百萬人中大約會(huì)產(chǎn)生33人的癌癥病例,夏季每百萬人中大約會(huì)產(chǎn)生11人的癌癥病例.

圖8 寧東基地冬季和夏季大氣∑16PAHs的超額致癌風(fēng)險(xiǎn)ECR值

左邊軸癌癥風(fēng)險(xiǎn)計(jì)算時(shí)采用的URBaP=8.7×10-5per ng/m3(WHO,2000);右邊軸采用URBaP=1.1×10-6per ng/m3(CalEPA, 1998)

3 結(jié)論

3.1 寧東基地PM2.5、PM1.0及氣相中∑16PAHs年均濃度分別為(99.42±117.48),(78.88±100.58), (57.89± 47.39)ng/m3,濃度范圍分別為17.95~325.12,12.66~ 11.96,26.33~97.88ng/m3.寶豐大氣PM2.5、PM1.0和氣相中∑16PAHs濃度水平均明顯高于英力特;寶豐和英力特基地采暖期大氣PM2.5、PM1.0中∑16PAHs濃度水平均明顯高于非采暖期.寧東基地大氣中∑16PAHs的濃度水平要高出國(guó)內(nèi)外其他城市數(shù)倍,大氣PAHs處于較嚴(yán)重的污染水平.

3.2 寧東基地冬夏季大氣中PAHs均主要以4環(huán)為主,但冬夏的次要PAHs污染物有所不同.冬季以3環(huán)為次要污染物,夏季以5環(huán)為次要污染物.表明在夏季寧東大氣PAHs的主要排放源可能為工業(yè)煤燃燒和機(jī)動(dòng)車尾氣,而在冬季可能為工業(yè)煤燃燒和木材、薪柴等生物質(zhì)燃燒.

3.3 結(jié)果顯示,在夏季寶豐和英力特基地大氣中PM2.5中PAHs的主要貢獻(xiàn)源為液體化石燃料燃燒和汽車尾氣;PM1.0中PAHs的主要貢獻(xiàn)源為煤炭、生物質(zhì)燃燒;而兩個(gè)觀測(cè)點(diǎn)氣相中有所不同,寶豐基地主要貢獻(xiàn)源為石油源和煤炭、生物質(zhì)燃燒的混合源,而英力特為石油源和液態(tài)化石燃料燃燒混合源.在冬季,寶豐基地大氣PM2.5和PM1.0中PAHs的主要貢獻(xiàn)源均為煤炭、生物質(zhì)燃燒源,而英力特基地為煤炭、生物質(zhì)燃燒源和石油源的混合源;對(duì)于氣相,寶豐基地主要貢獻(xiàn)源為液態(tài)化石燃料燃燒源和汽車尾氣,而英力特基地為石油源和燃燒源.

3.4 寧東基地冬季高分子量PAHs主要分布在顆粒相,而低分子量PAHs主要分布在氣相中,且PAHs在氣相中所占比例隨環(huán)數(shù)及分子質(zhì)量增加而減少.在夏季3環(huán)以上PAHs和采暖期呈現(xiàn)相同的氣粒分配趨勢(shì),氣相中2環(huán)PAHs所占比例明顯低于冬季.

3.5 寧東基地冬季大氣∑16BaPeq濃度值是國(guó)家標(biāo)準(zhǔn)的12.1倍,而夏季是標(biāo)準(zhǔn)值的3.8倍.根據(jù)所得∑16BaPeq濃度值估算ECR值,估算得寧東基地人群因暴露于大氣PAHs可造成平均冬季每百萬人中大約會(huì)產(chǎn)生33~2628案例罹患癌癥的風(fēng)險(xiǎn),夏季每百萬人中大約會(huì)產(chǎn)生11~834案例罹患癌癥.

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Pollution characteristics and inhalation exposure risk of atmospheric PAHs in Ningdong Base.

WANG Zhan-xiang1, GUO Jiu-jiu2, MU Xi1, LI Ji-xiang1, GAO Hong1*, HUANG Tao1, MA Jian-min3

(1.Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China；2.China Power Construction Group International Engineering co. LTD, Beijing 100036, China；3.College of Urban and Environmental Science, Peking University, Beijing 100871, China)., 2019,39(7)：3102~3112

The active sampling technique was adopted to investigate the concentration levels, profiles and spatial temporal distribution as well as the source apportionments of atmospheric PAHs in PM2.5, PM1.0and gas phase. The inhalation exposure risk of local population to atmospheric PAHs was evaluated based on atmospheric observation data in Ningdong Base. The ranges of atmospheric concentration levels of ∑16PAHs for PM2.5, PM1.0and gas phase were 17.95~325.12ng/m3, 12.66~311.96ng/m3and 26.33~97.88ng/m3respectively, and the average annual concentrations were (99.42±117.48)ng/m3, (78.88±100.58)ng/m3and (57.89±47.39)ng/m3, respectively. The spatial distributions of atmospheric PAHs levels for PM2.5, PM1.0and gas phase in Baofeng site were significantly higher than that in Yinglite site for both winter and summer. The seasonal pollution characteristics indicated that ∑16PAHs concentration levels were significantly higher in Baofeng site than that in Yinglite site not only in winter but in summer. Comparison of atmospheric PAHs levels in Ningdong Base with that of other cities or regions worldwide, which exhibited higher concentration levels, suggesting atmospheric PAHs pollution was more serious in Ningdong Base. Source apportionment indicated that the main emission sources of PAHs in Ningdong Base were industrial coal combustion and motor vehicle exhaust in summer, while industrial coal combustion and biomass burning in winter. The average excess inhalation cancer risks (ECR) due to human exposure to atmospheric PAHs were about 33~2628 cases per million people in Ningdong Base in winter, while 11~834 cases per million people in summer.

Ningdong Energy and Chemical Industry Base；polycyclic aromatic hydrocarbons；atmospheric concen-tration levels；source apportionment；inhalation exposure risk

X53

A

1000-6923(2019)07-3102-11

王占祥(1994-),男,甘肅慶陽人,蘭州大學(xué)博士研究生,研究方向污染物區(qū)域環(huán)境過程及風(fēng)險(xiǎn).發(fā)表論文2篇.

2018-12-24

國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目子課題(2017YFC0212002);國(guó)家自然科學(xué)基金資助項(xiàng)目(41671460);國(guó)家自然科學(xué)基金青年基金資助項(xiàng)目(41701582)

* 責(zé)任作者, 教授, honggao@lzu.edu.cn