| 引用本文: | 张 璐，王格慧，王佳媛，吴 灿，曹 聪，李建军.2017.西安供暖前后细颗粒物化学特征及棕碳吸光特性[J].地球环境学报,8(5):451-458 |
| ZHANG Lu, WANG Gehui, WANG Jiayuan, WU Can, CAO Cong, LI Jianjun.2017.Chemical composition of fine particulate matter and optical properties of brown carbon before and during heating season in Xi’an[J].Journal of Earth Environment,8(5):451-458 |
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| 摘要: |
| 2015年11月1 — 30日在西安用大流量采样器每12 h进行1次细颗粒物（PM2.5）样品采集，分析供暖前后PM2.5中有机碳（OC），元素碳（EC），水溶性有机碳（WSOC）与无机离子的浓度和棕碳吸光度的变化特征，探讨供暖对城市大气气溶胶理化特性的影响。结果显示：供暖前（11月1 — 15日）与供暖后（11月16 — 30日）PM2.5浓度分别为127 ± 59 μg ∙ m−3和164 ± 126 μg ∙ m−3，供暖后比供暖前增加了30%，其中K+、Cl−、SO42−和NH4+分别增加了30%、70%、40%和38%。洁净期（PM2.5 < 75 μg ∙ m−3）与灰霾期（PM2.5 >150 μg ∙ m−3）对比显示：洁净期Na+、Ca2+、Mg2+的相对含量均大于灰霾期，这是由于灰霾发生时不利的静稳天气条件（风速<1 m ∙ s−1）使得粉尘粒子干沉降效应增加所致。洁净期[NO3−]/[SO42−]质量比均大于1而灰霾期均小于1，这是因为灰霾期高湿条件有利于二氧化硫液相转化为硫酸盐所致。供暖前灰霾期[NO3−]/[SO42−]比值要高于供暖后的灰霾期，这与西安及其周边地区燃煤取暖排放二氧化硫增加有关。供暖前后棕碳的质量吸收效率（MAE）值均是洁净期大于灰霾期，表明：与非灰霾天相比，当灰霾发生时不利的静稳天气条件使得细粒子在大气中长时间存留，延长其二次氧化反应时间，使得棕碳中含C = C不饱和键的吸光性物质被深度氧化，从而降低其吸光性能。 |
| 关键词: 棕碳 化学组成 光学特征 来源 形成机制 |
| DOI：10.7515/JEE201705008 |
| CSTR：32259.14.JEE201705008 |
| 分类号: |
| 基金项目:国家杰出青年科学基金（41325014）；中国科学院战略性先导科技专项（B类）（XDB0502040） |
| 英文基金项目:National Science Fund for Distinguished Young Scholars (41325014); Strategic Priority Research Program of the Chinese Academy of Sciences (XDB05020401) |
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| Chemical composition of fine particulate matter and optical properties of brown carbon before and during heating season in Xi’an |
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ZHANG Lu, WANG Gehui, WANG Jiayuan, WU Can, CAO Cong, LI Jianjun
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Background, aim, and scope Extremely high levels of ambient fine particulate matter (PM2.5) have frequently occurred in Xi’an and many other Chinese cities in winter mainly due to the enhanced emissions from house heating. Source and formation of the fine particulate matter are still illusive. This paper aims to identify the difference in chemical composition of PM2.5 and optical properties of brown carbon (i.e. water-soluble organic carbon) before and during the heating season in Xi’an, China in order to understand the impact of coal combustion and biomass burning for house heating on the urban air quality. Materials and methods PM2.5 samples were collected during 1st — 30th Nov. 2015 at the urban center of Xi’an, China by using a high-volume sampler (1.13 m3 ∙ min−1) with a 12 h interval. The samples were measured for element carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), inorganic ions, optical mass absorption efficiency (MAE) at 365 nm light wavelength and Ångstrӧm absorption exponent (AAE). Results Mass concentrations of PM2.5 ranged from 39 μg ∙ m−3 to 261 μg ∙ m−3 with an average of 127 ± 59 μg ∙ m−3 before the heating period (1st — 15th Nov.) and from 51 μg ∙ m−3 to 511 μg ∙ m−3 with an average of 164 ± 126 μg ∙ m−3 during the heating period (16th — 30th Nov.). Carbonaceous fractions (EC+OC) of PM2.5 were 21% ± 10% and 24% ± 10% before and during the heating season, respectively. Discussion Relative abundances of Na+, Ca2+ and Mg2+ in PM2.5 in clean days (classified as the daily PM2.5 <75 μg ∙ m−3) was higher than in hazy days (classified as the daily PM2.5 >150 μg ∙ m−3), suggesting an increased deposition effect under the humid and stagnant conditions. MAE before the heating season were 2.5 ± 0.8 m2 ∙ g−1 and 1.6 ± 0.3 m2 ∙ g−1 on the clean and hazy days, while MAE during the heating season were 1.7 ± 0.4 m2 ∙ g−1 and 1.3±0.2 m2 ∙ g−1 on the clean and hazy days, indicating that light absorption in clean days is stronger than that in hazy days. Conclusions Compared to those before the heating period concentrations of K+ and Cl−1 of PM2.5 increased by 30% and 70% during the heating season, indicating a significant impact of biomass burning for house heating on the urban air quality. Due to the favorable humid and stagnant conditions, sulfate and ammonium of PM2.5 increased by 40% and 38% in the heating season compared to those in the non-heating season. Optical absorption capacity of brown carbon in the heating season was 15% — 80% higher than that in the non-heating season due to the abundant WSOC. In contrast, MAE in the heating season was lower than those in the non-heating season, which was probably caused by an enhanced photochemically bleaching effect due to the longer reaction time under the stagnant hazy days. Recommendations and perspectives In the current work we only measured the optical properties of brown carbon, i.e., WSOC. Details in molecular compositions of WSOC are necessary for understanding the source and formation mechanism of the brown carbon. |
| Key words: brown carbon chemical composition optical properties source formation mechanism |
