One-year of NMHCs hourly observations in São Paulo megacity: meteorological and traffic emissions effects in a large ethanol burning context

São Paulo Megacity (MASP), with more than 20 million inhabitants, is among the world's most populous cities. Brazil is the only area in the world where fuel with a high ethanol content has been used since 1975 and its usage have increased in the last decade with the development of flex-fuel vehicles. Here, the biofuel effect on VOCs burden and composition it is discussed by a crossed analysis of long-term ambient data and emission data over the last decades in MASP. The most abundant NMHCs in ppbv were propane (5.02 ± 5.94), ethylene (3.97 ± 4.55), ethane (2.28 ± 1.89), acetylene (1.98 ± 2.11), 2,2,4-trymethylpentane (2.05 ± 1.48), i-propylbenzene (1.96 ± 1.85), n-butane (1.97 ± 2.24), toluene (1.62 ± 2.02), i-pentane (1.30 ± 1.61) and propylene (1.26 ± 1.54). The comparison with studies performed in MASP over the last 15 years showed a decrease in the NMHC concentration levels, in spite of the growth of the vehicular fleet and fuel consumption. Nevertheless, NMHCs mean concentrations were higher in MASP compared to those in other megacities worldwide (Beijing, London, Los Angeles and Paris) by a factor of 1.1 to 10, although showing similar composition. This suggests that NMHC distribution is dominated by traffic emissions regardless of regional characteristics like fuel usage and composition. Diurnal profiles of NMHC in MASP confirm these findings by all showing the same patterns as CO and acetylene, both recognized as combustion emission tracers. Finally large-scale ethanol usage would not affect the distribution of NMHCs in MASP and gasoline vehicular emissions seem to be the most important source of hydrocarbons in urban areas.