Investigation of the Influence of Planetary Boundary Layer Evolution and Meteorology on Air Quality in Mexico City

The evolution of the planetary boundary layer (PBL) is critical to air pollution studies as it impacts the concentration of pollutants in the lower troposphere. Pollutants emitted at the surface are being trapped and raised to unhealthy levels within the PBL during stable atmospheric conditions. Meteorology plays a major role, especially when a high pressure system (associated with warm, clear sky conditions) is present. This enhances the formation of ozone (O₃) due to strong insolation during such atmospheric conditions. This study estimates the PBL height using the parcel method based on the potential temperature profiles measured continuously by a MP-3000A microwave radiometer and wind speed and direction data up to 3-5 km (a.g.l) by a 915 MHz RAPTOR radar wind profiler during two weeks in March 2016 from a monitoring site in Mexico City. Both instruments were deployed and maintained by SEDEMA (Secretaría del Medio Ambiente), the Environment Department of the Mexico City Municipality. Mexico City is located in a basin, which prevents proper ventilation of the polluted air. The hourly average concentration of the pollutants (O₃, NOx, and PM_2.5) were provided by the SEDEMA station at General Hospital of Mexico in the downtown area of Mexico City. The peak O₃ concentration of ~ 189 ppb observed on March14, 2016 (and even higher at some other stations) were the highest since 2007 and thus presented the most severe smog episode for almost a decade. The peak pollutant concentrations correlate well with the meteorological observations (weak winds, stablePBL) as well as air masses circulation within the Mexico basin.