楊 磊,袁 斌*,鄭 鍔,葉晨朔,王思行,何賢俊,張瀟瀟,黃 山,胡偉偉,邵 敏

珠江三角洲秋季生物質(zhì)燃燒對(duì)有機(jī)氣溶膠的貢獻(xiàn)

楊 磊1,袁 斌1*,鄭 鍔1,葉晨朔2,王思行1,何賢俊1,張瀟瀟1,黃 山1,胡偉偉3,邵 敏1

(1.暨南大學(xué)環(huán)境與氣候研究院,粵港澳環(huán)境質(zhì)量創(chuàng)新聯(lián)合實(shí)驗(yàn)室,廣東 廣州 511443；2.北京大學(xué)環(huán)境科學(xué)與工程學(xué)院,北京 100871；3.中國(guó)科學(xué)院廣州地球化學(xué)研究所,有機(jī)地球化學(xué)國(guó)家重點(diǎn)實(shí)驗(yàn)室,廣東 廣州 510640)

本研究基于2018年和2019年秋季在珠江三角洲地區(qū)的兩次外場(chǎng)觀測(cè),應(yīng)用熱脫附-化學(xué)電離飛行時(shí)間質(zhì)譜(FIGAERO-ToF-CIMS)獲取了高時(shí)間分辨率(每小時(shí))的生物質(zhì)燃燒示蹤物左旋葡聚糖的濃度數(shù)據(jù),并估算出生物質(zhì)燃燒對(duì)有機(jī)氣溶膠(OA)的貢獻(xiàn)值.結(jié)果表明,秋季珠江三角洲地區(qū)城市站點(diǎn)和區(qū)域站點(diǎn)的左旋葡聚糖平均濃度分別為(0.07±0.08)和(0.14±0.12)μg/m3,呈現(xiàn)區(qū)域站點(diǎn)高于城市站點(diǎn)的空間分布特征以及早晨和夜間出現(xiàn)峰值的日變化特征.觀察到兩個(gè)站點(diǎn)的左旋葡聚糖與CO和乙腈之間相關(guān)性較低,但與OA之間呈現(xiàn)顯著正相關(guān)關(guān)系.進(jìn)一步基于受體示蹤物法估算出生物質(zhì)燃燒對(duì)OA的平均貢獻(xiàn)分別為7.4%(城市站點(diǎn))和11.4%(區(qū)域站點(diǎn)),且兩個(gè)站點(diǎn)均顯示出生物質(zhì)燃燒對(duì)OA的貢獻(xiàn)在夜間明顯高于白天.

生物質(zhì)燃燒；示蹤物；左旋葡聚糖；有機(jī)氣溶膠

生物質(zhì)燃燒是一種重要的空氣污染源,對(duì)全球范圍內(nèi)的空氣質(zhì)量、氣候變化和人類健康都有著復(fù)雜且重要的影響[1-3].特別是農(nóng)作物秸稈露天焚燒和家庭爐灶燃燒等生物質(zhì)燃燒過程[4-5],會(huì)釋放多種氣體及顆粒物,包括溫室氣體(如二氧化碳)、揮發(fā)性有機(jī)化合物(VOCs)和由黑碳(BC)、棕碳(BrC)及其他有機(jī)物組成的顆粒物[6].這些污染物不僅會(huì)對(duì)區(qū)域大氣產(chǎn)生不利影響,而且還可以通過長(zhǎng)距離輸送影響全球空氣質(zhì)量[7].

