Mexico City provides a unique location for the study of air pollution since it has one of the world's most serious problems. There are 20 million people, 3 million private vehicles, and 300,000 industries in the basin enclosing the urban area. The surrounding mountains hinder ventilation, and concentrations of ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide, hydrocarbons, total suspended particulate, and particulate matter less than 10 microns regularly exceed local standards. Visibility and human health are both strongly impacted and as a large metropolis trace species swept from the basin can also contribute significantly to budgets of free tropospheric ozone precursors. In order to investigate these issues in detail complex three dimensional coupled atmospheric-chemistry models are necessary. Also sophisticated higher order turbulent closure schemes can significantly improve the accuracy of turbulent transport of heat, momentum, moisture, and pollutants; however, at issue is the effect of these schemes on the accuracy of gas and aerosol phase predictions. In this study, variations of second order turbulence closure schemes have been implemented in the Regional Atmospheric Modeling System (RAMS) and the effect of these schemes on the pollutant concentrations in Mexico City are underway. One of the objectives of this effort is to develop an understanding of the importance of better representation of meteorological variables for modeling gas and aerosol phase chemistry, and hence the effect on emision control strategies. Better modeling of turbulent transport can lead to accurate representations of temperature (important for gas phase chemistry) and humidity (important for aerosol chemistry)
Symposium on Interdisciplinary Issues in Atmospheric Chemistry