Impact of vehicular technological improvements on emissions and air quality across Brazil

Controlling vehicular emissions is a critical priority, particularly in developing countries like Brazil, where the vehicular fleet has expanded significantly. Although Brazil's Program to Control Vehicular Emissions has reduced certain air pollutants by mandating technological advancements in new vehicles, it did not consider the substantial increase in vehicle numbers and density across the country. To date, no comprehensive national-scale evaluation has been conducted to assess the program's effectiveness in Brazil. This study investigates the impact of technological upgrades in the vehicular fleet on air quality across Brazil. The methodology includes different emissions inventories and integrates the Weather Research & Forecasting Model (WRF) with the Community Multiscale Air Quality Modeling System (CMAQ) to simulate air quality under different scenarios, including a scenario where vehicular technological improvements are implemented nationwide. Results indicate that while technological renewal of the vehicular fleet significantly reduces concentrations and exceedances of air quality standards mainly for carbon monoxide (CO) and nitrogen dioxide (NO₂), it is insufficient to control secondary pollutants such as tropospheric ozone (O₃) and fine particulate matter (PM_2.5). Our findings underscore the need for regionally tailored emission control plans. In the South, Southeast, and Northeast regions, where vehicular emissions are more dominant, combining fleet renewal with vehicle inspection and scrappage programs may be effective. In contrast, in the North and Midwest, where vehicular sources are less dominant, these measures should be complemented with broader multi-source strategies targeting the other relevant local emitters. This work contributes to guiding subnational authorities in developing regional emission control plans.