珠江三角洲地區(qū)(以下簡(jiǎn)稱“珠江三角洲”)是中國(guó)最發(fā)達(dá)的地區(qū)之一,也是我國(guó)重要的農(nóng)業(yè)生產(chǎn)基地,農(nóng)作物殘余物露天焚燒引起的大氣污染事件經(jīng)常發(fā)生[8-9].有機(jī)氣溶膠(OA)作為大氣細(xì)顆粒物(PM2.5)的重要組成部分,占PM2.5總質(zhì)量的20～90%[10-11].而生物質(zhì)燃燒排放則被認(rèn)為是大氣顆粒物中OA的重要來源[12],特別是在生物質(zhì)燃燒影響較大的地區(qū)(例如我國(guó)關(guān)中盆地),甚至可以貢獻(xiàn)31.9%的OA[13].此前研究表明,OA能夠影響大氣顆粒物的物理化學(xué)特性,如吸濕性和光學(xué)特性等,進(jìn)而通過改變光的散射和吸收影響大氣能見度和氣候變化.例如,Zong等[14]研究發(fā)現(xiàn)OA中的水溶性有機(jī)物(WSOM)可以改變氣溶膠吸濕性,從而影響氣溶膠作為云凝結(jié)核的能力.Saleh等[15]研究發(fā)現(xiàn)BrC作為一類吸光性的OA組分,其在近紫外線和可見光譜區(qū)域具有很強(qiáng)的吸光能力,從而影響大氣輻射傳輸過程.大量研究都關(guān)注到生物質(zhì)燃燒對(duì)大氣氣溶膠中OA的貢獻(xiàn)及影響[16-18],但目前人們對(duì)我國(guó)珠江三角洲地區(qū)秋季城市站點(diǎn)和區(qū)域站點(diǎn)的生物質(zhì)燃燒貢獻(xiàn)差異了解甚少,在此地區(qū)開展研究有利于補(bǔ)充對(duì)珠江三角洲不同地區(qū)大氣有機(jī)氣溶膠受生物質(zhì)燃燒源影響現(xiàn)狀的認(rèn)識(shí),為制定城市和區(qū)域尺度大氣細(xì)顆粒物防治策略提供依據(jù).

左旋葡聚糖(1,6-脫水-β-D-吡喃糖)是纖維素的主要熱解產(chǎn)物,被廣泛作為生物質(zhì)燃燒的示蹤劑[19-21].左旋葡聚糖的測(cè)定通常采用氣相色譜-質(zhì)譜法(GC-MS)或高效液相色譜法(HPLC),分析方法成熟,但兩種方法都涉及復(fù)雜的樣品處理和分析過程,且時(shí)間分辨率較低[22-23].近年來,將氣粒雙通道采樣器(FIGAERO)作為進(jìn)樣口的熱脫附-化學(xué)電離飛行時(shí)間質(zhì)譜儀(FIGAERO-ToF-CIMS)測(cè)定左旋葡聚糖的方法已被運(yùn)用[24-25].這種新型的在線檢測(cè)技術(shù)使用軟電離的化學(xué)電離方式以實(shí)現(xiàn)待測(cè)物離子最小程度的碎片化,并且具有極低的檢測(cè)限,可在分子水平上在線檢測(cè)和定量含氧化合物,無需復(fù)雜的樣品處理過程,同時(shí)具有高時(shí)間分辨率[26-27].

本文使用FIGAERO-ToF-CIMS在珠江三角洲地區(qū)開展秋季外場(chǎng)觀測(cè),獲取高時(shí)間分辨率(每小時(shí))的左旋葡聚糖濃度數(shù)據(jù),分析其空間分布特征和日變化特征,并與其他生物質(zhì)燃燒示蹤物進(jìn)行相關(guān)性分析,以了解珠江三角洲地區(qū)城市站點(diǎn)和區(qū)域站點(diǎn)之間生物質(zhì)燃燒活動(dòng)的差異.通過左旋葡聚糖濃度和OA濃度對(duì)生物質(zhì)燃燒貢獻(xiàn)值進(jìn)行估算以分析大氣氣溶膠中OA受生物質(zhì)燃燒的影響程度,為我國(guó)珠江三角洲地區(qū)秋季生物質(zhì)燃燒引起的大氣細(xì)顆粒物污染的防控提供數(shù)據(jù)支持.

