A Study Of Atmospheric CH₄ Concentration Spatio-temporal Variation And Its Response To Anthropogenic Emissions In China Based On The Ground-based And Satellite Observations

Methane（CH₄）is the second largest anthropogenic greenhouse gas after carbon dioxide（CO₂）,and it also affects the abundance of other greenhouse gases,thus exacerbating the trend of global warming.However,the global average atmospheric CH₄ concentration has performed an irregular interannual trend,and has increased rapidly in recent years.At this stage,the reasons for the changes of atmospheric CH₄concentration are not clear,and there are still great limitations and uncertainties in the sources and sinks research of CH₄.China is the world’s largest CH₄ emitter and located in the hot spot area of CH₄ concentration.Understanding and mastering the spatio-temporal variation of atmospheric CH₄ concentration and its driving mechanism in China is of great significance for improving the balance of CH₄ sources and sinks,scientifically and effectively formulating CH₄ emissions reduction policies,and then achieving the 1.5℃temperature control target and mitigating regional and even global climate change.This study objectively analyzed the spatio-temporal variation of atmospheric CH₄ concentration in China based on the data observed by ground-based stations and satellite,associated with driving factors about regional human activities,meteorological conditions and natural environment.Meanwhile,based on the EDGAR emission inventory,the spatio-temporal distribution of anthropogenic CH₄ emissions and its driving effect on CH₄ concentration in China were conducted.The major conclusions of this study are as follows:（1）Based on the ground-based observations from three atmospheric background stations in China（including Shangdianzi[SDZ]station in Beijing,Lulin[LLN]station in Taiwan,Waliguan[WLG]station in Qinghai）,while the monitoring data of the global atmospheric background station（Mauna Loa[MLO]station in Hawaii）were selected for comparison,the spatio-temporal variation of atmospheric CH₄concentration and its determinants was analyzed.The results showed that the atmospheric CH₄ concentration at WLG station（R=0.92,P<0.01）and LLN station（R=0.89,P<0.01）was highly similar with that at MLO station,which exhibited a rapid growth trend after 2007.Meanwhile,the atmospheric CH₄ concentration at SDZ station（R=-0.01）was very different from that at MLO station,and its seasonal and monthly dispersion fluctuated greatly,indicating that the variation of atmospheric CH₄ concentration under urban background was more complex.In addition,the CH₄concentration at four stations above mentioned was SDZ station（1948.43±39.20 ppb）>WLG station（1873.17±14.29 ppb）>LLN station（1846.04±24.09 ppb）>MLO station（1825.12±15.23 ppb）,which further confirmed that the atmospheric CH₄concentration in China was higher than the global average.Compared with temperature and wind speed,precipitation had a greater impact on CH₄ concentration.Local anthropogenic CH₄ emissions had a significant positive effect on CH₄concentration at some stations.（2）The Sentinel-5P satellite inversion product showed that the CH₄concentration in China had obvious spatial aggregation and temporal variation characteristics during 2018.Spatially,the CH₄ concentration ranged from 1779.80ppb to 1928.53 ppb,with the high-value areas concentrated in the Tarim Basin,the Turpan Basin,the North China Plain,the middle and lower reaches of the Yangtze River Plain and the Sichuan Basin;while the low-value areas were distributed in the Qinghai-Tibet Plateau and north of Northeast China.Among the different land use types,the value and stability of CH₄ concentration were highest in both impervious surface（1875.28±13.62 ppb）and farmland（1867.48±13.56 ppb）.There existed sensitive areas with high CH₄ concentration and high fluctuation in Shanxi and Tibet,which were presumed to be related to coal mining as well as melting of glaciers and permafrost.In terms of time,the seasonal average of CH₄ concentration was autumn（1863.87±17.68 ppb）>summer（1857.53±16.29 ppb）>winter（1843.43±26.70 ppb）>spring（1841.09±27.15 ppb）,and the highest CH₄ concentration occurred in South Central China during summer and autumn.As a low-value area in the whole country,the CH₄ concentration in the Qinghai-Tibet Plateau increased significantly during both summer（1845.04±14.21 ppb）and autumn（1849.32±14.67 ppb）.（3）The influencing factors of atmospheric CH₄ concentration were investigated based on the Geodetector model,and the results showed that the explanatory power of eight driving factors on the spatial distribution of CH₄ concentration was temperature（0.74）>elevation（0.60）>gross domestic product（0.41）>population（0.35）>sunshine duration（0.20）>precipitation（0.15）>enhanced vegetation index（0.13）>wind speed（0.08）.Besides,the interactive explanatory power of temperature and elevation was the highest（0.82）,which was probably related to the source-sink changes of CH₄ caused by the above factors;while the socio-economic factors had the weakest explanatory power in Northeast and Western China.（4）The anthropogenic CH₄ emissions had obvious spatio-temporal variation over China from 1970 to 2018.In terms of interannual change,it can be roughly divided into four stages:the low value stage with slow growth rate（0.69%）（1970～2001）,the median value stage with high growth rate（3.18%）（2002～2010）,the high value stage with slow growth rate（0.73%）（2011～2014）and the high value stage with slow downtrend（-0.67%）（2015～2018）.Taking Heihe—Tengchong line as the boundary,the spatial distribution of anthropogenic CH₄ emissions presented high in the east and low in the west.Meanwhile,the center of gravity of anthropogenic CH₄ emissions had been transferred from Hubei to Henan province.For the long-term trend,anthropogenic CH₄ emissions performed uptrends in most areas,with positive sustainability.The areas with the largest uptrend and downtrend were the North China Plain and Southeast China respectively.From the response of CH₄ concentration to anthropogenic emissions,the eastern region had the characteristics of obvious high emissions and high concentration,the Qinghai Tibet Plateau and north of Northeast China had the characteristics of obvious low emissions and low concentration;while three major basins in Xinjiang（Tarim,Junggar and Turpan Basin）showed the abnormal phenomenon of low emissions and high concentration,which presumed to be related to the underestimation of CH₄ emissions from the oil and natural gas systems.In 2018,the total anthropogenic CH₄ emissions in China reached 64.48million tons,of which the emission from energy activities accounted for a large proportion（40.77%）,followed by the agricultural activities emission（34.75%）,and finally the waste treatment emission（24.48%）.