School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China; State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China.
Sci Total Environ. 2018 Mar 15;618:793-803. doi: 10.1016/j.scitotenv.2017.08.202. Epub 2017 Oct 21.
Apportionment of ambient extinction coefficient is essential for quantifying the causes of visibility degradation. Previous studies focused on either seasonal or episode-average extinction coefficients. The extinction evolution during different types of low visibility events was still unclear and seldom investigated. In this study, hourly-resolution apportionment of ambient extinction coefficient, including dry extinction coefficient and hygroscopic portion, during three low visibility events (i.e., dust storm, autumn and winter haze) and one clear episode was retrieved through online measurement in Shanghai, China. PM soil and coarse particles contributed 90% of PM mass and 62% of total extinction coefficient throughout the dust storm event. Secondary inorganic aerosol and organic matter dominated the autumn and winter haze events, accounting for 52% and 31% of PM mass, 35% and 27% of extinction coefficient, respectively. Hygroscopic enhancement by inorganic particles contributed another 22-27% of extinction coefficient during the two haze events. However, higher relative humidity elevated the extinction percentage of inorganic aerosol and hygroscopic enhancement during the autumn haze, and the percentage of organic matter decreased correspondingly. In contrast, the extinction of each contributor increased proportionally and the percentages could keep at a stable level during the winter haze. Furthermore, the mass extinction efficiency of major PM chemical components was found to increase with the accumulation of mass loading. These findings indicated the importance of reducing the mass level of organic matter and secondary inorganic aerosol during the autumn or winter haze events. The control of precursors of sulfur and nitrogen oxides seemed more effective for visibility improvement during the autumn events with higher relative humidity.
环境消光系数的分配对于量化能见度下降的原因至关重要。先前的研究主要集中在季节性或事件平均消光系数上。不同类型低能见度事件期间的消光演变仍不清楚，很少有研究涉及。本研究通过在中国上海的在线测量，获取了三次低能见度事件（沙尘暴、秋冬霾和一次晴朗天气）和一次晴朗天气期间每小时分辨率的环境消光系数分配，包括干消光系数和吸湿部分。在沙尘暴事件中，PM 土壤和粗粒子贡献了 PM 质量的 90%和总消光系数的 62%。在秋冬霾事件中，二次无机气溶胶和有机物分别占 PM 质量的 52%和 31%，占消光系数的 35%和 27%。在两次霾事件中，无机粒子的吸湿增强作用还贡献了另外 22-27%的消光系数。然而，在秋冬霾期间，较高的相对湿度提高了无机气溶胶和吸湿增强的消光百分比，相应地有机物的百分比降低。相比之下，每个贡献者的消光比例都在增加，且百分比可以保持稳定。此外，主要 PM 化学组分的质量消光效率随着质量负荷的积累而增加。这些发现表明，在秋冬霾期间降低有机物和二次无机气溶胶的质量水平非常重要。在相对湿度较高的秋季事件中，控制硫和氮氧化物的前体对改善能见度更为有效。
