ABSTRACT
O ozônio é o principal problema de poluição do ar na cidade de São Paulo. Este estudo, que foi realizado em uma estação de monitoramento da qualidade do ar da Companhia de Tecnologia de Saneamento Ambiental (CETESB), enfoca a elucidação dos principais compostos orgânicos voláteis precursores de ozônio na atmosfera paulistana. Foram coletadas 36 amostras nos meses de agosto e setembro de 2006, nos quais o consumo de etanol era de aproximadamente 50 por cento nesta época. Foram quantificadas 69 espécies de compostos orgânicos voláteis, nos quais os dez compostos mais importantes na formação de O3 foram: 1-buteno (6,8 por cento), eteno (6,5 por cento), formaldeído (6,1 por cento), acetaldeído (5,5 por cento), tolueno (4,8 por cento), 1-etil-4-metilbenzeno (3,7 por cento), trans-2-penteno (3,7 por cento), propeno (3,7 por cento), trans-2-buteno (3,5 por cento) e 1-metilciclopenteno (3,5 por cento). As classes mais abundantes em concentração no ar foram: alcanos (45 por cento), alcenos (26 por cento), aromáticos (14 por cento), aldeídos (13 por cento) e alcadienos (2 por cento).
Ozone is the main problem of air pollution in the city of São Paulo. This study, which was carried out in the Brazilian Basic Sanitation Engineering Company (CETESB, acronym in Portuguese) monitoring station of air quality, focused on the elucidation of the main volatile organic compounds ozone precursors in São Paulo atmosphere. Thirty-six samples were collected in August and September 2006, when the consumption of ethanol was about 50 percent, 69 species of volatile organic compounds were quantified, the ten major urban pollutants compounds in the formation of O3 were: 1-butene (6.8 percent), ethylene (6.5 percent), formaldehyde (6.1 percent), acetaldehyde (5.5 percent), toluene (4.8 percent), 1-ethyl-4-methylbenzene (3.7 percent), trans-2-pentene (3.7 percent), propylene (3.7 percent), trans-2-butene (3.5 percent), and 1-methylcyclopentene (3.5 percent). The most abundant classes of air concentration were: alkanes (45 percent), alkenes (26 percent), aromatics (14 percent), aldehydes (13 percent), and alkadyenes (2 percent).
ABSTRACT
Ozone represents the main atmospheric pollutant in the São Paulo Metropolitan Area (SPMA). In this region, its concentration exceeds the national air quality standards for several days out of the year. Ozone is a secondary pollutant and is a product of VOCs, NO(x), and sunlight. Thus, it is very difficult to elaborate efficient strategies for its reduction. Computational simulations may provide an interesting alternative to evaluate the many factors that affect ozone formation. In this study, the trajectory model OZIPR was used together with the SAPRC chemical mechanism to determine the incremental reactivity scale for VOCs in the SPMA. VOC input data were obtained from two campaigns that were performed in the studied area in 2006. Values for CO, NO(x), and meteorological parameters were obtained by automatic monitors. Five base-cases were created to verify the variation in maximum ozone concentration and thus determine the ozone formation potential of each VOC. NO(x) and VOC emissions were independently and simultaneously reduced by 5, 10, 20, and 30% to verify variations in ozone formation. With the simulator output data, ozone isopleths charts were generated for the city of São Paulo. Analysis of the obtained results shows that the most frequent compounds found among the ten main ozone precursors in São Paulo, using the reactivity scales created from the five base-cases, were: formaldehyde, acetaldehyde, propene, isoprene, cis-2-butene, and trans-2-butene, with formaldehyde being always the main ozone precursor compound. The simulations also show that an efficient strategy to decrease ozone concentrations in the SPMA would be to reduce total VOC emissions. The same strategy is not possible for NO(x), as the reduction of these pollutants would increase ozone concentrations.
