南昌市PM_(2.5)中硫酸盐、硝酸盐及其气态前体物的分布特征与转化机制

Sulfate and Nitrate Distribution Characteristics and Conversion Mechanism of PM_(2.5) and Its Gaseous Precursors in Nanchang City

2014年1月至2015年1月,在南昌市3种类型采样点(混合区、主干道旁侧、燃煤电厂附近),对大气PM_(2.5)中SO_4^(2-)和NO_3^-及其气体前体物SO_2、NO_2进行同步采样,通过分析硫氧化速率(SOR)和氮氧化速率(NOR),对PM_(2.5)中硫酸盐和硝酸盐的来源、形成机制和影响因素进行探讨。结果表明,南昌市SO_2浓度18.9~74.8μg/m^3,NO_2浓度29.7~62.6μg/m^3,PM_(2.5)中SO_4^(2-)浓度13.7~28.4μg/m^3,NO_3^-浓度3.9~39.9μg/m^3,SOR值0.28~0.60,NOR值0.09~0.33。SO_2、NO_2、SO_4^(2-)、NO_3^-和SOR、NOR的季节分布和日分布,反映硫酸盐和硝酸盐的二次生成受气象条件、环境条件和排放源的影响。SOR与NOR的季节分布正好相反,日分布也差异较大,反映生成机制不同。SO_2、NO_2、SO_4^(2-)、NO_3^-和SOR、NOR在不同采样点的分布,反映燃煤烟气和机动车尾气增加SO_2、NO_2的浓度,促进SO_4^(2-)、NO_3^-的二次生成。[NO_3^-]/[SO_4^(2-)]春、夏、秋、冬分别为0.86、0.15、0.83、0.70,反映南昌市机动车尾气贡献比例较大;[NO_3^-]/[SO_4^(2-)]受硫酸盐和硝酸盐在不同季节的二次生成机制和速率的影响,也受排放源的影响。

From January 2014 to January 2015,PM（2.5）and gaseous precursors（SO2,NO2）of sulfate（SO4^2-）and nitrate（NO3^-）in PM（2.5）were collected in three types of sampling sites（mixing area,roadside of a main street and nearby a coal-fired power plant）of Nanchang.Sources,conversion mechanism and affecting factors of sulfate and nitrate in PM（2.5） were studied by discussing sulfur oxidation ratio（SOR）and nitrogen oxidation ratio（NOR）.It was shown that the concentrations of gasous precursors and speices in PM（2.5）in Nanchang ranged from 18.9to 74.8μg/m^3（SO2）,29.7to 62.6μg/m^3（NO2）,13.7to28.4μg/m^3（SO4^2-）and 3.9to 39.9μg/m^3（NO3^-）,respectively.And SOR and NOR ranged from 0.28 to 0.60 and 0.09 to 0.33,respectively.Under analyzing the seasonal distribution and diurnal variation of SO2,NO2,SO4^2-,NO3^-,SOR and NOR,it was indicated that secondary generation sulfate and nitrate were influenced by meteorological conditions,environmental conditions and emission sources.Seasonal distribution of SOR was found opposite to that of NOR,and diurnal variation of them was also different,reflecting different generation mechanism.In addition,the results of SO2,NO2,SO4^2-,NO3^-,SOR and NOR in difference sampling sites implied that coal-fired emission and vehicle exhaust increased the concentration of SO2,NO2 and promoted more secondary SO4^2-,NO3^- generation.[NO3^-]/[SO4^2-]ratio of spring,summer,autumn and winter in mixing site were 0.86,0.15,0.83,0.70,respectively,reflecting high contribution from vehicle exhaust.[NO3^-]/[SO4^2-]ratios were influenced by generation mechanism and generation rate of secondary SO4^2-,NO3^-in various season and also impacted by emission sources.