蘭州市葉面塵磁性與黑碳特征對(duì)大氣污染的響應(yīng)

王 博,陳 紅,夏敦勝,李 剛,馬 珊,劉 慧

蘭州市葉面塵磁性與黑碳特征對(duì)大氣污染的響應(yīng)

王 博1*,陳 紅2,夏敦勝2,李 剛3,馬 珊2,劉 慧2

(1.浙江師范大學(xué)地理與環(huán)境科學(xué)學(xué)院,浙江 金華 321004；2.蘭州大學(xué)資源環(huán)境學(xué)院西部環(huán)境教育部重點(diǎn)實(shí)驗(yàn)室,甘肅 蘭州 730000；3.中國(guó)氣象局蘭州干旱氣象研究所/甘肅省干旱氣候變化與減災(zāi)重點(diǎn)實(shí)驗(yàn)室/中國(guó)氣象局干旱氣候變化與減災(zāi)重點(diǎn)開(kāi)放實(shí)驗(yàn)室,甘肅 蘭州 730020)

通過(guò)采集蘭州市不同功能區(qū)小葉黃楊和刺柏葉片樣品,對(duì)葉片表面滯塵量、葉表顆粒物磁性特征和黑碳(EC)濃度進(jìn)行系統(tǒng)分析,探究其對(duì)周圍大氣污染的響應(yīng).結(jié)果顯示,小葉黃楊和刺柏葉表顆粒物磁性特征以低矯頑力的亞鐵磁性礦物為主導(dǎo),磁晶體粒徑以假單疇(PSD)顆粒為主.交通區(qū)小葉黃楊和刺柏飽和等溫剩磁(SIRM)(489.40×10-6A,290.73×10-5A·m2/kg)顯著高于公園(99.56×10-6A,74.00×10-5A·m2/kg)和生活區(qū)(61.91×10-6A,209.79× 10-5A·m2/kg),表明SIRM明顯受到周圍環(huán)境中污染物濃度的影響.小葉黃楊和刺柏葉表顆粒物亞鐵磁性礦物濃度與黑碳濃度的高值分布區(qū)域在空間上具有一致性,并且二者高度相關(guān)(=0.94,0.94;<0.0001),表明二者來(lái)源具有一致性.同時(shí),不同采樣高度不同樹(shù)種葉片磁性對(duì)葉表顆粒物中黑碳濃度均有穩(wěn)定的指示性,進(jìn)一步表明葉表顆粒物SIRM可以作為指示葉表顆粒物黑碳污染的重要磁學(xué)參數(shù).以城市綠化植物葉片為載體的環(huán)境磁學(xué)研究可實(shí)現(xiàn)顆粒物污染高空間分辨率的環(huán)境友好型監(jiān)測(cè).

