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中国西南部三峡库区PM2.5中棕色碳的光吸收:生物质燃烧和二次生成的影响

发布时间:2020-11-04

  

  摘要

  棕色碳作为一种在对流层中能影响可见度和辐射强迫平衡的吸光有机物而被熟知。本研究对中国三峡库区三个城市点和一个农村点从2015年冬天到2016年夏天通过膜采样收集到的PM2.5进行了光学性质研究。棕色碳在405nm的平均光吸收系数(βabs, 405,BrC)在冬季为12.1?±?7.0?Mm−1,占总气溶胶吸光的23.8?±?9.1%,均高于在夏季的相应值(1.7?±?0.8?Mm-1 与 11.2?±?4.1%)。从空间上看,城市地区的βabs, 405,BrC(13.4?±?7.3?Mm−1)要高于农村地区的相应值(7.8?±?3.2?Mm−1)。棕色碳在405nm的平均质量吸收系数(MAE405,BrC)在冬季为0.8?±?0.4?m2?g−1,是夏季(0.3?±?0.1?m2?g−1)的2.7倍。此外,在405到980纳米的Ångström吸收指数(AAE405−980)在夏季为1.1?±?0.1,而在冬季为1.3?±?0.2.相关性分析表明,生物质燃烧在冬季的βabs, 405,BrC中起到了很重要的作用。另外,冬季相对较高的AAE405−980主要是生物质燃烧和二次有机气溶胶中棕色碳共同影响的结果。棕色碳在405-445nm对于太阳能吸收的贡献相对于黑炭而言在夏季和冬季分别占23.9?±?7.8%与63.7?±?14.2%,显著高于405nm到980nm的相应值(分别为11.9?±?3.4% 与29.9?±?6.1%)。总的来说,本研究主要贡献在于帮助人们更好的了解对气候较为敏感的中国西南部三峡库区的棕色碳的来源。

  关键词:棕色碳;光吸收;生物质燃烧;三峡库区

  亮点:

  · 通过膜采样测量了三峡库区棕色碳的光吸收。

  · 从夏季到冬季,黑炭的平均质量吸收系数(MAEBC)相对较为稳定,而棕色碳的平均质量吸收系数(MAEBrC)增加了。

  · 生物质燃烧是冬季棕色碳的一个显著来源。

  · AAE405−980在冬季同时受到生物质燃烧和二次有机气溶胶的显著影响

  · 发现了棕色碳在近紫外区域(405–445?nm)对太阳能的显著吸收。

  Fig. 1. Temporal variations of aerosol light absorption coefficients (βabs, Mm−1) measured at 405, 445, 635, 780, 808, and 980?nm, and concentrations of ECand K+at the YB, FL, WZ, and JY sites respectively.

  Fig. 2. Fractions (a) and contributions (b) of BC and BrC to βabs from 405 to 980?nm during the sampling campaign inthe TGR region.

  Fig. 3. Seasonal average of βabs,BrC at 405?nm during summer and winter at the foursites. The percentages over the bars are the contributions of βabs,BrC to βabs. The error bar represents the standard deviation (1σ) of βabs,BrC.

  Fig. 4. Correlations between βabs,405,BrC and concentrations of K+, Cl−, POC, and SOC during summer (e, f, g, h) and winter (a, b, c, d) in theTGR region.

  Fig. 5. Correlations between βabs,405,BrC and concentrations of K+ and Cl− at the YB, FL, WZ, and JY sites in winter.

  Fig. 6. Relationship between AAE at 405–980?nm and BC-to-OA ratios during summer(a) and winter (b) in the TGR region (OA?=?1.6?×?OC). The best fit lines todata taken from Luet al. (2015) (redline) and Salehet al. (2014) (greyline) are indicated in panel (b). (For interpretation of the references tocolor in this figure legend, the reader is referred to the Web version of thisarticle.)

  Fig. 7. Correlations between AAE at 405–980?nm and the mass fractions (f) ofnitrate (NO3−), ammonium (NH4+), and sulfate (SO42−) during winter (a, b, and c) and summer (d, e, and f) in the TGR region.