There is a consensus that particulate matter and gases pollutants originating from industry and vehicle emission processes in urban areas are important from the point of view of public health and climate change. Local anthropogenic emissions, especially those resulting from energy generation processes from the industrial and transport sector, are connected with those occurring at the regional and global scales. A major concern in the Metropolitan Area of Sao Paulo (MASP) is the impact of the large scale use of ethanol as a fuel and as an additive for Otto vehicles. In this study, atmospheric concentrations of ozone, nitrogen oxides (NO and NO2), formaldehyde and acetaldehyde were measured in the MASP in Brazil, over four seasons in 2012 and 2013. The results were compared with data collected in previous studies. Our results demonstrate that, although there was a large increase in the number of vehicles in the MASP that use ethanol ("flex-fuel" vehicles), technological advances in vehicle emissions control have prevented any significant increase in the atmospheric concentrations of aldehydes. In addition, an increase in the formaldehyde/acetaldehyde ratio has been observed. (C) 2014 Elsevier Ltd. All rights reserved.