Dry deposition of ammonia around paddy fields in the subtropical hilly area in southern China
This study measured the ammonia (NH3) concentration and dry deposition within 100 m around paddy fields (0.6 ha) with double rice cropping in the subtropical hilly area in southern China, with the aims to quantify the dry deposition of NH3 around the emission source and to clarify its temporal and spatial variability. The results showed that high NH3 concentrations were found during the 15 d after nitrogen (N) fertilizer application at downwind sites within 100 m around the paddy fields, and the NH3 concentrations were 12–62, 2.8–7.3, 13–38, and 4.9–36 μg N m−3 during the 15 d after basal fertilizer application and topdressing in the early rice season and after basal fertilizer application and topdressing in the late rice season, respectively. The NH3 concentrations were relatively low (1.5–3.8 μg N m−3) during other periods of the rice season at the downwind sites, which indicated that N fertilizer application in paddy fields highly affected the NH3 concentration at downwind sites. The NH3 concentrations at the downwind sites decreased significantly with the increase in distance from the paddy fields. The total NH3 dry deposition around 100 m of the paddy fields accounted for approximately 79% and 81% of the emitted NH3 from the paddy fields in the early and late rice seasons, respectively. The results indicate that dry deposition of NH3 around emission sources may be an important way to remove the NH3 volatilized from croplands in this subtropical hilly area.
