Modeling of reducing NH4NO3 in PM2.5 under high ammonia emission in urban areas: Based on high-resolution data

At present, the air quality in urban areas in China has continued to improve, but PM2.5 is still severely polluted in autumn and winter and is difficult to meet the Chinese standard. With the renovation of coal-fired boilers and the transformation of ultra-low emissions in factories, NO3− has gradually become the main inducing species for high levels of PM2.5. In this study, a high-resolution (1 h) online instrument was used to analyze the characteristics of atmospheric PM2.5 in the autumn and winter periods from October 2019 to February 2020 at Zhengzhou University in Zhengzhou. The inorganic nitrate in PM2.5 mainly existed in the form of semivolatile NH4NO3, and the method of reducing NH4NO3 was studied through data analysis. The basic method of reducing particulate nitrate in PM2.5 is not only to reduce nitrate precursors (NOx) but also to transform particulate nitrate into gas by reducing the aerosol pH value (enhancing aerosol acidity). The simulation analysis of NHx (NHx = NH3+NH4+), NO3T (NO3T=HNO3+NO3−), and SO42− reduction using the thermodynamic model ISORROPIA-II revealed that total ammonia (TA) has an obvious peak clipping effect on particulate NO3− when it is reduced by 60% and can effectively reduce NH4NO3 in PM2.5. The reliability and credibility of the data results were enhanced through long-term observation and local time analysis, and reducing TA and NO3− in areas with high ammonia emissions was proven to be feasible. This study is beneficial for formulating measures to reduce the average annual concentration of PM2.5 in ammonia-rich areas.