Estimation of Aerosol Mass Scattering Efficiencies under High Mass Loading: Case Study for the Megacity of Shanghai, China

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• 作者：Zhen Cheng ; Jingkun Jiang ; Changhong Chen ; Jian Gao ; Shuxiao Wang ; John G. Watson ; Hongli Wang ; Jianguo Deng ; Buying Wang ; Min Zhou ; Judith C. Chow ; Marc L. Pitchford ; Jiming Hao
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：January 20, 2015
• 年：2015
• 卷：49
• 期：2
• 页码：831-838
• 全文大小：584K
• ISSN：1520-5851

文摘

Aerosol mass scattering efficiency (MSE), used for the scattering coefficient apportionment of aerosol species, is often studied under the condition of low aerosol mass loading in developed countries. Severe pollution episodes with high particle concentration frequently happened in eastern urban China in recent years. Based on synchronous measurement of aerosol physical, chemical, and optical properties at the megacity of Shanghai for two months during autumn 2012, we studied MSE characteristics at high aerosol mass loading. Their relationships with mass concentrations and size distributions were examined. It was found that MSE values from the original US IMPROVE algorithm could not represent the actual aerosol characteristics in eastern China. It results in an underestimation of the measured ambient scattering coefficient by 36%. MSE values in Shanghai were estimated to be 3.5 卤 0.55 m²/g for ammonia sulfate, 4.3 卤 0.63 m²/g for ammonia nitrate, and 4.5 卤 0.73 m²/g for organic matter, respectively. MSEs for three components increased rapidly with increasing mass concentration in low aerosol mass loading, then kept at a stable level after a threshold mass concentration of 12鈥?4 渭g/m³. During severe pollution episodes, particle growth from an initial peak diameter of 200鈥?00 nm to a peak diameter of 500鈥?00 nm accounts for the rapid increase in MSEs at high aerosol mass loading, that is, particle diameter becomes closer to the wavelength of visible lights. This study provides insights of aerosol scattering properties at high aerosol concentrations and implies the necessity of MSE localization for extinction apportionment, especially for the polluted regions.