PM2.5中類(lèi)腐殖質(zhì)表面活性測(cè)定方法與實(shí)例分析

白 瑤,吳志軍,劉玥晨,王玉玨,郭 松,胡 敏

PM2.5中類(lèi)腐殖質(zhì)表面活性測(cè)定方法與實(shí)例分析

白 瑤,吳志軍*,劉玥晨,王玉玨,郭 松,胡 敏

(北京大學(xué)環(huán)境科學(xué)與工程學(xué)院,環(huán)境模擬與污染控制國(guó)家重點(diǎn)聯(lián)合實(shí)驗(yàn)室,北京 100871)

建立了大氣細(xì)粒子中類(lèi)腐殖質(zhì)(HULIS)表面活性的動(dòng)態(tài)表征方法,并以華北平原鄉(xiāng)村站點(diǎn)冬季大氣PM2.5樣品為例,對(duì)PM2.5中HULIS的表面活性進(jìn)行表征.HULIS碳質(zhì)組分(HULIS-C)濃度為2.0~4.6μg C/m3,占水溶性有機(jī)碳和總有機(jī)碳的比例分別為31%~40%和20%~26%.濃度為88~200mg C/L的HULIS水溶液,其表面張力相對(duì)于純水降低了18%~22%.HULIS-C濃度在低于70mg C/L時(shí)表面張力降低顯著,在88~320mg C/L之間降低相對(duì)緩慢.動(dòng)態(tài)表面張力隨著時(shí)間變化逐漸降低,在液滴形成后200s以?xún)?nèi)表面張力下降迅速,之后趨于平緩,說(shuō)明表面活性分子在液滴中擴(kuò)散趨于穩(wěn)定需要一定的時(shí)間,該特征時(shí)間可能影響表面活性物質(zhì)在云凝結(jié)核活化時(shí)的作用.證實(shí)了在污染地區(qū)的大氣PM2.5中含有一定量的表面活性物質(zhì),這些物質(zhì)可能對(duì)顆粒物活化為云滴、霧滴過(guò)程產(chǎn)生顯著影響;表面活性物質(zhì)的存在可能在外界濕度變化過(guò)程中導(dǎo)致顆粒物發(fā)生液-液相分離現(xiàn)象,在顆粒物表面形成有機(jī)膜,影響活性分子攝取以及半揮發(fā)性物質(zhì)的氣-粒分配過(guò)程,從而影響大氣非均相反應(yīng)過(guò)程.

表面活性物質(zhì)；表面張力；類(lèi)腐殖質(zhì)；大氣細(xì)粒子

目前,人們對(duì)氣溶膠與云相互作用的認(rèn)識(shí)有限,不能精確預(yù)測(cè)全球和區(qū)域尺度的氣候變化[1].大氣氣溶膠中可溶性無(wú)機(jī)組分如硫酸鹽、硝酸鹽、銨鹽等對(duì)云凝結(jié)核(CCN)活化成為云滴的影響得到了廣泛的研究[2-3],但有機(jī)物質(zhì)與水相互作用的機(jī)制還不清楚[4].有機(jī)物成分復(fù)雜,占顆粒物總質(zhì)量的20%~ 90%[5],需要進(jìn)一步研究有機(jī)物的理化性質(zhì)以厘清它們?cè)谠频涡纬蛇^(guò)程中的角色.

描述云滴的形成和生長(zhǎng)的寇拉理論考慮到顆粒物的化學(xué)組分和粒徑對(duì)顆粒物吸濕活化的影響,分為溶質(zhì)效應(yīng)和開(kāi)爾文效應(yīng).表面張力是開(kāi)爾文效應(yīng)中的一個(gè)重要參數(shù),表面張力的降低可能會(huì)降低液滴活化的臨界過(guò)飽和度,形成更多的云滴[6],這可能導(dǎo)致云的生命周期延長(zhǎng),從而增強(qiáng)云的反照率[7-8].為了簡(jiǎn)化寇拉理論的應(yīng)用,基于寇拉理論發(fā)展的к-K?hler理論考慮化學(xué)組分對(duì)水活度的影響并忽略表面張力效應(yīng)[9-11].然而最近的研究[12-13]提出表面活性物質(zhì)除了作為溶質(zhì)影響水活度外,其表面活性也會(huì)影響CCN活性,這意味著目前的計(jì)算方法可能還不夠準(zhǔn)確.進(jìn)一步的優(yōu)化模型可通過(guò)測(cè)定不同濃度的表面張力獲得經(jīng)驗(yàn)公式,結(jié)合計(jì)算[14-15]或測(cè)量[9]的水活度輸入寇拉方程模擬顆粒的吸濕活化.

