Particulate Nitro-Aromatic Compounds At Coastal Qingdao:Pollution Characteristics And Source Analysis

Nitro-aromatic compounds,among the important components of atmospheric aerosols and brown carbon,have impacts on regional climate,air quality,and ecological health.There are many different types of nitro-aromatic compounds in atmospheric fine particulate matters and their sources are rather complex.Up to date,due to the lack of observations and exploration in the northern coastal regions of China,the pollution characteristics and main sources of particulate nitro-aromatic compounds in coastal atmosphere remain unclear.Therefore,it is necessary to carry out comprehensive investigations on their pollution characteristics and sources by means of integrated atmospheric observations in coastal areas.In this study,fine particulate matter samples were collected at coastal sites in Qingdao in winter and spring.Fourteen particulate nitro-aromatic compounds including nitrophenols,nitrocatecols,nitro-salicylic acids,dinitrophenols,nitroguaiacols and their methyl derivative were detected by using ultra-high performance liquid chromatography-mass spectrometer and their contents were determined.During the sampling periods,relevant gaseous pollutants and meteorological parameters were monitored online simultaneously.The concentrations of organic and elemental carbon were determined by carbon aerosol analyzer and the concentrations of inorganic water-soluble ions were determined by ion chromatography.With combination of the above data,the concentration levels,chemical composition,seasonal variation,diurnal difference,and key influencing factors of atmospheric particulate nitroaromatic compounds at coastal sites in Qingdao were analyzed.The concentration weighted trajectory model was improved by adding horizontal and vertical coefficients and their main sources and potential source areas were explored in conjunction with the positive matrix factorization model.The results show that the mean concentrations of particulate nitro-aromatic compounds in the winter of 2018,2019 and in the spring of 2021 were 125.0 ± 89.5,27.7 ± 21.1,and 11.3 ±9.9 ng/m3 respectively.Their concentration was significantly higher in winter than in spring.4Nitrophenol was the most abundant species in both winter and spring.Based on the diurnal difference,the concentration of particulate nitro-aromatic compounds was significantly higher at nighttime than daytime in winter,while it was higher at daytime than nighttime in spring.In addition,time series and correlation analyses showed that anthropogenic primary emissions and high relative humidity had significant effects on the concentration of particulate nitro-aromatic compounds.The positive matrix factorization model was applied to apportion the sources of particulate nitro-aromatic compounds.Four main sources were identified in Qingdao in winter,i.e.,coal combustion,biomass combustion,secondary formation,vehicle exhaust,while a total of six sources were identified in spring,including coal combustion,biomass combustion,secondary formation,marine sources,dust sources,and vehicle exhaust.Among these sources,combustion sources(coal and biomass burning)were the most important sources of particulate nitro-aromatic compounds in winter and spring in coastal Qingdao,with an average contribution of over 70%.The results of the Spatial Concentration Weighted Trajectory model show that particulate nitro-aromatic compounds in winter dominated by coal combustion were mainly from the Shandong Peninsula and a small part of northern and central Shandong Province,while those dominated by biomass burning were mainly from the local Qingdao and the western Shandong Province.The potential source areas in spring dominated by coal combustion were distributed in local Qingdao,central Shandong Province,and south-central Jiangsu Province,while those dominated by biomass burning were concentrated in Qingdao.This study solves the problem of overestimation of contributions for remote and marine areas and improves the accuracy of the traceability by modifying the concentration weighted trajectory model.In addition,it also revealed the large contributions of coal and biomass combustion activities in the local and surrounding areas to the atmospheric particulate nitroaromatic compounds in coastal areas of Qingdao,which provides scientific basis for atmospheric pollution control and air quality improvement in coastal areas.