趙茜 姜蘇 史貴濤, 陳振樓 孫波

研究進(jìn)展

極地雪冰中高氯酸鹽的研究進(jìn)展

趙茜1,2姜蘇1史貴濤2,1陳振樓2孫波1

(1自然資源部極地科學(xué)重點(diǎn)實(shí)驗(yàn)室, 中國(guó)極地研究中心, 上海 200136;2地理信息科學(xué)教育部重點(diǎn)實(shí)驗(yàn)室, 華東師范大學(xué), 上海 200241)

環(huán)境中普遍存在著自然條件下產(chǎn)生的高氯酸鹽(ClO4–), 其同位素組成的顯著特征(如17O異常和/或36Cl正值)表明這些ClO4–很可能來(lái)自于大氣平流層且臭氧(O3)參與了其形成過程。極地冰蓋是保存大氣來(lái)源ClO4–的天然檔案, 能夠提供大氣來(lái)源ClO4–的含量、空間分布、長(zhǎng)時(shí)間尺度內(nèi)的變化序列及不同歷史時(shí)期的來(lái)源等信息。這些信息對(duì)于明確人類活動(dòng)對(duì)大氣來(lái)源ClO4–的影響, 大氣中產(chǎn)生ClO4–的機(jī)理, 以及大氣中ClO4–的產(chǎn)量與大氣化學(xué)、環(huán)境條件之間的關(guān)系具有重要意義。在總結(jié)了極地雪冰中ClO4–的來(lái)源、含量水平、時(shí)間變化序列及大氣中產(chǎn)生ClO4–的機(jī)理等方面的研究進(jìn)展之后, 提出今后應(yīng)利用極地雪冰樣品研究不同區(qū)域ClO4–的大氣圈層(平流層、對(duì)流層)主要來(lái)源, 并開展雪冰中ClO4–的沉積后過程研究, 從而能夠更好地理解ClO4–的大氣化學(xué)過程, 并獲取大氣中ClO4–的產(chǎn)量及其變化的真實(shí)信息。

極地 雪冰 高氯酸鹽 來(lái)源 產(chǎn)生機(jī)理

0 引言

高氯酸鹽(ClO4–)是一種持久性無(wú)機(jī)污染物, 由于其強(qiáng)氧化性和高穩(wěn)定性被廣泛應(yīng)用于軍事、工業(yè)以及航空航天等領(lǐng)域[1-3]。痕量水平的ClO4–就能夠影響人體甲狀腺對(duì)于碘離子的吸收[4], 進(jìn)而危害人體健康[5]。美國(guó)是最早對(duì)供水系統(tǒng)中ClO4–含量水平開展調(diào)查的國(guó)家[6], 20世紀(jì)90年代, 研究人員在加利福尼亞州的飲用水中檢測(cè)出了含量高達(dá)260μg·L–1的ClO4–[7], 此后多個(gè)國(guó)家和地區(qū)針對(duì)于不同環(huán)境介質(zhì)中ClO4–的含量水平開展了廣泛的調(diào)查。研究表明, ClO4–普遍存在于各種環(huán)境介質(zhì)中, 比如食品和飲料[8-10]、水體[11-15]、土壤[11,16]、大氣[17-18]、植物[19-20]、動(dòng)物[21-22]以及人體血液[23-24]。由于具有極高的水溶性和非揮發(fā)性, 進(jìn)入環(huán)境中的ClO4–會(huì)隨著水流遷移擴(kuò)散, 進(jìn)而擴(kuò)大污染范圍[25]。