葉面塵；黑碳；磁學(xué)特征；大氣污染；蘭州市

在特定的時(shí)間和地點(diǎn),由于顆粒物分布和濃度受到固定源和移動(dòng)源等人為因素以及地形和氣象等自然因素的影響,城市大氣污染在城市內(nèi)部表現(xiàn)出復(fù)雜多變的特征,傳統(tǒng)站點(diǎn)監(jiān)測(cè)方法能夠獲得高時(shí)間分辨率的連續(xù)監(jiān)測(cè)數(shù)據(jù),但是由于監(jiān)測(cè)站點(diǎn)的建設(shè)和監(jiān)測(cè)儀器的運(yùn)行需要耗費(fèi)大量資源,并且維護(hù)費(fèi)用較高,難以實(shí)現(xiàn)在城市范圍內(nèi)大面積高密度布點(diǎn)監(jiān)測(cè)的目標(biāo),這為掌握城市小環(huán)境內(nèi)部顆粒物污染變化規(guī)律增加了難度.城市植物葉片由于在生長(zhǎng)季節(jié)內(nèi)長(zhǎng)期定點(diǎn)暴露在污染環(huán)境中,大氣顆粒物通過(guò)干濕沉降的方式在葉片表面累積,一定時(shí)間段內(nèi),葉表顆粒物在不斷累積與失去的過(guò)程中達(dá)到動(dòng)態(tài)平衡,因此,植物葉片表面滯留的顆粒物含量能夠有效反映周圍大氣顆粒物的階段性累積狀況[1-4].近年來(lái),國(guó)內(nèi)外學(xué)者在植物滯塵機(jī)理、滯塵特點(diǎn)和滯塵能力等方面開(kāi)展了大量研究[1,5-8],發(fā)現(xiàn)空氣中的顆粒物主要通過(guò)沉降、擴(kuò)散、撞擊和截留的方式降落到葉片表面,因此,城市綠化植物是大氣顆粒物的優(yōu)良天然接收器.葉片表面約96%的顆粒物為細(xì)顆粒物[5],且多積聚于葉片表面褶皺區(qū)、絨毛或者氣孔周圍等粗糙位置.受到交通、工業(yè)以及地面揚(yáng)塵等活動(dòng)影響強(qiáng)烈的顆粒物中往往攜帶大量磁性顆粒物質(zhì),這些磁性顆粒物質(zhì)通常記錄了人為活動(dòng)施加的信號(hào)[9-11].污染物來(lái)源和強(qiáng)度顯著影響葉片磁性,前人對(duì)比利時(shí)根特[12-14]、安特衛(wèi)普[15]以及歐洲28個(gè)城市[16]懸鈴木磁性特征及葉表顆粒物粒徑、質(zhì)量、含鐵粒子等指標(biāo)的分析表明,葉表顆粒物的數(shù)量和大小主要取決于區(qū)域背景顆粒物的濃度,而含鐵顆粒物的比例則是大部分城市交通污染的一個(gè)明顯標(biāo)志,相比于校園清潔區(qū)的葉片,交通區(qū)尤其是十字路口葉片表現(xiàn)出較高的磁性礦物濃度[17];胡守云等[18]的研究結(jié)果表明樹(shù)葉磁性受到工業(yè)排放影響顯著,與工業(yè)區(qū)距離增加,植物葉片樣品磁性呈減弱趨勢(shì);此外,污染物來(lái)源、城市微地形、采樣高度、葉片特征(如是否有絨毛、氣孔密度、葉片親水性)、降水[19-21]等因素均會(huì)影響葉片磁性,但是當(dāng)葉面顆粒物累積達(dá)到動(dòng)態(tài)平衡的時(shí)候,葉片SIRM可以作為環(huán)境中PM濃度的定量代用指標(biāo)[10].因此,通過(guò)對(duì)葉表顆粒物磁性特征的測(cè)量有利于識(shí)別和判定葉表顆粒物的來(lái)源和污染程度[13-14],實(shí)現(xiàn)城市PM來(lái)源的解析.

已有研究結(jié)果表明表土黑碳濃度與磁化率[22]以及重金屬元素[23]之間顯著相關(guān),表明黑碳與磁性顆粒物可能存在共同的物質(zhì)來(lái)源.葉表顆粒物作為大氣顆粒物的一個(gè)潛在匯,可能同時(shí)承載和匯集黑碳粒子、重金屬元素和磁性顆粒物質(zhì),但是葉表顆粒物的磁性特征是否可以有效指示黑碳濃度變化,進(jìn)而反映顆粒物來(lái)源的研究鮮見(jiàn)報(bào)道.本研究小組通過(guò)對(duì)蘭州市25種闊葉樹(shù)種和6種針葉樹(shù)單位葉面積滯塵量的分析[24]顯示,小葉黃楊和刺柏分別為0.5m和1.5m高度上的優(yōu)勢(shì)滯塵樹(shù)種.因此,本文選取中國(guó)西北典型的干旱半干旱城市—蘭州市作為研究區(qū)域,采集不同功能區(qū)的小葉黃楊和刺柏葉片,對(duì)葉面滯塵量、葉面顆粒物磁性和黑碳特征的空間分布及內(nèi)在聯(lián)系進(jìn)行研究,探究葉面磁性特征與周圍大氣污染之間的關(guān)系,以期為城市大氣顆粒物污染監(jiān)測(cè)提供可靠參考.

