Estimation Of Area And Livestock Point Sources NH₃ Emissions In China Based On Satellite Observations

As an important alkaline gas in the atmosphere,ammonia（NH3）has attracted considerable attention due to its excessive emissions and negative impacts on the environment and human health.The formulation and evaluation of NH3 emission reduction policies in China require accurate estimation of ammonia emissions.Existing NH3 emission inventories are typically constructed using a bottom-up approach,which has significant uncertainties and cannot fully capture the spatiotemporal characteristics of NH3 emissions.In contrast,top-down NH3 emission estimation methods based on remote sensing data offer advantages in terms of timeliness and spatial continuity.China is a hotspot region for NH3 emissions,yet research on NH3 emission retrieval based on remote sensing in China is limited and needs further exploration.This study estimates the NH3 emissions from area sources and confined livestock point sources in China using a top-down approach based on satellite observations.The study utilizes NH3 columns obtained from the IASI during 2008-2020,in conjunction with the GEOS-Chem atmospheric chemistry transport model and Random Forest model,to establish a non-point source NH3 emission estimation model for China.Additionally,the study improves the one-stage atmospheric box model used to estimate NH3 emissions from confined livestock point sources.Additionally,an improved first-order atmospheric box model is developed for estimating NH3 emissions from livestock point sources.The study calculates NH3 emissions from regional sources and feedlot point sources in China and analyzes their spatiotemporal patterns and associated influencing factors.The main conclusions are as follows:（1）A top-down NH3 emission estimation model for area sources in China is constructed based on the GEOS-Chem model and Random Forest model.The model performed well on the validation set,with an R²=0.86,RMSE=0.34 kg N ha^-1,and MAE=0.16 kg N ha^-1.The top-down estimated NH3 emissions are compared with the EDGAR,REAS,and MIX emission inventories for major regional and hotspot sources in China,showing high consistency with the bottom-up results（REAS and MIX）.（2）The regional distribution characteristics of non-point sources NH3 emissions in China were clarified.The key regions for NH3 emissions from non-point sources in China are the North China Plain,Sichuan Basin,Northeast Plain,and northwestern Xinjiang were key regions for non-point sources NH3 emissions.Different spatial distributions of land use types had distinct characteristics of regional sources NH3emissions,with the order of emission intensities being urban areas(43.85 kg N ha^-1,0.15 Tg N),agricultural land(43.47 kg N ha^-1,8.17 Tg N),forest land(14.71 kg N ha^-1,3.0 Tg N),grassland(8.12 kg N ha^-1,2.74 Tg N),water bodies(14.71 kg N ha^-1,0.03Tg N),and bare land(1.02 kg N ha^-1,0.21 Tg N).This demonstrated the importance of agricultural areas as major NH3 emission sources in China.（3）The temporal variation characteristics of non-point source NH3 emissions in China were clarified.During 2008-2020,the total NH3 emissions in China showed an increasing trend(0.3 Tg N yr^-1),rising from 10.42 Tg N in 2008 to 14.31 Tg N in 2020.Chinese non-point sources NH3 emissions remained relatively stable between 2008 and2011(0.01 Tg N yr^-1)but increased significantly from 2012 to 2020(0.43 Tg N yr^-1),especially in the North China Plain and Sichuan Basin,while some areas in the Qinghai-Tibet Plateau showed a slight decreasing trend.Overall,the NH3 emissions exhibited distinct seasonal characteristics,with the highest emissions in summer（3.6 Tg）,followed by spring（2.92 Tg）,autumn（2.61 Tg）,and winter（2.5 Tg）.（4）NH3 emissions from limited livestock point sources in China are estimated based on an improved first-order atmospheric box model considering background emissions.The spatial distribution map of limited-scale farm point sources in China is supplemented by POI search,showing a higher number of feedlots in the eastern regions and fewer feedlots in the western regions.Subsequently,NH3 emissions from livestock point sources are estimated from top-down using IASI-NH3 columns and the improved box model.The results showed that the average emission intensity of livestock point sources in 2020 was 26.45 kg N ha^-1,with a range between 1.41 kg N ha^-1 and 117.13kg N ha^-1.（5）The temporal variation characteristics of NH3 emissions from confined livestock point sources in China were clarified,and the changes in NH3 emissions from specific feedlot sources are analyzed as examples.NH3 emissions with confined livestock point sources in China generally showed an increasing trend(2.3 kg N ha^-1 yr^-1)during 2008-2020.The seasonal characteristics of fthe point source emissions are higher in summer and lower in autumn and winter.The analysis of NH3 emissions from example livestock point sources reveals differences in emission changes compared to the overall trend.（6）The NH3 emissions from livestock point sources were assessed using the top-down method and compared with bottom-up emission inventories for livestock emissions.The comparison focused on the median regional NH3 emissions from livestock point sources calculated at the city level.In approximately 58.2%of the cities,the NH3 emissions estimated from point sources using IASI were within four times of those obtained from REAS.In comparison to the EDGAR inventory,the results show that only 36.51%of the cities had IASI-based estimates within four times.The comparison results indicate significant underestimation of NH3 emissions from livestock sources in China by both types of emission inventories.This study constructs and improves remote sensing estimation models for non-point source and confined livestock point source NH3 emissions in China,providing an important supplement to the top-down NH3 emission monitoring methods.The research explores the potential application of remote sensing in estimating NH3 emissions from confined livestock point sources,aiming to serve as a reference for future related studies.The study analyzes the spatiotemporal patterns of NH3 emissions from regional sources and livestock point sources in China,contributing to a comprehensive understanding of NH3 emissions from these sources and providing scientific basis for relevant authorities in formulating ecological environmental protection and NH3 reduction policies.