Computer modeling study of ethanol and aldheyde reactivities in Rio de Janeiro urban air

An empirical kinetic modeling approach was used in order to simulate ozone, formaldehyde and acetaldehyde 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, Brazil. The simulated ozone peak was obtained at 3:15 PM (23.00 ppb) in good agreement with experimental results. Calculated acetaldehyde and formaldehyde concentrations peaked at 21–24 and 14–17 ppb, respectively, between 11:00 AM and 13:00 PM, depending on the effective solar flux. Tagged species were used to discriminate between primary and secondary compounds and to follow the reaction paths of individual species. Computational results show that the primary contribution to acetaldehyde and formaldehyde concentrations is higher in the early morning and reaches a maximum, which approximately coincides with the peak automobile traffic. The secondary contribution increases during the morning and reaches a maximum in the early afternoon. As a consequence, total acetaldehyde and formaldehyde levels peak after the primary pollutants’ maximum, obtained in the early morning, and before the secondary pollutants’ maximum as previously noted in experimental determinations. The simulations also confirm the experimental evidence that the high acetaldehyde/formaldehyde ratios are due to the use of alcohol-based fuels.