Sensitivity Of Ozone Concentrations To Diurnal Variations Of Surface Emissions In Mexico City: A Wrf/chem Modeling Study

摘要

Sensitivity of ozone (O_3) concentrations in the Mexico City area to diurnal variations of surface air pollutant emissions is investigated using the WRF/Chem model. Our analysis shows that diurnal variations of nitrogen oxides (NO_χ = NO + NO_2) and volatile organic compound (VOC) emissions play an important role in controlling the O_3 concentrations in the Mexico City area. The contributions of NO_X and VOC emissions to daytime O_3 concentrations are very sensitive to the morning emissions of NO_χ and VOCs. Increase in morning NO_χ emissions leads to decrease in daytime O_3 concentrations as well as the afternoon O_3 maximum, while increase in morning VOC emissions tends to increase in O_3 concentrations in late morning and early afternoon, indicating that O_3 production in Mexico City is under VOC-limited regime. It is also found that the nighttime O_3 is independent of VOCs, but is sensitive to NO_χ. The emissions of VOCs during other periods (early morning, evening, and night) have only small impacts on O_3 concentrations, while the emissions of NO_χ have important impacts on O_3 concentrations in the evening and the early morning. This study suggests that shifting emission pattern, while keeping the total emissions unchanged, has important impacts on air quality. For example, delaying the morning emission peak from 8 am to 10 am significantly reduced the morning peaks of NO_χ and VOCs, as well as the afternoon O_3 maxima. It suggests that without reduction of total emission, the daytime O_3 concentrations can be significantly reduced by changing the diurnal variations of the emissions of O_3 precursors.