The Structure of the Planetary Boundary Layer in the Mexico City Metropolitan Area during the MCMA-2003 Field Campaign

The structure and evolution of the planetary boundary layer over Mexico City was observed by Lidar during a collaborative field campaign in April 2003. A typically complicated layering of different abundant aerosols up to 4500 m above ground made it necessary to develop a new data retrieval technique for the mixed layer recognition, taking advantage of the measured laser light depolarization. Lidar results are discussed and compared with mixing and boundary layer heights retrieved from carbon monoxide and meteorological radiosonde measurements as well as model calculations. The knowledge of the mixing and the stable nocturnal boundary layer height is crucial for the interpretation of the numerous ground-based measurements of chemical gas phase and aerosol components. Integral column measurements like photometer soundings are much more useful in conjunction with altitude resolved profiles, because most of the atmospheric aerosol is concentrated in the boundary layer. Results from different measurement techniques will be combined to present a coherent picture of the boundary layer structure during the campaign.