环境地球化学国家重点实验室知识库

Enhanced ammonia (NH3) emissions and deposition caused negative effects on air quality and ecosystems. Precipitation is an efficient pathway to remove NH3 and particulate ammonium (p-NH4+) from the atmosphere into ecosystems. However, precipitation scavenging of p-NH4+ in chemical transport models has often considered fine p-NH4+, with inadequate constraints on NH3 and coarse p-NH4+. Based on distinct delta N-15 values between NH3 and NH4+ in PM2.5 (particulate matters with aerodynamic diameters <= 2.5 mu m) or TSP (total suspended particulates), this paper interpreted intra-event variations of precipitation NH4+ concentrations and delta N-15 values (delta N-15-NH4+ values) at Guiyang (Xiao et al., 2015). Generally decreased NH4+ concentrations across rain events reflected decreasing scavenging of NH3 and p-NH4+. Using a Bayesian isotope mixing model, we found that differing contributions between N-15-depleted NH3 and N-15-enriched p-NH4+ were responsible for the three-stage variations of intra-event delta N-15-NH4+ values. The decreases of delta N-15-NH4+ values across the first and third stages indicated more decreases in scavenging p-NHZ than NH3, while the increases of delta N-15-NH4+ values across the second stage were resulted primarily from more increases in scavenging p-NH4+ (particularly fine p-NH4+) than NH3. These results stressed influences of differing scavenging between NH3 and p-NI-14- on precipitation delta N-15-NH4+ values, which should be considered in modeling precipitation scavenging of atmospheric p-NH4+.