| Atmospheric methane(CH4)is the second most important greenhouse gas only after carbon dioxide(CO2),and it is a chemically active gas and organic trace gas.It has high concentration and long life,which has an important impact on global climate change and atmospheric environment.China is a major emitter of CH4,understanding the emission and concentration characteristics of it is of great significance for scientifically and effectively controlling CH4 emissions,slowing down the greenhouse effect and climate change.The research area is focused on China,we studied the temporal and spatial variation of atmospheric CH4 concentration in China through observation data analysis.We also used statistical methods and dynamic methods to establish a methane emission inventory in China and analyze its emission characteristics.We combined the improved model RegAEMS and dynamic CH4 emission inventory to simulate the temporal and spatial distribution characteristics of CH4 concentration in China.The main results are shown as follows:Firstly,based on satellite and ground-based observations,the spatial distribution characteristics and temporal variation of atmospheric CH4 in China are studied.The results show that China’s CH4 concentration is high in the north and low in the south through 2013-2018 AIRS satellite data analysis.The high-value(1900～1950ppb)areas are mainly concentrated in Heilongjiang,Inner Mongolia,Shanxi,Qinghai,northern Xinjiang and Sichuan.While the low-value(1800～1850ppb)areas are mainly distributed in the Tarim Basin and the Qinghai-Tibet Plateau.The concentration of CH4 in the vertical direction decreases with height,and which in the northern hemisphere in the troposphere is significantly higher than that in the southern hemisphere.The concentration distribution in the northern and southern hemispheres in the stratosphere and above is basically symmetrical.It also has obvious seasonal variation characteristics,and the concentration reaches the maximum in summer and autumn,and the lowest in winter and spring.Through the ground-based observation analysis of Nanjing site,we found that the diurnal variation of CH4 is obvious,which is characterized by lowest value in the daytime and highest value at night.The seasonal variation is characterized by the highest in summer(2052ppb),the second in autumn(2019ppb),and the lowest in winter(1921ppb).With Hysplit model,backward trajectory was found vary from season to season.In summer,it is mainly affected by the transmission of short-and medium-distance air masses.The long distances air mass in winter is from northern,and locally is only 35%.The paths in spring and autumn are very similar.In the spring,about 66%of the local air masses come from the central and eastern parts of Jiangsu Province.While in autumn,about 29%of the long-distance air masses come from the inland areas of the north,passing through Jiangsu’s local short-distance transmission,the air mass ratio is about 61%.Secondly,based on statistical and dynamic methods,the emission inventory of atmospheric CH4 in China is compiled and its variation characteristics are analyzed.Results show that the total methane emission in China is 61.59 Tg in the year of 2015.Agricultural and energy activities were the main sources of emissions,reaching 20.42 Tg and 20.39 Tg,respectively,accounting for 33.2%and 33.1%of the total emissions.Vegetation and wetland emissions are considered in the natural sources,and the emissions from natural sources is 11.77Tg,accounting for 19.1%.Waste treatment contributes 8.64 Tg to the total emission,accounting for 14.0%.The amount of emissions from artificial wetland is 0.37 Tg,accounting for 0.6%.We found that the CH4 emissions are heterogeneously distributed over China,and the distribution is closely related to local resources and environment,population density and the economic situation.Large emissions are concentrated in North China,Southwest China and Southeast China,while the emissions over Northwest China’s are relatively low.Finally,with the combination of improved regional atmospheric environment model and the dynamic CH4 emission inventory,we studied the temporal and spatial distribution characteristics of CH4 concentration in China.The simulation results and observations in 2016 were verified to have a FAC2 value of 1,MG of 1.0437,FB of 0.0453,hourly RMSE of 0.2298,correlation coefficient of 0.3325,daily mean RMSE of 0.0370,and correlation coefficient of 0.3894.The simulation results of the inferred model are basically reliable.In terms of time change,the seasonal variation of the simulation results is high in summer and low in winter.The highest value appears in July,while the low value appears in December,which is basically consistent with the monthly variation of observation data.The model diurnal variation of the atmospheric CH4 displayed a very clear cycle,generally with the lowest value in the daytime and the highest at night,which is consistent with the variation of the observed values.The peaks are reached at 6 and 7 o’clock and the concentration is reduced to the lowest at around 16 o’clock.In the perspective of spatial distribution,it is affected by the distribution of methane emission,the variation of seasonal OH radical concentration,the change of wind field and the topographical effect.The overall distribution is characterized by high in the southeast and low in the northwest.The main low-value area is located in the Qinghai-Tibet Plateau.The overall CH4 concentration is the largest,and the overall CH4 concentration is the smallest in spring.In summary,we analyzed the spatial distribution characteristics and temporal variation of atmospheric CH4 in China,and established an emission model of various atmospheric CH4 emission sources,combined the improved regional atmospheric environment model and dynamic inventory to studied the characteristics and causes of atmospheric CH4 variation in China.The research results can provide a scientific basis for controlling atmospheric CH4 emissions in China,and provide technical basis for future CH4 climate and atmospheric environmental problems. |
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