Sources of Carbonaceous Aerosol in the Amazon Basin

The quantification of sources of carbonaceous aerosol is important to understand their atmospheric concentrations and study possible effects on climate and air quality, in addition to develop mitigation strategies. In the framework of the European Aerosol Cloud Climate Interaction (EUCAARI) project fine and coarse aerosol particles were sampled from February to June (wet season) and from August to September (dry season) 2008 in the central Amazon basin. The mass of fine particles averaged 2.4 ug m-3 during the wet season and 4.2 ug m-3 during the dry season. The average coarse aerosol mass concentration during wet and dry periods was 7.9 and 7.6 ug m-3, respectively. The overall chemical composition of fine and coarse mass did not show any seasonality with the largest fraction of fine and coarse aerosol mass explained by organic carbon (OC); the average OC to mass ratio was 0.4 and 0.6 in fine and coarse aerosol modes, respectively. The mass absorbing cross section of soot was determined by comparison of elemental carbon and light absorption coefficient measurements and it was equal to 4.7 m2g-1 at 637 nm. Carbon aerosol sources were identified by Positive Matrix Factorization (PMF) analysis of thermograms: 42% of fine total carbon mass was assigned to biomass burning, 41% to secondary organic aerosol (SOA), and 17% to volatile species likely due to wood smoldering. In the coarse mode, primary biogenic aerosol par-ticles (PBAP) dominated the carbonaceous aerosol mass. The results confirmed the importance of PBAP on the global carbon budget. The source apportionment results were employed to evaluate the ability of global chemistry transport model to simulate carbonaceous aerosol sources in a regional background site. The comparison showed an overestimation of elemental carbon (EC) during the dry season and OC both during the dry and the wet periods. The overestimation was likely due to the overestimation of biomass burning emission inventories and SOA production.JRC.H.2-Air and Climat