The Characterization Methods And Pollution Characteristics Of The Brown Carbon In Atmospheric Particulate Matters In Shanghai

Brown carbon(BrC)is a kind of organic carbon which has light absorption ability.When the wavelength is close to the ultraviolet wavelength,the light absorption ability of BrC will have a rapid increase.Since the brown carbon in particulate matters makes a positive contribution to the climate warming,it has caused great concern by domestic and foreign scholars.But national researches are still not enough about BrC at present.To study the contribution of particles to the climate warming,it is of great significance to research the characterization methods and pollution characteristics of the brown carbon.In this study,two sampling sites were set up in Xuhui and Fengxian campus of East China University of Science and Technology(ECUST)to collect PM2.5 samples(membrane filter)for analysis of brown carbon.Meanwhile a seven-band black carbon instrument was set up in Fengxian campus for continuous observation of black carbon.The measurement methods of concentration and optical property of brown carbon were studied and compared,and finally the pollution characteristics of brown carbon was initially investigated.The structure,physic and chemical properties of HULIS-C and the BrC were similar in theory,but there were still some differences on definition and nature.When there were less polycyclic aromatic hydrocarbons and more water-soluble matters in BrC,it would be more appropriate to use HULIS-C concentrations represent BrC concentrations.The methods based on optical properties to estimate brown carbon concentrations were very simple and the monitoring results were continuous.Since it was difficult to directly obtain the BrC concentrations,it was feasible to utilize optical properties to estimate BrC concentrations for the variation characterization and trend of BrC concentrations,as well as the optical properties of BrC.Based on the measurement of optical properties by sampling of the membrane filter,within the range of near ultraviolet to near infrared wavelength,the light attenuation was always reduced with the increase of wavelength.The results showed that the light attenuation was greater in winter than other seasons,which was caused by the high concentrations of carbonaceous aerosol in winter.While the optical properties of membrane extraction was measured,it was found that the maximum values of absorption coefficient and mass absorption efficiency of BrC all occurred at about 200 nm wavelength.When the wavelength was greater than 200 nm,the absorption coefficient and mass absorption efficiency of BrC would decrease with the increase of the wavelength.At the same wavelength,the absorption coefficient of BrC was generally highest in winter,but the mass absorption efficiency of BrC was generally highest in spring.The Absorption Angstrom Exponent of BrC pointed out that there was consistency in the sources of BrC,and the sources of brown carbon in Shanghai were relatively complex and were comprised of primary sources and secondary sources.To research the optical properties of BrC,it is better to measure the extraction of BrC than measure the membrane directly,but it is necessary to consider how to extract all BrC out in the future.To get the properties of BrC completely,the concentration and optical measurement of BrC should be discussed together.The correlation efficiencies of HULIS-C,WSOC,OC,BC and BrC decreased sequently and the strong correlation between HULIS-C and BrC provided an experimental basis for the characterization of BrC by HULIS-C.The BrC pollution in Chinese lunar New Year was observed,it was found that fireworks could increase the AQI,PM2.5 concentrations and other carbon composition concentrations,and the increase intensity of the carbon composition concentrations was larger,which was related to the carbon element in the fireworks.The fireworks could increase BrC concentrations,as well as the contribution to the mix light absorption effect by BrC.The implementation of the new rule to prihibit fireworks could effectively reduce pollution of air pollutants including BrC in Shanghai during the Spring Festival,which was beneficial to improve the air quality in Shanghai during the Spring Festival.