1 材料與方法

1.1 采樣地點(diǎn)

本研究使用2018年和2019年秋季在珠江三角洲地區(qū)分別進(jìn)行的兩次外場(chǎng)觀測(cè)數(shù)據(jù).珠江三角洲地區(qū)包括廣州、佛山、肇慶、深圳、東莞、惠州、珠海、中山和江門9個(gè)城市,是我國(guó)經(jīng)濟(jì)最活躍、人口最密集的區(qū)域之一,工業(yè)化、城市化水平較高.城市站點(diǎn)位于廣東省廣州市中國(guó)科學(xué)院廣州地球化學(xué)研究所(23.1°N,113.2°E),周邊主要是居民區(qū)和學(xué)校,無明顯工業(yè)排放源,屬于典型的城市環(huán)境[28-29],觀測(cè)時(shí)間自2018年9月27日～2018年11月12日.區(qū)域站點(diǎn)位于廣東省江門市鶴山市廣東省大氣環(huán)境超級(jí)監(jiān)測(cè)站(22.7°N,112.9°E),距離廣州市市區(qū)約80km,周邊無明顯工業(yè)源且處于城市下風(fēng)向,是珠江三角洲地區(qū)典型的區(qū)域受體站點(diǎn)[30-31],觀測(cè)時(shí)間自2019年10月2日～2019年11月15日.

1.2 左旋葡聚糖分析方法

觀測(cè)期間采用以FIGAERO為進(jìn)樣口的碘離子化學(xué)電離飛行時(shí)間質(zhì)譜(I--ToF-CIMS)測(cè)量左旋葡聚糖, I--ToF-CIMS可檢測(cè)的質(zhì)量范圍為1～603Th,質(zhì)量分辨率為10000～11000[32-33].FIGAERO作為一個(gè)多端口進(jìn)氣裝置,擁有單獨(dú)的氣體采樣口和顆粒物采樣口,并通過FIGAERO內(nèi)可移動(dòng)滑塊來控制氣體或顆粒物從不同進(jìn)樣口進(jìn)入儀器來實(shí)現(xiàn)在線測(cè)量大氣中微量氣體和氣溶膠顆粒物的化學(xué)組分.具體采樣方法為6h的采樣循環(huán),在每1h的采樣周期內(nèi)FIGAERO以兩種模式進(jìn)行工作:(1)前24min進(jìn)行氣態(tài)物質(zhì)實(shí)時(shí)分析和顆粒物的采集,顆粒物被收集在Teflon膜上;(2)后36min將收集到的顆粒物經(jīng)高溫氮?dú)鉄峤馕M(jìn)行顆粒物分析.在每36min的顆粒態(tài)模式下將收集到的顆粒物熱解吸,以2L/min的氮?dú)鉃檩d氣引入儀器,氮?dú)庠?2min內(nèi)從環(huán)境溫度升高到175℃,并保持20min.當(dāng)經(jīng)歷5個(gè)相同的采樣周期后,通過電磁閥切換進(jìn)行顆粒物空白采樣作為背景,形成6h的采樣循環(huán),以實(shí)現(xiàn)顆粒態(tài)數(shù)據(jù)為1h的高時(shí)間分辨率.左旋葡聚糖的標(biāo)定在實(shí)驗(yàn)室和外場(chǎng)觀測(cè)中進(jìn)行,以保證儀器運(yùn)行期間數(shù)據(jù)的準(zhǔn)確性.儀器運(yùn)行期間,人為將不同濃度的左旋葡聚糖標(biāo)準(zhǔn)溶液注射在FIGAERO的Teflon膜上并按顆粒態(tài)熱脫附模式升溫以確定左旋葡聚糖的響應(yīng)因子.

1.3 其他數(shù)據(jù)分析方法

本次觀測(cè)對(duì)于乙腈的測(cè)量,使用在線質(zhì)子轉(zhuǎn)移反應(yīng)飛行時(shí)間質(zhì)譜(PTR-ToF-MS),因其具有高時(shí)間分辨率,高靈敏度,檢測(cè)限較低等特點(diǎn),已廣泛應(yīng)用于外場(chǎng)觀測(cè)[34-35].儀器運(yùn)行期間,每天利用標(biāo)準(zhǔn)氣體在干燥條件和濕度條件進(jìn)行多點(diǎn)標(biāo)定,并根據(jù)實(shí)驗(yàn)室濕度實(shí)驗(yàn)以準(zhǔn)確定量乙腈濃度[30,36].對(duì)于常規(guī)痕量氣體CO的測(cè)量,使用增強(qiáng)型痕量CO分析儀(型號(hào):48i-TLE)進(jìn)行了連續(xù)在線監(jiān)測(cè).對(duì)于顆粒物中OA濃度的測(cè)量,使用Aerodyne公司所研發(fā)的高分辨率黑碳飛行時(shí)間質(zhì)譜儀(SP-HR-ToF-AMS)[37-38],可滿足對(duì)環(huán)境大氣中氣溶膠的化學(xué)組分(包括有機(jī)物、硫酸鹽、硝酸鹽、銨鹽和氯鹽)的監(jiān)測(cè).

