The secondary formation of inorganic aerosols in the droplet mode through heterogeneous aqueous reactions under haze conditions
The secondary formation of inorganic aerosols in the droplet mode through heterogeneous aqueous reactions under haze conditions
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DOI：
10.1016/j.atmosenv.2012.09.029
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发表时间：
2012-12-01
影响因子：
5
通讯作者：
Wang, Zhe
中科院分区：
文献类型：
--
作者：
Wang, Xinfeng;Wang, Wenxing;Wang, Zhe
二次无机气溶胶在能见度降低和区域霾污染中起着重要作用。为了研究霾天气下二次硫酸盐和硝酸盐的粒径分布特征及其形成机制，2007年12月至2008年10月在中国济南的一个城市站点，使用微撞击器（MOUDI）按粒径收集了四个季节的气溶胶。在霾天气过程中，二次硫酸盐和硝酸盐主要在细颗粒物中形成，在液滴模态（0.56 - 1.8微米）下浓度峰值升高。细颗粒的硫酸盐和硝酸盐被氨完全中和，分别以(NH₄)₂SO₄和NH₄NO₃的形式存在。研究发现，硫酸盐、硝酸盐和铵盐（SNA）的二次形成与非均相水相反应有关，并且在很大程度上取决于环境湿度。随着相对湿度的升高，液滴模态SNA浓度、液滴模态SNA与总SNA的比值、液滴模态颗粒中SNA的占比以及SNA的质量中值空气动力学直径呈现指数、对数或线性增长。对冬季和夏季两次重度污染的多日霾天气过程进行了详细分析。冬季，二次硫酸盐与SO₂的非均相吸收有关，随后在铁和锰的作用下被氧气催化氧化。细颗粒硝酸盐的形成与NH₄NO₃、气态HNO₃和NH₃之间的热力学平衡密切相关，并且在冬季和夏季表现出不同的温度依赖性。© 2012 Elsevier Ltd.保留所有权利。
Secondary inorganic aerosols play important roles in visibility reduction and in regional haze pollution. To investigate the characteristics of size distributions of secondary sulfates and nitrates as well as their formation mechanisms under hazes, size-resolved aerosols were collected using a Micro-Orifice Uniform Deposit Impactor (MOUDI) at an urban site in Jinan, China, in all four seasons (December 2007-October 2008). In haze episodes, the secondary sulfates and nitrates primarily formed in fine particles, with elevated concentration peaks in the droplet mode (0.56-1.8 mu m). The fine sulfates and nitrates were completely neutralized by ammonia and existed in the forms of (NH4)SO4 and NH4NO3, respectively. The secondary formation of sulfates, nitrates and ammonium (SNA) was found to be related to heterogeneous aqueous reactions and was largely dependent on the ambient humidity. With rising relative humidity, the droplet-mode SNA concentration, the ratio of droplet-mode SNA to the total SNA, the fraction of SNA in droplet-mode particles and the mass median aerodynamic diameter of SNA presented an exponential, logarithmic or linear increase. Two heavily polluted multi-day haze episodes in winter and summer were analyzed in detail. The secondary sulfates were linked to heterogeneous uptake of SO2 followed by the subsequent catalytic oxidation by oxygen together with iron and manganese in winter. The fine nitrate formation was strongly associated with the thermodynamic equilibrium among NH4NO3, gaseous HNO3 and NH3, and showed different temperature-dependences in winter and summer. (C) 2012 Elsevier Ltd. All rights reserved.