Characteristics Of Atmospheric Particulate Matter Emission During Agricultural Tilling And Harvesting In Northeast China

Atmospheric particulate matter emitted during agricultural tilling and harvesting is one of the important sources of atmospheric particulate matter in China,affecting the rural or regional atmospheric environment.As an important commodity grain base,farmland cultivation area in the northeast China accounts for 20%of the country's arable land area.Therefore,clarifying the emission characteristics of atmospheric particulate matter during agricultural tilling and harvesting could help determining emission mechanism,key parameters and control measures of agricultural atmospheric particulate matter in Northeast China.The experiments were condected on Shenyang Agricultural University Science Experiment Base?Shenyang Station?,Changchun Comprehensive Experimental Station?Changchun Station?,Yushu City Agricultural Demonstration Zone?Yushu Station?,Da'an Sodic Land Experiment Station?Da'an Station?,Hailun Experiment Station of Agricultural Ecology,Chinese Academy of Sciences?Hailun Station?and Sanjiang Plain Experimental Station of Wetland Ecology?Sanjiang Station?.Using the weight method?i.e.,membrane sampling-balance weighing method?and the online rea-time monitoring method?i.e.,Dustrak 8520 smart dust meter?,atmospheric particles(PM_2.5)were daily sampled at agricultural sites during agricultural tilling and harvesting from October to November 2017 and from April to June 2018.The data of PM_2.5 mass concentration,minutely ratios of PM_2.5 and PM₁₀,and PM_2.5 chemical components?i.e.,OC,EC,elements and ions?were obtained.Furthermore,combined with meteorological data?i.e.,wind speed,wind direction and relative humidity?,we analyzed the temporal and spatial variations PM_2.5,meteorological effect on PM_2.5 and potential source of PM_2.5 in typical agricultural areas.The main results are as follows:?1?During the agricultural harvest period from October to November in 2017,the average PM_2.5.5 mass concentration at Yushu station?143?g/m³?was higher than the average PM_2.5 mass concentration of Changchun station?83?g/m³?.The average concentration of PM_2.5 at the six stations from April to June 2018 in spring agricultural cultivation was as follows:Yushu station>Da'an station>Changchun station>Hailun station>Shenyang station>Sanjiang station.From April to June2018,the real-time concentration of PM_2.5 and PM₁₀ during agricultural tilling operation showed that the particulate matter emitted from agricultural tilling is affected by the wind speed,soil moisture and mechanical disturbance.Larger soil particulate matter emissions occurred with higher wind speed,stronger mechanical disturbance and lower soil moisture.Under different cultivation methods,the disturbance intensity of large tilling machines is strongest.Followed by household small tilling machines and artificial cultivation is weakest.?2?The relationship of PM_2.5 and PM₁₀ with wind speed and wind direction showed that the transport of pollutants from the Southwest and South direction was the main cause of pollution in Changchun station.Hailun station was less pollution.Yushu station has heavy local pollution,and the East,South and North were high pollution areas.The intensity of agricultural activity and the location of sampling sites all had significant effect on the mass concentration of particulate matters.Temporal variation analysis showed the highest concentrations at the time of 5:00-6:00 and18:00-20:00,and kept higher concentrations last from night to early morning.Temporal variation of concentration values was significantly influenced by local traditional farming custom.The LIDAR data analysis showed that the main causes of haze episodes on May 3-7 2018 in Yushu station were the external transport of pollutants and dust events.?3?The Total Carbon Content?TC?concentrations of PM_2.5 at observed stations followed the order:Yushu Station>Hailun Station>Da'an Station>Changchun Station>Shenyang Station>Sanjiang Station.The proportion of total carbon in particulate matter(the ratios of TC and PM_2.5)was 5%⁴5%,with the maximum in Yushu station,and minimum in Sanjiang station.The ratios of OC and EC at six stations ranged from 3 to 15,which indicated secondary organic pollutants with different extents.The OC and EC at stations of Shengyang,Changchun and Yushu may originate from motor vehicle exhaust.At Da'an station and Sanjiang station,OC and EC sources may be straw burning,and these were motor vehicle exhaust and straw burning at Hailun station.The order of water soluble ions mass concentrations at eight stations was:2017autumn?Yushu station>Changchun station?>2018 spring?Yushu station>Shenyang station>Changchun station>Da'an station>Hailun station>Sanjiang station?.The ratios of NO₃^-and SO₄^2-showed that PM_2.5 were mainly affected by mobile pollutants at Changchun station,Yushu station and Sanjiang station,while at Shenyang station,Da'an station and Hailun station they were mainly affected by fixed pollutants.The anion-cation balance analysis found that the ions in PM_2.5 in autumn were mainly acidic because of the excess of anions such as SO₄^2-and NO₃^-caused by fossil fuel combustion.The ions in PM_2.5 in the spring were mainly alkaline,due to the increase in soil dust ions Mg²⁺and Ca²⁺.As well as the increase in cations such as NH₄⁺obtained by secondary conversion of NH₃ produced during agricultural planting.The elemental analysis showed that the K element in PM_2.5 in autumn was significantly higher than in spring,while the concentrations of Al,Ca,Fe and Mg in spring were higher than in autumn.The main reason is that severe straw burning in autumn,and the strong disturbance of soil during agricultural tilling in spring release soil dust into the air.The concentration of atmospheric particles in agricultural areas varies greatly among different seasons and different stations.Emission types,emission intensity and meteorological conditions around agricultural areas are the main factors affecting the agricultural areas and the surrounding ambient environment.The parameters and verification data(i.e.,PM_2.5 mass concentration,chemical composition and LADIR data)obtained in this study could help accurately quantifying the atmospheric particulate matter emission inventories and providing scientific basis for mitigation measures and policies.