1 材料與方法

1.1 研究區(qū)概況

蘭州市是典型的河谷城市,位于青藏高原、內(nèi)蒙古高原和黃土高原的交匯處,南北群山環(huán)繞,平均海拔大約1500m;年均降水量少,約為327mm.截至2016年底[25-27],蘭州市汽車保有量達(dá)到89.88萬(wàn)輛,同比增長(zhǎng)11.71%,機(jī)動(dòng)車已經(jīng)成為蘭州市主要的污染來(lái)源之一,且由于蘭州市獨(dú)特的河谷地形和常年靜風(fēng)天氣,污染物質(zhì)難以向外擴(kuò)散.

1.2 樣品采集

圖1 采樣點(diǎn)位置

2016年8月,在蘭州市交通區(qū)(路邊和路中)、生活區(qū)(小區(qū)、學(xué)校和醫(yī)院)和公園等不同功能區(qū)共采集灌木小葉黃楊葉片樣品70個(gè)(交通區(qū):54個(gè),生活區(qū):11個(gè),公園:5個(gè)),采樣高度距離地面0.5m,針葉樹(shù)種刺柏葉片樣品35個(gè)(交通區(qū):23個(gè),生活區(qū):8個(gè),公園:4個(gè)),采樣高度距離地面1.5m(圖1).樣品采集前半個(gè)月內(nèi)區(qū)域無(wú)降水,采樣期間天氣晴朗無(wú)風(fēng),無(wú)沙塵事件發(fā)生.隨后,在樹(shù)冠外圍選取15片大小一致的成熟小葉黃楊葉片,用保鮮膜裹實(shí)后裝入8cm3磁學(xué)樣品盒,刺柏樣品選取適量,可裝滿樣品盒即可,用于葉片表面顆粒物理化性質(zhì)分析和巖石磁學(xué)測(cè)量,所有樣品在5℃冷藏箱中保存和運(yùn)輸.

1.3 實(shí)驗(yàn)方法

葉片表面顆粒物收集采用洗脫-抽濾法[24],用直徑為47mm的石英濾膜(英國(guó):whatman)收集洗脫后的葉面顆粒物,并測(cè)量清洗前后樣品的飽和等溫剩磁(SIRM),小葉黃楊磁學(xué)結(jié)果進(jìn)行面積(m2)歸一化,刺柏磁學(xué)結(jié)果進(jìn)行質(zhì)量(kg)歸一化.每個(gè)樣品設(shè)置三個(gè)平行樣.具體實(shí)驗(yàn)步驟如下:

1.3.1 葉表滯塵量分析 滯塵量表示單位面積(或質(zhì)量)植物葉片表面滯留顆粒物的質(zhì)量,其計(jì)算公式如下:

小葉黃楊滯塵量(g/m2)=樣品葉面滯塵質(zhì)量/

樣品葉片總面積 (1)

刺柏滯塵量(g/kg)=樣品葉面滯塵質(zhì)量/

樣品針葉質(zhì)量 (2)

具體步驟如下:將測(cè)量過(guò)飽和等溫剩磁的植物葉片樣品置于燒杯中,用去離子水沖洗葉片,并用軟毛刷刷掉葉片表面殘留的附著物,然后使用KQ- 500DE型數(shù)控超聲波清洗器振蕩20min,最后用鑷子將葉片小心取出.使用連接真空泵的抽濾裝置,將清洗液用已烘干稱重(1)的石英濾紙(whatman, 1851- 047)過(guò)濾,將濾紙于50℃下烘24h,再用1/10000天平稱重(2),2次質(zhì)量之差即為采集的植物葉片樣品上所附著顆粒物的質(zhì)量.

清洗后的小葉黃楊葉片置于50℃恒溫箱中烘干表面水分,使用掃描儀(CanoScan LiDE120)和坐標(biāo)紙獲取葉片形狀,采用Image J軟件計(jì)算單片葉片面積,樣品總?cè)~片面積()等于單片葉片面積相加;(21)/即為小葉黃楊葉片的滯塵量(g/m2),刺柏樣品用1/10000天平稱重();(21)/即為針葉樹(shù)種植物葉片的滯塵量(g/kg).