2 結(jié)果與討論

2.1 左旋葡聚糖的濃度水平及空間分布特征

圖1 觀測(cè)期間氣象參數(shù)和左旋葡聚糖的時(shí)間序列

觀測(cè)期間各站點(diǎn)氣象參數(shù)的時(shí)間序列如圖1所示,可以看出城市站點(diǎn)和區(qū)域站點(diǎn)的平均溫度分別為(24.2±2.7)和(24.4±3.6)℃,平均濕度分別為(70.1± 17.5)和(66.9±15.4)%,且兩個(gè)站點(diǎn)的主導(dǎo)風(fēng)向?yàn)槠憋L(fēng),平均風(fēng)速分別為(2.4±1.4)和(1.5±0.8)m/s,較快的風(fēng)速有利于污染物區(qū)域輸送[39].

表1 國(guó)內(nèi)外主要城市秋冬季節(jié)大氣顆粒物中左旋葡聚糖濃度水平

通過高時(shí)間分辨率測(cè)量,觀測(cè)期間兩個(gè)站點(diǎn)的左旋葡聚糖平均濃度及變化范圍見表1和圖1.由表1可知,珠江三角洲地區(qū)城市站點(diǎn)的平均濃度低于區(qū)域站點(diǎn),分別為(0.07±0.08)和(0.14±0.12)μg/m3.在2018和2019年10月中旬前左旋葡聚糖的濃度水平未出現(xiàn)明顯高值,基本處于0.40μg/m3以下的較低水平,于10月中下旬才會(huì)在傍晚及夜間出現(xiàn)高值,其原因可能是由于此時(shí)珠江三角洲地區(qū)已經(jīng)步入秋收時(shí)期,大量農(nóng)作物殘余物被就地露天焚燒,較高的左旋葡聚糖濃度與周邊及當(dāng)?shù)氐纳镔|(zhì)燃燒事件直接相關(guān)[40].這與Yuan等[41]以乙腈為生物質(zhì)燃燒示蹤物,發(fā)現(xiàn)珠江三角洲地區(qū)10月下旬開始存在普遍焚燒農(nóng)作物殘余物的現(xiàn)象一致.具體來看,城市站點(diǎn)的最高小時(shí)平均濃度出現(xiàn)在10月20日的夜間(0.69μg/m3),區(qū)域站點(diǎn)于10月17日開始濃度有所上升,最高小時(shí)平均濃度出現(xiàn)在11月18日的傍晚(0.97μg/m3).表明我國(guó)珠江三角洲地區(qū)秋季左旋葡聚糖濃度呈現(xiàn)區(qū)域站點(diǎn)高于城市站點(diǎn)的空間分布特征.

本研究將測(cè)量的左旋葡聚糖與其他國(guó)內(nèi)外城市秋冬季節(jié)報(bào)道的濃度水平進(jìn)行了比較.從表1可以看出,城市站點(diǎn)測(cè)得的左旋葡聚糖平均濃度遠(yuǎn)低于秋季成都(0.66μg/m3)和西安(0.58μg/m3)[42-43],與冬季西班牙巴塞羅那(0.06μg/m3)相近[44].區(qū)域站點(diǎn)測(cè)得的左旋葡聚糖平均濃度與秋季南京(0.18± 0.12)μg/m3相近[45],但遠(yuǎn)高于冬季法國(guó)多姆山(0.02μg/m3)等海洋地區(qū)[46].總體而言,我國(guó)珠江三角洲地區(qū)秋季左旋葡聚糖濃度低于華北及西南等地區(qū),與歐洲地區(qū)觀察到的濃度大致相當(dāng).

