Study On The Characteristics Of Carbonaceous Aerosols In The Industrial Area In Northern Nanjing And The Effect Of Biomass Burning

Carbonaceous species,as significant chemical components of PM2,5,have been found to be widely associated with global climate change,regional air quality,visibility deterioration and health problems.Carbonaceous aerosol is usually divided into organic carbon(OC)and elemental carbon(EC)fractions,which have different emission features.Brown carbon(BrC),as a kind of light-absorbing organic carbon,has caused global concerning due to its positive climate effect.China has large BrC emissions from agricultural biomass burning,together with coal combustion and secondary transformation.The Yangtze River Delta(YRD),as one of the economically developed areas,has experienced large-scale atmospheric pollution in recent years.Carbonaceous aerosols,especially SOC are considered to be the important factors of visibility deterioration.Study on the characteristics and transport of carbonaceous aerosols in Nanjing,one of the typical representative cities of the YRD,is of great significance to pollution control and emission reduction.In this study,the characteristics of carbonaceous aerosols concentrations and the seasonal variation,the diurnal patterns and the impact of meteorological parameters were analyzed based on the real-time observation of OC,EC and BrC from June 2015 to August 2016 using the semi-continuous Sunset OCEC analyzers(Model RT-4,sunset Laboratory Inc.,Portland,OR).The minimum R squared(MRS)method was used to derive primary organic carbon(POC)and secondary organic carbon(SOC).In addition,the effect of biomass burning during a biomass burning event in October,2015 and the carbonaceous aerosols transport and transformation was estimated based on the OC,EC,BrC and Levoglucosan measurement in 12-hour resolution PM2.5 samples and the open MODIS fire spots and hybrid receptor models.The results show that:(1)OC and EC concentrations remained at a middle level in North Nanjing compared with other sites in China.High(low)OC and EC concentrations were found in Winter(summer),indicating the significant impact of coal combustion in winter and wet scavenging of rain in summer.Similar diurnal cycles for OC and EC concentrations were found in four seasons with high at night and low in daytime,strongly effected by the boundary layers.(2)The high SOC/OC in summer indicated the strong contribution of SOC due to the higher temperature,stronger solar radiation and more volatile organic compounds emissions in summer.The low SOC/OC in winter and spring indicated the relatively single sources of carbonaceous aerosols.(3)Local sources made great contributions to high OC and EC concentrations in winter and spring.Except for local sources,highly polluted air masses in winter and spring were mainly from North China in winter and spring and from inland areas in autumn.Clean air masses in summer were coming from ocean areas.(4)A heavy biomass burning event was found in October,2015 and analysis on dEC reflected that dEC could be a good tracer of biomass burning.The mechanism of dEC formation is closely associated with SOC formation.The estimated contribution of biomass burning to OC was about 20%.