Positioning Observation And Regional Simulation Of Atmospheric Nitrogen Emission And Deposition

The atmospheric ammonia and nitrogen oxides emissions in China are serious,and the atmospheric nitrogen deposition has an important impact on the atmospheric environment and ecosystem.Therefore,it is of great scientific significance to carry out the positioning observation and regional simulation of atmospheric nitrogen emission and deposition.In this paper,the gradient concentration distribution of atmospheric pollutants in Xianlin area and the variation characteristics of ammonia emission and deposition fluxes in farmland of Nanjing are analyzed by means of field observation and numerical simulation.The differences of calculation schemes affecting dry deposition fluxes and the correlation between ammonia volatilization and deposition in farmland are discussed.RegAEMS,a regional atmospheric environment simulation system with organic nitrogen module added,is used to simulate the atmospheric environment in China.The atmospheric nitrogen deposition in the region was simulated.The main results are as follows:Firstly,the gradient concentration distribution and dry deposition flux of atmospheric pollutants were analyzed based on the observation data of tower gradient of common pollutants in Xianlin area of Nanjing from September 2016 to September 2017.The results show that the dry deposition velocities of air pollutants in Xianlin area of Nanjing are:CO 0.038 cm/s;SO2 0.27cm/s;NO 0.019cm/s;NO2 0.089 cm/s;O3 0.449 cm/s;PM2.5 0.147 cm/s,respectively.Dry deposition velocity has obvious diurnal variation characteristics.Generally,it is larger in daytime than at night,and the maximum value appears in the afternoon.The average dry deposition fluxes of SO2,NO,NO2,O3,CO and PM2.5 calculated by concentration method and gradient method are 0.037,0.005,0.036,0.271,0.273 and 0.056μg·m-2·s-1,respectively.The results of calculation of dry deposition flux by comprehensive concentration method and gradient method show that for NO,O3and PM2.5,the correlation coefficients are 0.438,0.225 and 0.392,respectively.For NO2,SO2 and CO,the correlation coefficients are 0.020,0.015 and 0.101,respectively.When calculating the dry deposition flux,different methods should be selected according to the actual equipment.Both methods can be applied to the numerical model.Secondly,based on the data collected from the field ammonia volatilization and deposition experiments in May-August 2017 and May-August 2018,as well as the ammonia concentration data in the atmosphere near the farmland,the effects of different treatments(normal planting,peanut intercropping,straw mulching,double row spacing)on ammonia volatilization emission reduction were analyzed.The results of field experiments in 2017 showed that the ammonia volatilization fluxes of normal planting group,peanut intercropping group,straw mulching group and double row spacing group were 1481.6 μg·m-2·h-1,1409.4 μg·m-2·h-1,and 1472.5 μg·m-2·h-1,1472.7 μg·m-2·h-1,respectively.Field experiments in 2018 showed that ammonia volatilization fluxes in normal planting group,peanut intercropping group and straw mulching group were as follows:2033.02 μg m-2·h-1,2050.35 μg·m-2·h-1,2102.45μg·m-2·h-1.Compared with 2017,the volatilization flux of farmland ammonia increased in 2018,which was consistent with the high concentration of ammonia.The average concentration of ammonia in the atmosphere was 69.57 μg/m3 in the observation experiment in 2017.The average dry deposition flux of ammonia in the whole observation period was 855.03μg·m-2·h-1,and the average dry deposition velocity of ammonia was 0.34cm/s.The average concentration of ammonia in the atmosphere was 91.56μg/m3 in the observation experiment in 2018.The average value of dry deposition flux of ammonia in the whole observation period was 1273.20μg·m-2·h-1.The average value of dry deposition velocity of ammonia was 0.38 cm/s.The difference of dry deposition flux of ammonia in the two-year experiment was mainly caused by the increase of ammonia concentration.In the observation experiment of 2017,the average net ammonia volatilization flux of normal planting treatment,peanut intercropping treatment,straw mulching treatment and double row spacing treatment were 684.17μ·m-2·h-1,373.18 μg· m-2·h-1,1472.51 μg·m-2·h-1,and 0.1875μg·m-2·h-1.In the observation experiment of 2018,the average net volatilization flux of ammonia in normal planting treatment,peanut intercropping treatment and straw mulching treatment was 823.60·g·m-2·h-1,713.27μg·m-2·h-1 and 810.09μg ·m-2·h-1.Two-years research showed that different crop intercropping and treatments had different effects on the volatilization of NH3 in the field,and peanut intercropping had better effects on inhibiting the volatilization of NH3 in the field.Finally,through the improvement of dry deposition module and organic nitrogen module in RegAEMS,the concentration distribution of monomethylamine,dimethylamine and trimethylamine was quantitatively analyzed.The national atmospheric nitrogen deposition in 2016 was simulated,and the proportion of organic nitrogen and inorganic nitrogen components and the contribution of dry and wet deposition were estimated.In the simulation results of organic nitrogen concentration,the concentration range of MMA is about 0.006-0.03 μg/m3,that of DMA is about 0.006-0.06μg/m3,and that of TMA is about 0.001-0.03μg/m3.In2016,the mean total deposition flux of methylamine substances was 0.015 kg N ha-1·yr-1,of which the dry deposition flux was 0.006 kg N ha-1·yr-1 and the wet deposition flux was 0.009 kg N ha-1·yr-1.The average value of total deposition flux of atmospheric organic nitrogen is 1.785kg N ha-1·yr-1,of which the dry deposition flux is 0.78kg N ha-1·yr-1,accounting for 41.3%,and the wet deposition flux is 1.005 kg N ha-1·yr-1,accounting for 58.7%.In 2016,the average value of total deposition flux of inorganic nitrogen in China was 12.361 kg N ha-1·yr-1,of which the dry deposition flux was 8.941 kg N ha-1·yr-1,accounting for 72.3%,and the wet deposition flux was 3.420kg N ha-1·Yr-1,accounting for 27.7%.In 2016,the total amount of atmospheric nitrogen deposition in China was 14.146 kg N ha-1·yr-1,of which the dry deposition flux was 8.590 kg N ha-1·yr-1,accounting for 60.7%,and the wet deposition flux was 5.556 kg N ha-1·yr-1,accounting for 39.3%.The total organic nitrogen deposition flux was 1.785 kg N ha-1·yr-1,accounting for 12.6%,and the total inorganic nitrogen deposition flux was 12.361 ha-1·yr-1,accounting for 87.4%.