2.2 左旋葡聚糖的日變化特征

化學(xué)示蹤物是目前辨析生物質(zhì)燃燒事件和量化其對(duì)大氣環(huán)境影響的常用研究手段[54].作為典型的生物質(zhì)燃燒示蹤物,觀測(cè)期間兩個(gè)站點(diǎn)的左旋葡聚糖日變化特征如圖2所示,從圖2反映了各站點(diǎn)左旋葡聚糖濃度隨時(shí)間基本呈現(xiàn)早晨和夜間出現(xiàn)峰值的變化趨勢(shì).在早晨,區(qū)域站點(diǎn)的濃度持續(xù)上升,并于早晨8:00左右出現(xiàn)峰值,而城市站點(diǎn)則一直呈現(xiàn)緩慢下降的變化趨勢(shì),未觀察到明顯的峰值變化,表明區(qū)域站點(diǎn)在早晨較為明顯的生物質(zhì)燃燒活動(dòng),城市站點(diǎn)缺乏重要的生物質(zhì)燃燒排放源.在夜間,兩個(gè)站點(diǎn)的左旋葡聚糖濃度均于下午16:00左右開始有明顯上升趨勢(shì),但上升幅度有所不同.城市站點(diǎn)最大上升幅度出現(xiàn)在19:00～20:00左右,從0.09μg/m3上升到0.14μg/m3,上升幅度為55.6%,并在夜間21:00左右達(dá)到峰值,隨后濃度開始下降.區(qū)域站點(diǎn)最大上升幅度出現(xiàn)在17:00～18:00左右,從0.12μg/m3上升到0.25μg/m3,上升幅度高達(dá)108.3%,隨后在夜間19:00左右達(dá)到峰值,表明我國(guó)珠江三角洲地區(qū)秋季區(qū)域站點(diǎn)受到了更為嚴(yán)重的生物質(zhì)燃燒污染.相較于區(qū)域站點(diǎn),城市站點(diǎn)的峰值較小且達(dá)峰值時(shí)間較晚,這種差異可能是因?yàn)橹榻侵薜貐^(qū)秋收后農(nóng)田秸稈露天燃燒活動(dòng)主要發(fā)生在農(nóng)村地區(qū),城市上風(fēng)向地區(qū)生物質(zhì)燃燒所排放的污染物可傳輸至城市區(qū)域[55].

除了峰值變化外,同時(shí)觀察到兩個(gè)站點(diǎn)左旋葡聚糖濃度總體上均具有夜間高、日間低的特點(diǎn),通常在午后達(dá)到最低值,隨著光照的減弱和排放量的增加,濃度開始上升并在夜間達(dá)到峰值.這不僅因?yàn)橹榻侵薜貐^(qū)夜間生物質(zhì)燃燒活動(dòng)頻繁以及夜間邊界層高度降低等原因,還因?yàn)樽笮暇厶亲鳛榘霌]發(fā)性有機(jī)物,其物理化學(xué)性質(zhì)以及環(huán)境條件(溫度、濕度、懸浮顆粒物濃度等)決定了其在氣相和顆粒相中的分配,隨著日間環(huán)境溫度的升高,左旋葡聚糖從顆粒相揮發(fā)進(jìn)入氣相[56].同時(shí),目前的研究還發(fā)現(xiàn)左旋葡聚糖在大氣環(huán)境中并不穩(wěn)定,會(huì)與大氣中OH自由基發(fā)生光化學(xué)降解,尤其是在高相對(duì)濕度條件下[57-58].因此,左旋葡聚糖的濃度變化會(huì)受到源排放、光化學(xué)和環(huán)境條件等作用的影響.

圖2 左旋葡聚糖日變化特征圖

2.3 左旋葡聚糖與其他生物質(zhì)燃燒示蹤物的相關(guān)性

典型的生物質(zhì)燃燒示蹤物有左旋葡聚糖等有機(jī)物以及非海鹽鉀離子等無機(jī)物,氣態(tài)物質(zhì)如乙腈和氯甲烷等也被認(rèn)為是生物質(zhì)燃燒的示蹤物[59-61]. CO和乙腈因其穩(wěn)定性較好且壽命相對(duì)較長(zhǎng)的特點(diǎn),已被廣泛用于指示生物質(zhì)燃燒活動(dòng)[62-63].但研究表明,除了生物質(zhì)燃燒外,工業(yè)排放、汽車排放和燃煤排放也有助于提高它們?cè)诖髿庵械臐舛人絒64-65].

