Traffic‐related air quality trends in São Paulo, Brazil

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 São 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 (NO x ), ozone (O 3 ), and coarse particulate matter (PM 10 ), mostly from mobile sources, in the Metropolitan Region of São 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 NO x , CO, and PM 10 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 NO x and PM 10 . 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 (−5 ppb month −1 ) decrease in the concentrations of LDV‐emitted CO, together with (less dramatic) decreases in the concentrations of HDV‐emitted NO x and PM 10 (−0.25 and −0.09 ppb month −1 , respectively). Variability was greater for HDV‐emitted NO x and PM 10 ( 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 NO x and PM 10 ; 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 NO x emissions resulted in increases in O 3 observations.