| Atmospheric reactive nitrogen(Nr)is the main precursor of haze pollution and excessive nitrogen deposition.With the deepening of air pollution prevention and control actions in recent years,the task of reducing atmospheric Nr emissions has gradually been put on the agenda.The sources of atmospheric Nr include cropland fertilization,farms,vehicles,industry,coal-fired power plants.biomass burning,and coal-fired boilers,etc.,identifying the emission characteristics of different sources and the sources of atmospheric Nr are the key to reducing atmospheric Nr emissions.However,previous field measurements of Nr in the atmosphere from various sources are scarce,and existing studies have mostly focused on the estimation of emission inventory,while few studies carried out source analysis from the perspective of receptor.In view of this,this paper considered the North China Plain as the main research object,simultaneously collected four major Nr species,namely ammonia(NH3),nitric acid(HNO3)、particle ammonium(p-NH4+)and nitrate(p-NO3-),from cropland fertilization,farms,vehicles,biomass burning,and coal combustion environment.The concentrations of Nr and δ15N values of NH3 were measured in the laboratory,and the chemical composition and change rules of Nr from various sources were analysed.Finally,a set of δ15N-NH3 values inventory of five main NH3 sources was established and used to source apportionment of atmospheric NH3 in urban atmosphere.The major results and conclusions are as bellow:(1)Atmospheric Nr concentrations in pig farm were significantly(P<0.05)higher than those in poultry farm.The average concentrations of NH3 and p-NH4+inside the pig house(1250.9 and 76.6 μg/m3,respectively)were significantly(P<0.05)higher than those outside the pig house(378.5 and 4.2 μg/m3 respectively),while the average concentrations of HNO3 and p-NO3-(10.0和21.5 μg/m3,respectively)inside and outside the pig house were comparable.For the poultry house,the measured Nr concentrations were at alike levels between inside and outside for all Nr species(overall ranged from 6.2 to 10.7 μg/m3)except for NH3,which showed significantly higher(P<0.05)inside conceGtrations(197.7 μg/m3)compared to outside concentration(77.3 μg/m3).(2)The average concentrations of NH3 from five sources,including outside the farm,copland,tunnel,biomass burning and coal combustion,were 227.9,21.4,111.1,372.5(wheat straw),26358.7(corn straw),411.9(corn core)and 209.6 μg/m3,respectively.Among them,the NH3 concentration produced by biomass burning was the highest,followed by the concentration outside the farm,coal combustion and tunnel,while the concentration of NH3 in cropland atmosphere was the lowest.(3)The average concentrations of p-NH4+ from five sources,including outside the farm,copland,tunnel,biomass burning and coal combustion,were 7.4、2.0、2.6、1074.1(wheat straw),11529.7(corn straw),628.5(corn core)and 146.5 μg/m3,respectively.Among them,the p-NH4+ concentration produced by biomass burning was the highest,followed by the coal combustion,while the concentration of p-NH4+from farm,tunnel and cropland atmosphere were lower(4)The average concentrations of HNO3 from five sources,including outside the farm,copland,tunnel,biomass burning and coal combustion,were 9.9,4.4,7.6,35.8(wheat straw),77.5(corn straw),117.7(corn cob)and 29.6 μg/m3,respectively Among them,the HNO3 concentration produced by biomass burning was the highest,followed by the coal combustion,while the concentration of HNO3 from farm,tunnel and cropland atmosphere were lower(5)The average concentrations of p-NO3-from five sources,including outside the farm,copland,tunnel,biomass burning and coal combustion,were 14.6,5.5,5.3,48.0(wheat straw),314.9(corn straw),69.1(corn cob)and 31.2 μg/m3,respectively Among them,the p-NO3-concentration produced by biomass burning was the highest,followed by the coal combustion,while the concentration of p-NO3-from farm,tunnel and cropland atmosphere were lower(6)From the aspect of chemical composition,the Nr in these environments mainly existed in the form of reduced nitrogen(NHx,NHx=NH3+p-NH4+).Among them,in farm,cropland,tunnel and coal combustion environments,NH3-N was the most important component accounted for more than 50%,while in the biomass burning environment,p-NH4+-N was the most important component accounted for more than 50%.It indicated that except biomass burning,the Nr produced by other sources mainly diffused outward through the form of NH3 instead of quickly transforming into particles locally.(7)The variation range of δ15N-NH3 values from cropland fertilization,farm,vehicle,coal combustion and biomass burning were-36.5%‰～-15.0‰,-15.6‰～-9.2‰,0.8‰～4.3%‰,1.4‰～2.4‰ and-10.8‰～-3.4‰,respectively,And the value of δ15N-NH3 from agricultural source was significantly lower than that from non-agricultural source,so it can be used to distinguish agricultural and non-agricultural source according to δ15N-NH3 value(8)The average concentrations of atmospheric NH3 in Beijing,Shijiazhuang,Zhengzhou.Shenyang,Pingdingshan(Ye County and Jia County)and Langfang(Xianghe County)were 14.3、19.1.12.9,10.0,25.2(Ye County),15.0(.lia county)and 16.4 μ9/m3mrespectively.Non-agricultural sources were the main source of atmospheric NH3 in urban atmosphere with contribution of 52.7%～73.0%. |
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