泰山大气棕色碳的光吸收特性、吸光贡献及影响因素

棕色碳是大气气溶胶中重要的吸光性物质,会影响大气光化学过程、改变区域气候。本次研究于2017年冬季和2018年春季在泰山顶采集了大气细颗粒物(PM2.5)样品,在实验室测定了样品中棕色碳和黑碳的光吸收系数,并测定了棕色碳成分硝基苯酚类化合物的含量。测定结果表明,泰山冬、春两季PM2.5样品中棕色碳的平均吸收系数Abs365分别为(4.61±2.42)Mm^?1和(2.38±0.98)Mm^?1,质量吸收效率MAE365分别为(0.72±0.12)m^2/g和(0.52±0.24)m^2/g,棕色碳在365 nm处的吸收系数分别占碳质气溶胶总吸收系数的(32±7)%和(20±9)%。通过对比与相关性分析,发现泰山周边地区人为活动对泰山顶上棕色碳的光学特性有重要影响,泰山冬季受邻近区域煤炭燃烧活动影响很大,排放的大量一次有机物增强了棕色碳的吸光能力和吸收系数,导致泰山冬季棕色碳的吸收系数与吸光贡献显著高于春季。根据测定结果,泰山冬、春两季硝基苯酚类化合物在365 nm处对棕色碳吸收系数的贡献分别为(3.5±1.2)%和(2.5±1.0)%,其中在紫外和紫光区域4-硝基酚的吸光贡献最大,而在420~450 nm的蓝光区域4-甲基-2,6二硝基酚的贡献最大。硝基苯酚类化合物的吸光贡献相对较小,说明泰山棕色碳的吸光作用大部分来自于其他有机成分,将来有待进一步的识别和评估。

Light absorption properties,absorption contributions,and the influencing factors of atmospheric brown carbon on Mount Tai

Brown carbon(Br C)is a kind of important light-absorbing compounds in atmospheric aerosols.It has significant effects on atmospheric photochemical reactions and regional climate change.In this study,samples of fine particulate matters(PM2.5)were collected in the winter of 2017 and the spring of 2018 at the summit of Mount Tai.The light absorption coefficients of brown carbon and black carbon in the samples were measured in a laboratory and the concentrations of nitrated phenols,a major component of brown carbon,were also determined.The measurement results show that the average values of light absorption coefficients at 365 nm for brown carbon in PM2.5 during winter and spring on Mount Tai were(4.61±2.42)Mm–1 and(2.38±0.98)Mm–1,respectively and the mass absorption efficiencies at 365 nm were(0.72±0.12)m2/g and(0.52±0.24)m2/g,respectively.The contributions of the absorption coefficient of brown carbon at 365 nm to the total light absorption of carbonaceous aerosols in winter and spring reached(32±7)%and(20±9)%,respectively.Based on comparison and correlation analyses,it was found that anthropogenic activities from the surrounding areas had considerable influences on the optical properties of brown carbon at the summit of Mount Tai.Particularly,coal combustion processes in adjacent regions strongly affected the brown carbon on Mount Tai in winter.A large amount of primary organic matters released from coal combustion enhanced the light absorption efficiency and the light absorption coefficient of brown carbon and led to substantially higher absorption coefficients and absorption contributions of brown carbon in winter than in spring on Mount Tai.According to the determination results,the contributions of nitrated phenols to the absorption coefficients of brown carbon at 365 nm in winter and spring were(3.5±1.2)%and(2.5±1.0)%,respectively.Among the 12 nitrated phenolic compounds,4-nitrophenol was identified as the largest contributor in the ultraviolet and violet regions,whereas 4-methyl-2,6-dinitrophenol had the largest contribution at a wavelength of 420-450 nm in the blue region.The contribution of nitrated phenols was relatively small,indicating that most brown carbon light absorption came from other organic components,which require further identification and evaluation in the future.