本研究將測(cè)量的左旋葡聚糖與一次示蹤物CO和乙腈進(jìn)行相關(guān)性分析,如圖3所示.通過高時(shí)間分辨率測(cè)量的數(shù)據(jù),發(fā)現(xiàn)城市和區(qū)域站點(diǎn)左旋葡聚糖與CO的具有一定相關(guān)性(r=0.43～0.57),在區(qū)域站點(diǎn)乙腈的相關(guān)性稍高(r=0.59).這表明除了生物質(zhì)燃燒外,我國(guó)珠江三角洲地區(qū)秋季CO和乙腈受其他排放源貢獻(xiàn)顯著,如機(jī)動(dòng)車排放以及燃煤排放.同時(shí),城市站點(diǎn)與區(qū)域站點(diǎn)獲得的左旋葡聚糖與CO的回歸線斜率基本相同,證實(shí)城市和區(qū)域影響左旋葡聚糖排放的生物質(zhì)燃燒類型基本相同.此外,傳統(tǒng)離線采樣提供數(shù)據(jù)集的時(shí)間分辨率一般為1d[16],而高時(shí)間分辨率測(cè)量則能夠捕捉到明顯的生物質(zhì)燃燒排放事件.通過小時(shí)值和日均值的比較,可以發(fā)現(xiàn)兩個(gè)站點(diǎn)日均值的相關(guān)性要高于小時(shí)值,小時(shí)值的相關(guān)性低,更加凸顯高時(shí)間分辨率測(cè)量條件下,普通城市排放和生物質(zhì)燃燒排放的差異.因此,高時(shí)間分辨率的測(cè)量更易捕捉到生物質(zhì)燃燒排放事件,也更有助于了解生物質(zhì)燃燒排放與城市其他排放的差異.

圖3 左旋葡聚糖與一氧化碳和乙腈的散點(diǎn)圖

2.4 生物質(zhì)燃燒排放對(duì)OA的貢獻(xiàn)

在生物質(zhì)燃燒過程中,植物的纖維素和半纖維素高溫裂解形成脫水糖類物質(zhì),其中左旋葡聚糖是氣溶膠中含量最高的脫水糖類化合物,其次是甘露糖和半乳糖,故將左旋葡聚糖作為示蹤物判斷生物質(zhì)燃燒對(duì)OA的貢獻(xiàn)[66-67].珠江三角洲地區(qū)城市站點(diǎn)和區(qū)域站點(diǎn)的OA平均濃度分別為(19.2±12.6)和(19.2±8.9)μg/m3.從圖4可以看出,兩個(gè)站點(diǎn)中測(cè)得的左旋葡聚糖與OA之間均呈現(xiàn)顯著的正相關(guān)關(guān)系,這表明生物質(zhì)燃燒是我國(guó)珠江三角洲地區(qū)秋季大氣氣溶膠中OA的重要來源.

左旋葡聚糖與OA的比值(Levoglucosan/OA)已被用于估算生物質(zhì)燃燒對(duì)OA的貢獻(xiàn),本研究進(jìn)一步通過受體示蹤物法,利用示蹤物左旋葡聚糖與OA濃度通過下式對(duì)生物質(zhì)燃燒貢獻(xiàn)進(jìn)行估算:

