The urban population of South America has grown at 1.05%/yr, greater urbanization increasing problems related to air pollution. In most large cities in South America, there has been no continuous long-term measurement of regulated pollutants. One exception is SAo Paulo, Brazil, where an air quality monitoring network has been in place since the 1970s. In this paper, we used an air quality-based approach to determine pollutant trends for emissions of carbon monoxide (CO), nitrogen oxides (NOx), ozone (O-3), and coarse particulate matter (PM10), mostly from mobile sources, in the Metropolitan Region of SAo Paulo for the 2000-2013 period. Mobile sources included light-duty vehicles (LDVs, comprising gasoline- or ethanol-powered cars and motorcycles) and heavy-duty vehicles (HDVs, comprising diesel-powered trucks and buses). Pollutant concentrations for mobile source emissions were measured and correlated with fuel sales by the emission factors. Over the 2000-2013 period, concentrations of NOx, CO, and PM10 decreased by 0.65, 0.37, and 0.71%month(-1), respectively, whereas sales of gasoline, ethanol, and diesel increased by 0.26, 1.96, and 0.38%month(-1), respectively. LDVs were the major mobile source of CO, whereas LDVs were the major source of NOx and PM10. Increases in fuel sales and in the corresponding traffic volume were partially offset by decreases in pollutant concentrations. Between 2000 and 2013, there was a sharp (-5ppbmonth(-1)) decrease in the concentrations of LDV-emitted CO, together with (less dramatic) decreases in the concentrations of HDV-emitted NOx and PM10 (-0.25 and -0.09ppbmonth(-1), respectively). Variability was greater for HDV-emitted NOx and PM10 (R=-0.47 and -0.41, respectively) than for LDV-emitted CO (R=-0.72). We draw the following conclusions: the observed concentrations of LDV-emitted CO decreased at a sharper rate than did those of HDV-emitted NOx and PM10; mobile source contributions to O-3 formation varied significantly, LDVs making a greater contribution during the 2000-2008 period, whereas HDVs made a greater contribution during the 2009-2013 period, and decreases in NOx emissions resulted in increases in O-3 observations1201262906340CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ400419/2014-9Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Sao Paulo Research Foundation) Research Program on Global Climate Change; Coordenacao de Acoes Nacionais do Programa Ciencia sem Fronteiras (Office for the Nationwide Activities of the Science Without Borders Program
