10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Primary Sources and Secondary Formation of Organic Aerosols in Diadema, São Paulo, Brazil
DJACINTO MONTEIRO DOS SANTOS, Luciana Rizzo, Patrick Schlag, Samara Carbone, Paulo Artaxo, University of São Paulo
Abstract Number: 209 Working Group: Source Apportionment
Abstract The Diadema city is one of the 39 municipalities within São Paulo Metropolitan Area (SPMA), very impacted by industrial and vehicular emissions, but also near to preserved Atlantic forest areas. This combination of different anthropogenic and biogenic sources results in complex physicochemical processes that culminate in the formation of secondary aerosols and ozone. An aerosol and trace gas monitoring station was operated at Federal University of São Paulo Campus, in Diadema, from 15 November 2016 to 15 March 2017, spring to summer in south hemisphere. Aerosol chemical composition was analyzed using an Aerodyne ACSM instrument. Measurements of aerosol properties like size distribution, number concentration, scattering and absorption coefficients, and gas phase (NO2, SO2 and O3) concentrations were taken. During campaign, the average concentration of PM1 was 10.1 (7.2) µg m-3. On average, the chemical composition of submicron aerosol is dominated by organics (55%), followed by equivalent black carbon (eBC), sulfate, nitrate and ammonium, with 15%, 15%, 8% and 6%, respectively. Average NO2 and SO2 concentrations were 13 ppb and 0.6 ppb, respectively, while ozone peaks 33 ppb at the middle of the day. Using Positive Matrix Factorization (PMF), the organic component was divided into different factors, identified as oxygenated organic aerosol (OOA), biomass burning organic aerosol (BBOA) and two components of hydrogenated-like organic aerosol (HOA). The OOA factor, dominated by m/z 44, was described as aged particles associated with secondary organic aerosols (SOA). The respective mass spectrum shows a good correlation with typical low volatile OOA mass spectrum. Moreover, time series of OOA factor correlates with time series of secondary species (SO4, O3 and NO3) and its average diurnal profile presents maximum concentration during afternoon, which evidences the role of photochemical activity in the formation of SOA in Diadema. The two HOA factors showed similar mass spectrum characterized by a hydrocarbon-like structure typically associated to vehicle exhaust emissions. The time series of these factors has high correlation with primary vehicular emission tracers and its diurnal profile presents peak concentrations during the local morning rush hour. The average contributions of OOA, HOA (sum of two HOA factors) and BBOA factors to total OA mass concentration were 44%, 41% and 15%, respectively.