东北三江平原地区生物质燃烧对PM_(2.5)中WSOC吸光能力的影响

Contribution of Biomass Burning on Light Absorption Property of Water Soluble Organic Carbon in PM_(2.5) in Sanjiang Plain, Northeast China

生物质燃烧排放大量具有光吸收能力的水溶性有机碳(Water-Soluble Organic Carbon,WSOC),对空气质量、气候变化和人体健康均有重要影响。为了研究东北地区生物质燃烧对气溶胶光吸收特性的作用,于2013年5月-2014年1月采集三江平原的PM_(2.5)样品,分析了样品中生物质燃烧指示剂(左旋葡聚糖)、有机碳(OrganicCarbon,OC)和WSOC的质量浓度,以及WSOC的光吸收强度(A_(365a))。根据左旋葡聚糖的质量浓度水平,将采样期间划分为生物质燃烧(BB)期和非生物质燃烧(NBB)期。对BB和NBB期间WSOC的光吸收强度与PM_(2.5)、OC、WSOC和左旋葡聚糖之间的相关性分别进行了分析,并计算了生物质燃烧产生的WSOC对总WSOC的质量浓度和吸光能力的贡献。结果表明,在BB期间,PM_(2.5)、WSOC和左旋葡聚糖的质量浓度是NBB期间的10倍以上,WSOC的光吸收强度也相应增高了13倍。BB与NBB期间,PM_(2.5)与A365a的相关指数(R^2)分别为0.98和0.34。BB期间左旋葡聚糖和A365a的相关指数(0.91)高于NBB期间(0.09),表明BB期间生物质燃烧对PM_(2.5)有显著贡献,且排放了大量的吸光性棕色碳。在BB期间,生物质燃烧对WSOC的贡献高达74.6%,对WSOC的光吸收强度贡献高达46.2%;而在NBB期间,生物质燃烧对WSOC的贡献为26.8%,对WSOC的的光吸收强度贡献为22.6%。因此,BB期间生物质燃烧对三江平原WSOC的质量浓度和光吸收强度都具有重要影响。

Biomass burning(BB) activities emit a large quantity of water-soluble organic carbon(WSOC) aerosols into atmosphere,resulting in adverse effects on air quality, climate change and human health. In order to investigate the influences of BB activities on mass concentrations and light absorption of WSOC aerosols, PM2.5 samples were collected from May 2013 to January 2014 in Sanjiang Plain, Northeast China. The concentrations of levoglucosan, organic carbon(OC) and WSOC, as well as light absorption of WSOC were also analyzed. The sampling days were categorized into BB and non-BB(NBB) periods based on the concentrations of determined levoglucosan. During the BB period, the concentration of PM2.5, WSOC and levoglucosan were 10 times higher than those of NBB days. Meanwhile, light absorption of WSOC increased by a factor of 13. The correlation index(R2) between PM2.5 and A365 a increased from 0.34 on the NBB days to 0.98 on the BB events. Moreover, the strong correlation(R2=0.91) between A365 a and levoglucosan were also found during the BB period, while that(R2=0.09) was not observed during the NBB period. This indicated that BB contributed significantly to PM2.5 and emitted a large amount of brown carbon. Furthermore, we estimated that BB contributed, respectively, 74.6% and 46.2% to the total mass and light absorption of WSOC during the BB period. Although some uncertainty was existed in the estimations, our results demonstrated that biomass burning emissions have very important influence on both mass concentrations and light absorption of airborne WSOC aerosols at the sampling site.