Investigating Dual Character of Atmospheric Ammonia on Particulate NH4NO3: Reducing Evaporation Versus Promoting Formation

作者：Hongxiao Huo, Yating Gao, Lei Sun, Yang Gao, Huiwang Gao, Xiaohong Yao · 发表于：Atmosphere · 年份：2025 · DOI：10.3390/atmos16060685 · 被引用次数：4 · 研究领域：Atmospheric chemistry and aerosols、Atmospheric Ozone and Climate、Air Quality Monitoring and Forecasting

Ammonium nitrate (NH4NO3) is a major constituent of fine particulate matter (PM2.5), playing a critical role in air quality and atmospheric chemistry. However, the dual regulatory role of ammonia (NH3) in both the formation and volatilization of NH4NO3 under ambient atmospheric conditions remains inadequately understood. To address this gap, we conducted high-resolution field measurements at a clean tropical coastal site in China using an integrated system of Aerosol Ion Monitor-Ion Chromatography, a Scanning Mobility Particle Sizer, and online OC/EC analyzers. These observations were complemented by thermodynamic modeling (E-AIM) and source apportionment via a Positive Matrix Factorization (PMF) model. The E-AIM simulations revealed persistent thermodynamic disequilibrium, with particulate NO3− tending to volatilize even under NH3gas-rich conditions during the northeast monsoon. This suggests that NH4NO3 in PM2.5 forms rapidly within fresh combustion plumes and/or those modified by non-precipitation clouds and then undergoes substantial evaporation as it disperses through the atmosphere. Under the southeast monsoon conditions, reactions constrained by sea salt aerosols became dominant, promoting the formation of particulate NO3− while suppressing NH4NO3 formation despite ongoing plume influence. In scenarios of regional accumulation, elevated NH3 concentrations suppressed NH4NO3 volatilization, thereby enhancing the stability of particulate NO3− in PM2.5. PMF analysis identi...