Changes in the Spatial Distribution of Ozone, NO, NO2 and CO Brought About by Different Vehicular Emission Scenarios in Sao Paulo, Brazil, During an Atmospheric High-Pressure Event.

Abstract:

Atmospheric pollution in the Sao Paulo Metropolitan Area (SPMA) has been investigated using the WRF/Chem model version 3.2.1 in a 1X1 km emission grid. Based on a local emission inventory, a control simulation (CTRL) was performed for the period 28/01-02/02/2014, during a summer season characterized by intense solar radiation and temperature positive anomalies, which resulted in high pollutant concentration. Sensitivity tests were performed using different vehicular emission scenarios and CTRL. In scenario A), emissions were removed from a region which encompasses almost the entire urban area of the SPMA, only roads in the outskirts had regular emissions. Comparing scenario A) to CTRL, sharp decreases in CO, NO and NO2 were observed inside the SPMA. Ozone decreased slighlty during the day, probably due to the significant absence of precursor emissions which form ozone during the day in the presence of sunlight. On the other hand, ozone concentrations increased at night, influenced by the absence of ozone-consuming precursors inside the densely urbanized SPMA, in the absence of sunlight. In scenario B), we removed emissions from a smaller area, corresponding roughly to an expanded downtown area (where a few traffic restriction laws operate). The goal of this scenario was to observe possible impacts if more strict traffic restriction laws were implemented. In scenario C), emissions were decreased by 50% in the same area, in an attempt to characterize concentrations in an urban toll scenario. Results from scenarios B) and C) showed a decrease in NO, NO2 and CO, but less intense than in scenario A). On the other hand, a higher increase in ozone was detected both during the day and at night compared to the CTRL and scenario A). These results suggests that, along with lower concentrations of precursor gases and CO, higher ozone concentrations are likely to be expected in downtown Sao Paulo if more severe traffic restriction laws should be implemented. This is concerning because ozone exceeds air quality standards more often than primary gaseous pollutants in the SPMA, especially during periods with favourable atmospheric conditions. These simulations are part of the partial results of the PhD thesis of the author; further experiments are planned to improve the accuracy and spatial representativeness of the simulations.