然而環(huán)境中的ClO4–并非都來(lái)自于人類活動(dòng), 也有在大氣中自然產(chǎn)生的[26-28]。智利阿塔卡馬沙漠的硝酸鹽礦石是已知的富含自然來(lái)源ClO4–的典型代表[29], 此外, 在遠(yuǎn)離人類污染的南極大陸[30-31]、在沒有污染源輸入的大面積地下水中[32-34]、在北極高海拔冰川[27,35-36]以及在大氣濕沉降中[34,37-38]均廣泛分布著自然來(lái)源的ClO4–[28,39]。極區(qū)獨(dú)特的地理優(yōu)勢(shì)與氣候條件(遠(yuǎn)離人類和生物活動(dòng)頻繁的大陸、極低的氣溫、干燥的空氣等)使攜帶著大氣化學(xué)成分和氣候環(huán)境信息的化學(xué)物質(zhì)沉降至冰蓋表面, 并按照年代序列保存在極地冰蓋上[40-41]。因此極地雪冰是大氣來(lái)源ClO4–的天然檔案, 能夠提供大氣來(lái)源ClO4–的背景值及其在歷史時(shí)期的變化, 這些信息不僅是制定ClO4–污染防治政策的重要依據(jù), 而且能夠?yàn)檠芯看髿庵挟a(chǎn)生ClO4–的機(jī)理以及ClO4–產(chǎn)量與大氣化學(xué)、環(huán)境條件之間的關(guān)系提供重要數(shù)據(jù)。本文在闡述了極地雪冰中ClO4–研究進(jìn)展的基礎(chǔ)上, 提出了未來(lái)可能的研究方向。

1 極地雪冰中ClO4–的來(lái)源

通常情況下, ClO4–的生產(chǎn)、使用和處理過程造成的污染僅局限在當(dāng)?shù)氐牡乇憝h(huán)境和地下水中[36]。盡管來(lái)自于人類活動(dòng)的ClO4–能夠進(jìn)入大氣并經(jīng)由大氣環(huán)流被輸送至其他地區(qū), 但是具有非揮發(fā)性質(zhì)的ClO4–只有吸附在塵埃顆粒上才能夠進(jìn)入大氣[42]。研究表明, 塵埃被大氣輸送至遙遠(yuǎn)極區(qū)的可能性非常小[43], 然而, 在遠(yuǎn)離人類污染的南極雪冰和沙土中卻檢測(cè)到了高水平的ClO4–[30-31]。針對(duì)遠(yuǎn)離人類活動(dòng)且/或無(wú)污染源輸入地區(qū)ClO4–的來(lái)源, 研究人員展開了系列研究。

早在1996年, 研究人員通過實(shí)測(cè)發(fā)現(xiàn), 大氣平流層中無(wú)機(jī)氯的總量顯著高于3種已知含氯無(wú)機(jī)化合物(HCl、ClONO2和HOCl)含量的總和, 他們以模式模擬的方式預(yù)測(cè)平流層內(nèi)應(yīng)存在HClO4, 這樣才能夠解釋無(wú)機(jī)氯總量與已知含氯無(wú)機(jī)化合物含量之間的差異, 且模擬結(jié)果顯示HClO4可能是在16~22 km高空中的氣溶膠上形成的[44]。此后, Murphy和Thomson[18]對(duì)采自于5~19 km高空中的氣溶膠進(jìn)行了檢測(cè), 結(jié)果證實(shí)在平流層底部(距地面約19 km)的硫酸鹽氣溶膠中確實(shí)存在ClO4–。隨著高靈敏度檢測(cè)技術(shù)手段的發(fā)展, 研究人員依據(jù)物質(zhì)的同位素組成能夠準(zhǔn)確判斷其來(lái)源[28,39,45-53], 并獲悉物質(zhì)產(chǎn)生過程的相關(guān)信息[26,28,31,45,54-56], Bao和Gu[45]研究發(fā)現(xiàn)阿塔卡馬沙漠土壤中的ClO4–存在顯著的17O異常(通常情況下, O的穩(wěn)定同位素分餾遵循δ17O≈0.52×δ18O這一線性關(guān)系[57], 不遵循上述線性關(guān)系的分餾被稱為非質(zhì)量分餾, 用Δ17O=δ17O–0.52×δ18O表示[58]), 且具有較高的Δ17O值(在4.2‰~9.6‰之間), 而人工合成ClO4–的Δ17O值接近于0, 他們提出阿塔卡馬沙漠土壤中的ClO4–很可能是大氣中的含氯化合物經(jīng)臭氧(O3)氧化的產(chǎn)物。Jackson等[28]報(bào)道了美國(guó)加利福尼亞州死谷地區(qū)土壤樣品中ClO4–的Δ17O值為8.6‰~18.4 ‰, 他們認(rèn)為該地區(qū)土壤中的ClO4–同樣來(lái)自于有O3參與的大氣化學(xué)過程。Cl的放射性同位素36Cl在平流層中由宇宙射線照射產(chǎn)生[46], 因此平流層內(nèi)形成的ClO4–應(yīng)能夠檢測(cè)到36Cl, 而在對(duì)流層或地表形成的ClO4–中幾乎檢測(cè)不到36Cl[47]。Sturchio等[39]檢測(cè)了不同地區(qū)的地下水和沙漠土壤及人工合成的ClO4–中36Cl/ Cl比值, 結(jié)果發(fā)現(xiàn)美國(guó)西南部地區(qū)地下水和沙漠土壤中ClO4–的36Cl/Cl比值最高, 在3 100×10–15~28 800×10–15之間, 阿塔卡馬沙漠中36Cl/ Cl比值范圍為0.9×10–15~590×10–15, 而人工合成的ClO4–中36Cl/Cl比值接近于0, 由此證實(shí)了美國(guó)西南部地區(qū)地下水和沙漠土壤以及阿塔卡馬沙漠土壤中的ClO4–存在大氣平流層來(lái)源。

