NH₃ release during the evaporation of different types of atmospheric precipitation: A case study in Changchun, China

Ammonia (NH₃) is a key precursor of secondary inorganic aerosols. During precipitation, NH₃ in the atmosphere can be captured by rain and converted to NH₄⁺, whereas during evaporation, NH₄⁺ can become NH₃ and be released again. The northeastern region of China experiences diverse precipitation types, making the study of the NH₃ release flux and its influencing factors during evaporation highly significant. In this study, precipitation samples of haze (HZ), dust (DS), convective (CC), and monsoon (MN) events were collected three times in Changchun from March to September 2024 (a total of twelve rain events), and indoor simulation evaporation experiments were conducted. The results revealed significant differences in the NH₄⁺ conversion rate (R), NH₃ release flux (F) and release rate (V) across the precipitation types (P < 0.05). The NH₃ flux released from precipitation evaporation was 20.33 µg/m² in spring and 64.53 µg/m² in summer, accounting for approximately 4.14% and 7.70%, respectively, of the corresponding atmospheric NH₃ concentrations. Meteorological factors influenced NH₃ release similarly across precipitation types. R peaked and then decreased with increasing temperature and was significantly negatively correlated with wind speed and precipitation amount (P < 0.05). In addition, this study calculates the temperature coefficient (K₁), wind speed coefficient (K₂), and precipitation amount coefficient (K₃) by considering these factors. These findings provide valuable insights for estimating NH₃ release fluxes from precipitation evaporation in different regions.