| Black carbon（BC）,as the product of incomplete combustion of carbon-containing substancesas,its positive climate forcing is second only to CO2.Due to small particle size,large specific surface area and radiative forcing,BC seriously affects to human health,as well as regional and global environment and climate.As a sensitive and significantly influencing zone of global climate change,China’s BC emission is at a high level,which brings great pressure to China in the international climate negotiations.The objectives of the this paper are to（1）explore long-term trends and spatial differentiation patterns of atmospheric BC concentrations in China at the pixel,provincial,regional and national scales during 1980-2019 based on ground-based observations and MERRA-2 reanalysis dataset;（2）identify BC total emissions,spatial evolutions as well as anthropogenic sectorial distributions,and discuss the applicabilities and differences of multi-source BC emissions inventories in China from a spatial-temporal perspective;（3）evaluate the spatio-temporal correlation characteristics between atmospheric BC concentrations and emissions in China quantitatively,and discuss the influencing mechanism of seasonal meteorological conditions and regional transports,taking Shanghai Pudong Station as an example.The main results of this paper are as follows:（1）The MERRA-2 BC concentrations generally present a good correlation（R=0.61）with 852 monthly ground observations from 64 stations around China,with the highest accuracy in Southwest（R=0.91）and the lowest in Central South（R=0.05）.The long-term variation trends of atmospheric BC concentrations over China can be divided into three stages:（1）the“low value”stage of slow growth（1.68%）（1980-1999,0.91±0.1μg/m~3）,（2）the fluctuating“median value”stage of high growth（4.44%）（2000-2007,1.28±0.13μg/m~3）and（3）the“high value”stage of slow downtrend（-0.87%）（2008-2019,1.32±0.06μg/m~3）.In terms of spatial differentiation,the atmospheric BC concentrations show a clear pattern of high in the east and low in the west,dividing by the Hu Line,a geographical demarcation line of population density and urbanization around China,and form three BC high-value areas in Sichuan Basin,Northern Henan area and Beijing-Tianjin-Hebei（BTH）region.The areas with fastest growth are mainly distributed in the ground elevation ranged 0-500 m,with an annual-averaged growth rate of 3.47%.The growth rate is close to zero as the ground elevation increases.The pixel-scale Mann-Kendall trend test shows that significant overall uptrends are detected in MERRA-2BC concentrations over China,especially during 1980-1999 and 2000-2007.Whereas,a downward trend is appeared in the plains and basins of southeast China during 2008-2019.The average atmospheric BC concentrations under different land use types over China from high to low are construction land,arable land,woodland,water,grass and unused land.（2）China’s annual BC emissions vary greatly among multi-source inventories because of activity data and emission factors,with ratio between pairwise inventories ranging from 0.61 to 1.65 in 2010.The annual-averaged emission in China estimated by PKU-2020 is the highest（1719.63 Gg）,while EDGAR is always the lowest（919.99 Gg）.The monthly BC emissions over China show a“U”-shaped trend presented as winter（554.67 Gg）>spring（364.16 Gg）>autumn（360.92 Gg）>summer（318.83 Gg）.From1970 to 2015,the standard deviation ellipse（SDE）area of China’s BC emissions decreases by 85,000 km~2 with higher spatial differentiation in the north-south direction than east-west.North China,East China and Central South are three main contributors of China’s BC emissions,resulting in the SDE extending to the northeast and rotating counterclockwise.China’s BC emission center is always located in Henan with larger and faster eastward movement.The multi-source inventories show a consistent temporal trend and all appear a peak during 1995-1998.（3）Multi-source inventories show that the largest anthropogenic emission sector over China is residential.The average contributions of main anthropogenic emission sectors are residential 49.6%-79.86%,industry 5.21%-33.46%,transportation 2.49%-18.66%,and power generation 0.09%-10.72%.The contributions of transportation and power generation increase,while those of residential decrease,and industry rise and then fall.Anthropogenic emission sectors present obvious seasonal variation characteristics.BC emissions are influenced by residential and industry in spring,summer and autumn.Nevertheless,residential has the greatest impact in winter with an average contribution of61.29%.The contribution of power generation in summer（0.12%）is slightly higher than that in other seasons（0.08%-0.11%）.In 2008,the largest emission sectors of 70.97%provinces are all residential and the rest are industrial sectors.By 2017,transportation makes the biggest contributions to the emissions of Beijing,Tianjin,Shandong,Jiangsu,Shanghai,Zhejiang and Guangdong.（4）In general,both atmospheric BC concentrations and emissions over China show a fluctuating trend.There is a significantly positive correlation between atmospheric BC concentrations and emissions during 1980-2015 in China（r=0.9;p<0.01）,with annual-averaged growth rate of 1.84%and 2.07%,respectively.The atmospheric BC concentrations and emissions show a notably positive correlation in Northeast（ρ=0.93;p<0.01）and Northwest（ρ=0.92;p<0.01）.However,North China is 0.79（p<0.05）,maximal information coefficient（MIC）is 0.55.As a BC emission center,Henan is also a high-value areas of BC concentrations.The peak time of atmospheric BC concentrations and emissions in 26.33%areas over China is the same stage,mainly distributed in Xinjiang,northern Tibet and western Qinghai.The peak time over China shows a clear pattern of west later than east.The effect of different meteorological factors on atmospheric BC concentrations from strong to weak is temperature,boundary layer height,relative humidity,wind speed and precipitation.Different seasonal regional transports make seasonal influence on atmospheric BC concentrations over China. |
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