Abstract: Air pollution is a global concern and is not limited to the geographical boundaries of a region: the pollutants in the atmosphere are subject to transport processes and chemical transformations that affect their composition and the level of contamination in a specific area. Pollutants transported from distant regions can affect local atmospheric concentrations. High concentrations of ozone (O3) are challenging to control, because, as a secondary pollutant, produced through photochemical reactions between its precursors, nitrogen oxides (NOx) and Volatile Organic Compounds (VOCs), O3 concentrations depend on the emission of its precursors, favorable weather conditions for its formation and the geographical location that influences its dispersion. Therefore, there is no long-term spatial distribution trend. This study aims to investigate the transportation of primary pollutants among the metropolitan regions of São Paulo, Campinas, and Baixada Santista to understand the implications of precursor transportation for O3 formation. The spring and summer seasons show higher concentrations of O3 from September to March, due to conditions that favor its formation: high solar incidence, due to low cloudiness; temperatures above 20o C; and low humidity. Frequent episodes of O3 levels being exceeded throughout the state are measured and reported daily through CETESB’s Air Quality Information System (QUALAR). A preliminary analysis of the total days of exceedances of state air quality standards for O3 throughout the state of São Paulo showed a significant decrease from 2014 to 2016; in 2017, there was a slight increase, decreasing again in 2018. However, in 2019, there was a sudden increase in these exceedances, making it clear that O3 is a difficult pollutant to control, which generated interest in this study period. To analyze the interaction of air pollution by O3 among more than one region, the three main metropolitan regions of the state of São Paulo were chosen, which are not only close to each other but also have great political and economic importance: Metropolitan Region of São Paulo (MRSP), Metropolitan Region of Campinas (MRC) and the Metropolitan Region of Baixada Santista (MRBS). To perform the simulations, we chose a week with high daily O3 concentrations episodes during spring, from 1 to 8/Oct/2019, a favorable season for the formation of O3. Meteorological simulations were carried out with the WRF (Weather Research Forecasting Model) using a 271 × 271 km domain, including the entire state of São Paulo, centered at the coordinates of – 23.21° S, – 46.44° W. The transport of primary precursors was represented by seven tracers with continuous and constant emission: three in the MRSP, two in the MRC, and two in the MRBS. The meteorological simulations during the study period showed good agreement with observations, representing the temperature profiles adequately, especially the high temperatures in the first five days, which favors the formation of O3. Considering the geographical location, the sea breeze, and the wind predominant direction of the studied regions, it can be seen that during the day, part of the pollution plume from the MRSP will be transported to the MRC; the plume from the MRC will be transported to the northwest; and the plume from the MRBS, will climb the Serra do Mar escarpment arriving at the MRSP. At night, the wind direction changes to northwest, reversing the dispersion direction. The results indicate an interaction between the primary pollutants in these regions, which has implications for the concentrations of secondary pollutants such as O3.

Keywords: Metropolitan regions, pollutant transport, air pollutant dispersion modeling, interregional pollutants transport.