Abstract
Smoke particles ejected into the atmosphere from biomass burning can modify the atmospheric composition around and even 30 far from the sources. In late winter and early spring, biomass burning emissions from inland regions can be efficiently 31 transported to urban areas in south-eastern South America, thus affecting air quality in those areas. In this study, the Weather 32 Research and Forecasting with Chemistry (WRF-Chem) model was applied in order to investigate the impact of biomass 33 burning sources on aerosol loadings and properties over the São Paulo Metropolitan Area (SPMA), in south-eastern Brazil, 34 during the period from 19 August to 3 September 2014. The model performance was evaluated using available aerosol 35 measurements from the Narrowing the Uncertainties on Aerosol and Climate Change in São Paulo State (NUANCE-SPS) 36 project. The combined application of aerosol data and WRF-Chem simulations made it possible to represent some of the most 37 important aerosol properties, such as particle number concentration (PNC) and cloud condensation nuclei (CCN) activation, in 38 addition to evaluation of the impact of biomass burning by analysing a five-day transport event, from 22 August to 26 August 39 2014. During this transport event, differences in the average predicted PM2.5 concentration reached 15 μg m−3 (peaking at 20 40 μg m−3 during the night-time hours) over the SPMA, compared with 35 μg m−3 over inland areas northwest and north of the 41 SPMA. Biomass burning accounted for up to 20 % of the baseline PNC- and CCN-weighted relative differences over the 42 SPMA (2300 cm−3 and 1400 cm−3, respectively).