Temporal and spatial patterns of nitrogen wet deposition in different weather types in the Pearl River Delta (PRD),...

The temporal and spatial patterns of nitrogen wet deposition were investigated in the Pearl River Delta (PRD) under different weather types. The study was carried out in 27 monitoring sites with reliable meteorological data from 2010 to 2017. Large spatial variation data showed that both annual volume weighted mean (VWM) concentrations and fluxes were higher in the central PRD while lower in the outer area. The annual mean concentrations and fluxes were in the range of 0.8-1.3 mg N L^-1 and 10.9-20.6 kg N ha^-1 yr^-1, respectively. The monthly mean concentrations and fluxes ranged from 0.1 to 0.2 mg N L^-1 and 0.4 to 2.4 kg N ha^-1, respectively. Further the study data revealed that the ratio of NH₄⁺/NO₃^- was 1.1 which was much lower than the ratio reported in other regions like Northern China, Sichuan Basin, the US and Europe. The flux of NH₄⁺ in urban sites was comparable to rural sites, implying that potential non-agricultural NH₃ emissions were likely to be high in the PRD. The top three weather types were E, C and SE, with the total contribution of more than a half to the flux. Multiple linear regression was used to set up an equation to predict the variation of annual fluxes under the changes in weather conditions. The result hints that the variation on annual fluxes in the PRD tends to be stable in the next 30 years. Considering the increasing impact on the ecosystem, more effort should be exerted to reduce nitrogen wet deposition in the future.