Furdui和Tomassini[27]研究發(fā)現(xiàn)北極Devon冰帽上采集的雪坑中ClO4–具有明顯的季節(jié)變化, 其含量峰值出現(xiàn)在夏季, 而且這些峰值與其對(duì)應(yīng)的Cl–之間呈現(xiàn)出顯著的正相關(guān)關(guān)系, 由此推測(cè)該地區(qū)夏季的ClO4–很可能存在對(duì)流層來(lái)源。同樣, 在北極Agassiz冰帽上采集的淺冰芯中也發(fā)現(xiàn)了ClO4–與Cl–在1940—1959年間呈現(xiàn)出顯著的正相關(guān)關(guān)系, Furdui等[35]認(rèn)為此期間的ClO4–很可能來(lái)自于對(duì)流層的閃電作用。然而, 在西南極WAIS Divide地區(qū)的雪坑中, ClO4–的峰值出現(xiàn)在秋季, 且其與Cl–并未表現(xiàn)出明顯的相關(guān)性[55]。因此, 有必要針對(duì)更多地點(diǎn)采集的雪冰樣品開展研究, 明確其中是否存在大氣對(duì)流層來(lái)源的ClO4–。

2 極地雪冰中ClO4–的含量水平及時(shí)間變化序列

圖1給出了在南北兩極與高海拔冰川上已開展ClO4–相關(guān)研究的站點(diǎn)[27,31,35-36,59-61], 各站點(diǎn)雪冰中ClO4–平均含量的研究結(jié)果匯總于圖2。從圖2中可以看出, 極地雪冰中ClO4–的含量均為ng·L–1級(jí), 顯著低于普通環(huán)境樣品中ClO4–的含量。比如, Smith等[11]對(duì)美國(guó)Las Vegas Wash流域3個(gè)采樣點(diǎn)收集的水樣進(jìn)行了檢測(cè), 發(fā)現(xiàn)其中ClO4–的平均含量可達(dá)0.45 mg·L–1。Her等[13]對(duì)在韓國(guó)周邊海域采集的海水樣品進(jìn)行了檢測(cè), 其中ClO4–的平均含量為1.15 μg·L–1。Kanan等[15]報(bào)道, 來(lái)自印度不同地區(qū)的地下水樣品中ClO4–的平均含量為1.0μg·L–1。

