Characteristics of Carbonaceous Aerosol in Northern Thailand during 2014 Spring-Time Biomass Burning Season

2014年泰北地區乾季生質燃燒排放之氣溶膠化學特性研究

古翊廷(Ku, I Ting)

指導教授 ： 白光宇

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2015年)

摘要

本文於2014年乾季於泰北清邁安康山(海拔1,536公尺進行氣膠採樣。研究目的為探討近生質燃燒源區氣膠特性。除了24小時的樣本採集，期間也進行日(早上八點至晚上八點)、夜(晚上八點至隔日早上七點)樣本的採樣，並藉由分析無機離子、單醣無水化合物、醣醇類、有機碳、無機碳、水溶性有機碳、異戊二烯氧化物(2-甲基丁四醇)、及計算二次有機碳成分，了解當地空氣的汙染來源。此外，彙整2013-2015年安康山氣膠特性資料探討近年氣膠化學特性的變化。
　　研究結果顯示，PM1及PM2.5氣膠水溶性離子以硫酸根離子為優勢物種。高濃度生質燃燒指標物種(鉀離子與左旋葡萄糖)及其與其他物種(有機碳、水溶性有機碳、硝酸根離子)間高度相關性(R2高達0.8以上)，顯示本地氣膠受生質燃燒影響。透過特定氣膠成分比值特性，可推測本地氣膠顆粒主要來自木頭或農業廢棄物燃燒，而物種可能為混合燃燒硬木及軟木，燃燒狀態為燜燒狀態。日、夜樣本分析結果顯示多數汙染物濃度在夜間時較高，此現象可能受到生質燃燒活動及對流層高度在日、夜間差異的影響；另外比較2013-2015年安康山地區生質燃燒物種濃度，發現2013年與2014年結果相近，2015年鉀離子及左旋葡萄糖濃度有升高的趨勢，可能受天氣變化所影響。異戊二烯氧化產物(2-甲基丁四醇異構物)間高度相關性，暗示兩者可能由同一汙染源或形成機制產生(二次氧化過程)。此外，除了氣候因素(環境溫度及濕度)，硝酸根濃度也會影響異戊二烯氧化產物的生成。高濃度的異戊二烯氧化物濃度，加上其與水溶性有機碳、二次有機碳在採樣期間呈現相同的增長趨勢，判斷安康山在乾季期間的空氣品質除了受到生質燃燒活動影響，二次有機氣膠的衝擊也不容忽視。

關鍵字

清邁 ； 生質燃燒 ； 脫水醣類 ； 碳成分 ； 2-甲基丁四醇 ； 二次有機碳

並列摘要

Ambient aerosol samples (PM1 and PM2.5) were collected at mountain site in Doi Ang Khang (1536 m, a.s.l.), Chiang Mai Province, Thailand, during 2014 dry season (March to April). Besides 24-h samples, daytime and nighttime samples were collected, and the detailed chemical speciation of the aerosol samples included water-soluble ion species, anhydrosugar, sugar alcohol, carbonaceous species, water-soluble organic carbon (WSOC), along with isoprene-derived SOA molecular markers (2-methyltetrols). Moreover, using EC-tracer method, the contributions of secondary organic carbon (SOC) were estimated from OC. Overall, the average concentration ratios of PM1/PM2.5 were high for most species and good correlation was observed between various species concentrations in PM1 and PM2.5 samples, indicating that most of components were present in submicron particles (PM1) and might have come from similar PM emission sources. Sulfate was the major ion species in ambient aerosols samples, comprising 14.28% and 37.6% of total ion species in PM1 and PM2.5, respectively. Enhanced biomass burning tracers in the collected aerosols, such as non-sea-salt-potassium (nss-K+) and levoglucosan, revealed that the air quality at Doi Ang Khang was significantly influenced by biomass burning activities. The good correlation between levoglucosan and threitol suggested that threitol might be a good biomass burning tracer at the sampling site. The analysis also showed that directly-emitted organic carbon (OC) and formed from secondary processes enhanced the carbonaceous pollution simultaneously. The biomass burning tracers, i.e., levoglucosan and nss-K+, exhibited significant positive correlation with nitrate (NO3-), others anhydrosugar and sugar alcohol (mannosan, galactosan and xylitol), OC and WSOC suggested biomass burning emission as a dominant source. According to marker ratios (Lev/OC, Lev/Man, K+/Lev), the collected biomass burning aerosols might be contributed by wood or agriculture waste burning, and burning was predominantly in the smoldering phase. Using an emission factor obtained from previous chamber studies, the biomass smoke contributions to organic carbon were estimated to 49.41±8.43% and 50.32±9.29% in PM1 and PM2.5 at Doi Ang Khang. The mass concentrations of most species and the amount of biomass smoke contribution to OC (%) increased during nighttime, indicating higher strength of biomass burning emission during nighttime. Compared the chemical composition data from 2013 to 2015 at Doi Ang Khang site, the maximum concentrations of biomass burning tracers, levoglucosan and nss-K+, was observed in 2015. For SOA formed from oxidation of isoprene, a strong correlation between two diastereoisomeric 2-methyltetrols (2-methylerythritol and 2-methylthreitol) was observed, indicating the similar photochemical origin and formation mechanism of these two SOA species. The 2-methyltetrols also exhibited a significant relationship with relative humidity and temperature, while the positive correlation between 2-methyltetrols and NO3- implied that high concentrations of NO3- can increase the formation rate of 2-methyltetrols from isoprene. The significant high concentrations of 2-methyltetrols and consistent trends with 2-methyltetrols, WSOC and OCsec during the sampling period, suggesting SOA formations might impose strong influence on ambient air quality besides the biomass burning emission at Doi Ang Khang site during the dry season.

並列關鍵字

Chiang Mai ； biomass burning ； anhydrosugars ； carbonaceous aerosols ； 2-methyltetrols ； secondary organic carbon

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