**6. Concluding remarks**

occurring in the MASP are primarily associated with vehicular emissions, some reports in literature examined the impact that the implemented control program for mobile emissions (PROCONVE) had on tropospheric ozone concentrations and evaluate the impact of using reformulated gasoline-ethanol blend (gasohol) and of hydrous ethanol on the ozone formation [88-93]. Studies related to the formation of fine particles are more sparse, Albuquerque et al. [94] analyzed the impact of reducing the sulfur content in the diesel and the secondary formation of sulfate-nitrate-amonnium system, showing that an increase in the nitrateammonium formation may occur while the decrease in the sulfate-ammonium system occurs.

402 Biofuels - Status and Perspective

Sanchez-Ccoyllo et al. [92] evaluated the impact of the PROCONVE implementation based on an episode of high surface ozone concentrations that occurred in the MASP during March, 2000, employing the California Institute of Technology/Carnegie Mellon University threedimensional photochemical model (CIT model [95-97]). In this work, different scenarios of emissions were considered according to the implementation of the PROCONVE. Scenario 1 assumed that all vehicles in the fleet were operating within PROCONVE guidelines. Scenarios 2 and 3 considered hypothetical situations in which PROCONVE had not been implemented. Scenario 2 established the premise that all vehicles were using pre-1989 technology, whereas scenario 3 allowed the existence of technological advances. That work showed that tropo‐ spheric ozone concentrations predicted for scenario 2 (vehicles pre-1989 technology) were higher than those predicted for scenarios 1, 3, and for the base case. The authors demonstrated that the PROCONVE had great influence on the improvement of air quality concerning ozone in MASP. In another studied developed by Sanchez-Ccoyllo et al. [93], the analysis was concentrated in the meteorological impacts on the ozone formation. Three meteorological variables: mixing height, wind speed, and air temperature, were considered in the study. The study also evaluated the role of having a reactive hydrocarbon (RHC) limitation or NOx limitation configuration on ozone formation in the MASP. In addition, NOx and RHC emission inventory reductions were used to evaluate their sensitivities with the CIT model. The results showed that changes in mixing height, wind speed, and air temperature input files have the greatest effect on peak ozone production, and the isolated effect of RHC emission reduction lead to 26% lower ozone levels compared to the base case. Based on the results of this study, the authors concluded that reductions on RHC emission could provide the best scenario for promoting lower ozone concentrations in the MASP. In agreement to these results, Orlando et al. [91] showed that the occurrence of high ozone production is more dependent on VOC in a study employing the trajectory model OZIPR together with the SAPRC chemical mechanism. In that work, five base-cases were created to verify the variation in maximum ozone concen‐ tration related to the ozone formation potential of each VOC that was injected in the airbase. The NO(x) and VOC emissions were independently and simultaneously reduced by 5%, 10%, 20%, and 30% to induce variations in ozone formation and the results showed that the most frequent compounds found among the ten main ozone precursors in Sao 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. In addition, the simulations data showed that an efficient strategy to decrease ozone concentrations in the MASP would be to reduce the total VOC emissions, while the same

Almost 30 years after the creation of Brazilian Motor Vehicle Air Pollution Control Program (PROCONVE), results show that the adoption of increasingly restrictive phases was successful and environmental concentration data show a clear downward tendency for several pollutants over past years, except for ozone and fine particles. The reduction on concentrations of these atmospheric pollutants became the big challenge for the public policies to elaborate efficient control strategies in urban areas of Brazil.

The Brazilian experience demonstrates how the impact of vehicular emissions can be reduced with the use of biofuels associated with technological developments. Results addressed in studies conducted in Brazil demonstrate that, although a considerable increase occurred in the number of LDV able to run on hydrous ethanol, and the increased use of biodiesel by HDV, key technological improvements in the design of the vehicles mitigated increases in the emissions of pollutants such as aldehydes, CO, and NOx.