表面活性物質(zhì)含有親水基團(tuán)和疏水碳鏈,傾向于分布在液滴表面.一方面降低液滴的表面張力,影響成云活性.另一方面阻礙痕量氣體和水的吸收,影響氣溶膠的非均相反應(yīng)過(guò)程[16-17].大氣顆粒物中的表面活性物質(zhì)包括有機(jī)酸、二元酸、蛋白質(zhì)和類(lèi)腐殖質(zhì)(HULIS)[18-19]等.HULIS是一類(lèi)多官能團(tuán)的大分子有機(jī)物[20],從城市農(nóng)村、森林、海洋采集的顆粒物中都檢測(cè)到HULIS[21-22].目前針對(duì)HULIS的研究主要集中在化學(xué)組分、濃度水平及其來(lái)源解析上[23-25],對(duì)HULIS的表面活性以及對(duì)顆粒物成云活性影響的研究十分有限.另外,部分研究選用模型化合物替代實(shí)際環(huán)境HULIS進(jìn)行分析[9,26],這些物質(zhì)可能也無(wú)法完全代表實(shí)際環(huán)境下HULIS的性質(zhì),不足以作為HULIS的表面張力參數(shù)輸入寇拉方程.因此,進(jìn)一步研究實(shí)際大氣環(huán)境下HULIS的表面活性并優(yōu)化現(xiàn)有模型具有重要價(jià)值.尤其是我國(guó)霧霾的發(fā)生與顆粒物吸濕增長(zhǎng)消光和活化成為霧滴的過(guò)程密切相關(guān),對(duì)HULIS的表面活性研究有助于揭示霧霾形成機(jī)制.

為表征我國(guó)實(shí)際大氣顆粒物中HULIS的表面活性,本研究建立了系統(tǒng)的HULIS水溶液表面張力測(cè)定方法,以一次冬季觀測(cè)大氣PM2.5樣品為例表征大氣顆粒物中HULIS的表面活性.

1 HULIS表面活性測(cè)定方法

HULIS表面活性的測(cè)定方法可以分為大氣顆粒物采集、顆粒物質(zhì)量濃度分析、超聲提取以及固相萃取HULIS、碳質(zhì)組分分析、表面張力測(cè)定.采集后的PM2.5樣品進(jìn)行顆粒物質(zhì)量濃度分析和碳質(zhì)組分分析.其后樣品進(jìn)行超聲水提測(cè)定總水溶性有機(jī)碳(WSOC)濃度,使用固相萃取法提取樣品中的HULIS,并測(cè)定其中HULIS-C濃度,得到HULIS-C占總水溶性有機(jī)碳和有機(jī)碳的比例,最后測(cè)定HULIS水溶液的表面張力.具體操作步驟如下.

1.1 PM2.5樣品采集

本研究使用流量為1050L/min的大流量采樣器(TH-1000,武漢天虹公司)和流量為16.7L/min的TH-16A大氣顆粒物智能采樣器(武漢天虹公司)采集PM2.5樣品,分別配備石英纖維濾膜(Whatman Inc., 203mm×254mm)和Teflon膜(Whatman Inc,USA, 47mm).其中Teflon膜采集的樣品用于膜稱(chēng)重,石英纖維濾膜采集的樣品用于元素碳、有機(jī)碳以及HULIS組分分析.石英纖維濾膜在采樣前置于潔凈鋁箔中,在馬弗爐(550℃)中灼燒5.5h去除其中的有機(jī)物.采樣用的鑷子和棉花在使用前用二氯甲烷超聲清洗3次.采樣器和切割頭也在采樣前完成流量標(biāo)定和清洗,采樣后的樣品置于冷藏柜冷凍保存(?20℃),采樣期間記錄采樣時(shí)間、采樣流量和天氣等參數(shù).

1.2 顆粒物質(zhì)量濃度分析

將Teflon膜置于超凈實(shí)驗(yàn)室恒溫恒濕(溫度:(20±1)℃,相對(duì)濕度:(40±5)%)平衡24h后,用十萬(wàn)分之一天平(AX105DR型,瑞士Mettler Toledo公司)稱(chēng)重,并根據(jù)采樣前后樣品的質(zhì)量差除以采樣體積計(jì)算顆粒物的質(zhì)量濃度.

