張 揚(yáng),韓士杰,李勤勤,王文路,肖 揚(yáng),郭 嚴(yán),王 好,2,3*,王伯光,2,3**

低NO環(huán)境異戊二烯促進(jìn)甲苯生成甲基丁烯二醛的模擬實(shí)驗(yàn)

張 揚(yáng)1,韓士杰1,李勤勤1,王文路1,肖 揚(yáng)1,郭 嚴(yán)1,王 好1,2,3*,王伯光1,2,3**

(1.暨南大學(xué)環(huán)境與氣候研究院,廣東 廣州 511443；2.中澳空氣質(zhì)量科學(xué)與管理廣東國(guó)際聯(lián)合研究中心,廣東 廣州 511443；3.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)

在低NO濃度條件下開(kāi)展甲苯和異戊二烯復(fù)合體系的煙霧箱模擬實(shí)驗(yàn),使用高時(shí)間分辨率的在線質(zhì)子轉(zhuǎn)移反應(yīng)飛行時(shí)間質(zhì)譜(PTR-TOF-MS)實(shí)時(shí)監(jiān)測(cè)混合體系中反應(yīng)物與產(chǎn)物的濃度變化情況,探究人為源與天然源交匯過(guò)程中, 自然源揮發(fā)性有機(jī)物(BVOCs)對(duì)人為揮發(fā)性有機(jī)物(AVOCs)化學(xué)降解的影響.結(jié)果表明,異戊二烯與甲苯競(jìng)爭(zhēng)OH自由基,從而抑制了甲苯的化學(xué)降解,該競(jìng)爭(zhēng)反應(yīng)開(kāi)始得越早,抑制效果越顯著.研究還發(fā)現(xiàn)異戊二烯會(huì)增強(qiáng)甲苯RO2降解途徑產(chǎn)物的產(chǎn)量,生成更多1,4不飽和-二羰基化合物(如丁烯二醛和甲基丁烯二醛)與二羰基化合物(如乙二醛和甲基乙二醛),其中甲基丁烯二醛增量最高可達(dá)38.6%.此外,異戊二烯快速氧化生成的RO2自由基碳數(shù)更少,可能與甲苯氧化生成的RO2自由基發(fā)生了快速的交叉反應(yīng),有利于甲苯RO自由基的生成及裂解,最終導(dǎo)致甲苯RO2途徑裂解產(chǎn)物的增加.

甲苯；異戊二烯；煙霧箱模擬；人為源-天然源交匯作用；RO2途徑；甲基丁烯二醛；揮發(fā)性有機(jī)物

與大氣中的羥基自由基(OH)反應(yīng)是甲苯化學(xué)降解的主要途徑[13-14],多項(xiàng)研究對(duì)甲苯的氧化降解反應(yīng)展開(kāi)了煙霧箱和計(jì)算機(jī)模型模擬研究[15-18].最新的準(zhǔn)特定化學(xué)機(jī)理(MCM)表明,甲苯與OH自由基的反應(yīng)包含4個(gè)途徑,分別為醛途徑、酚途徑、雙環(huán)過(guò)氧自由基(RO2)途徑和環(huán)氧化物途徑[19].其中RO2途徑是甲苯氧化降解過(guò)程中的最關(guān)鍵反應(yīng)途徑,分支比高達(dá)65%,亦是甲苯氧化生成O3和SOA的關(guān)鍵途徑[20].甲苯RO2產(chǎn)物進(jìn)一步裂解開(kāi)環(huán),生成甲基丁烯二醛和丁烯二醛等不飽和二羰基化合物.這些物質(zhì)是羧酸類、氫過(guò)氧化物類、O3和過(guò)氧乙酰硝酸酯(PAN)等的重要前體物,也是大氣自由基的重要來(lái)源之一[21].然而,由于甲苯氧化產(chǎn)生的不飽和二羰基化合物化學(xué)性質(zhì)高度活潑[22],不同研究得出的產(chǎn)率結(jié)論差異較大[23-26],甲苯氧化產(chǎn)物在不同條件下的生成情況需要進(jìn)一步研究.

隨著我國(guó)森林蓄積面積增加和城鎮(zhèn)綠化程度上升,生物源揮發(fā)性有機(jī)物(BVOCs)對(duì)城市大氣環(huán)境的影響不容忽視[27-29],但目前針對(duì)BVOCs影響人為污染物降解的研究較少.人為源與天然源交匯過(guò)程中,不僅大氣氧化性以及O3和SOA的生成會(huì)發(fā)生改變[30-34],BVOCs和AVOCs的降解產(chǎn)物與反應(yīng)途徑也可能發(fā)生變化[35].但BVOCs如何影響AVOCs的降解仍然不太確定.異戊二烯是大氣環(huán)境中排放量最大且化學(xué)性質(zhì)最活潑的BVOCs[36],現(xiàn)有煙霧箱實(shí)驗(yàn)對(duì)異戊二烯如何影響甲苯降解的認(rèn)識(shí)差異較大. Jaoui等[37]在其設(shè)定的甲苯/異戊二烯混合體系中發(fā)現(xiàn),異戊二烯會(huì)抑制甲苯光化學(xué)降解反應(yīng),降低甲苯氧化產(chǎn)物的產(chǎn)量.相反,Chen等[38]在不同異戊二烯/甲苯濃度比值的混合體系下發(fā)現(xiàn)異戊二烯促進(jìn)了甲苯的降解,提高了O3和SOA等二次產(chǎn)物的產(chǎn)量;甲苯初始濃度越低,二次產(chǎn)物的增長(zhǎng)率越大.綜上所述,在人為源與天然源交匯過(guò)程中,異戊二烯等BVOCs如何影響甲苯等AVOCs的降解仍需要進(jìn)一步研究.