通過對(duì)一支采集自加拿大Eclipse地區(qū)淺冰芯(其中記錄的ClO4–的時(shí)間變化序列不連續(xù), 存在含量記錄的年代序列分別為1970—1973、1982—1986、1999—2002年)的研究, Rao等[60]首次報(bào)道了雪冰中ClO4–含量在1980年之后顯著上升的現(xiàn)象。此后, 研究人員依據(jù)采集自不同地區(qū)的雪冰樣品證實(shí)了上述結(jié)論。Peterson等[62]對(duì)北極格陵蘭Summit地區(qū)采集的一支淺冰芯(記錄的年代序列為1950—2006年)的研究結(jié)果表明ClO4–在1980年之前的平均含量為(0.8±0.6)ng·L–1, 1980年之后的平均含量為(2.7±2.1)ng·L–1。采集自南極點(diǎn)(South Pole)區(qū)域的一支粒雪芯中記錄了ClO4–在1920—2005年間的變化序列, 其中ClO4–的含量在1970年之前較低, 1970年之后呈現(xiàn)出上升趨勢(shì), 這一上升趨勢(shì)在20世紀(jì)80年代中期開始顯著增強(qiáng); 在東南極冰蓋最高點(diǎn)Dome A地區(qū), 積雪中的ClO4–也表現(xiàn)出與上述相同的時(shí)間變化序列[31]。

對(duì)于ClO4–的這一時(shí)間變化趨勢(shì), 研究人員試圖從其產(chǎn)生機(jī)理方面給出解釋。Jiang等[31]發(fā)現(xiàn)南極South Pole和Dome A雪層中ClO4–的時(shí)間變化序列與平流層中等價(jià)有效氯(EESC)的變化趨勢(shì)一致, 認(rèn)為南極雪冰中的ClO4–很可能來(lái)自于平流層。在北極Agassiz地區(qū)采集的淺冰芯(記錄的年代序列為1936—2007年)中, Furdui等[35]發(fā)現(xiàn)ClO4–含量在1979年之后開始上升且在1990年之后呈現(xiàn)出下降的趨勢(shì), 他們對(duì)比分析了與冰芯記錄同時(shí)期的有機(jī)氯化合物一氟二氯乙烷(HCFC- 141b)和甲基氯仿(CH3CCl3)的排放記錄, 發(fā)現(xiàn)CH3CCl3與ClO4–的含量變化趨勢(shì)吻合, 因此認(rèn)為CH3CCl3很可能是影響Summit地區(qū)1980—2000年間大氣中ClO4–產(chǎn)量的主要物質(zhì)。同樣, 在北極格陵蘭Summit地區(qū)采集的時(shí)間序列為1700—2007年的冰芯中, Cole-Dai等[36]發(fā)現(xiàn)1980年之后ClO4–的平均含量是1980年之前的2—3倍, 且ClO4–的含量在20世紀(jì)90年代中期出現(xiàn)略微下降的趨勢(shì), 通過對(duì)比發(fā)現(xiàn)ClO4–與有機(jī)氯化合物的變化趨勢(shì)相似, 他們同樣認(rèn)為人類活動(dòng)使得ClO4–前體物質(zhì)——有機(jī)氯的排放量增加, 由此導(dǎo)致大氣中ClO4–產(chǎn)量在1980年后顯著上升; 然而, 冰芯中ClO4–的含量在工業(yè)革命前后并未表現(xiàn)出顯著差異, 說(shuō)明始于1850年的工業(yè)革命所帶來(lái)的大范圍人類活動(dòng)并未影響北極格陵蘭地區(qū)大氣中ClO4–的產(chǎn)量。

