Smoke particles ejected into the atmosphere from biomass burning can modify the atmospheric composition around and even far from the sources. In late winter and early spring, biomass burning emissions from inland regions can be efficiently transported to urban areas in southeastern South America, thus affecting air quality in those areas. In this study, the Weather Research and Forecasting with Chemistry model was applied in order to investigate the impact of biomass burning sources on aerosol loadings and properties over the S??o Paulo Metropolitan Area (SPMA), in southeastern Brazil, during the period from 19 August to 3 September 2014. The model performance was evaluated using available aerosol measurements from the Narrowing the Uncertainties on Aerosol and Climate Change in S??o Paulo State project. The combined application of aerosol data and Weather Research and Forecasting with Chemistry simulations made it possible to represent some of the most important aerosol properties, such as particle number concentration and cloud condensation nuclei activation, in addition to evaluation of the impact of biomass burning by analyzing a 5???day transport event, from 22 to 26 August 2014. During this transport event, differences in the average predicted PM2.5 concentration reached 15 ??g/m3 (peaking at 20 ??g/m3 during the nighttime hours) over the SPMA, compared with 35 ??g/m3 over inland areas northwest and north of the SPMA. Biomass burning accounted for up to 20% of the baseline particle number concentration??? and cloud condensation nuclei???weighted relative differences over the SPMA (2,300 and 1,400 cm???3, respectively).Funda????o de Amparo ?? Pesquisa do Estado de S??o Paulo (FAPESP)FAPESP: 08/58104-8; 11/14365-5