Improving Air Quality Modeling in São Paulo, Brazil, Through an Enhanced Emissions Methodology

Introduction: Besides simulating the secondary formation of air pollutants, anthropogenic emissions classified by sectors are essential to represent sources and their primary contributions to air contamination. The urban megacity, depicted by the metropolitan area of São Paulo (MASP), has faced unsafe fine inhalable particles of 2.5 µm or less in diameter (PM_2.5) and ground-level ozone concentrations. Previous source apportionment studies have confirmed that the road transport sector's contribution is more significant than other activities, such as industry and residential emissions.

Methodology: A bottom-up approach was used to enhance the emission inventory by applying emission factors from tunnel experiments and information from vehicles in São Paulo. Source apportionment studies conducted in the MASP were valuable for adjusting global emissions inventories from the EDGAR-HTAPv3 for road transport, industry, energy, residential, waste, agricultural, and aviation for the region. According to the receptor model study, PM_2.5 emissions from industry and other sectors in São Paulo account for 10% and 25%, respectively. Results from the receptor model suggest that the road transport sector could contribute approximately 65% of fine particulate matter emissions, with about 40% originating from exhaust and around 25% from resuspension. Moreover, these emission inventories were validated using a photochemical grid model (CMAQ), which accounts for secondary aerosol formation. This model is essential to be applied because a local study conducted in São Paulo demonstrated that secondary processes contribute approximately 56% of the concentration of particles smaller than 1 µm. 

Results: The model performance evaluation for PM_2.5 demonstrated promising simulation results compared with stations located within and outside the MASP.

Conclusion: Consequently, simulation results for PM_2.5 improved in representing not only observed air mass concentrations but also direct emission contributions by sectors consistent with source apportionment studies, which is very useful for policymakers’ decisions regarding public health.