1.3 HULIS提取

本研究采用固相萃取法提取HULIS,主要包括3個(gè)步驟:(1)超純水超聲提取;(2)固相萃取分離和濃縮HULIS組分;(3)洗脫目標(biāo)物.

在大流量采樣膜上切一個(gè)Φ47mm的圓形樣品放于提取罐中,用20mL去離子水(Milli-Q Gradient, Millipore Company,美國(guó))超聲提取40min(防止水溫過(guò)高,每20min向超聲儀中換冰水).其后用0.45μm PTFE微孔濾膜過(guò)濾提取液,除去不溶性顆粒和雜物,收集濾液;取出2mL稀釋至10mL用于測(cè)定水溶性有機(jī)碳濃度;用2.4mol/L鹽酸將剩余提取液酸化至pH=2.使用固相萃取柱(DSC-18,Sigma-Aldrich,USA)分離和富集HULIS,用3mL甲醇活化柱子、3mL去離子水和1mL 0.01mol/L鹽酸分別對(duì)萃取柱活化、清洗、平衡;將酸化后的提取液過(guò)柱,經(jīng)固相萃取,水溶液中的無(wú)機(jī)組分、極性較強(qiáng)的低分子量有機(jī)酸和糖類(lèi)未被保留[27],極性相對(duì)較弱的有機(jī)組分被填充物保留.樣品加完后用2mL去離子水清洗柱子2次,以除去填充柱中的殘留提取液;用1.5mL甲醇洗脫下被SPE小柱保留的組分,即為HULIS.將洗脫液用高純氮?dú)獯蹈?用1.5mL去離子水再溶解HULIS,取0.5mL稀釋至10mL用于測(cè)定HULIS-C的濃度,另外1mL用于表面張力測(cè)定.Lin等[28]選用HULIS的替代物SRFA和NAFA測(cè)定提取方法的回收率分別為94%和92%.關(guān)于SPE步驟的具體討論詳見(jiàn)文獻(xiàn)[29].

1.4 PM2.5中含碳組分測(cè)定

使用美國(guó)Sunset Laboratory 的碳分析儀分析石英纖維濾膜上采集的有機(jī)碳(OC)和元素碳(EC),分析方法為熱光透射法(NIOSH5040),儀器最低檢出限為0.2μg/m2,儀器精密度為±5%,具體儀器分析原理、分析方法和質(zhì)量控制詳見(jiàn)文獻(xiàn)[30].

采用日本島津公司總有機(jī)碳分析儀(TOC- LCPH)測(cè)定樣品溶液總水溶性有機(jī)碳(WSOC)濃度和HULIS-C濃度.由于樣品量有限(10mL),本研究采用NPOC法測(cè)定,樣品先經(jīng)酸化曝氣除去無(wú)機(jī)碳,注入燃燒管在高溫條件下氧化為CO2,再用檢測(cè)器測(cè)量CO2濃度.每個(gè)樣品測(cè)定2次,差值大于3%進(jìn)行第3次測(cè)定.測(cè)量樣品前先測(cè)定配制好的標(biāo)液,當(dāng)測(cè)量結(jié)果與實(shí)際濃度差值在5%以?xún)?nèi)可進(jìn)行樣品水溶性有機(jī)碳測(cè)定.

1.5 表面張力測(cè)定

本研究選用懸滴法測(cè)量HULIS溶液的動(dòng)態(tài)表面張力,懸滴法的優(yōu)點(diǎn)是用量少,適合測(cè)定含量較低的實(shí)際大氣樣品[14].此外,該方法不僅可以獲得表面張力的平衡值,還可以捕捉到表面活性物質(zhì)分布到液滴表面的變化過(guò)程[26].