1.3.2 磁學(xué)分析 所有植物葉片樣品分別于清洗前后在脈沖強(qiáng)磁儀MMPM10上獲得剩磁,用高速旋轉(zhuǎn)磁力儀JR-6A測(cè)量其飽和等溫剩磁(SIRM),小葉黃楊飽和等溫剩磁特征值采用葉片面積(m2)歸一化,刺柏飽和等溫剩磁特征值采用針葉質(zhì)量(kg)歸一化,清洗前樣品的飽和等溫剩磁特征值記為SIRMpre(分別為×10-6A和×10-5Am2/kg),代表植物葉片樣品總的磁學(xué)信號(hào)(包括植物葉片表面、內(nèi)部滯塵及葉片本身),清洗后樣品的飽和等溫剩磁特征值記為SIRMaft(分別為×10-6A和×10-5Am2/kg),代表葉片本身及內(nèi)部滯留的顆粒物磁學(xué)信號(hào),SIRMpre-SIRMaft值記為SIRM,代表葉片表面滯留的顆粒物磁學(xué)信號(hào),前期研究結(jié)果表明[24],清洗前后葉片的飽和等溫剩磁之差可以很好地表征葉片表面滯留顆粒物的磁學(xué)信號(hào),所以本文中的SIRM是指葉表滯留顆粒物的磁學(xué)特征.

選取代表樣品(小葉黃楊:XYHY49,刺柏:CB25),采用VFTB居里秤進(jìn)行磁滯回線參數(shù)(包括飽和剩余磁化強(qiáng)度M、飽和磁化強(qiáng)度M、矯頑力B;最大磁場(chǎng)為1T)和一階反轉(zhuǎn)曲線FORC(First-Order Reversal Curve)測(cè)量.

1.3.3 黑碳濃度分析 葉面塵中EC濃度的測(cè)量采用美國(guó)沙漠研究所(DRI)研制的DRI-2001A熱/光碳分析儀,采用IMPROVE_A協(xié)議的熱光反射法(TOR)進(jìn)行檢測(cè),葉面塵中EC濃度計(jì)算如下:

小葉黃楊單位面積EC濃度(μg/cm2)=

刺柏單位質(zhì)量EC濃度(g/kg)=

2 結(jié)果與分析

2.1 植物葉面滯塵量和碳組分含量及空間分布特征

圖2 各功能區(qū)植物葉表滯塵量和EC含量

如圖2所示,小葉黃楊滯塵量為0.55~37.10g/ m2,平均值為6.36g/m2,略高于北京市小葉黃楊平均滯塵量(6.10g/m2)[28];EC含量1.39~134.88μg/ cm2,平均值為20.06μg/cm2.二者在各功能區(qū)之間差異顯著,均表現(xiàn)為交通區(qū)>公園>生活區(qū).刺柏滯塵量為1.63~158.02g/kg,平均值為35.95g/kg;EC含量范圍為0.08~4.99g/kg,平均值為1.08g/kg,二者在各功能區(qū)之間差異顯著,表現(xiàn)為交通區(qū)>生活區(qū)>公園,這種差異主要由環(huán)境顆背景顆粒物濃度差異造成,這與北京市區(qū)刺柏滯塵量顯著高于郊區(qū)的結(jié)果一致[29].

小葉黃楊和刺柏葉面滯塵量、SIRM和EC含量在空間上的高值區(qū)主要集中于城關(guān)區(qū)中部東崗西路附近、蘭東建材市場(chǎng)東部,城關(guān)區(qū)-七里河區(qū)中部西關(guān)十字以西的狹窄路段、七里河區(qū)中部東西大通道沿線(G312)以及西固區(qū)北部G109國(guó)道地區(qū).低值區(qū)分布較為分散,主要在城關(guān)區(qū)東北部、西固區(qū)中部部分地區(qū)(圖3).

圖3 小葉黃楊和刺柏葉表滯塵量、SIRM和EC濃度空間分布Fig.3 The spatial distribution of weight of leaf deposited particles, SIRM and concentration of EC

2.2 葉表顆粒物SIRM特征

圖4 各功能區(qū)葉面塵SIRM

小葉黃楊葉表顆粒物SIRM范圍為19.24~ 2777.07×10-6A(圖4),平均值為394.38×10-6A,空間上表現(xiàn)為交通區(qū)(489.40×10-6A)(=54)顯著大于生活區(qū)(61.91×10-6A)(=11)和公園(99.56×10-6A)(=5),生活區(qū)和公園差異不大.刺柏葉表顆粒物SIRM范圍為4.55×10-5-869.10×10-5Am2/kg,平均值為247.46× 10-5Am2/kg,空間上表現(xiàn)為交通區(qū)(290.73×10-5Am2/ kg)(=23)最高,其次為生活區(qū)(209.79×10-5Am2/kg) (=8),且這2個(gè)功能區(qū)SIRM值顯著大于公園(74.00×10-5Am2/kg)(=4);SIRM空間分布特征與滯塵量、黑碳較為一致(圖3).

