Ammonia Nitrogen Pollution Characteristics of Natural Rainfall in Urban Business District in Southern China: A Case Study of Chengdu City

Chengdu city was chosen as the representative of southern cities in China in this work, characteristics of ammonia nitrogen (NH₃-N) pollution in natural rainfall were analyzed by measuring the concentration in 15 natural rainfalls from April to September in 2017. The influence of ammonia emission from toilet vent of building on NH₃-N pollution in rainfall was investigated, and the variation of total NH₃-N pollutants and its influencing factors were expounded. The results showed that the average concentration of NH₃-N in first rainfall was the highest, reaching 18.2mg/L, the average concentration of NH₃-N in the subsequent 14 rainfalls was between 2.0 and 5.0mg/L, which is higher than Grade V (?2mg/L) of Environmental Quality Standards of Surface Water (GB 3838-2002), and was an important source of NH₃-N pollution in water. The concentration of NH₃-N in natural rainfalls decreased with the increase of the distance between the sampling point and the toilet vent, indicating that the ammonia discharged from toilet exhaust is a major source of NH₃-N pollution in urban atmosphere. The main factors affecting total NH₃-N pollutants in natural precipitation include rainfall intensity, rainfall duration and drought days. The total amount of NH₃-N pollutants in surface runoff is less than that in natural rainfall.