Source-Directional and Micrometeorological Influences on Short-Term NH3 Variability in a Livestock- and Agriculture-Influenced Peri-Urban Environment

Atmospheric ammonia (NH3) is an important alkaline precursor of secondary inorganic aerosols, but its variability in livestock- and agriculture-influenced peri-urban environments remains poorly constrained. In this study, atmospheric NH3 was measured at a peri-urban site in Chuncheon, South Korea and its variability was examined in relation to micro-meteorology, source direction, and surface–atmosphere exchange. Mean NH3 concentrations were 200.8 ± 91.1 ppb during the April campaign, 83.0 ± 34.4 ppb during the May campaign, and 27.9 ± 16.2 ppb during the December campaign, indicating higher NH3 levels during the April and May campaigns than during the December campaign. Campaign-specific correlation analyses showed that the relationships between NH3 and micrometeorological variables differed among the observation periods, with robust associations observed in April and May but not in December. Moreover, the higher NH3 concentration in the April campaign than in the May campaign, despite the lower mean temperature, indicates that the observed variability was not controlled by temperature alone. Conditional probability function analysis showed that elevated NH3 concentrations in the April and May campaigns were mainly associated with southwesterly winds, suggesting the influence of nearby livestock and agricultural sources. The Penman–Monteith-derived latent heat flux further showed that daytime NH3 enhancement coincided with evaporative surface-exchange conditions potentially favorable for volatilization, although it did not directly quantify manure-derived NH3 emissions. In contrast, the December campaign showed lower NH3 concentrations, weaker source-directional patterns, and limited latent heat flux influence, suggesting suppressed volatilization and intermittent local accumulation under stable conditions. These results indicate that the conditions associated with short-term NH3 variability differed among the selected campaigns, reflecting complementary influences of source direction and campaign-specific micrometeorological and surface-exchange conditions, highlighting the need for concurrent gas- and particle-phase measurements to assess potential implications for PM2.5 formation.