2.3 葉表顆粒物巖石磁學(xué)分析

分別選取小葉黃楊(XYHY49)和刺柏(CB25)葉面顆粒物樣品進(jìn)行巖石磁學(xué)特征分析,結(jié)果顯示,典型樣品磁滯回線在250mT內(nèi)閉合,樣品磁滯回線呈瘦高型,主要以亞鐵磁性礦物為主,包含少量的順磁性礦物(圖5b,d);2個(gè)樣品在Day圖上的投影均落于PSD范圍之內(nèi)(圖5a);結(jié)合FORC圖分析(圖5c,e),結(jié)果顯示樣品FORC圖等值線沿著縱軸具有大開(kāi)口的特征,內(nèi)部等值線差異較小,但在縱軸中心軸線兩側(cè)分布不對(duì)稱,顯示了PSD顆粒的特征,中心矯頑力大約為20mT.由此可見(jiàn),葉表顆粒物磁性特征以低矯頑力的亞鐵磁性礦物為主導(dǎo),與張俊輝等[17]的研究結(jié)果一致.

圖5 典型樣品葉面塵磁性特征Fig.5 Magnetic characteristic of typical samples

3 討論

3.1 葉面顆粒物磁性及黑碳特征對(duì)周圍大氣污染的響應(yīng)

研究表明,黑碳粒子直徑約為0.1~1μm,主要富集在PM2.5中[30],而葉片表面滯留顆粒物一般在50μm以內(nèi),針葉樹(shù)種葉表顆粒物粒徑甚至小于10μm[31],因此,沉降在葉片表面的顆粒物質(zhì)同時(shí)是黑碳粒子一個(gè)良好的匯.本研究均在小葉黃楊和刺柏樹(shù)種內(nèi)部對(duì)比葉面EC濃度變化,消除了樹(shù)種滯塵差異帶來(lái)的影響,葉表顆粒物中EC濃度主要受控于大氣背景環(huán)境污染濃度.因此,葉片磁性以及黑碳濃度呈現(xiàn)出顯著的空間分布差異.從功能區(qū)來(lái)看,受試植物葉片表面顆粒物中黑碳含量主要表現(xiàn)為交通區(qū)顯著高于公園和生活區(qū),并且在交通區(qū)不同路段,葉片磁性也呈現(xiàn)出明顯的區(qū)域差異.其中,城關(guān)區(qū)東崗路及東部建材市場(chǎng)附近和G109國(guó)道等交通要道由于車流量大,交通活動(dòng)中柴油和汽油等化石燃料燃燒等過(guò)程會(huì)產(chǎn)生大量磁性顆粒[19-20]和黑碳粒子[32].導(dǎo)致磁性礦物和黑碳濃度均呈現(xiàn)顯著高值;西關(guān)十字附近因其特殊的狹窄地形,東西來(lái)往車輛在此匯集,并且容易發(fā)生交通擁堵,車輛頻繁剎車和啟動(dòng)的過(guò)程亦會(huì)增加磁性顆粒物和黑碳粒子排放,先前的研究表明附近狹長(zhǎng)路段表土也表現(xiàn)出較高的磁性特征[33-34].此外,車輛擾動(dòng)會(huì)帶動(dòng)路面塵土并向外擴(kuò)散,再懸浮顆粒物在擴(kuò)散和沉降過(guò)程中易于附著到葉片表面,這些細(xì)顆粒物質(zhì)容易被葉片表面滯留,磁性顆粒物和黑碳粒子隨之在葉表累積,加劇葉片表面污染程度,導(dǎo)致交通區(qū)葉表滯塵量、葉片磁性及黑碳濃度明顯增大,說(shuō)明交通活動(dòng)是導(dǎo)致葉片磁性增強(qiáng)[17]和葉面塵中黑碳累積[35]的重要影響因素之一.公園和生活區(qū)一般遠(yuǎn)離交通和其他污染源,葉面顆粒物主要來(lái)源于自然降塵和路面清掃等過(guò)程產(chǎn)生的二次揚(yáng)塵,磁性較弱,且公園和生活區(qū)內(nèi)部植被覆蓋度較高,植被本身對(duì)周圍環(huán)境中的污染物有稀釋和凈化作用,所以葉片表面顆粒物中磁性礦物濃度和黑碳濃度均顯著低于交通區(qū).

