资源环境科技发展态势分析平台

Particulate nitrate (NO3-) not only influences regional climates but also contributes to the acidification of terrestrial and aquatic ecosystems. In 2016 and 2017, four intensive online measurements of water-soluble ions in PM2.5 were conducted in Nanjing City in order to investigate the potential formation mechanisms of particulate nitrate. During the sampling periods, NO3- was the predominant species, accounting approximately for 35 % of the total water-soluble inorganic ions, followed by SO42- (33 %) and NH4+ (24 %). Significant enhancements of nitrate aerosols in terms of both absolute concentrations and relative abundances suggested that NO3- was a major contributing species to high-PM2.5 events (hourly PM2.5 >= 150 mu g m(-3)). High NO3- concentrations mainly occurred under NH4+-rich conditions, implying that the formation of nitrate aerosols in Nanjing involved NH3. During the high-PM2.5 events, the nitrogen conversion ratios (F-n) were positively correlated with the aerosol liquid water content (ALWC; R > 0.72 and p < 0.05). Meanwhile, increasing NO(3)(-)concentrations regularly coincided with increasing ALWC and decreasing O-x (O-x = O-3 +NO2). These results suggested that the heterogeneous reaction was probably a major mechanism of nitrate formation during the high-PM2.5 events. Moreover, the average production rate of NO3 by heterogeneous processes was estimated to be 12.6 % h(-1) (4.1 mu g m(-3) h(-1)), which was much higher than that (2.5 %h(-1); 0.8 mu g m(-3) h(-1)) of gas-phase reactions. This can also explain the abrupt increases in nitrate concentrations during the high-PM2.5 events Utilizing the ISORROPIA II model, we found that nitrate aerosol formation in Nanjing during the high-PM2.5 events was HNO3 limited. This indicated that control of NOx emissions will be able to efficiently reduce airborne particulate nitrate concentrations and improve the air quality in this industrial city.