Characteristics And Sources Apportionment Of Water-Soluble Organic Nitrogen （WSON） In PM_2.5 In Wuhai

Water-soluble organic nitrogen(WSON)is an important component of atmospheric particulate matter.With the increasing consumption of fossil fuels and the scale of agricultural activities,the concentration of WSON in the atmosphere is gradually increasing and its environmental effects are gaining attention.As a typical resource-based city in northwest China,the severe atmospheric pollutants emission and the canyon-type topographical conditions make the atmospheric particulate pollution characteristics highly representative in Wuhai.According to the significant seasonal differences of Wuhai,this study systematically collected the atmospheric fine particulate matter samples in the heating and non-heating seasons,and carried out the spatial and temporal distribution characteristics of WSON in PM2.5,the correlations of WSON with water-soluble organic carbon,water-soluble ions,organic carbon,elemental carbon and other indicators,and analyze the sources of WSON.Using the potential source contribution function model and the concentration weight trajectory model,the geospatial sources were identified and the contributions of various sources to WSON were quantitatively estimated by the positive matrix factorization model.The main results as follows:(1)The spatial and temporal distribution characteristics of WSON and other components in atmospheric fine particulate matter from Wuhai were determined.The concentrations of WSON in PM2.5 were 2.36±2.14 μg/m3 and 0.78±0.37μg/m3 in the heating and non-heating seasons,respectively,indicating the seasonal driven trend in WSON levels.The spatial distribution presented the trend of “high in the south and low in the north” in the heating season,while no significant trend in the non-heating season.The spatial patterns of other components in PM2.5 were found consistent with WSON.(2)The correlations between WSON and other components were revealed the possible sources.The significant correlations of WSON with SO42-,NO3-,NH4+,Cl-,K+,OC,and EC in the heating and non-heating seasons indicated that secondary aerosol generation,coal combustion,biomass combustion,and vehicle exhaust emissions were the sources of WSON in Wuhai,the N:C values indicated that amino acids and organic nitrates may be the main components of WSON.The ratios of NO3-/SO42-showed that PM2.5 in Wuhai was mainly influenced by stationary combustion sources.(3)The geospatial sources of WSON were identified.Both the potential source contribution function model(PSCF)and the concentration weight trajectory model(CWT)suggested that WSON was predominanted by local contributions,while regional transport was limited in Wuhai.(4)The results of the positive matrix factorization model(PMF)indicated that there were significant seasonal differences in WSON source in Wuhai,but coal combustion(56.61% in the heating season and 42.47% in the non-heating season)and vehicle exhaust emission(30.87% in the heating season and 25.64% in the non-heating season)were the predominant sources.