圖1 本文綜述的極區(qū)雪冰ClO4–研究站點(diǎn)分布圖

Fig.1. Locations of snow pit and ice core sites referred to in the text

然而, 南極Dome A和South Pole地區(qū)雪層中ClO4–含量隨深度的變化趨勢(shì)與具有沉積后過程的某些化學(xué)物質(zhì), 如NO3–、Cl–、甲基磺酸(MSA)在雪層中的變化十分相似[63]。研究表明, 在南極低積累率地區(qū)(如Dome A和Dome C), 雪層中的NO3–經(jīng)歷了顯著的沉積后過程[64], 其含量在表層雪中較高, 隨著雪層深度的增加含量逐漸降低, 直至1 m深度處NO3–含量基本保持不變[65-66]。在Dome A地區(qū)3 m深雪坑中, ClO4–表現(xiàn)出與NO3–相似的變化趨勢(shì), 說(shuō)明ClO4–很可能也發(fā)生了沉積后過程[31]。沉積后過程能夠顯著改變NO3–在雪冰中的初始含量及其同位素組成[67-68]。如果ClO4–的沉積后過程確實(shí)存在, 那么很可能同樣會(huì)改變其在雪冰中的初始含量及同位素組成, 導(dǎo)致雪冰中測(cè)量到的數(shù)值無(wú)法真實(shí)反應(yīng)ClO4–初始沉降時(shí)的情況, 而這些初始沉降信息對(duì)于認(rèn)識(shí)和理解大氣中ClO4–的產(chǎn)量及大氣圈層(平流層、對(duì)流層)來(lái)源至關(guān)重要。因此有必要針對(duì)積雪中ClO4–的沉積后過程及機(jī)理開展相關(guān)研究。

從圖2中還可以看出, 南極雪冰中ClO4–的含量明顯高于北極(高1~2個(gè)數(shù)量級(jí))。如前所述, 極地雪冰中的ClO4–主要在大氣中自然產(chǎn)生, 其前體物質(zhì)來(lái)自于人類活動(dòng)排放的含氯化合物, 相對(duì)于北極地區(qū)而言, 南極受到人類活動(dòng)的影響更小, 然而南極雪冰中ClO4–含量卻更高。目前, 對(duì)這一現(xiàn)象的解釋還缺乏相關(guān)的研究, 需要針對(duì)ClO4–的產(chǎn)生機(jī)理及其影響因素, 以及兩極地區(qū)的氣候環(huán)境差異等因素開展系列研究。

圖2 對(duì)數(shù)標(biāo)尺表示的不同地區(qū)雪冰中ClO4–平均含量. 廟兒溝淺冰芯記錄的年代序列為1956—2004[59]; Agassiz淺冰芯為1936—2007[35]; Devon雪坑為1996—2005[27]; Summit冰芯為1700—2007[36]; Eclipse淺冰芯為1970—2002[60]; UFG冰芯為1726—1993[60]; Dome A雪坑為1967—2010[31]; South Pole粒雪芯為19{Rao, 2012 #6}20—2005[31]; WAIS Divide粒雪芯為1929—2002[61]

Fig.2. Average concentrations of ClO4–at different sitespresented in log scale. Ice cores and snow pits cover the time period of 1956—2004 (Miaoergou)[59], 1936—2007 (Agassiz)[35], 1996—2005 (Devon)[27], 1700—2007 (Summit)[36], 1970—2002 (Eclipse)[60], 1726—1993 (UFG)[60], 1967—2010 (Dome A)[31], 1920—2005 (South Pole)[31]and 1929—2002 (WAIS Divide)[61]

綜上所述, ClO4–在極地雪冰中的分布具有以下特點(diǎn): 極地雪冰中ClO4–的含量明顯低于普通環(huán)境樣品中ClO4–的含量, 且北極雪冰中ClO4–的含量比南極雪冰中的含量低1~2個(gè)數(shù)量級(jí); 同時(shí), 雪冰中記錄了1980年之后ClO4–含量顯著上升的現(xiàn)象。

3 大氣中產(chǎn)生ClO4–的機(jī)理

依據(jù)環(huán)境樣品ClO4–中顯著的17O異常, 研究人員推測(cè)O3很可能參與了ClO4–的生成過程[45]; 此后, 他們通過模擬實(shí)驗(yàn)證實(shí)了在O3存在的條件下, Cl–、OCl–、ClO2–等前體物質(zhì)確實(shí)能夠被氧化成ClO4–[54,69]。Kang等[69]研究了前體物質(zhì)的固液狀態(tài)對(duì)ClO4–產(chǎn)量的影響, 他們發(fā)現(xiàn)水溶液對(duì)O3氧化前體物質(zhì)生成ClO4–的反應(yīng)有一定抑制作用, 因此液態(tài)Cl–生成ClO4–的產(chǎn)量要低于固態(tài)Cl–。Rao等[54]進(jìn)一步研究了溶液中不同的含氯前體物(Cl–、OCl–、ClO2–、ClO3–)被O3氧化生成ClO4–的速率, 發(fā)現(xiàn)反應(yīng)速率取決于初始條件下前體物質(zhì)的氧化狀態(tài), 低氧化狀態(tài)的OCl–反應(yīng)速率要低于高氧化狀態(tài)的ClO2–, 而更高氧化狀態(tài)的ClO3–則不與O3發(fā)生反應(yīng); 此外, Cl–雖然能被O3氧化為ClO4–, 但與OCl–和ClO2–相比, 其反應(yīng)速率低幾個(gè)數(shù)量級(jí)。

