Impacts of regional interactions on spatial and temporal variation of ozone and its precursors

Air quality continues to be an issue for cities around the world, causing public health and environmental problems. Actions to improve air quality must address emissions, but secondary pollutants, such as tropospheric ozone, are difficult to control, not only because of the complexity of reactions that form them but also because of the number of their precursor sources and the interactions caused by atmospheric transport and dispersion. This work analyzes regional interactions of ozone precursors over three metropolitan regions in Sao Paulo state, Brazil, and how they contribute to the spatial and temporal ozone concentration during a high concentration episode. The metropolitan regions are Sao Paulo, Campinas, and Baixada Santista, located in the southeast part of Brazil, and approximately aligned in a northwest-southeast axis. They form a relevant economic axis, bringing the agricultural production of the countryside, that concentrates in Campinas, where there is relevant industrial production, passing through the greatest city of the country, Sao Paulo, with massive vehicular emissions, and exiting in the port of Santos, in Baixada Santista, to be shipped abroad. Baixada Santista also has industrial emissions. Most of the transportation is road-based. The northwest-southeast axis is also the prevalent direction of the wind, shaping the atmospheric interaction between these sites. Results show relevant interactions between the metropolitan areas: the sea breeze brings the marine air and the air pollutants from Baixada Santista to Sao Paulo; the prevalent east-northeast wind takes the pollution from Sao Paulo to Campinas. Mostly at night, the wind comes from the northwest, rotating the transport of pollutants. Sea breeze also influences the vertical transport and dispersion of pollutants, affecting ozone concentration. In conclusion, to improve air quality, actions must be aware of the regional interactions and decisions must consider the complexity of regional economic activities and pollution sources.