Locally induced surface air confluence by complex terrain and its effects on air pollution in the valley of Mexico

Using a meteorological computational model it is shown how, in the Valley of Mexico, a high pressure system together with the complex orography of the region induce the formation of a local confluence line. With the aid of a prognostic air quality model it is shown that the maximum pollutant mixing ratios are placed on and follow the confluence line which crosses over the most populated areas of Mexico City. This phenomenon provides an explanation of why and when pollutants assume its geographical distribution in the valley during high mixing ratio episodes.