式中:(Levoglucosan/OA)環(huán)境代表觀測(cè)期間左旋葡聚糖與OA的平均比值;(Levoglucosan/OA)源代表生物質(zhì)燃燒源譜中左旋葡聚糖與OA的比值.基于Zhang等[68]和Li等[69]研究得到中國(guó)谷類秸稈(水稻、小麥和玉米)燃燒排放的PM2.5中左旋葡聚糖對(duì)OC的平均排放因子(8.2%)和OA/OC比值(1.3),本研究估算出兩個(gè)站點(diǎn)中生物質(zhì)燃燒對(duì)OA的平均貢獻(xiàn)分別為7.4%(城市站點(diǎn))和11.4%(區(qū)域站點(diǎn)).由圖5可知,生物質(zhì)燃燒對(duì)城市站點(diǎn)OA的貢獻(xiàn)在夜間22:00左右達(dá)到峰值(13.3%),對(duì)區(qū)域站點(diǎn)OA的貢獻(xiàn)在夜間19:00左右達(dá)到峰值(18.3%).表明我國(guó)珠江三角洲地區(qū)秋季生物質(zhì)燃燒排放對(duì)OA的貢獻(xiàn)在夜間明顯高于白天.

同時(shí),Huang等[16]和He等[17]分別于2008年和2009年利用受體模型正矩陣因子分解法(PMF)對(duì)高分辨率氣溶膠質(zhì)譜儀測(cè)得的秋季珠江三角洲農(nóng)村站點(diǎn)和城市站點(diǎn)的OA進(jìn)行來源識(shí)別與定量,解析出生物質(zhì)燃燒源(BBOA)對(duì)OA的貢獻(xiàn)分別為24.5%和24.1%.本研究結(jié)果要低于該值,但與Zhu等[70]和Cao等[71]分別于2014年和2015年秋冬季在珠江三角洲城市站點(diǎn)的觀測(cè)結(jié)果(12.6%和8.9%)相近,說明近年來通過實(shí)施嚴(yán)格的空氣污染防治措施,使珠江三角洲地區(qū)大規(guī)模露天焚燒農(nóng)田秸稈的生物質(zhì)燃燒活動(dòng)得到了一定控制[72-73].此外,除了對(duì)珠江三角洲地區(qū)的研究, Zhang等[74]發(fā)現(xiàn)長(zhǎng)三角地區(qū)夏季小麥?zhǔn)斋@和秋季水稻收獲期間的BBOA的貢獻(xiàn)值為36%～39%,以及Xu等[75]發(fā)現(xiàn)與以往其他季節(jié)相比,生物質(zhì)燃燒源對(duì)北京城市地區(qū)OA的貢獻(xiàn)在秋季更加顯著(20%).因此,我國(guó)珠江三角洲地區(qū)秋季生物質(zhì)燃燒排放對(duì)大氣氣溶膠中OA的貢獻(xiàn)雖然沒有京津冀和長(zhǎng)三角地區(qū)高,但對(duì)珠江三角洲地區(qū)大氣細(xì)顆粒物污染的影響不可忽視,特別是珠江三角洲農(nóng)村及周邊地區(qū)秋收后大規(guī)模的生物質(zhì)開放式燃燒活動(dòng).

圖5 生物質(zhì)燃燒對(duì)OA貢獻(xiàn)的日變化特征

3 結(jié)論

3.1 通過高時(shí)間分辨率測(cè)量,觀測(cè)期間城市站點(diǎn)和區(qū)域站點(diǎn)的左旋葡聚糖平均濃度分別為(0.07±0.08)和(0.14±0.12)μg/m3,表明我國(guó)珠江三角洲地區(qū)秋季左旋葡聚糖濃度呈現(xiàn)區(qū)域站點(diǎn)高于城市站點(diǎn)的空間分布特征,且與其他國(guó)內(nèi)外城市相比,珠江三角洲地區(qū)濃度低于華北及西南等地區(qū),與歐洲地區(qū)大致相當(dāng).

3.2 兩個(gè)站點(diǎn)的左旋葡聚糖濃度隨時(shí)間基本呈現(xiàn)早晨及夜間出現(xiàn)峰值的變化趨勢(shì),相較于區(qū)域站點(diǎn),城市站點(diǎn)的峰值較小且達(dá)峰值時(shí)間較晚,這種差異可能是因?yàn)橹榻侵薜貐^(qū)秋收后農(nóng)田秸稈露天燃燒活動(dòng)主要發(fā)生在農(nóng)村地區(qū),城市上風(fēng)向地區(qū)生物質(zhì)燃燒所排放的污染物可傳輸至城市區(qū)域.