本研究測(cè)定儀器(Krüss DSA30)主要包括液滴形成系統(tǒng)、照明系統(tǒng)、溫度控制系統(tǒng)、成像系統(tǒng)以及計(jì)算機(jī)計(jì)算系統(tǒng).采用1mL一次性注射器和(1.812±0.02)mm的針頭,測(cè)量時(shí)將注射器安裝在進(jìn)樣器上使之插入一個(gè)封閉溫控腔內(nèi),在注射器針頭形成液滴直到增大到快要掉落達(dá)到最大穩(wěn)定體積.照明系統(tǒng)在溫控箱的一側(cè)產(chǎn)生均勻照明的背景.溫度控制系統(tǒng)主要由控溫箱,溫度傳感器和恒溫水槽組成,本研究測(cè)定溫度為(20±0.3)℃.懸掛的液滴圖像由一個(gè)配置了顯微鏡鏡頭的相機(jī)記錄.實(shí)驗(yàn)過(guò)程中保留2~3mm長(zhǎng)度的針頭,使針頭與液滴在同一畫(huà)面內(nèi)以便對(duì)液滴圖像放大倍率進(jìn)行校準(zhǔn),懸滴連同針頭的圖像被采集到同一畫(huà)面內(nèi)(見(jiàn)圖1),在穩(wěn)定的光源下呈現(xiàn)出清晰的圖像,計(jì)算機(jī)將圖像數(shù)字化得到液滴的形狀因子和半徑,使用公式1獲得液滴表面張力值,計(jì)算方法為:

式中:為液滴的表面張力(mN/m);Δ為液滴與周?chē)鷼庀嘞嗖畹拿芏?g/cm3);為重力加速度(N/kg);d為液滴半徑(mm);為液滴形狀因子.溶液的密度用分析天平測(cè)定(AX105DR型,瑞士Mettler Toledo公司).液滴形成穩(wěn)定后,每隔5s拍一張照,記錄15~ 20min,之前有研究報(bào)道動(dòng)態(tài)測(cè)定時(shí)長(zhǎng)為10min[4],本研究在此基礎(chǔ)上多測(cè)量5~10min.

使用超純水對(duì)儀器進(jìn)行校準(zhǔn),測(cè)定9次,每次20min,液滴形成相同時(shí)間下9個(gè)測(cè)量值的相對(duì)標(biāo)準(zhǔn)偏差為0.61%~0.88%,測(cè)定過(guò)程中液滴的體積變化<5%.每次測(cè)定樣品表面張力前先測(cè)定超純水的表面張力,與理論值差值小于5%,進(jìn)行樣品表面張力測(cè)定,每個(gè)樣品測(cè)定3次.

圖1 懸滴示意

2 實(shí)例分析

本研究采樣點(diǎn)位于山東德州平原縣氣象局(37.09°N,116.26°E).于2017年12月13日~12月20日共采集了7套大氣環(huán)境PM2.5樣品,采樣時(shí)間為早晨8:30~次日8:00.12月21號(hào)采集空白樣品,將石英膜放置在采樣器上不開(kāi)泵采集30min.

2.1 顆粒物質(zhì)量濃度和碳質(zhì)組分濃度

表1 HULIS-C?WSOC和OC的濃度

碳質(zhì)組分濃度如表1所示,HULIS占 WSOC的31%~40%,可見(jiàn)HULIS在水溶性有機(jī)碳組分中占重要比例.

表2為研究報(bào)道的生物質(zhì)燃燒排放顆粒物、城市和鄉(xiāng)村大氣顆粒物中HULIS的濃度及其在WSOC和OC中的占比.根據(jù)換算系數(shù)HULIS/ HULIS-C=1.94[28],本研究HULIS的濃度為3.9~ 8.9μg/m3,略高于歐洲地區(qū)和西藏地區(qū),與珠江三角洲和上海相近,低于巴西地區(qū).HULIS-C對(duì)WSOC的貢獻(xiàn)在15%~74%之間,對(duì)OC的貢獻(xiàn)范圍在5%~51%之間,測(cè)定結(jié)果在報(bào)道研究的范圍內(nèi),較寬的變化范圍可能由于HULIS的來(lái)源、形成途徑和老化程度不同造成.采樣期間PM2.5濃度為66.5~125.0μg/m3, HULIS占PM2.5的6%~10%,該比例與我國(guó)廣東玉米秸稈(11.2±7.5)%和松樹(shù)枝(11.4±3.8)%燃燒排放顆粒物的測(cè)量結(jié)果[31]及珠江三角洲地區(qū)環(huán)境大氣顆粒的測(cè)量結(jié)果(11.7±2.1)%相近[28].

表2 不同環(huán)境大氣顆粒物中HULIS濃度及其對(duì)WSOC?OC的貢獻(xiàn)

2.2 HULIS溶液表面張力

本研究測(cè)定20℃下超純水的表面張力均值為72.3mN/m,空白樣品HULIS碳濃度為2mg C/L,表面張力均值為71.9mN/m,兩者都與理論值72.8mN/m相差很小,說(shuō)明測(cè)定的表面張力結(jié)果可信且提取過(guò)程未影響目標(biāo)物的表面張力.各采樣日HULIS溶液的表面張力如圖2所示,濃度為88~200mg C/L的HULIS溶液的表面張力在液滴形成20min后為56.7~59.4mN/m,與純水的表面張力相比降低了18%~22%.液滴表面張力的降低程度與HULIS含量并未呈現(xiàn)單調(diào)的遞增或遞減,不同天樣品的HULIS溶液表面張力有細(xì)微差別.

