| 摘要: | 每年春季為中南半島地區生質燃燒活動極為盛行的時期，本研究於2013年春季在越南北部的山羅省(海拔675m)配合7-SEAS (七個東南亞國家研究)活動進行氣膠採樣，主要目的是在北越南探討相關資料很稀少的近污染源生質燃燒氣膠化學組成。
研究結果顯示在生質燃燒事件期間，2013年春季山羅省PM10氣膠受PM2.5氣膠(平均值: 57 ± 27 μg m-3, 範圍: 13—134 μg m-3)主導，PM2.5佔PM10的比例為75 ± 9 %。關於水溶性離子分析結果，硫酸根離子為PM2.5質量濃度主要貢獻物種，平均濃度為5.51 ± 2.43 μg m-3，所佔比例為11.04 ± 5.62 %。接下來為銨根離子、硝酸根離子及鉀離子，其平均濃度分別為1.94 ± 0.94 μg m-3、1.18 ± 0.57 μg m-3、1.18 ± 0.57 μg m-3；佔PM2.5質量濃度平均比例分別為4.09 ± 2.52 %、 2.13 ± 0.80 %及 1.08 ± 0.53 %。氣膠碳成分分析結果，有機碳及元素碳中主要物種分別為OC3及EC1-OP，且其平均濃為20.16 ± 9.57 μg m-3 、3.45 ± 1.77 μg m-3。此外，水可溶性有機碳(WSOC)佔有機碳比例為56 ± 12%，這表示於BB事件中所產生的碳成分氣膠具有潛在的含水特性。HULIS (Humic-like-substances)為一種可吸光有機物質，其含量為7.40 ± 4.54 μg m-3，佔有機碳的比例為35 ± 9%。同時氣膠單醣無水化合物則以左旋葡萄糖為主，所佔比例為3.09 ± 0.72%而平均濃度則是1.80 ± 0.96 μg m-3 。當生質燃燒指標物種K+、OC3、EC1-OP、HULIS 及左旋葡萄糖彼此間相關性判定係數R2都達0.62以上(N=44)，印證本地區氣膠受BB影響。
對於生質燃燒追蹤物探討，在越南北方山羅省採樣期間的樣品，以及用於氣相層析-質譜儀分析的14個選定樣品，左旋葡聚醣及甘露醣濃度比值為15.6 ±1.4， 顯示山羅省主要燃燒的物質為硬木及草地植披。
本研究也測定環境中PM2.5顆粒裡一次及二次有機氣膠追蹤物隨時間變化的組成，可偵測到多於50種有機化合物包括醣類、木質素、樹脂產物、脂肪酸、芳香族酸和生物氧化產物(如： 2-methyltetrols, 烯烴三元醇, 3 - 羥基戊二酸)。考慮不同來源地區的氣流軌跡並比較追蹤物的結果，根據氣膠中有機分子的組成我們能更了解中南半島北方生質燃燒的影響途徑，以及更多氣膠資訊和氧化過程。
最後，本文首次應用穩定同位素碳-13 (δ13C)在北越南PM2.5 氣膠的研究，其範圍落在−26.6 和 −25.4‰之間，這指出有C3植物和化石燃料燃燒的貢獻。
關鍵字：中南半島生質燃燒，氣膠化學物種，有機氣膠追蹤物，左旋葡萄糖、同位素碳-13
;Every spring, biomass burning (BB) is very active in the northern Indochina peninsula. Atmospheric aerosol was collected at Sonla, northern Vietnam (675 m a.s.l.) during 7-SEAS (Seven SouthEast Asian Studies) campaign in 2013. The objective of this study was to investigate comprehensively the chemical characteristics of near-source BB aerosol in the northern Vietnam where related data were scarce.
During the BB period, the results revealed that PM2.5 (particulate matter with an aerodynamic diameter less than or equal to 2.5 μm) dominated PM10 at Sonla in 2013 (mean: 57 ± 27 μg m-3, range: 13—134 μg m-3) with a PM2.5 to PM10 ratio of 0.75 ± 0.09. With regard to bulk water-soluble inorganic component, SO42- is the dominated specie, the average concentration was 5.51 ± 2.43 μg m-3, accounting for 11.04 ± 5.62 % in PM2.5 mass, followed by NH4+ (1.94 ± 0.94 μg m-3, 4.09 ± 2.52 %), NO3- (1.18 ± 0.57 μg m-3, 2.13 ± 0.80 %), and K+ (1.18 ± 0.57 μg m-3, 1.87 ± 0.53 %). As for the bulk carbonaceous content, organic carbon (OC) and elemental carbon(EC) were averaged at 20.16 ± 9.57 μg m-3 (35.62 ± 6.64 %) and 3.45 ± 1.77 μg m-3 (6.22 ± 2.03 %), respectively; OC3 was the most significant fraction in OC and EC1-OP was dominated in elemental carbon (EC) fractions. Furthermore, the high water-soluble OC (WSOC) fraction in OC (56 ± 12%) implies that carbonaceous aerosol from BB plume would be potentially hygroscopic. Humic-like-substances (HULIS), known as light-absorbing-organic component, was found at 7.40 ± 4.54 μg m-3, constituting 35 ± 9% in OC. Meanwhile, levoglucosan, as a biomass burning marker, is noted as the predominant species in aerosol anhydrosugars, averaged at 1.80 ± 0.96 μg m-3 (3.09 ± 0.72%). The linear correlation matrix of the near-source BB tracers such as K+, OC3, EC1-OP, HULIS and levoglucosan were correlated well with each other (R2≧0.62, N=44), indicating that aerosols were influenced intensively by BB in the area.
By employing the ratio of PM2.5 levoglucosan to mannosan, averaged at 15.6 ± 1.4 during the study period at the Sonla site, as well as 14 selected samples for the analysis of BB markers by gas chromatography–mass spectrometry, the major burnt materials was inferred to be from hardwood and grass/non-woody vegetation.
The temporal variations of both primary and secondary aerosol tracers from the 14 selected samples were also identified. More than 50 organic compounds including saccharide compounds, lignin and resin products, fatty acids, aromatic acids, poly-acids, and biogenic oxidation products (e.g., 2-methyltetrols, alkene triols, 3-hydroxyglutaric acid) were resolved in the aerosol particles. By comparing the tracers of aerosol samples classified with backward airflow trajectories from different source regions, one can better understand the influence of BB on the organic molecular composition of the transported aerosols and provide additional important information on aerosol sources and oxidation processes.
Finally, stable carbon δ13C isotopic data ranged from −26.6 to −25.4‰ in PM2.5 were revealed for the first time in the northern Vietnam, which indicated a contribution from burning of C3 plants and fossil fuel combustion |
