Carbonyls in urban air continue to receive scientific and regulatory attention as toxic air contaminants and for their important role in photochemical smog. However, few data are available for speciated carbonyls in urban air. Ambient concentrations of up to 61 carbonyls have been measured in Rio de Janeiro, Brazil. The most abundant carbonyls were formaldehyde and acetaldehyde (study-averaged concentrations of 10.8 +/- 4.1 and 10.4 +/- 4.6 microg m(-3), respectively, in samples of 3-h duration collected from May to November 2000 at a downtown location during the morning vehicle commute) followed by acetone, 2-butanone, and benzaldehyde. Ambient concentrations of other carbonyls (except acetophenone) correlated well with those of acetaldehyde and of formaldehyde. This study examines the ambient acetaldehyde/ambient formaldehyde concentration ratio in Brazilian cities since the mid-1980s in the context of changes in Brazil's reliance on ethanol as a vehicle fuel. This ratio has begun to decrease in recent years due to fleet turnover and is likely to decrease further as older cars fueled with ethanol are replaced by lower-emitting models that run on a gasoline-ethanol blend. The carbonyls measured are ranked with respect to ozone formation potential (using MIR coefficients) and reaction with OH (using carbonyl-OH reaction rate constants). Ozone formation is dominated by formaldehyde (43% of total) followed by acetaldehyde (32%) and methylglyoxal (8%); other carbonyls each contributed < or = 4% of total. For reaction with OH, acetaldehyde ranks first closely followed by formaldehyde.

As concentrações de ozônio para um área urbana, com alto fluxo veicular, no centro da cidade, foram simuladas usando um modelo cinético empírico. Foi desenhado um caso base usando dados experimentais, do mês de dezembro de 1999, para a Avenida Presidente Vargas, Rio de Janeiro. O acordo entre os resultados calculados e os dados experimentais é satisfatório. O pico de ozônio calculado acontece às 15:15 horas (23,0 ppb). Foi realizada uma análise de sensibilidade e incertezas e desenhados alguns cenários hipotéticos para ilustrar a capacidade preditiva do modelo.An empirical kinetic modeling approach is used in order to simulate ozone concentrations for an urban downtown area with high vehicular traffic. A base case was designed using experimental data for December 1999 in Presidente Vargas Avenue, Rio de Janeiro. The agreement between experimental and simulated results was quite good. The simulated ozone peak was obtained at 3:15 PM (23.0 ppb). A sensitivity-uncertainty analysis was performed and hypothetical scenarios were designed to illustrate the predictive potential of Air Quality Models.

Meassurements of pollutants concentrations in tunnels can reflect the actual characteristics of mobile sources in order to provide a control strategy to reduce emissions and secondary pollutants formation. Concentration levels of CO, NOx, SO2 and PM10 (particulate matter less than 10 m in diameter) were recorded inside Rebouças Tunnel, in a continuous monitoring station installed at about 1,500 m from the entrance. The reported data are the hourly average values through the year of 2002, bracketed only for the weekdays, weekends excluded. In terms of typical day cycles, the highest concentration levels occur close to traffic peaks and the criteria pollutants show good overall correlation levels with CO, as expected, given their common combustion-bound origin. CO hourly averages ranged from 10 to 50 ppm and the average CO/NO ratio (on a ppm basis) was 0.011, in good agreement with preliminary data for other locations in Brazil. NO concentration levels ranged from less than 1 ppm to about 4 ppm and this form is by far the dominant for nitrogen oxides (NOx) found in the tunnel, accounting for more than 90% of the sum of NO plus NO2. Sulfur oxides (measured as SO2 ) and inhalable particles concentrations ranged from 55 to 140 ppb and about 60 to 250 µg m-3 , respectively, for the composite annual profiles.