Characterization of aerosol chemical composition from urban pollution in Brazil and its possible impacts on the aerosol hygroscopicity and size distribution

Abstract

We studied the effect of aerosols inorganic chemical composition on the aerosol hygroscopicity of urban pollution in Brazil, where biofuels have been used in large scale. We applied size segregated inorganic chemical composition analysis using ISORROPIA II model and κ-Köhler theory to determine the hygroscopicity parameter (κ) of submicrometer aerosols measured in São Paulo city. The size dependence of organic and black carbon (BC) mass were estimated by chemical mass balance and mean observed values.

Results showed ultrafine mode particles with diameter smaller than 100 nm with a relatively K2SO4 and Na2SO4 large amount inducing further growth by diffusive condensation and coagulation of low-volatile organic compounds. The process could lead to modifications of aerosol size distribution and also to formation of more active Cloud Condensation Nuclei (CCN) due to the formation of aerosols with considerably increase of hygroscopicity (>40%). The contribution from BC can decreases up to 40% of the observed hygroscopicities values of particles around 100 nm in diameter.

Moreover, we present a parameterization based on aerosol mass fraction to accurately predict κ derived from data of Aerosol Mass Spectrometer (AMS) collected in urban pollution in Brazil. Results are compared to hygroscopicity derived from observations of the pollution plume downwind Manaus, on the northern region of Brazil. Both cases were analogous indicating that, despite the fact of receiving influences of organic components from the forest, the pollution plume of Manaus shows the same characteristics of hygroscopicity, and can be modeled following the same parameterization.