| China is a big agricultural country with abundant straw resources.In recent years,China has strengthened policies such as prohibition of straw burning,promoting straw resources,and straw subsidies,however,there are still many areas about straw burning in field or as household fuels.The large-scale of straw burning not only causes waste of resources,but also has made a great negative impact on the occurrence of haze and human health.Although a large number of studies have focused on the pollutant emissions from straw burning,due to the uncertainty of the basic data and the huge changes about the amount of straw burning in recent years,the existing understanding and actual situation are quite different.Therefore,exploring high-resolution temporal and spatial characteristics of pollutant emissions from straw burning would help us to control the pollutant emissions from straw burning and improve the ambient air quality.This study focused on the following aspects:(1)Based on the activity level data and emission factor data,quantitative analysis of pollutants from crop straw burning in 296 prefecture-level cities across the China were constructed,including straw burning in-field and as household fuels.(2)Based on the pollutant emissions from various cities,combined with land use type data(paddy fields and dry land),population distribution data(rural population distribution)and MODIS monitoring fire point data(farmland fires),the spatial distributions of pollutant emissions from straw burning were redistributed in detail.(3)Based on MODIS satellite remote sensing data and land use type data,the temporal distribution of pollutant emissions from straw burning in 2017 were calculated,and interannual trends of fire points of straw burning in recent 20 years were obtained.In addition,this study used the Monte-Carlo simulation to evaluate the uncertainty of the correlation results.The main conclusions of this study are as follows:(1)This study comprehensively calculated the 11 pollutants emissions from straw burning in China in 2017.The total emissions of BC,OC,PM2.5,PM10,SO2,NOx,NH3,CH4,NMVOC,CO and CO2 from straw burning in 2017 were 14.6,81.6,189.9,225.8,22.9,59.6,13.5,115.6,203.6,1961.0 and 32961.5 ten thousand tons,of which straw burning as household fuels accounted for 40.7%to 68.8%of the total pollutant emissions.Our results are remarkably lower than reported in previous studies,especially in-field burning,because of the policy about prohibition of straw burning and the improvement of comprehensive utilization rate in recent years.About three major crops,the contribution rate of corn was 40.8%?53.8%,the contribution rate of rice was 14.0%?24.2%,and the contribution rate of wheat was 10.6%-29.5%.(2)On the basis of the administrative region,this study conducted a refined study on the spatial distribution of pollutant emission intensities.Pollutant emissions from total straw burning in 2017 were mainly concentrated in Jilin,Liaoning and Heilongjiang in Northeast China,Shandong in North China,and Anhui in the middle and lower reaches of the Yangtze River.The main source of pollutants in Northeast China were from straw in-field burning.The main sources of pollutants in North China and the middle and lower reaches of the Yangtze River were from straw burning as household fuels.The emission intensities of pollutants from straw burning were the highest in Northeast China,among which BC,OC,PM2.5,PM10,SO2,NOx,NH3,CH4,NMVOC,CO and CO2 emission intensities were concentrated on 0.02?0.5,0.1?3.8,0.3?8.1,0.3?9.5,0.02?0.6,0.009?2.7,0.002?0.5,0.1?3.9,0.3?8.0,1.8?58.3 and 39.5?1169.3 t/(km2 yr).On the scale of municipal city and smaller scales,the spatial difference of emission intensity is large,and the ratio between high value area and low value area could be up to 4 times.(3)Pollutant emissions from straw burning in 2017 were mainly concentrated in March,April,July and October.From January to December,the pollutant emissions from straw burning accounted for 6.3%,7.5%,11.1%,12.8%,8.6%,7.5%,8.4%,7.0%,5.8%,10.0%,8.2%and 6.9%,respectively.In the Northeast China,field fires were mainly concentrated in March,April,October and November.In the North China,they were mainly concentrated in March,June and October.In the middle and lower reaches of the Yangtze River,they were mainly concentrated in March,June,July and November.In addition to the northwestern region in North from 2001 to 2017,the number of fire points has shown a rising trend,and the number of fire points in South has shown a downward trend.(4)This study used Monte-Carlo simulation to analyze the uncertainty of the results.The results showed that the uncertainty of total BC,OC,PM2.5,PM10,SO2,NOx,NH3,CH4,NMVOC,CO and CO2 emissions from straw burning were-47?92%,-48?92%,-48?91%,-50?100%,-59?133%,-55?105%,-47?93%,-55?102%,-43?74%,-46?85%and-45?80%.Due to the more comprehensive and representative factors considered when selecting the basic data and related parameters,the uncertainty ranges of this study are generally smaller than most previous studies.Compared with the anthropogenic source air pollutant emissions,the total pollutant emissions from straw burning were relatively small,and the main pollutants accounted for 3?4%.Due to the pollutant emission nonuniformity of spatial and temporal distribution from crop straw burning,it is significant to improve air quality about strengthening the control of crop burning from special areas and times. |
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