研究發(fā)現(xiàn)在紫外光照射下, OCl–、ClO2–、ClO3–也能夠生成ClO4–[70-71]。Kang等[70]通過模擬實(shí)驗(yàn)研究了不同初始濃度的Cl–、OCl–、ClO2–、ClO3–溶液在紫外光(λ = 253. 7nm)和太陽(yáng)光照射下生成ClO4–的速率, 結(jié)果表明Cl–溶液在紫外光和太陽(yáng)光照射下均不能生成ClO4–, 而紫外光可將濃度高達(dá)10 000mg L–1的OCl–、ClO2–、ClO3–轉(zhuǎn)化為ClO4–; 用太陽(yáng)光和紫外光分別照射濃度為100 mg·L–1的ClO2–時(shí), ClO4–的產(chǎn)量相當(dāng)。Kang等[71]進(jìn)一步研究了液態(tài)ClO2–在紫外光照射下產(chǎn)生ClO4–的反應(yīng)過程, 他們發(fā)現(xiàn)紫外光波長(zhǎng)和前體物質(zhì)ClO2–的初始含量均能夠顯著影響ClO4–的產(chǎn)量; 當(dāng)分別使用波長(zhǎng)為253.7 nm、300 nm和350 nm的紫外光照射初始含量為15 mM的ClO2–溶液時(shí), 在300 nm和350 nm的紫外光照射下ClO4–的產(chǎn)量是在253.7 nm照射下的5倍, 這主要是因?yàn)檩^長(zhǎng)的波長(zhǎng)有利于ClO4–產(chǎn)生過程中關(guān)鍵中間產(chǎn)物的生成; 而使用波長(zhǎng)為253.7 nm的紫外光分別照射初始含量為15 mM和150 mM的ClO2–溶液, ClO4–的最大產(chǎn)量分別為1 μM和100 μM。

此外, 研究人員發(fā)現(xiàn)對(duì)流層中的閃電也能夠促進(jìn)大氣中ClO4–的產(chǎn)生。Dasgupta等[26]首次報(bào)道了實(shí)驗(yàn)室模擬的放電條件下, NaCl氣溶膠能夠轉(zhuǎn)化為ClO4–。Parker等[34]對(duì)同一采樣點(diǎn)不同時(shí)段的雨水進(jìn)行了長(zhǎng)期觀測(cè), 發(fā)現(xiàn)在雷電交加的暴風(fēng)雨天氣條件下收集的雨水樣品中ClO4–的檢出率較其他氣候條件下的樣品高。Rao等[72]對(duì)不同濕度條件下的含Cl–氣溶膠進(jìn)行模擬放電實(shí)驗(yàn), 研究得出外加電壓的增加有利于ClO4–產(chǎn)生, 外加電壓從10 kV升高到24 kV時(shí), ClO4–的產(chǎn)量從0.5 μg增加到4.8 μg; 而水分的存在會(huì)抑制ClO4–的產(chǎn)生, 當(dāng)相對(duì)濕度從～46%增加到～62%時(shí), ClO4–的產(chǎn)量從(2.8±0.1)μg降低到(0.9±0.1)μg。然而, 對(duì)于火山噴發(fā)作用能否影響大氣中ClO4–的產(chǎn)量, 研究人員們卻沒有形成統(tǒng)一意見。在北極Agassiz冰芯中, Furdui等[35]發(fā)現(xiàn)火山事件與ClO4–含量之間不存在任何相關(guān)性, 他們認(rèn)為火山活動(dòng)不會(huì)導(dǎo)致北極Agassiz地區(qū)ClO4–的產(chǎn)量增加。而在北極格陵蘭Summit地區(qū)鉆取的一支記錄過去300年氣候記錄的冰芯中, Cole-Dai等[36]發(fā)現(xiàn)在大規(guī)模火山噴發(fā)期間, ClO4–的含量均出現(xiàn)峰值, 他們認(rèn)為火山噴發(fā)向平流層注入了大量硫酸鹽氣溶膠, 從而影響了大氣中ClO4–的產(chǎn)量, 但是對(duì)于火山活動(dòng)如何影響ClO4–生成的具體過程尚不清楚。

