Influence of Aerosol Sources on Atmospheric Black Carbon Absorption Enhancement in the Region of Paris, France

Abstract : Atmospheric black carbon (BC) and light absorbing organic aerosol (also referred as brown carbon, BrC) have strong effects on the Earth’s climate by absorbing direct solar radiation. To better characterize and quantify these effects, a better understanding of specific underlying mechanisms is needed such as the influence of primary emissions and secondary processes on absorption properties over long term periods. We report here results of a three year continuous field observations conducted from March 2014 to March 2017 at a suburban background station (SIRTA) in the Paris region (France). Submicron nonrefractory aerosol species were measured in near real time using an aerodyne aerosol chemical speciation monitor and were apportioned using Positive Matrix Factorization (PMF) analysis to identify and quantified major organic aerosol (OA) sources. Light absorption properties of BC and BrC were determined by direct measurements using a 7 wavelength aethalometer equipped with the dual spot technology. Co located 24 h filter based analyses were performed by thermo optical technique to quantify the mass concentration of elemental carbon (EC) in PM2.5. Absorption enhancement (Eabs) of BC containing particles was obtained using mass absorption coefficient (MAC) ratios calculated between observed (= babs / [EC]) and expected values for uncoated BC. Results showed that the observed Eabs significantly increased with the mass ratio of secondary aerosols to EC, suggesting a strong influence of this secondary components on BC absorption enhancement. Important BrC contribution to the total absorption in the near UV could be attributed to residential wood burning activities in winter and led to significant Eabs, independently of internal or external BrC mixing with BC particles. Finally, new findings on summertime aerosol optical properties are also presented and discussed here.