本研究使用煙霧箱開(kāi)展了甲苯-異戊二烯混合體系的模擬實(shí)驗(yàn)研究,通過(guò)分析甲苯和甲基丁烯二醛濃度的變化情況,探討異戊二烯對(duì)甲苯降解及其RO2途徑產(chǎn)物的影響.

1 材料與方法

1.1 煙霧箱

模擬實(shí)驗(yàn)采用暨南大學(xué)環(huán)境與氣候研究院搭建的煙霧箱系統(tǒng)JNU-VMDSC.該煙霧箱以Teflon- FEP薄膜(DuPont,0.05mm)制成,體積為8m3,置于溫度濕度穩(wěn)定的室內(nèi),頂部和兩側(cè)均勻布設(shè)有120盞黑光燈(GE F40BLB,365nm)提供光源,最大光解速率為no2=0.362min-1.煙霧箱配置有精密的溫濕度控制系統(tǒng)及多個(gè)傳感器,可實(shí)時(shí)采集和記錄煙霧箱內(nèi)環(huán)境參數(shù)(如光照、溫度、濕度、壓強(qiáng)等)的變化.

由零氣發(fā)生器(熱電Model 111)提供背景反應(yīng)空氣.空氣在進(jìn)入零氣發(fā)生器前先通過(guò)硅膠干燥管和顆粒物過(guò)濾器,再依次通過(guò)硅膠干燥管、Purafil催化劑、活性碳和霍賈拉特催化劑,分別去除水蒸氣、NO/SO2等酸性氣體以及臭氧和CO等.在正式實(shí)驗(yàn)之前,分別以掃描電遷移率粒徑譜儀(SMPS, Scanning mobility particle sizer,TSI,3938L75)和質(zhì)子轉(zhuǎn)移反應(yīng)飛行時(shí)間質(zhì)譜(PTR-TOF-MS, Ionicon Analytik GmbH, Innsbruck,澳大利亞)實(shí)時(shí)采樣至少0.5h,記錄煙霧箱反應(yīng)本底.甲苯和異戊二烯等前體物初始濃度均小于0.1×10-9,顆粒物初始數(shù)濃度小于1個(gè)/cm3.

開(kāi)燈前10min,向煙霧箱內(nèi)通入NO標(biāo)氣(Air Liqui-de, 99.99%),再以氮?dú)夥謩e將甲苯(99.5%,默克)和過(guò)氧化氫(30%,默克)引入煙霧箱.之后,擾流風(fēng)扇繼續(xù)工作10min使反應(yīng)物充分混合;接著關(guān)閉風(fēng)扇,打開(kāi)黑光燈與制冷機(jī),開(kāi)始實(shí)驗(yàn).每次實(shí)驗(yàn)結(jié)束后,開(kāi)啟臭氧發(fā)生器(CH-ZTW3g)向煙霧箱內(nèi)通入300× 10-9的O3,光照反應(yīng)至少1h,再打開(kāi)零氣發(fā)生器和擾流風(fēng)扇連續(xù)清洗48h以上,以去除煙霧箱中的殘留前體物和產(chǎn)物.

1.2 監(jiān)測(cè)儀器

實(shí)驗(yàn)中全過(guò)程開(kāi)啟常規(guī)氣態(tài)污染物監(jiān)測(cè)儀器和PTR-TOF-MS進(jìn)行在線監(jiān)測(cè).其中,氣態(tài)常規(guī)污染物O3、CO、SO2、NO、NO2和NO分別使用Thermo 系列的O3分析儀(49i)、CO分析儀(48i)、SO2分析儀(43i)和NO分析儀(42i)實(shí)時(shí)測(cè)量.氣態(tài)污染物監(jiān)測(cè)儀器定期使用零氣發(fā)生器(Thermo 111)和動(dòng)態(tài)稀釋儀(Thermo 146i)進(jìn)行零點(diǎn)、跨點(diǎn)校準(zhǔn).

PTR-TOF-MS配備有四級(jí)離子向?qū)?每5s記錄一次數(shù)據(jù),可實(shí)時(shí)精確測(cè)量煙霧箱中VOCs的變化情況.煙霧箱內(nèi)的氣體樣品通過(guò)全氟烷氧基(PFA)特氟龍管與外部泵(2.0L/min)連接后進(jìn)入儀器.特氟龍管被保溫海綿包裹,防止因煙霧箱與外界環(huán)境的溫差而導(dǎo)致低揮發(fā)性有機(jī)物在管內(nèi)凝結(jié).PTR-TOF- MS以H3O+電離模式運(yùn)行,漂移管壓力為380Pa,溫度為50℃,電壓為920V,/比率(是電場(chǎng)強(qiáng)度,是氣體在漂移管的數(shù)密度)為120Td.在此條件下,水簇離子的數(shù)量相對(duì)較小,大多數(shù)VOC產(chǎn)物離子的破碎性不顯著,定量結(jié)果相對(duì)更準(zhǔn)確[39-40].

According to the traditional RNN and LSTM,a traditional checking model of Chinese read-backs was proposed in Ref.35.To compare the proposed checking model,the experiments based on traditional model were conducted.The procedure of traditional checking model is shown in Fig.5.