3.2 葉面顆粒物磁性特征對(duì)黑碳的指示

圖6 SIRM與滯塵量和EC濃度回歸分析Fig.6 Regression analysis of SIRM and weight of foliar dust and EC concentration

巖石磁學(xué)分析結(jié)果表明,蘭州市葉表顆粒物主要以亞鐵磁性礦物為主導(dǎo),因此可采用SIRM作為指示樣品中亞鐵磁性礦物富集程度的磁學(xué)參數(shù).研究結(jié)果顯示,受試植物葉片表面顆粒物SIRM也表現(xiàn)出交通區(qū)高于公園和生活區(qū)的變化趨勢(shì),并且葉表滯塵量與SIRM之間均具有良好的相關(guān)性,線性回歸結(jié)果顯示(圖6),小葉黃楊滯塵量與SIRM線性擬合時(shí)=0.93,回歸方程式為=1.07+1.69;刺柏滯塵量與SIRM線性擬合時(shí)=0.95,回歸方程式為=1.17+0.55.由于沉降在葉片表面的顆粒物中同時(shí)包含了大量磁性礦物,導(dǎo)致葉片磁性增強(qiáng)[15,35-37],而植物葉片本身磁性較小,幾乎可以忽略不計(jì),因此,可以通過(guò)對(duì)葉片磁性的測(cè)量,根據(jù)其空間變化趨勢(shì),評(píng)估植物生長(zhǎng)點(diǎn)周圍階段內(nèi)大氣環(huán)境質(zhì)量狀況.

同時(shí),黑碳作為大氣顆粒物的重要組成部分,在葉面塵中的累積濃度同樣受到大氣背景環(huán)境的主導(dǎo),趙月等[38]的研究結(jié)果顯示,南京市工業(yè)區(qū)、交通區(qū)葉面塵中黑碳濃度遠(yuǎn)高于生活區(qū)和旅游區(qū),進(jìn)一步表明交通、工業(yè)等人為活動(dòng)顯著影響葉面塵中黑碳濃度.在本研究中,受試樹(shù)種葉面顆粒物SIRM與EC濃度之間具有良好的相關(guān)性,回歸分析結(jié)果顯示(圖6),小葉黃楊SIRM與EC線性擬合時(shí)=0.89,回歸方程式為=1.05+1.16;刺柏SIRM與EC線性擬合時(shí)=0.84,回歸方程式為=1.04+2.32,回歸方程式中,小葉黃楊和刺柏斜率極為接近,可見(jiàn),葉片磁學(xué)對(duì)葉表顆粒物中黑碳濃度的指示較為穩(wěn)定,不同采樣高度以及不同樹(shù)種間的差異對(duì)此影響較小,更進(jìn)一步證明了葉片SIRM可以指示葉表顆粒物黑碳濃度.

此外,先前的研究表明,蘭州市土壤中黑碳的主要來(lái)源分為兩類[23],一類是交通、工業(yè)化石燃料燃燒,另一類是工業(yè)粉塵沉積.在本研究中,黑碳高值主要分布在交通要道沿線,表明交通活動(dòng)是葉表顆粒物中黑碳的主要貢獻(xiàn)源,同時(shí),葉片磁性與黑碳高值分布區(qū)域在空間上具有一致性,且二者高度相關(guān),表明植物葉表顆粒物磁性顆粒也主要來(lái)自于交通源.由此可見(jiàn),化石燃料燃燒同時(shí)釋放大量亞鐵磁性礦物和黑碳粒子,二者來(lái)源具有一致性,故而葉表顆粒物磁性特征可以有效指示樣品中黑碳濃度.

