Organic nitrogen deposition in precipitation in metropolitan Guangzhou city of southern China

Organic nitrogen (N) has been shown to be an important component of atmospheric N deposition. However, its contribution to total N deposition and its sources have not been well investigated under severe air N pollution. We quantified dissolved inorganic and organic N deposition in bulk precipitation over two years in Guangzhou, a city suffering from long-term acid rain in southern China, and linked organic N to other atmospheric components to explore the potential sources. We found that dissolved organic N (DON) in precipitation contributed a considerable amount of N (8.1 and 8.4 kg N ha− 1 yr− 1 in 2008 and 2009, respectively) to total N deposition in the study city, although the percentage to total dissolved N (17–21%) was lower than often reported (approximately 30%). Including DON, precipitation N deposition in the study city reached 39–49 kg N ha− 1 yr− 1, suggesting an important N source to natural ecosystems. We also found that DON concentration was positively correlated with both ammonium and nitrate concentrations, indicating their anthropogenic sources. The anthropogenic source of DON was further supported by close correlations of DON with precipitation non-sea-salt sulfate concentration and with air concentration of nitrogen and sulfur oxides. Our results suggest that atmospheric DON deposition may also be considerable in many other cities.