實(shí)驗(yàn)過(guò)程中,定期使用包含39種VOCs組分的混合標(biāo)準(zhǔn)氣體在干燥(RH<1%)條件下對(duì)PTR-TOF- MS進(jìn)行標(biāo)定校正,以保證儀器運(yùn)行期間數(shù)據(jù)的準(zhǔn)確性.實(shí)驗(yàn)期間,標(biāo)準(zhǔn)氣體組分響應(yīng)因子波動(dòng)范圍均在20%以內(nèi).各種儀器測(cè)量數(shù)據(jù)的不確定度在15%～ 20%.考慮到部分物質(zhì)缺失校準(zhǔn)因子和換算過(guò)程中產(chǎn)生的誤差對(duì)靈敏度的影響,本研究中所有物質(zhì)均采用歸一化的每秒計(jì)數(shù)(cps)信號(hào)進(jìn)行分析.

1.3 實(shí)驗(yàn)設(shè)計(jì)

表1 煙霧箱模擬實(shí)驗(yàn)初始條件

注:-表示無(wú); TOL代表甲苯,ISO代表異戊二烯.TOL實(shí)驗(yàn)表示實(shí)驗(yàn)過(guò)程中煙霧箱內(nèi)只有甲苯一種前體物.TOL-ISO表示煙霧箱內(nèi)同時(shí)存在甲苯和異戊二烯兩種前體物.

煙霧箱模擬實(shí)驗(yàn)的初始條件見(jiàn)表1.本研究NO濃度參考實(shí)際大氣中低NO濃度設(shè)置[26].開(kāi)燈前10min,向煙霧箱內(nèi)注射等量過(guò)氧化氫(H2O2)溶液,作為每個(gè)模擬實(shí)驗(yàn)早期的OH自由基來(lái)源[41].在甲苯降解實(shí)驗(yàn)進(jìn)行至不同階段,注入異戊二烯,觀測(cè)煙霧箱中氣態(tài)產(chǎn)物的變化.為了探究異戊二烯對(duì)甲苯的實(shí)際影響,設(shè)置TOL-ISO-2.5h實(shí)驗(yàn),表示實(shí)驗(yàn)進(jìn)行2.5h后往煙霧箱內(nèi)注入異戊二烯;平行1和平行2為一對(duì)重復(fù)性實(shí)驗(yàn).實(shí)驗(yàn)過(guò)程中的溫度均為25℃、相對(duì)濕度均為30%.

2 結(jié)果與討論

2.1 煙霧箱重復(fù)性實(shí)驗(yàn)

可重復(fù)性是衡量煙霧箱實(shí)驗(yàn)質(zhì)量的一個(gè)重要指標(biāo)[18].兩組甲苯-NO重復(fù)性實(shí)驗(yàn)(平行1和平行2)的結(jié)果如圖1所示.兩組實(shí)驗(yàn)甲苯、NO等前體物濃度相近,甲苯濃度偏差為3.5%,NO濃度偏差為6.8%,由初始反應(yīng)條件引起的偏差在可接受的范圍之內(nèi).兩組實(shí)驗(yàn)中的甲苯及其產(chǎn)物甲基丁烯二醛的變化曲線相似.平行1與平行2實(shí)驗(yàn)中甲苯最終反應(yīng)量分別為6.7′104cps和6.8′104cps,偏差約為1.9%.甲基丁烯二醛在實(shí)驗(yàn)平行1和平行2中的最終產(chǎn)量分別為4.9′103cps和5.0′103cps,對(duì)應(yīng)的偏差為3.4%.前體物及其產(chǎn)物的偏差均小于5%,表明本研究使用的煙霧箱體系中甲苯及其產(chǎn)物變化的重復(fù)性較好.

圖1 重復(fù)實(shí)驗(yàn)中甲苯及其典型產(chǎn)物甲基丁烯二醛的時(shí)間序列

2.2 異戊二烯對(duì)甲苯降解量的影響

Chen等[38]對(duì)比了純甲苯體系和甲苯-異戊二烯混合體系中甲苯的消耗量,發(fā)現(xiàn)實(shí)驗(yàn)結(jié)束后,混合體系中甲苯消耗了22.2μg/m3,為起始濃度的35%.而純甲苯體系中,甲苯僅消耗了3.1μg/m3,占起始濃度的5.6%,表明異戊二烯對(duì)甲苯降解有顯著的促進(jìn)作用.而Jaoui等[37]發(fā)現(xiàn),在甲苯-蒎烯/異戊二烯體系中加入異戊二烯后,甲苯消耗量從1900μg/m3降低到1000μg/m3,甲苯從30%的消耗量降低至15%,異戊二烯的加入顯著抑制了甲苯的降解.本研究根據(jù)PTR- TOF-MS在線監(jiān)測(cè)數(shù)據(jù)結(jié)果分析異戊二烯加入前后對(duì)甲苯降解的影響.如圖2所示,相比于純甲苯體系,甲苯-異戊二烯混合體系中甲苯的消耗量更小.實(shí)驗(yàn)至8h時(shí),純甲苯體系中,甲苯消耗了62%,但在混合體系中,甲苯的消耗量均在50%左右.同時(shí),在甲苯不同反應(yīng)階段加入異戊二烯,其對(duì)甲苯反應(yīng)的影響也有所不同.在甲苯反應(yīng)開(kāi)始前加入異戊二烯,對(duì)甲苯氧化的的抑制效果要高于反應(yīng)2.5h后加入.結(jié)合Jaoui等[37]的研究,表明異戊二烯不但抑制了甲苯的降解,同時(shí)也反映出異戊二烯參與反應(yīng)的時(shí)間越早,其抑制作用也越明顯.這可能歸因于異戊二烯與甲苯的OH競(jìng)爭(zhēng)反應(yīng),異戊二烯與OH的反應(yīng)速率遠(yuǎn)大于甲苯,在異戊二烯加入后,OH優(yōu)先與異戊二烯反應(yīng),使得甲苯的消耗量降低.同時(shí),由于甲苯與OH的反應(yīng)為一級(jí)反應(yīng),甲苯在反應(yīng)初期的消耗量高于反應(yīng)后期,因此異戊二烯參與反應(yīng)的時(shí)間越早,競(jìng)爭(zhēng)效應(yīng)帶來(lái)的抑制效果越顯著.

