Molecular Characterization And Source Apportionment Of Fine Organic Aerosols In Rural Site Of Beijing

Organic aerosols?OA?not only influence air quality,climate and affect cloud condensation nuclei,cause ecosystem damage and visibility reducion,but also adversely affect human health.The main object of this study includes the determination of emission sources of OA and their contributions.And then it will discuss the major factor for the formation of OA in different air quality,leading to development of the efficient measures to decrease the air pollutants.It is difficult to update the information for source profiles and develop the accuracy of instruments,resulting in few previous study information about the source apportionment of OA in Beijing.The study quantified the organic tracers by GC/MS technique and measured OC and EC using DRI Multi-wavelength Carbon Analyzer.SOA could be calculated by?OC/EC?_min.Based on the China-UK Plan"Atmospheric Pollution and Human Health in a Chinese Megacity",the study identified the molecular characteristics of OA in winter of 2016 and summer of 2017,and then apportioned the source contribution of OA by CMB and PMF model.We combined the characteristics of organic tracers with air mass back trajectary to determine the major factor of organic aerosol formation.As a result,the average PM_2.5 concentration in winter was136.2?g/m³.The average concentrations of OC were 15.3?g/m³ in clean days and52.3?g/m³ in haze days.The average EC concentration in haze days was 5.4?g/m³which was 2.8 times higher than that during non-haze days.The total quantified concentration of organic tracers was 1.73?g/m³ in clean days and 3.64?g/m³ in haze days with 11.3%and 7.0%of OC,respectively.In summer,the mean OC and EC concentration were 7.4 and 0.8?g/m³,respectively.Pragmatic mass closure method has been conducted to apportion PM_2.5 in winter.It shows that the major components of PM_2.5 were organic materials and secondary inorganic aerosols,which accounted for 30-60%and 20-44%of PM_2.5,respectively.Moreover,the other materials in PM_2.5presented higher proportion in haze days?10-16%?than that in clean days?lower than10%?.Source apportionment of fine OC has been used CMB and PMF model.The CMB model shows the dominant contributions to OC are coal combustion?23.3%?and biomass burning?20%?at haze days in winter.Coal combustion includes industrial and residential coal combustion with contribution of 3.9%and 19.4%respectively to OC.The main emission source is industrial coal combustion in summer?37%?.Generally,it suggests that OA in winter was significantly affected by local sources,but the regional air mass transport played a dominant role in haze days,especially the air mass from southwestern and southern.The concentration of OA at nighttime is higher than that at daytime,which is consistent with the distribution of OC.The low temperature and low boundary layer heights have been shown to affect the accumulation of OA.In summer,industrial coal combustion and cooking are main sources,suggesting that local emission is the dominant factor for OA.