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In this paper, the spatial, temporal distribution, transformation and source simulation of NO3- were analyzed systematically based on the monitoring data, literature review and numerical simulation (CMAQ4.7.1). Analysis results showed that annual average concentration of NO3- in Beijing was between 6.69 and 12.48 Mg/m3 with an increasing trend in recent years; concentration of NO3- in Beijing in 2013 was higher in winter and autumn than that in spring and summer and diurnal variation of NO3- showed bimodal distribution and spatial distribution of NO3- showed significant north-south gradient distribution; annual average N0R in Beijing was between 0.12 and 0.17 while it was between 0.17 and 0.20 during heavy air pollution days in 2013; the average ratio of NO3-/S02- was between 0.97 and 1. 06 while it was between 1. 00 and 1. 07 during heavy air pollution days in 2013; the emission sources of Beijing was being changed from fixed source to both fixed and moving sources in feature development; simulated local, external transportation, background and boundary condition were 40%, 44% and 16% respectively to the annual average concentration of NO3- in Beijing in 2013 while they were 31%, 57% and 12% respectively in heavy air pollution days, which indicated that external source played an important role to the concentration of NO3- in Beijing. [ABSTRACT FROM AUTHOR]

In this paper, atmospheric environmental background, weather conditions and formation mechanism of one typical air pollution episode in Beijing during October 6th -12th, 2014 were investigated by combining observed data with numerical model CAMx. Results showed that the occurrence of heavy air pollution resulted mainly from stable atmospheric conditions regionally or locally. Observed heavy pollution episodes were characterized by a stagnant atmospheric structure with average wind speed of 1.56 m/s, high humidity of 83.13%, large inversion strength of 3.42 cC/100 m which were disadvantageous to the dispersal of air pollutants. The air pollution episode during October 8th -11th was the most serious with daily average PM25 concentration of 264 μ/m³ in Beijing, and heavily polluted land area at Beijing, Tianjin and Hebei districts was about 2 × 105 km². Model research showed that regional transmission contributions to the receptor sites in Beijing were between 61% -69% during 8th -11th, and regional transportation played a more important role in this serious air pollution episode. [ABSTRACT FROM AUTHOR]