圖2 各實(shí)驗(yàn)結(jié)束時(shí)甲苯消耗量占比情況

2.3 異戊二烯對(duì)甲苯RO2途徑產(chǎn)物的影響

圖3 MCM中甲苯氧化機(jī)制

改編自文獻(xiàn)[19,25]

根據(jù)MCM機(jī)制,甲苯的RO2降解途徑進(jìn)一步可分為5個(gè),各占20%(圖3),主要產(chǎn)物包括乙二醛、甲基乙二醛、丁烯二醛和甲基丁烯二醛等.在純甲苯和異戊二烯-甲苯實(shí)驗(yàn)過(guò)程中觀測(cè)到甲苯RO2途徑的產(chǎn)物信號(hào)變化如圖4所示,相比于純甲苯實(shí)驗(yàn),加入異戊二烯的實(shí)驗(yàn)中雖然觀察到的甲苯消耗量減少了,但RO2途徑主要產(chǎn)物之一的甲基丁烯二醛信號(hào)總量卻顯著增加.

圖4 實(shí)驗(yàn)結(jié)束時(shí),未加入異戊二烯和加入異戊二烯的甲苯實(shí)驗(yàn)中的物質(zhì)信號(hào)對(duì)比

在TOL-ISO-2.5h實(shí)驗(yàn)中,加入異戊二烯后丁烯二醛和甲基丁烯二醛的信號(hào)變化如圖5所示,二者信號(hào)均出現(xiàn)迅速上升的現(xiàn)象.甲基丁烯二醛信號(hào)濃度在短時(shí)間內(nèi)快速上升,然后達(dá)到平衡,而丁烯二醛信號(hào)則持續(xù)上升至實(shí)驗(yàn)結(jié)束.加入異戊二烯前后1h的甲苯及其產(chǎn)物信號(hào)變化量存在明顯差異,如圖6所示.加入異戊二烯后,產(chǎn)物增加的信號(hào)遠(yuǎn)高于未加異戊二烯時(shí)的信號(hào)增加結(jié)果,加入異戊二烯后1h的甲苯消耗量也小于未加入異戊二烯前1h消耗量.

綜上所述,加入異戊二烯后甲苯消耗量降低,而甲苯RO2途徑產(chǎn)物產(chǎn)量增大, 表明異戊二烯增強(qiáng)甲苯RO2途徑降解生成不飽和二羰基化合物.

Wang等[42]發(fā)現(xiàn)異戊二烯會(huì)搶奪煙霧箱內(nèi)OH自由基進(jìn)行氧化分解,因而本研究中觀測(cè)到的甲苯氧化產(chǎn)物整體信號(hào)上升的原因不能簡(jiǎn)單排除是異戊二烯降解產(chǎn)物與甲苯降解產(chǎn)物相同,或者產(chǎn)生了相同質(zhì)荷比產(chǎn)物的可能性.通過(guò)匯總文獻(xiàn)中已報(bào)道的異戊二烯和甲苯主要降解產(chǎn)物及其產(chǎn)率(表2)并做了多方比較分析,部分排除來(lái)自異戊二烯產(chǎn)物信號(hào)的干擾.

Smith等[24]在甲苯氧化實(shí)驗(yàn)中發(fā)現(xiàn)甲苯氧化過(guò)程中RO2途徑會(huì)產(chǎn)生/=84的物質(zhì),Jang等[43]進(jìn)一步確定甲苯氧化反應(yīng)中產(chǎn)生的/為84的物質(zhì)是丁烯二醛.此外,Fan[44]和Healy等[45]研究發(fā)現(xiàn)異戊二烯的主要初級(jí)產(chǎn)物為甲基乙烯基甲酮(MVK)和異丁烯醛(MACR),推測(cè)初級(jí)產(chǎn)物經(jīng)過(guò)進(jìn)一步氧化分解產(chǎn)生其它化合物,如羰基類化合物等.Pan等[46]在分析異戊二烯氧化實(shí)驗(yàn)中產(chǎn)生的氣態(tài)和顆粒態(tài)物質(zhì)時(shí),發(fā)現(xiàn)異戊二烯產(chǎn)物中含有/=84的C5-羰基化合物和2-甲基-3-烯醛.即異戊二烯的部分產(chǎn)物理論上可能會(huì)對(duì)甲苯氧化產(chǎn)物丁烯二醛的信號(hào)造成一定干擾.

