亚热带丘陵区稻田周边氨气干沉降研究

Dry deposition of ammonia around paddy fields in the subtropical hilly area in southern China

农业源在氨(NH3)排放清单中占比较大,但农业排放的NH3是否全部进入大气亟待评估。本文选择亚热带丘陵区双季稻田为研究对象,研究了农田排放NH3的去向和沉降过程。结果表明,稻田(0.6 ha)下风向100 m范围较高的NH3浓度主要出现在施用基肥和追肥后15 d内。随着距稻田距离的增加,下风向大气中NH3浓度呈指数下降。稻田下风向100 m范围内NH3沉降量约占挥发量的80%,表明近源沉降是亚热带丘陵区稻田排放NH3的重要汇机制。该机制大幅减少了农业排放NH3进入大气的总量,应该在清单编制过程中予以考虑,以期客观评价农业排放对大气污染的潜在影响。

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 100maround the paddy fields,and the NH3 concentrations were 12–62,2.8–7.3,13–38,and 4.9–36μg 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–-3.8μg 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.