Air quality status and trends over the Metropolitan Area of São Paulo, Brazil as a result of emission control policies

Fourteen years of regulated air pollutants concentrations were analyzed in order to characterize the benefits of Brazil's emission control policies on air quality conditions and to evaluate the temporal patterns between 1996 and 2009 over the Metropolitan Area of São Paulo (MASP). MASP includes one of the largest cities in the world (São Paulo) and its light-duty vehicular fleet has a very important characteristic in that it uses, on a large scale, fuels such as ethanol derived from sugar cane and compressed natural gas. Nowadays, ethanol makes up more than 50% of the fuel used in Brazil. The frequent episodes with high ozone and PM10 concentration values in the MASP are mostly associated with vehicular emissions - primary emission of particles and gases enrolled in ozone photochemical production and formation of secondary fine particles. Although the fleet has increased at a substantial rate, annual mean values show a diminishing tendency for all pollutants except for ozone, which presents no significant tendency. This diminishing tendency in the analyzed period is due to the vehicular emission control program established by the Brazilian Government in 1986, called PROCONVE (Program for the Control of Vehicular Emission). Monthly mean values, as expected, show higher concentrations of all pollutants except for ozone during wintertime. The diurnal cycle of the pollutants in most of the stations shows two peaks, associated with rush hours, except for ozone, whose peak follows the maximum radiation incidence. Secondary (nocturnal) ozone concentration maxima were sometimes verified around three and four LST. Average values for weekdays and weekends showed that the different air quality stations showed different patterns for the pollutants. For ozone the concentrations were higher during the weekend when compared to weekdays.