Wennberg等[47]確定的異戊二烯氧化產(chǎn)物質(zhì)譜中未檢出甲基丁烯二醛,也未檢出其它/=98的物質(zhì),這一結(jié)果與Kroll等[48]的研究發(fā)現(xiàn)相同.然而諸多研究發(fā)現(xiàn)甲苯的氧化產(chǎn)物中有3種物質(zhì)具有相同的/=98,分別是甲基丁烯二醛、4-氧-二戊烯醛和呋喃酮[23-24,49],其中甲基丁烯二醛、4-氧-二戊烯醛互為同分異構(gòu)體.雖然Smith在高NO實(shí)驗(yàn)條件下測(cè)到了痕量的呋喃酮[24],但在Seuwen等[50]的低NO實(shí)驗(yàn)條件中并未檢測(cè)出呋喃酮.另外,Zaytsev等[26]最近一項(xiàng)研究認(rèn)為4-氧-二戊烯醛信號(hào)可以歸為甲基丁烯二醛.且Mattias等[51]的RO2‘池’反應(yīng)理論指出實(shí)驗(yàn)中的RO2產(chǎn)物可以進(jìn)行異構(gòu)化和自氧化,同一途徑產(chǎn)出的同分異構(gòu)體可以視為同一物質(zhì),這進(jìn)一步支持了Zaytsev的結(jié)論.Ji等[1]從Schwantes等[52]的研究結(jié)果推測(cè)羰基化合物也可能是酚途徑氧化產(chǎn)物,但Schwantes等研究發(fā)現(xiàn)酚途徑產(chǎn)物進(jìn)一步氧化生成的多為保環(huán)物質(zhì),如二羥基甲苯、三羥基甲苯、四羥基甲苯、五羥基甲苯等,少量的1,4不飽和羰基化合物僅在高NO條件下的顆粒態(tài)產(chǎn)物中被檢測(cè)到.本研究的甲苯實(shí)驗(yàn)在低NO條件下開(kāi)展,呋喃酮和酚途徑羰基化合物對(duì)研究結(jié)果的影響可以忽略不計(jì),因此認(rèn)為實(shí)驗(yàn)中/=98物質(zhì)信號(hào)豐度主要來(lái)自RO2途徑的甲基丁烯二醛,其信號(hào)增強(qiáng)是異戊二烯對(duì)甲苯RO2途徑降解生成不飽和二羰基化合物的增強(qiáng)結(jié)果.

雖然實(shí)驗(yàn)中丁烯二醛的實(shí)驗(yàn)結(jié)果可能會(huì)受到異戊二烯產(chǎn)物的影響,但通過(guò)對(duì)比中途加入異戊二烯的實(shí)驗(yàn)中甲基丁烯二醛的信號(hào)結(jié)果發(fā)現(xiàn),此實(shí)驗(yàn)中雙環(huán)過(guò)氧自由基途徑(RO2)產(chǎn)物丁烯二醛和甲基丁烯二醛的增速和增量變大,根據(jù)公式(5)計(jì)算出甲基丁烯二醛增量達(dá)38.6%.結(jié)合Wang等[42]關(guān)于混合體系中不同RO2之間存在的機(jī)理,異戊二烯增強(qiáng)甲苯RO2途徑產(chǎn)物生成的一個(gè)可能原因如公式(1)(2)(3)所示,異戊二烯通過(guò)快速提供R2O2,與甲苯降解生成的R1O2之間發(fā)生進(jìn)一步反應(yīng),正向促進(jìn)甲苯的RO2向RO轉(zhuǎn)化[47],而后RO可發(fā)生公式(4)的反應(yīng),產(chǎn)生甲基丁烯二醛、HO2自由基等產(chǎn)物[19].

圖6 在甲苯氧化實(shí)驗(yàn)中期加入異戊二烯前后1h的物質(zhì)信號(hào)變化

R1O2+R2O2→R1O+R2O+O2(1)

R1O2+R2O2→R1OH+R2′HO+O2(2)

R1O2+R2O2→R1′HO+R2OH+O2(3)

RO→C2H2O2+C5H6O2+HO2(4)

產(chǎn)物增量=(－)/(5)

式(5)中:為加入異戊二烯前的產(chǎn)物產(chǎn)率,為加入異戊二烯后的產(chǎn)物產(chǎn)率.

表2 已有研究中關(guān)于異戊二烯和甲苯的主要氧化產(chǎn)物及其產(chǎn)率的比較

3 結(jié)論

3.1 異戊二烯通過(guò)競(jìng)爭(zhēng)OH自由基,抑制了甲苯的降解,且該抑制效果隨競(jìng)爭(zhēng)反應(yīng)時(shí)間的提前而增強(qiáng).

3.2 同時(shí),根據(jù)Hallquist的RO2的‘池’反應(yīng)理論,發(fā)現(xiàn)異戊二烯會(huì)增加甲苯RO2途徑產(chǎn)物的產(chǎn)量,生成更多1,4不飽和-二羰基化合物(丁烯二醛、甲基丁烯二醛)和二羰基化合物(乙二醛、甲基乙二醛),產(chǎn)物增量最高可達(dá)38.6%.

3.3 研究表明,異戊二烯能更快速生成碳數(shù)更少的RO2自由基.異戊二烯-RO2自由基可通過(guò)與甲苯-RO2自由基進(jìn)行交叉反應(yīng),促進(jìn)甲苯RO自由基生成,進(jìn)而增強(qiáng)甲苯RO2途徑裂解產(chǎn)物的生成.

3.4 同時(shí),RO2途徑產(chǎn)物進(jìn)一步氧化裂解可生成大量的HO2自由基,顯著影響OH自由基的再生濃度,從而導(dǎo)致甲苯二次產(chǎn)物生成量增加.RO2途徑產(chǎn)物產(chǎn)量和HO2等自由基的變化,可能是甲苯等芳香烴研究中碳缺失和自由基不閉合問(wèn)題的一個(gè)重要影響因素.

[1] Ji Y, Zhao J, Terazono H, et al. Reassessing the atmospheric oxidation mechanism of toluene [J]. Proceedings of the National Academy of Sciences, 2017,114(31):8169-8174.

[2] Kurtenbach R, Ackermann R, Becker K H, et al. Verification of the contribution of vehicular traffic to the total NMVOC emissions in germany and the importance of the NO3chemistry in the city air [J]. Journal of Atmospheric Chemistry 42:395–411:2002.

[3] Velasco E, Lamb B, Westberg H, et al. Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 & 2003 field campaigns [J]. Atmospheric Chemistry and Physics, 2007,7:329-353.