綜上所述,周圍環(huán)境中污染物來(lái)源和濃度差異影響葉表顆粒物特性,以SIRM為基礎(chǔ)的環(huán)境磁學(xué)技術(shù)可在更高空間分辨率上有效指示葉片表面滯塵量及葉面塵中黑碳分布狀況,通過(guò)對(duì)葉片表面顆粒物記錄的環(huán)境信息的解讀,進(jìn)而明確人為活動(dòng)對(duì)周圍環(huán)境產(chǎn)生的影響,利用普遍存在的城市綠化植物葉片作為研究載體,可以為城市大氣污染監(jiān)測(cè)提供更大范圍內(nèi)的階段性監(jiān)測(cè)數(shù)據(jù).

4 結(jié)論

4.1 蘭州市小葉黃楊和刺柏葉表顆粒物磁性特征以較粗的假單疇(PSD)亞鐵磁性礦物為主導(dǎo).

4.2 葉表顆粒物亞鐵磁性礦物含量在不同功能區(qū)存在顯著差異,主要表現(xiàn)為交通區(qū)大于公園和生活區(qū),交通活動(dòng)顯著影響葉表顆粒物中磁性顆粒的累積.

4.3 小葉黃楊和刺柏葉表顆粒物亞鐵磁性礦物濃度與黑碳濃度的高值分布區(qū)域在空間上具有一致性,并且二者高度相關(guān),表明二者來(lái)源一致.此外,不同采樣高度不同樹(shù)種葉片磁性對(duì)葉表顆粒物中黑碳濃度均有穩(wěn)定的指示性,SIRM可以作為指示葉表顆粒物黑碳污染的重要磁學(xué)參數(shù).

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On the magnetic characteristic of leaf-deposited particles and element carbon and its response to air pollution.

WANG Bo1*, CHEN Hong2, XIA Dun-sheng2, LI Gang3, MA Shan2, LIU Hui2

(1.College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua 321004, China；2.Key Laboratory of Western China's Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China；3.Institute of Arid Meteorology of China, Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province, Key Open Laboratory of Arid Climate Change and Disaster Reduction of China Meterological Administration, Lanzhou 730020, China)., 2019,39(8)：3178~3185

In order to explore the characteristic of magnetic and element carbon (EC) of the particles on the surface of leaf and their response to ambient atmospheric pollution, the weight of leaf deposited particles, magnetism and concentration of particles on the surface of leaf were measured which collected fromandin different functional areas of Lanzhou city. The results of magnetic parameters suggested that the magnetic characteristics of leaf deposited particles in traffic area were dominated by ferrimagnetic minerals with low coercivity, and the grain size was dominated by pseudo single domain (PSD) particles. The SIRM ofandin traffic area (489.40×10-6A, 290.73×10-5A·m2/kg, respectively) are higher than that in park (99.56×10-6A, 74.00×10-5A·m2/kg, respectively) and residential area (61.91×10-6A, 209.79×10-5A·m2/kg). and the spatial distribution of EC in line with SIRM,showed that SIRM were significantly influenced by the sources and concentration of pollutants in ambient environment. A significant correlation(=0.94,0.94;<0.0001) was observed between SIRM and EC, indicated that SIRM can effectively respond to the dust retention and element carbon concentration of particles on the leaf surface, and it can be used as an effective magnetic parameter to indicate the particulate pollution on the surface of leaf and then reflect the ambient atmospheric pollution. Environmental magnetic research with urban green plant leaves as the carrier can achieve environmental- friendly monitoring with high spatial resolution of particulate pollution

leaf deposited particles；element carbon；magnetic characteristics；atmospheric pollution；Lanzhou City

X513

A

1000-6923(2019)08-

王 博(1986-),女,新疆石河子人,講師,博士,從事城市污染與環(huán)境磁學(xué)研究.發(fā)表論文20余篇.

2018-12-27

國(guó)家自然科學(xué)基金青年基金資助項(xiàng)目(41504056);甘肅省科技支撐計(jì)劃項(xiàng)目(1604FKCA096);中國(guó)博士后科學(xué)基金資助項(xiàng)目(2015M580892,2017T100785)

* 責(zé)任作者, 博士, bowang@zjnu.edu.cn