3.3 兩個(gè)站點(diǎn)觀測(cè)到左旋葡聚糖與CO和乙腈的相關(guān)性較差,表明除了生物質(zhì)燃燒外,我國(guó)珠江三角洲地區(qū)秋季CO和乙腈受其他排放源貢獻(xiàn)顯著,如機(jī)動(dòng)車排放以及燃煤排放.通過小時(shí)值和日均值的比較,可以發(fā)現(xiàn)兩個(gè)站點(diǎn)日均值的相關(guān)性要高于小時(shí)值,小時(shí)值的相關(guān)性低,更加凸顯高時(shí)間分辨率測(cè)量條件下,普通城市排放和生物質(zhì)燃燒排放的差異.

3.4 基于受體示蹤物法估算出生物質(zhì)燃燒對(duì)OA的平均貢獻(xiàn)分別為7.4%(城市站點(diǎn))和11.4%(區(qū)域站點(diǎn)),生物質(zhì)燃燒對(duì)城市站點(diǎn)OA的貢獻(xiàn)在夜間22:00左右達(dá)到峰值(13.3%),對(duì)區(qū)域站點(diǎn)OA的貢獻(xiàn)在夜間19:00左右達(dá)到峰值(18.3%).表明我國(guó)珠江三角洲地區(qū)秋季生物質(zhì)燃燒排放對(duì)OA的貢獻(xiàn)在夜間明顯高于白天.且與其他國(guó)內(nèi)城市相比,我國(guó)珠江三角洲地區(qū)秋季生物質(zhì)燃燒排放對(duì)大氣氣溶膠中OA的貢獻(xiàn)雖然沒有京津冀和長(zhǎng)三角地區(qū)高,但對(duì)珠江三角洲地區(qū)大氣細(xì)顆粒物污染的影響不可忽視,特別是珠江三角洲農(nóng)村及周邊地區(qū)秋收后大規(guī)模的生物質(zhì)開放式燃燒活動(dòng).

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Contribution of autumn biomass burning to organic aerosol in the Pearl River Delta region.

YANG Lei1, YUAN Bin1*, ZHENG E1, YE Chen-shuo2, WANG Si-hang1, HE Xian-jun1, ZHANG Xiao-xiao1, HUANG Shan1, HU Wei-wei3, SHAO Min1

(1.Institute for Environmental and Climate Research, Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Jinan University, Guangzhou 511443, China；2.College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China；3.The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China)., 2023,43(1)：20～28

In this study, we applied thermal desorption chemical ionization Time-of-Flight mass spectrometer (FIGAERO-ToF-CIMS) to obtain high temporal resolution (i.e., hourly) measurements of levoglucosan, which is a widely-used tracer for biomass burning emissions. Using the dataset, we estimate the contributions of biomass burning to organic aerosol (OA) at an urban and a regional site in the autumn of Pearl River Delta (PRD) region. The results demonstrated that the average concentrations of levoglucosan at the urban and regional sites in the autumn PRD region were (0.07 ± 0.08) and (0.14 ± 0.12) μg/m3, respectively. We show that concentrations observed at the regional site were higher than the urban site. The diurnal variation of levoglucosan peaked in the morning and at night at both sites. It was observed that levoglucosan was poorly correlated with CO and acetonitrile at both sites, whereas significantly positive correlation was obtained with OA. The average contributions ofbiomass burning to OA were further estimated based on the tracer method to be 7.4% (urban site) and 11.4% (regional site), respectively,with significantly higher contributions at night than during the day.

biomass burning；tracer；levoglucosan；organic aerosol

X513

A

1000-6923(2023)01-0020-08

楊 磊(1998-),男,安徽銅陵人,暨南大學(xué)環(huán)境與氣候研究院碩士研究生,主要從事大氣環(huán)境化學(xué)方面的研究.發(fā)表論文1篇.

2022-06-13

國(guó)家自然科學(xué)基金資助項(xiàng)目(41877302);國(guó)家重點(diǎn)研發(fā)項(xiàng)目(2019YFE0106300)

* 責(zé)任作者, 教授, byuan@jnu.edu.cn