Traffic Related Air Quality Trends in São Paulo, Brazil

Abstract:

An air quality based approach is used to determine pollutant-trends of carbon monoxide (CO), nitrogen oxides (NO_X), ozone (O₃) and particle matter (PM₁₀) mostly from road transport sources in the Metropolitan Region of São Paulo (MRSP) for the years 2000-2013. Road transport sources included flex (gasoline and ethanol) cars and motorcycles and diesel trucks and buses. Air pollutant concentrations for the transport sources were measured and related with the fuel sales by the emission factors (EFs) expressed in grams of pollutant per kilometer driven or unit of fuel consumed. Over the 14- year time period, pollutant concentrations of NO_X, CO and PM₁₀ decreased by 0.65, 0.37 and 0.71% month^-1, respectively. Oppossitely during this time, fuel sales of gasoline, ethanol and diesel increased by 0.26, 1.96 and 0.38% month^-1. Flex engines are the prevalent road source of CO, oppositely to diesel ones which appear to be the major source of NO_X and PM₁₀. Decrease in air pollutants are partially offset by the increment of fuel sales and related transport activity. For CO, there have been steep decreases in pollutant concentrations (rate of -5 parts per billion, ppb, month^-1) for gasoline and ethanol engines between 2000 and 2013. Similarly, diesel related NO_X and PM₁₀ concentrations decreased but at slower time rates (-0.25 and -0.09 ppb month^-1). Rates uncertainties are larger for diesel pollutants (coefficient of determination R of -0.47 and -0.41) than for gasoline and ethanol related CO (R equal to -0.72). This paper led to the following conclusions: (1) concentrations of gasoline and ethanol related CO, estimated by air quality network measurements, decreased at steeper rate than diesel pollutants NO_X and PM₁₀, (2) transport source contributions to the O₃ formation differ significantly through the time period focus of this work, with higher contributions coming from gasoline and ethanol engines at the beinning of the reviewed period (2000-2007) and from diesel engines at the end (2008-2013).