Meteorological Factors Controlling the Evolution of Trace Gases and Particulates in Mexico City

The U.S. Department of Energy sponsored two field campaigns in the vicinity of Mexico City: the 1997 Investigacion sobre Materia Particulada y Deterioro Atmosferico - Aerosol and Visibility Research (IMADA-AVER) and the 2006 Megacity Aerosol Experiment: Mexico City (MAX-Mex) field campaigns. MAX-Mex was also part of a larger multi-agency deployment under the Megacities Initiative: Local and Global Regional Observations (MILAGRO) umbrella organization. Chris Doran contributed to defining the scientific objectives and organizing the instrumentation deployment for both of these campaigns. The focus of the IMADA-AVER campaign was to better understand the evolving boundary layer properties associated with the complex topography surrounding Mexico City. Strong flow through a gap in the terrain resulting from differential heating between the plateau and the surrounding environment were measured for the first time during the campaign, that are now recognized as one process that ventilates the pollutants emitted in Mexico City on a daily basis. During the MAX-Mex campaign, Chris Doran proposed three measurement sites: the first within the city, the second at the northern edge of the city: and the third in a remote site northeast of the city. The sites were chosen to obtain detailed measurements of aerosol aging as the Mexico City plume is transported to the northeast, which was determined to occur ~30% of the time. Measurements at these sites coupled with those obtained from research aircraft described for the first time the spatial distribution of trace gases and particulates in the region affected by boundary layer mixing and ventilation into the free atmosphere. The measurement strategy has been an important component of a majority of the 100 papers that now appear in the Atmospheric Chemistry and Chemistry special issue on MILAGRO. This talk will consist of two parts: the first describing Chris Doran's contributions to both field campaigns, and the second describing how measurements from the MAX-Mex campaign are currently being used to better understand aerosol aging processes and evaluate how well coupled meteorological-chemical models represent those processes.