Monitoring volatile organic compounds in the Metropolitan Area of São Paulo

The main sources of volatile organic compounds (VOCs) in the Metropolitan Area of Sao Paulo (MASP) are vehicular emissions. The addition of ethanol to gasoline results in increased emissions of some carbonyl compounds inducing a problem in photochemical smog formation in urban areas. At the same time, tropospheric ozone represents one of the main atmospheric pollutants in MASP. \ud \ud The megacities play an important role in atmospheric chemistry and climate that not only affects local populations but also in regional and global scale. In São Paulo state, controlling ozone levels is a priority, not only in the urban area but also in the neighboring cities and agricultural areas affected by the photochemical precursors and ozone coming from the megacity. Since this pollutant is formed in the atmosphere by photochemical reactions that depend on VOCs concentrations, NOx and UV radiation (l≤394nm), the current study presents data from continuous sampling and analysis of their precursors in SP city.\ud Hourly ozone and NOx were measured during the sampling campaign. Automatic hydrocarbons measurements were carried out 24 hours a day during 2012 and analyzed on a CG-FID coupled to thermal desorption unit. Meanwhile carbonyl compounds were collected every 2-hour between 8 a.m. to 6 p.m. and analyzed by HPLC. \ud \ud During the sampling period were obtained 110 samples of carbonyls compounds and more than 800 samples of hydrocarbons. The results indicated that most abundant hydrocarbons were toluene, ethane, propylene, propane, ethylene, 2-methylpentane, trans-2-butene, cis-2- butene and 1-butene which are related with a greater photochemical ozone potential formation following the MIR reactivity scale of Carter. The average mixing ratios of carbonyls were 9.8 and 5.8 ppbv for formaldehyde and acetaldehyde respectively.\ud \ud Statistical analyses were applied. High correlations between aromatic compounds were found, and a negative correlation of some hydrocarbons with the ozone. The hourly time average evolution shows that most of the compounds follow a similar pattern, which is\ud inversed to the compared ozone daily pattern. The study demonstrates that the ambient concentration of aldehydes has presented a significant reduction over the years.FAPESPFAPERJCNP