[4] Li M, Zhang Q, Zheng B, et al. Persistent growth of anthropogenic non-methane volatile organic compound (NMVOC) emissions in China during 1990～2017: Drivers, speciation and ozone formation potential [J]. Atmospheric Chemistry and Physics, 2019,19(13):8897-8913.

[5] Karl T, Striednig M, Graus M, et al. Urban flux measurements reveal a large pool of oxygenated volatile organic compound emissions [J]. Proceedings of the National Academy of Sciences, 2018,115(6):1186- 1191.

[6] Li B, Ho S S H, Gong S, et al. Characterization of VOCs and their related atmospheric processes in a central Chinese city during severe ozone pollution periods [J]. Atmospheric Chemistry and Physics, 2019,19(1):617-638.

[7] Zhao Q, Bi J, Liu Q, et al. Sources of volatile organic compounds and policy implications for regional ozone pollution control in an urban location of Nanjing, East China [J]. Atmospheric Chemistry and Physics, 2020,20(6):3905-3919.

[8] Wu R, Xie S. Spatial distribution of secondary organic aerosol formation potential in China derived from speciated anthropogenic volatile organic compound emissions [J]. Environmental Science & Technology, 2018,52(15):8146-8156.

[9] Levine C, Marcillo A. Regarding several points of doubt of the structure of the olfactory bulb: as described by T. Blanes [J]. Anatomical Record-advances in Integrative Anatomy & Evolutionary Biology, 2008,291(7):751-62.

[10] Samet J M, Chiu W A, Cogliano V, et al. The IARC monographs: Updated procedures for modern and transparent evidence synthesis in cancer hazard identification [J]. International Agency for Research on Cancer, 2020,112(1):30-37.

[11] Moolla R, Curtis C J, Knight J. Occupational exposure of diesel station workers to BTEX compounds at a bus depot [J]. International Journal of Environmental Research and Public Health, 2015,12(4): 4101-4115.

[12] 王玉玨,胡 敏,李 曉,等.大氣顆粒物中棕色碳的化學(xué)組成、來(lái)源和生成機(jī)制[J]. 化學(xué)進(jìn)展, 2020,32(5):627-641.

Yujue Wang, Min Hu, Xiao Li, et al. Chemical Composition, Sources and Formation Mechanisms of Particulate Brown Carbon in the Atmosphere [J]. Progress in Chemistry, 2020,32(5):627-641.

[13] Le B G, Becker K H. Chemical processes in atmospheric oxidation [J]. Eurotrac, 1997,551.51l-dc20:96-41132.

[14] Bandow H, Washida N. Ring-cleavage reactions of aromatic hydrocarbons studied by FT-IR spectroscopy. II. Photooxidation of o-, m-, and p-xylenes in the NO-air system [J]. Bulletin of the Chemical Society of Japan, 2006,58(9):2541-2548.

[15] Wang S, Newland M J, Deng W, et al. Aromatic photo-oxidation, a new source of atmospheric acidity [J]. Environmental Science & Technology, 2020,54(13):7798-7806.

[16] Arey J, Obermeyer G, Aschmann S M, et al. Dicarbonyl products of the OH radical-initiated reaction of a series of aromatic hydrocarbons [J]. Environmental Science & Technology, 2009,43(3):683-689.

[17] Nehr S, Bohn B, Dorn H P, et al. Atmospheric photochemistry of aromatic hydrocarbons: OH budgets during SAPHIR chamber experiments [J]. Atmospheric Chemistry and Physics, 2014,14(13): 6941-6952.

[18] 賈 龍,徐 福.煙霧箱與數(shù)值模擬研究苯和乙苯的臭氧生成潛勢(shì)[J]. 環(huán)境科學(xué), 2014,35(2):495-503.

Long Jia, Yong fu Xu. Studies of Ozone Formation Potentials for Benzene and Ethylbenzene Using a Smog Chamber and Model Simulation [J]. Eevironmental Science, 2014,35(2):495-503.

[19] Lu S, Li X, Liu Y, et al. Advances on atmospheric oxidation mechanism of typical aromatic hydrocarbons [J]. Acta Chimica Sinica, 2021,79(10):18.

[20] Newland M J, Jenkin M E, Rickard A R. Elucidating the fate of the OH-adduct in toluene oxidation under tropospheric boundary layer conditions [J]. Proceedings of the National Academy of Sciences, 2017,114(38):E7856-7857.

[21] Liu X, Jeffries H E, Sexton K G J E S, et al. Atmospheric photochemical degradation of 1,4-Unsaturated dicarbonyls [J]. Environmental Science & Technology, 1999,33(23):4212-4220.

[22] Bierbach A, Barnes I, Becker K H, et al. Atmospheric chemistry of unsaturated carbonyls: Butenedial, 4-Oxo-2-pentenal, 3-Hexene-2, 5-dione, Maleic Anhydride, 3H-Furan-2-one, and 5-Methyl-3H- furan-2-one [J]. Environmental Science & Technology, 1994,28(4): 715-729.

[23] Wu R, Pan S, Li Y, et al. Atmospheric oxidation mechanism of toluene [J]. Journal of Physical Chemistry A, 2014,118(25):4533-4547.

[24] Smith D F, Mciver C D, Kleindienst T E J J O a C. Primary product distribution from the reaction of hydroxyl radicals with toluene at ppb NOmixing ratios [J]. Journal of Atmospheric Chemistry, 1998,30(2): 209-228.

[25] Birdsall A W, Elrod M J. Comprehensive NO-dependent study of the products of the oxidation of atmospherically relevant aromatic compounds [J]. Journal of Physical Chemistry A, 2011,115(21):5397-5407.