4 討論與展望

目前, 研究人員對(duì)ClO4–的大氣平流層來(lái)源已達(dá)成共識(shí), 尚未明確其對(duì)流層來(lái)源, 依據(jù)不同地區(qū)雪冰樣品重建的大氣來(lái)源ClO4–的季節(jié)變化規(guī)律存在差異, 對(duì)ClO4–的大氣化學(xué)過程及其影響因素的認(rèn)識(shí)也尚不全面。此外, 沉積后過程很可能導(dǎo)致雪冰中測(cè)量的ClO4–含量及其同位素組成無(wú)法真實(shí)反應(yīng)其初始沉降時(shí)的情況, 這些初始沉降信息對(duì)于認(rèn)識(shí)和理解大氣中ClO4–的產(chǎn)量、時(shí)間變化、產(chǎn)生機(jī)理以及來(lái)源等至關(guān)重要, 而文獻(xiàn)中尚未見有關(guān)ClO4–沉積后過程的研究報(bào)道。極地冰蓋是保存大氣中自然產(chǎn)生ClO4–的天然檔案, 利用極地雪冰樣品有望獲取ClO4–的大氣圈層(平流層、對(duì)流層)來(lái)源、產(chǎn)生機(jī)理及影響大氣中ClO4–產(chǎn)量的因素等方面信息, 并可以開展ClO4–沉積后過程及其影響因素的研究。這些研究工作取得的成果有助于人們理解ClO4–的大氣化學(xué)過程與沉積后過程, 并獲取大氣中ClO4–產(chǎn)量及其變化的真實(shí)信息。

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REVIEW OF PERCHLORATE RESEARCH IN POLAR SNOW AND ICE

Zhao Qian1,2, Jiang Su1, Shi Guitao2,1, Chen Zhenlou2, Sun Bo1

(1Ministry of Natural Resources Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, China;2Key Laboratory of Geographic Information Science (Ministry of Education), East China Normal University, Shanghai 200241, China)

Natural perchlorate (ClO4?) is widespread in the natural environment. Its isotopic composition (e.g.,17O anomaly and/or positive36Cl value) indicates that it probably comes from the stratosphere, and ozone (O3) is likely involved in its formation process. Polar ice sheets provide unique samples for the study of natural perchlorate. Snow and ice can provide chronological records indicating past perchlorate levels and spatial variability, and past and present primary perchlorate sources. This is important for understanding the influence of human activities on atmospheric perchlorate production and the relationships between atmospheric perchlorate production, atmospheric chemistry and environmental conditions. In this study, we reviewed the most recent findings in perchlorate research in polar snow, including findings on perchlorate sources, levels, trends, and production mechanism. We identified areas for future research. They include the dominant atmospheric (stratospheric or tropospheric) sources of perchlorate at different locations and the post-depositional processes of perchlorate in snow. Research results will contribute towards improving our understanding of the atmospheric chemistry of perchlorate and atmospheric perchlorate production and variability.

polar regions, snow and ice, perchlorate, source, formation mechanism

2020年1月收到來(lái)稿, 2020年2月收到修改稿

國(guó)家自然科學(xué)基金面上項(xiàng)目(41476169, 41576190)、國(guó)家自然科學(xué)基金優(yōu)秀青年基金(41922046)資助

趙茜, 女, 1996年生。碩士, 主要從事雪冰化學(xué)研究。E-mail: zhaoqian@pric.org.cn

姜蘇, E-mail:jiangsu@pric.org.cn

10. 13679/j.jdyj.20200001