液滴形成后,表面張力呈現(xiàn)出隨著時(shí)間變化逐漸降低接近平衡值,前200s表面張力值降低迅速,之后趨于平緩,說(shuō)明表面活性分子在液滴中擴(kuò)散趨于穩(wěn)定需要一定的時(shí)間.Nozièr等[32]測(cè)定大氣PM10中的表面活性物質(zhì)的動(dòng)態(tài)表面張力達(dá)到平衡時(shí)為30~50mN/m,表面張力快速下降的時(shí)間范圍為8~110s,達(dá)到平衡的時(shí)間為36~495s,本研究的樣品表面張力變化的時(shí)間尺度與該報(bào)道相似.研究還指出表面活性劑對(duì)低云或?qū)釉频却怪鄙仙龤饬骶徛脑频男纬捎绊戄^大,測(cè)量結(jié)果顯示表面活性物質(zhì)的表面張力達(dá)到平衡的時(shí)間在這類(lèi)云的形成時(shí)間范圍內(nèi)(1~30min),這將有助于云滴的形成.

不同濃度的HULIS溶液其液滴在形成15min后的表面張力變化如圖3所示.隨著HULIS溶液濃度增加,其表面張力降低,HULIS-C濃度在低于70mg C/L時(shí)表面張力降低迅速,88~320mg C/L之間表面張力降低相對(duì)緩慢.

結(jié)果表明華北平原污染環(huán)境大氣顆粒物中含有表面活性物質(zhì).表面活性物質(zhì)的存在可能影響顆粒物的吸濕增長(zhǎng),降低其活化的飽和蒸汽壓,進(jìn)而直接影響大氣顆粒物成為霧滴和云滴的活化過(guò)程.在未來(lái)研究中可將測(cè)定的HULIS溶液的表面張力輸入寇拉方程,量化HULIS的表面活性對(duì)液滴吸濕活化的影響.其次,在環(huán)境大氣濕度變化過(guò)程中,表面活性物質(zhì)的存在可能使得顆粒物出現(xiàn)液-液相分離,形成核殼結(jié)構(gòu),影響對(duì)活性分子的攝取,從而影響大氣多相化學(xué)過(guò)程,未來(lái)研究可測(cè)定HULIS顆粒在不同相對(duì)濕度下的形貌,在高相對(duì)濕度下是否發(fā)生液-液相分離現(xiàn)象.

圖2 HULIS液滴動(dòng)態(tài)表面張力

圖3 不同HULIS-C溶液表面張力

2.3 不同環(huán)境含碳物質(zhì)表面活性比較

目前,關(guān)于實(shí)際大氣顆粒物中表面活性物質(zhì)表面張力的研究十分有限,表3為不同環(huán)境大氣樣品中表面活性物質(zhì)表征的結(jié)果.與純水相比實(shí)際大氣樣品中表面張力降低范圍在15%~42%,表面張力受有機(jī)物濃度、液滴酸度、溫度、金屬離子等因素影響[42].Kiss等[43]研究發(fā)現(xiàn)鄉(xiāng)村環(huán)境大氣顆粒物中HULIS在溶液濃度為1g/L時(shí),與純水相比其表面張力降低25%~ 42%,濃度為0.2g/L時(shí),其表面張力降低13%~28%.樣品的表面活性呈現(xiàn)季節(jié)性的變化特征,不同季節(jié)樣品的元素組成相似時(shí),表面張力變化是由官能團(tuán)的位置、鏈長(zhǎng)度、芳香性等引起的.Salma等[44]測(cè)量顯示城市環(huán)境大氣(布達(dá)佩斯)HULIS液滴在1g/L和44mg/L濃度下表面張力與純水表面張力相比分別降低32%和18%,動(dòng)態(tài)表面張力結(jié)果顯示高濃度的HULIS溶液的表面張力達(dá)到平衡值所需的時(shí)間更短.Asa-Awuku等[45]報(bào)道了濃度0.85g C/L的生物質(zhì)燃燒顆粒物的水提液與純水相比表面張力降低18%.Facchini等[46]測(cè)定意大利霧水樣品中的WSOC濃度為0.1g C/L時(shí)表面張力降低15%~20%.將水溶性有機(jī)物分成中性化合物?單羧酸和多元羧酸3類(lèi),其中多元羧酸(類(lèi)腐殖質(zhì))的濃度最低,但是表面活性最強(qiáng).實(shí)際測(cè)量的云水和霧滴的表面張力與純水相比,分別降低了16%和30%,計(jì)算表明表面張力降低30%將導(dǎo)致云滴數(shù)量增加20%[8,47].標(biāo)準(zhǔn)腐殖酸對(duì)液滴表面張力的降低程度比大氣顆粒物中HULIS低7%~23%[43].腐殖酸濃度為1g/L時(shí),表面張力僅降低12%[48].本研究HULIS溶液濃度為0.09~ 0.20g C/L時(shí)與純水相比表面張力降低18%~22%,與匈牙利K-puszta、布達(dá)佩斯和意大利等地測(cè)量結(jié)果接近,比美國(guó)哥倫布生物質(zhì)燃燒顆粒的表面活性更顯著.

