北京市PM2.5组分NO3-浓度分布及来源模拟分析

An Analysis on Distribution and Source Simulation of Nitrate Constituent in PM2.5 in Beijing

采用观测与数值模拟相结合的方法,系统分析了北京市NO_3^-时空分布及来源特征,发现近10 a北京市NO_3^-年均浓度6.69~12.48μg/m^3,总体呈波动中缓慢上升趋势,近3 a下降趋势明显;北京市NO3-浓度整体呈重污染日〉秋冬季〉春夏季的特征,日变化浓度呈双峰型分布,空间上呈南北梯度分布特征;北京市NO_3^-/SO_4^（2-）年均值0.97~1.06,重污染日均值1.00~1.07;北京市的NO_3^-排放源有由固定源为主向固定源和移动源并重特征发展的趋势;重污染日NO_3^-本地、外来源、背景及边界条件分别贡献40%、44%、16%,重污染期间二次转化及区域传输对北京NO_3^-浓度起着更为重要的作用。

Spatial-temporal distribution and origins of nitrate constituent on particulate matter PM2.5 in the air of Beijing were analysed systematically based on the observation and numerical simulation （CAMx）. It has shown that in the recent ten years, the annually averaged concentration of nitrate appeared to be a slow rise in general with the ？uctuation in range of 6.69 12.48μg/m3 whilst tending to apparently descend in the latest three years. The nitrate content PM2.5 was higher in winter and autumn than that in spring and summer featuring with a diurnal variation of bimodal pattern and spatial north-to-south gradient distribution. The average ratio of nitrate to sulphate contents was in range of 0.97 to 1.06 whilst being between 1.00 and 1.07 on heavily polluted days. The emission sources in Beijing seemed to change from dominantly stationary ones to a combination of both ？xed and mobile ones. The contributions of local sources, external ones and boundary baseline on heavily polluted days accounted for 40%, 44% and 16%, respectively, when secondary transformation and regional transport made more contributions to nitrate concentration in PM2.5 in the air of Beijing.