Formation Mechanism Of Particulate Nitrate During Haze Period In Shandong

Aerosol pollution is an important environmental problem in China, have a series of significant impacts on the production and living of residents. Nitrate is the important component of aerosol, its enhanced formation is one of the major reasons lead to serious haze. For comprehensively understanding the condition of fine nitrate aerosol pollution during haze in Shandong region, atmospheric observation experiments with a Monitor for Aerosols and Gases (MARGA) and other relevant monitors have been done in a typical urban area in Jinan and a typical rural area under the downwind direction of city in Yucheng in Dezhou. In the spring, autumn, winter in Jinan and in the summer in Yucheng, more than 49.3%,37.6%,49.9% and 40.4% of fine nitrate concentrations were above 20μg m-3, more 29.0%,27.0%,34.3% and 25.9% of fine nitrate concentrations were above 30μg m-3, respectively. In addition, serious fine nitrate pollution cases with peak mass concentrations above 60 μg m-3 were frequently appeared. What is the notable about the mass concentration ratio between NO3- and SO42- in Jinan and Yucheng were much higher than the ratios measured in urban areas and rural areas of north China a few years ago, suggests that the nitrate aerosol pollution have become increasingly prominent. And the values of NO3-/SO42- in spring and autumn in Jinan up to 1.20 and 1.21, respectively, higher than the ratio of 1.05 in winter and 0.78 in summer.In the haze periods, NH3 can neutralize the vast majority of HNO3, and the formatted nitrate was mainly in the form of ammonium nitrate. In the dust and clean periods, NH3 can’t completely neutralize HNO3, part of nitrate was in form of calcium nitrate and magnesium nitrate. During the spring, autumn and winter, ammonium nitrate mainly exists in the form of solid phase. In the noon and afternoon of summer, ammonium nitrate mainly exists in the form of solid phase; and in the evening and early morning, ammonium nitrate mainly exists in the liquid phase on the surface of particles or small droplets.In this paper, nitrate aerosol pollution cases have been analyzed detailed, to research the role of ammonia in the process of fine nitrate formation. Results show that ammonia promoting nitrate formation is a ubiquitous atmospheric chemistry phenomenon in spring summer, autumn and winter in Shandong. Rich NH3 in the atmospheric environment not only can stimulate quickly fine nitrate formation, to cause the increase of PM2.5 concentration, ultimately result in the formation of haze; but also can lead to a rise of equivalent ratio of NH4+ to the sum of SO42- and NO3-. Considering ammonia can effectively promote fine nitrate formation, the control of NH3 emissions in rural and urban area will have important significance to reduce nitrate aerosol pollution.The method of combi between field observation and chemical steady-state model has been used to research the impact of photochemical pollution on fine nitrate formation at night-time in summer in rural area under the downwind direction. The results showed that the heterogeneous hydrolysis of N2O5 on the surface of wet aerosol not only can cause rapid formation of fine nitrate, but also can lead to a significant decline of equivalent ratio of NH4+ to the sum of SO42- and NO3-. The fine nitrate formation is widespreadin the evening of summer, and can be significantly promote by O3 which produced from photochemical reactions. Considering the important role of O3 in the fine nitrate formation process, we suggest to reduce the emissions of ozone precursors such as NOx and VOCs to address the serious pollution of fine nitrate in Shandong.The significance of this study is to research the actuality of nitrate aerosol pollution in Shandong region, and to research the mechanism of fine nitrate formation during the period of haze. Both of these can provide data support in depth research the mechanism of fine nitrate formation in the future.