[26] Zaytsev A, Koss A R, Breitenlechner M, et al. Mechanistic study of the formation of ring-retaining and ring-opening products from the oxidation of aromatic compounds under urban atmospheric conditions [J]. Atmospheric Chemistry and Physics, 2019,19(23):15117-15129.

[27] Hoyle C R, Boy M, Donahue N M, et al. A review of the anthropogenic influence on biogenic secondary organic aerosol [J]. Atmospheric Chemistry and Physics, 2011,11(1):321-343.

[28] Bryant D J, Dixon W J, Hopkins J R, et al. Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing [J]. Atmospheric Chemistry and Physics, 2020,20(12):7531-7552.

[29] Li L, Zhang B, Cao J, et al. Isoprenoid emissions from natural vegetation increased rapidly in eastern China [J]. Environmental Research, 2021,200(12):111462-111462.

[30] Wei D, Fuentes J D, Gerken T, et al. Influences of nitrogen oxides and isoprene on ozone-temperature relationships in the Amazon rain forest [J]. Atmospheric Environment, 2019,206:280-292.

[31] Makar P A, Staebler R M, Akingunola A, et al. The effects of forest canopy shading and turbulence on boundary layer ozone [J]. Nature Communications, 2017,8:15243.

[32] Lv S, Gong D, Ding Y, et al. Elevated levels of glyoxal and methylglyoxal at a remote mountain site in southern China: Prompt in-situ formation combined with strong regional transport [J]. Science of the Total Environment, 2019,672:869-882.

[33] Gong D, Wang H, Zhang S, et al. Low-level summertime isoprene observed at a forested mountaintop site in southern China: implications for strong regional atmospheric oxidative capacity [J]. Atmospheric Chemistry and Physics, 2018,18(19):14417-14432.

[34] Qin M, Hu A, Mao J, et al. PM2.5and O3relationships affected by the atmospheric oxidizing capacity in the Yangtze River Delta, China [J]. Science of the Total Environment, 2022,810:152268.

[35] Chen T, Jang M. Secondary organic aerosol formation from photooxidation of a mixture of dimethyl sulfide and isoprene [J]. Atmospheric Environment, 2012,46:271-278.

[36] 張?jiān)姛?龔道程,王 好,等.南嶺國(guó)家大氣背景站異戊二烯的在線觀測(cè)研究[J]. 中國(guó)環(huán)境科學(xué), 2017,37(7):2504-2512.

Shi-yang Zhang, Dao-cheng Gong, et al. Online measurement of isoprene at a national air background monitoring station in the Nanling Mountains, South China [J]. China Environmental Science, 2017, 37(7):2504-2512.

[37] Jaoui M, Edney E O, Kleindienst T E, et al. Formation of secondary organic aerosol from irradiated -pinene/toluene/NOmixtures and the effect of isoprene and sulfur dioxide [J]. Journal of Geophysical Research, 2008,113:D09303.

[38] Chen L, Bao K, Li K, et al. Ozone and secondary organic aerosol formation of toluene/NOirradiations under complex pollution scenarios [J]. Aerosol & Air Quality Research, 2017,17(7):1660-1671.

[39] De Gouw J, Warneke C. Measurements of volatile organic compounds in the earth's atmosphere using proton-transfer-reaction mass spectrometry [J]. Mass Spectrom Reviews, 2007,26(2):223-257.

[40] Yuan B, Koss A R, Warneke C, et al. Proton-transfer-reaction mass spectrometry: Applications in atmospheric sciences [J]. Chemical Reviews, 2017,117(21):13187-13229.

[41] Jorga S D, Kaltsonoudis C, Liangou A, et al. Measurement of formation rates of secondary aerosol in the ambient urban atmosphere using a dual smog chamber system [J]. Environmental Science & Technology, 2020,54(3):1336-1343.

[42] Wang Y, Zhao Y, Li Z, et al. Importance of hydroxyl radical chemistry in isoprene suppression of particle formation from α-pinene ozonolysis [J]. Earth and Space Chemistry, 2021,5(3):487-499.

[43] Jang M, Kamens R M. Characterization of secondary aerosol from the photooxidation of toluene in the presence of NOand 1-propene [J]. Environmental Science & Technology, 2001,35(18):3626-3639.

[44] Fan J W, Zhang R Y. Atmospheric oxidation mechanism of isoprene [J]. Environmental Chemistry, 2004,1:140-149.

[45] Healy R M, Wenger J C, Metzger A, et al. Atmospheric chemistry and physics gas/particle partitioning of carbonyls in the photooxidation of isoprene and 1,3,5-trimethylbenzene [J]. Atmospheric Chemistry and Physics, 2008,8:3215-3230.

[46] Pan G, Hu C J, et al. Direct detection of isoprene photooxidation products by using synchrotron radiation photoionization mass spectrometry [J]. Rapid Communications in Mass Spectrometry Rcm, 2011,26(2):189-194.

[47] Wennberg P O, Bates K H, Crounse J D, et al. Gas-phase reactions of isoprene and its major oxidation products [J]. Chemical Reviews, 2018,118,7:3337–3390.

[48] Kroll J H, Ng N L, Murphy S M, et al. Secondary organic aerosol formation from isoprene photooxidation [J]. Environmental Science & Technology, 2006,40(6):1869-1877.

[49] Birdsall A W, Andreoni J F, Elrod M J. Investigation of the role of bicyclic peroxy radicals in the oxidation mechanism of toluene [J]. Journal of Physical Chemistry A, 2010,114(39):10655-10663.