表3 實(shí)際大氣樣品表面張力測(cè)量結(jié)果

3 結(jié)論

3.1 建立了大氣顆粒物中HULIS動(dòng)態(tài)表面活性的測(cè)定流程與方法.以華北地區(qū)鄉(xiāng)村站點(diǎn)冬季大氣PM2.5樣品為例,基于上述方法對(duì)PM2.5中HULIS含量和表面活性進(jìn)行表征.測(cè)量結(jié)果顯示HULIS-C的濃度為2.0~4.6μg C/m3,分別占WSOC和OC的31%~40%和20%~26%.濃度在88~200mg C/L的HULIS水溶液的表面張力在液滴形成20min后數(shù)值范圍為56.7~59.4mN/m,與純水的表面張力相比降低了18%~22%.

3.2 動(dòng)態(tài)表面測(cè)量顯示HULIS液滴表面張力隨著時(shí)間變化逐漸降低,前200s下降迅速,之后趨于平緩.

3.3 HULIS-C濃度低于70mg C/L時(shí)表面張力降低顯著,88~320mg C/L之間表面張力降低相對(duì)緩慢.

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The surface activity of humic-like substances: methodology and case study.

BAI Yao, WU Zhi-jun*, LIU Yue-chen, WANG Yu-jue, GUO Song, HU Min

(State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China)., 2019,39(8)：3137~3143

A dynamic methodology was developed to characterize the surface activity of water soluble humic-like substances (HULIS) in PM2.5.As a case study, HULIS in PM2.5samples collected from a rural site during wintertime in North China Plain region were investigated. The HULIS carbon content varied from 2.0~4.6μg C/m3, accounting for 31%~40% of water-soluble organic carbon and 20%~26% of organic carbon, respectively. While the carbon content of HULIS aqueous solution ranged from 88~200mg C/L, correspondingly, the surface tension reduced by 18%~22% compared with that of pure water. The surface tension decreased significantly when the concentration was lower than 70mg C/L, while it decreased slowly between 88~320mg C/L. The dynamic measurements showed that surface tension gradually decreased with time consuming. Surface tension decreased rapidly within 200 seconds after droplet formation and then tended to be stable, indicating that the distribution of surface-active organic molecules onto the droplet surface was not instantaneous. Such process may affect droplet activation. There were substantial surface-active substances in atmospheric particulate matters in the polluted atmosphere. These surfactants may have significant impacts on the activation of aerosol particles into cloud or fog droplets. In addition, the HULIS may lead to liquid-liquid phase separation and form the core-shell structure of particles when ambient relative humidly fluctuates. Such structure could influence the uptake of reactive molecules and the gas-particle partitioning, therefore, affecting heterogeneous chemistry.

surfactants；surface tension；humic-like substances；PM2.5

X513

A

1000-6923(2019)08-3137-07

白 瑤(1993-),女,云南紅河人,北京大學(xué)碩士研究生,主要從事大氣顆粒物中類(lèi)腐殖質(zhì)的表面活性研究.

2019-01-02

國(guó)家自然科學(xué)基金國(guó)際(地區(qū))合作與交流項(xiàng)目(41571130021, 41875149) ;國(guó)家重點(diǎn)研發(fā)計(jì)劃(2016YFC0202801)

* 責(zé)任作者, 研究員, zhijunwu@pku.edu.cn