Characteristics And Source Apportionment Of Carbonaceous Aerosols ——Three Cities (Hohhot,Baotou And Bayannur) In Inner Mongolia

As one of the important components of atmospheric fine particulate matter(PM_2.5),carbonaceous aerosol is mainly composed of organic carbon（OC）and element carbon（EC）,which could exert the significant impact on air quality and physical health.In this study,PM_2.5 was collected simultaneously at 18 sampling sites in different functional areas of three resource-based cities（Hohhot,Baotou,and Bayannur）in Inner Mongolia during the heating season（January,2021）and the non-heating season（July,2021）.Then,we compared the characteristics and sources of carbonaceous aerosol in different functional areas and time periods of these three cities by measuring the concentrations of carbonaceous aerosol.These results could provide a scientific reference for the continuous improvement of air quality in the three cities and surrounding areas,as well as laying the foundation for future joint preventions of regional air pollutants.In addition,the correlations between OC/EC ratios and socioeconomic indicators in different types of cities were explored,which could serve as a reference for the strategy-making in carbonaceous aerosol pollution.The main results are as follows:（1）The concentrations of OC and EC,and the ratios of OC/EC in winter were higher than those in summer in the whole studying area.It followed the trend that in both winter and summer,the OC concentrations and the OC/EC ratios of regional areas were higher than those in urban areas（industrial and residential areas）while EC concentrations showed the opposite.Meanwhile,during the night,the OC and EC concentrations in urban areas were lower than those during the daytime,while at regional areas,the results were opposite.Besides,the OC concentrations in all functional areas of the three cities were significantly higher on dust and light pollution days compared to the clean days.However,EC concentrations decreased during the dust days but rebounded on the following light pollution days after the dust.Therefore,the OC/EC ratios in all three cities followed the order of"dust days>light pollution days>clean days".（2）The SOC/OC ratios of the three cities in winter were higher than those in summer.The ratios in regional areas were also higher than those in urban areas.Meanwhile,due to the increasing number of primary sources,the SOC/OC ratios in the whole studying area were lower during the daytime than those in the night.The ratios rose strikingly during the dust days,and then fell on light pollution days,which were still higher than those on clean days.（3）The proportions of each carbon fraction in the studying area were not notably different in both winter and summer,as well as day and night.On dust days,the proportions of OC4 increased significantly,while those of OC1 and EC1 decreased.（4）The Char-EC/Soot-EC ratios of the three cities were higher in winter than those in summer.The ratios followed the order of"regional areasurban areas"in summer.Meanwhile,the ratios during the night were significantly higher than those of daytime.The ratios on dust days were remarkably lower,but increased on light pollution days,which suggested opposition to the trend of OC/EC ratios.Besides,the sources of carbonaceous aerosols were all composed of coal combustion,vehicle exhaust emissions,road dust and biomass combustion.（5）The OC/EC ratios of cities nationwide were roughly positively correlated with population density and the proportion of urban green space area（p<0.05）but negatively correlated with energy consumption per unit of GDP（p<0.05）.Economic-based cities with significant secondary pollution showed higher OC/EC ratios,while resource-based cities with severe primary pollution suggested lower OC/EC ratios.