[50] Seuwen R, Warneck P. Oxidation of toluene in NOfree air: Product distribution and mechanism [J]. International Journal of Chemical Kinetics, 1996,28(5):315-332.

[51] Mattias H, John C. Wenger, et al. The formation, properties and impact of secondary organic aerosol: current and emerging issues [J]. Atmospheric Chemistry and Physics, 2009,9:5155-5236.

[52] Schwantes R H, Schilling K A, Mcvay R C, et al. Formation of highly oxygenated low-volatility products from cresol oxidation [J]. Atmospheric Chemistry and Physics, 2017,17(5):3453-3474.

[53] Baltaretu C O, Lichtman E I, Hadler A B, et al. Primary atmospheric oxidation mechanism for toluene [J]. Journal of Physical Chemistry A, 2009,113(1):221-230.

[54] Jenkin M E, Young J C, Rickard A R. The MCM v3.3.1degradation scheme for isoprene [J]. Atmospheric Chemistry and Physics, 2015, 15(20):11433-11459.

[55] Moschonas N, Glavas S, Danalatos D. The effect of O2and NO2on the ring retaining products of the reaction of toluene with hydroxyl radicals [J]. Atmospheric Environment, 1996,127:875-881.

[56] Jun Zhao, Renyi Zhang, et al. Quantification of hydroxycarbonyls from OH Isoprene reactions [J]. Journal of the American Chemical Society, 2004,126(9):2686–2687.

[57] Tuazon E C, Atkinson R , et al. A product study of the gas-phase reaction of Isoprene with the OH radical in the presence of NO[J]. International Journal of Chemical Kinetics, 1991,21(12):1221-1236.

[58] Sprengnether M, Demerjian K , et al. Product analysis of the OH oxidation of isoprene and 1,3-butadiene in the presence of NO. [J]. Journal of Geophysical Research Atmospheres, 2002,107(D15):ACH 8-1-ACH 8-13.

[59] Carlton A G, Wiedinmyer C, Kroll J H, et al. A review of Secondary Organic Aerosol (SOA) formation from isoprene [J]. Atmospheric Chemistry and Physics Discussions, 2009,9(14):4987-5005.

[60] Baker J, Arey J, Atkinson R, et al. Formation and reaction of hydroxycarbonyls from the reaction of OH radicals with 1,3-butadiene and isoprene [J]. Environmental Science & Technology, 2005,84(11): 4091-4099.

致謝：暨南大學(xué)環(huán)境與氣候研究院袁斌教授為本研究PTR-TOF-MS采樣提供了技術(shù)指導(dǎo),PTR-TOF-MS的數(shù)據(jù)處理由暨南大學(xué)環(huán)境與氣候研究院的陳鈺彬和王思行協(xié)助完成,在此表示感謝.

A chamber study on isoprene-promoting the production of toluene-derived methylbutenedial in low NOenvironment.

ZHANG Yang1, HAN Shi-jie1, LI Qin-qin1, WANG Wen-lu1, XIAO Yang1, GUO Yan1, WANG Hao1,2,3*, WANG Bo-guang1,2,3**

(1.Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China；2.Australia-China Centre for Air Quality Science and Management (Guangdong), Guangzhou 511443, China；3.Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou 511443, China)., 2022,42(9)：4401～4408

Toluene and isoprene are typical anthropogenic volatile organic compounds (AVOCs) and biological volatile organic compounds (BVOCs), respectively. In this study, smog chamber experiments were carried out to simulate photochemical reactions of toluene and isoprene at low NOlevels. In order to investigate the effect of BVOCs on the chemical degradation of AVOCs during the interaction between anthropogenic and biogenic emissions, a proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) was used to monitor the real-time concentration variations of the key gaseous substances in the mixed system. The results show that isoprene inhibited the chemical degradation of toluene, which might be related to the competitive reactions with OH radicals between isoprene and toluene. Moreover, the earlier competitive reaction began, the more significant the inhibition effect was. And isoprene enhanced the production of toluene RO2degradation pathway products, resulting in more unsaturated 1,4-dicarbonyl compounds (Butenedial, Methyl-butenedial) and dicarbonyl compounds (Glyoxal, Methylglyoxal). The increment in methylbutenedial was up to 38.6%. Also, the RO2? generated by the rapid oxidation of isoprene had less carbon number, which may have a rapid cross-reaction with the RO2? generated by toluene oxidation. The cross reaction was conducive to the generation and cleavage of toluene RO? and ultimately led to an increase of the products from toluene RO2? channel. This study can improve an understanding of the impact of BVOCs on AVOCs degradation during the interaction process between anthropogenic and biogenic emissions, and provide insights into regional air pollution prevention and control in the future.

toluene；isoprene；smog chamber simulation；anthropogenic biological source-interaction process；peroxide-bicyclic pathway；methylbutenedial；volatile organic compounds

X511

A

1000-6923(2022)09-4001-08

2022-02-14

國(guó)家自然科學(xué)基金面上項(xiàng)目(42077190,41877370);廣東省科技廳科技創(chuàng)新平臺(tái)類項(xiàng)目(2019B121202002);廣東省“珠江人才計(jì)劃”引進(jìn)創(chuàng)新創(chuàng)業(yè)團(tuán)隊(duì)項(xiàng)目(2016ZT06N263);國(guó)家自然科學(xué)基金資助項(xiàng)目(42121004)

*責(zé)任作者, 教授, wanghao@jnu.edu.cn,** 教授, tbongue@jnu.edu.cn

張 揚(yáng)(1996-),男,湖北黃岡人,暨南大學(xué)碩士研究生,主要從事光化學(xué)煙霧箱方面的研究.