Abstract: Vehicles and industries are the main sources of pollutants in large cities, but the pollution generated by biomass burning and even garbage from other places can also influence city’s air quality, such as São Paulo, Brazil. The fine particulate matter (PM2.5), in addition to influencing the earth’s climate, can affect human health and quality of life, so its effects must be constantly studied and the pollutant monitored. Studies show that this pollutant has a significant effect on morbidity and mortality of populations. Air pollution can be more harmful to the health of the elderly, people with chronic illnesses and children. However, especially children under the age of six, have physical characteristics that make them more vulnerable to the effects of air pollution, including impaired learning, because in this age group the immune system is not yet fully formed, and the rate of inhalation is higher than in adults. Due to these factors, studying and monitoring air quality in environments where children spend most of their time, such as schools, and including measures that can minimize the effects of high concentrations of pollutants in such environments, becomes extremely necessary to maintain children’s quality of life. In a joint effort with WRI-Brazil, this study monitored PM2.5 concentrations (June to November 2021) using low-cost sensors (Airbeam), in five schools in the metropolitan area of São Paulo, in order to know the concentration of the pollutant inside and outside the classrooms. In addition, PM2.5 was sampled with a specific equipment to know the chemical composition and identify the main sources, in order to subsidize the public authorities for future actions to reduce vulnerability in early childhood. The results showed that concentrations of the pollutant can be higher indoors, especially if the school is located near roads with heavy vehicle traffic. Meteorological conditions also have a strong influence on the concentration of particulate matter. Regarding the sources of PM2.5 in the outdoor environments near the schools, the analysis using Positive Matrix Factorization showed that 19.5% are due to local sources, 45.1% soil resuspension, 9.3% light vehicles and 26.1% heavy vehicles.

Keywords: low-cost sensors, PM2.5, early childhood, São Paulo.