Analysis of PM concentrations under pollutant emission control strategies in the metropolitan area of São Paulo, Brazil.

Great efforts have been made over the years to assess the effectiveness of air pollution controls in place in the metropolitan area of São Paulo (MASP), Brazil. In this work, the community multiscale air quality (CMAQ) model was used to evaluate the efficacy of emission control strategies in MASP, considering the spatial and temporal variability of fine particle concentration. Seven different emission scenarios were modeled to assess the relationship between the emission of precursors and ambient aerosol concentration, including a baseline emission inventory, and six sensitivity scenarios with emission reductions in relation to the baseline inventory: a 50% reduction in SO emissions; no SO emissions; a 50% reduction in SO, NO, and NH emissions; no sulfate (PSO) particle emissions; no PSO and nitrate (PNO) particle emissions; and no PNO emissions. Results show that ambient PM behavior is not linearly dependent on the emission of precursors. Variation levels in PM concentrations did not correspond to the reduction ratios applied to precursor emissions, mainly due to the contribution of organic and elemental carbon, and other secondary organic aerosol species. Reductions in SO emissions are less likely to be effective at reducing PM concentrations at the expected rate in many locations of the MASP. The largest reduction in ambient PM was obtained with the scenario that considered a reduction in 50% of SO, NO, and NH emissions (1 to 2 μg/m on average). It highlights the importance of considering the role of secondary organic aerosols and black carbon in the design of effective policies for ambient PM concentration control.