In order to understand the sources that affect air pollution exceedences, it is necessary to separate the role of synoptic, mesoscale and microscale meteorological influences in regions with poor air quality. In Baltimore, which has frequent concentrations above the National Ambient Air Quality Standards (NAAQS) for ozone, for example, the complex land-water-urban-suburban geography can influence both the local scale flows as well as the depth of the planetary boundary layer. A critical parameter in determining air pollution concentrations near the ground is the depth through which pollutants are vigorously mixed. The planetary boundary layer (PBL) height is an important meteorological parameter that affects near-surface atmospheric pollutant concentrations since it determines the volume of air into which pollutants and their precursors are emitted, and is a fundamental feature for weather forecasts because it provides insight on the thermodynamic structure. The displacement of cooler air by warm, buoyant air can create or suppress vertical motion in the PBL, therefore affecting its diurnal height variation. Determining the mixing in the PBL was one goal of a study of the spatial and diurnal variations of the PBL height over Maryland for July 2011, during NASA's Earth Venture mission DISCOVER-AQ. The PBL heights were obtained from elastic lidars (surface and airborne) and wind profiler observations by determining the convective mixed layer using the covariance wavelet technique (CWT) and comparing it to the virtual potential temperature measurements from soundings. This July, a total of 16 ozone episode days (NAAQS 8 hour ozone concentrations greater than 75 ppb) occurred. The relationship between PBL height and surface ozone concentrations was evaluated against ventilation coefficients (product of the PBL height times the surface wind speed) and PBL growth rates during ozone episode and non-episode days. The temporal and spatial distribution of the PBL heights in Maryland was modeled with the Weather Research and Forecasting (WRF) model to characterize the role of shoreline circulation and thermally-induced boundary layers on locations along the Chesapeake Bay.

National Research Council (2009), Observing Weather and Climate from the Ground Up: A Nationwide Network of Networks. Washington, DC: National Academy Press.