Dry Atmospheric Deposition Of Nitrogen Into Inner Mongolia

As the largest developing country,China has experienced rapid economic development after the reform and opening up,and the emission of anthropogenic ammonia and nitrogen oxides has increased linearly,and most of the reactive nitrogen emitted to the environment will return to the surface through dry deposition and wet deposition.Excessive input of exogenous nitrogen will lead to acidification and eutrophication of soil and water bodies,which will directly or indirectly lead to a series of environmental problems such as loss of biodiversity.There are relatively few reports on the dry deposition of nitrogen in Inner Mongolia.Therefore,in order to clarify the characteristics of atmospheric nitrogen dry deposition in Inner Mongolia,this study established a monitoring network of atmospheric nitrogen dry deposition in Inner Mongolia,covering various ecological types,including urban,forest,grassland,farmland and rural areas.The regional dry deposition of nitrogen from December 2020 to November 2021 was estimated using the extrapolation method,and the spatial and temporal distribution characteristics of dry deposition at the regional scale were initially analyzed,and the mechanisms of the influence of emission sources as well as meteorological factors on the dry deposition were explored.Based on our study,the following conclusions were obtained.Among the 12 monitoring sites in Inner Mongolia,the annual mean concentrations of NH₃and NO₂varied in the ranges of 2.72-29.76μg N m^-3and 1.02-5.24μg N m^-3,respectively,and the annual deposition amounts were 1.70-31.53 kg N ha^-1yr^-1and0.04-3.20 kg N ha^-1yr^-1,both of which exhibited large spatial variability characteristics.Divided by different land use types,the total atmospheric reactive N concentrations and deposition showed farmland>urban>rural>grassland>forest.The atmospheric NH₃,NO₂and total dry deposition in the whole region were 11.40,1.26 and 12.66 kg N ha^-1yr^-1,respectively,and NH₃deposition was the main mode of nitrogen dry deposition in Inner Mongolia,accounting for about 90%of the total.Atmospheric reactive nitrogen concentrations and deposition showed relatively obvious seasonal differences,with NH₃generally higher in summer and lower in winter,and NO₂generally higher in autumn and winter than in summer.The causes are mainly the differences in meteorological conditions and the intensity of emission sources in different seasons.The ratio of reduced to oxidized nitrogen in atmospheric reactive nitrogen concentration and dry deposition is 5.40 and 13.55,respectively,which indicates that there is more serious ammonia emission in Inner Mongolia and has a great influence on atmospheric nitrogen dry deposition.On the other hand,meteorological factors also have some influence on the dry deposition characteristics in the region.The effect of temperature on NH₃concentration and deposition is positive,mainly because high temperature promotes ammonia volatilization from soil,plants,and human and animal excreta,which increases the atmospheric ammonia concentration and thus shows high deposition;temperature has no significant effect on NO₂concentration and deposition.Precipitation may dissolve NH₃present in the air and reduce the atmospheric ammonia concentration and deposition,but the effect is not significant,and precipitation does not appear to have a significant effect on NO₂.