摘要
棕碳(brown carbon,BrC)气溶胶可通过吸收太阳光影响地球辐射平衡.为了认识棕碳的气候与环境效应,制定有针对性的控制对策,需要了解其光学特性和来源.目前较多研究以PM2.5中水溶性组分(WSOC)和甲醇溶组分(MSOC)作为棕碳代表物质,但不足之处在于大部分研究未考虑颗粒物中WSOC和MSOC的萃取效率.常州是长三角中部典型的工业城市,是长三角地区空气污染较为严重的城市.因此,本研究选择常州市区作为观测点,通过对不同浓度PM2.5滤膜,加入不同量的去离子水/甲醇,通过光学测定数据的对比及加标回收率的测定,确定了不同载荷的样品使用量范围、保证了样品的萃取效率.在此基础上,选择2017年3月到5月间采集的PM2.5样品,对WSOC和MSOC质量浓度、光学吸收系数(absorption coefficient,Abs)、Angstrom 指数(AAE)、单位质量吸收效率(mass absorption efficiency,MAE)进行分析,初步获取了常州地区春季棕碳气溶胶的光学特性,并通过潜在源贡献因子分析法分析了研究区域及周边城市对棕碳气溶胶的贡献.结果表明,采样期间,PM2.5的质量浓度平均值(101.8±34.7)g·m-3,WSOC 浓度范围为 2.2-17.0 μg·m-3,平均质量浓度(7.6±2.9)μg·m-3,MSOC 浓度范围为3.6-22.7 μg·m-3,平均质量浓度(12.1±4.6)μg·m-3,WSOC和MSOC大约占PM2.5质量浓度的7.8％±2.3％和12.3％±3.6％,说明两者是PM2.5中的重要化学组分之一;从光学数据上看,WSOC和MSOC在波长 365 nm光下的光学吸收系数(Abs365,WSOC,Abs365,MSOC)分别为(6.12±2.63)×10-6m-1与(8.95±3.93)×10-6m-1,虽低于我国北京、西安地区的观测数值,但在长三角属高值区,说明常州市颗粒物中BrC对大气中光学吸收所造成的影响不可忽视;365-550 nm波长范围下,WSOC和MSOC的AAE指数分别为(6.04±0.59)和(6.40±0.64),根据后向轨迹聚类分析,当气团轨迹途径常州西部(我国内陆区域),会导致较高的Abs和AAE值,而当气团路过较为洁净的东部海洋区域时,棕碳的Abs和AAE值显著降低.通过火点图对比对以及相关化学组分的相关性分析,常州市颗粒物中的棕碳光学受到了包括生物质燃烧、一次燃烧源、二次气溶胶生成等排放源的共同影响.本研究基于BrC的水和甲醇萃取液的性质分析,为长三角区域的大气颗粒物光学性质研究、模式模拟工作提供了基础数据.
Abstract
Atmospheric light-absorbing carbonaceous aerosols could impact the earth's radiative balance by absorbing sunlight.To understand the environmental and climate effects of these aerosols,it is necessary to have detailed knowledge of their concentrations,temporal variation,and sources.Previous studies focus on water-soluble brown carbon(WSOC)and methanol-soluble brown carbon(MSOC)in PM2.5 as representative substances of brown carbon(BrC)to study the characteristics of light absorption.However,most studies do not consider the extraction efficiencies of WSOC and MSOC.Changzhou,a typical industrial city located in the center of the Yangtze River Delta region,which experienced serious air pollution recent years.In this study,PM2.5 samples was collected from March to May 2017 in urban Changzhou,and the extraction efficiencies of WSOC and MSOC were determined by adding different amounts of deionized water/methanol into different concentrations of PM2.5 samples.Then,the concentrations and light-absorbing properties of WSOC and MSOC were studied.The results showed that averaged PM2.5 was(101.8±34.7)μg·m-3 during the sampling time.WSOC and MSOC ranged from 2.2 μg·m-3 to 17.0 μg·m-3 and 3.6 μg·m-3 to 22.7 μg·m-3,with averaged value of(7.6±2.9)μg·m-3 and(12.1±4.6)μg·m 3,contributing to 7.8％±2.3％and 12.3％±3.6％of PM2.5,respectively.The light absorption coefficients at 365 nm of WSOC and MSOC were(6.12±2.63)×10-6m-1 and(8.95±3.93)× 10-6m-1,respectively.Although the observed values are lower than those in Beijing and Xi'an,they are still high in the Yangtze River Delta region,indicating that the impact of BrC on optical absorption in the atmosphere cannot be ignored in Changzhou.The study also investigated the wavelength dependence of light absorption from both water and methanol extracts by the Absorption Angstrom Exponent(AAE),and found that AAEWSOC and AAEMSOC were(6.04±0.59)and(6.40±0.64)in the wavelength range of 365-550 nm.According to backward trajectory cluster analysis,when air masses passed through the western part of Changzhou City(inland region of China),higher Abs and AAE values were observed,while when air masses passed through cleaner eastern oceanic regions,the Abs and AAE values of BrC decreased significantly.By comparing hotspot maps and conducting correlation analysis with different chemical components,BrC in Changzhou was affected by biomass burning emissions,together with primary combustion sources and secondary aerosol formation.Overall,the study provides a comprehensive understanding of BrC aerosol based on water and methanol extraction,and the results may be beneficial for BrC optical researches as well as developing model simulation in the future.
基金项目
黄土与第四纪地质国家重点实验室开放基金(SKLLQG1944)
江苏省双创博士人才项目(2020-30865)
江苏理工工学院2021中吴科研创新团队项目(202101002)
江苏理工学院研究生实践创新计划项目(XSJCX23_77)
NETL
NSTL
万方数据