The atmospheric boundary layer plays a key role in air quality: wind transports pollutants from their various sources, turbulence mixes and dilutes pollution, boundary layer cumulus clouds vent pollution into the free troposphere, and temperature and humidity levels in the boundary layer affect chemical reactions and the rates at which many dangerous compounds are formed. Without accurate meteorological models, especially within the boundary layer, it would be impossible to forecast air quality reliably.
The boundary layer team in NOAA/PSD has been integrally involved in numerous recent air quality field programs. These programs include the Central California Ozone Study (CCOS 2000); the Texas Air Quality Study (TexAQS 2000); the New England Air Quality Study (NEAQS 2002?); and the Texas Air Quality Study (TexAQS 2006). The next large field program that we will take part in is the summer 2010 CalNex campaign that will take place in California.
The role of the boundary layer team in these field programs has been to deploy meteorological instruments, collect data, run meteorological models, and evaluate the models using the instruments we deploy. The most important instrumentation deployed for characterizing the boundary layer and its role on air quality are wind profiling radars. From these profilers we are able to characterize transport directions and speeds, as well as determine the depth of turbulent mixing in the convective boundary layer. Additional instrumentation we have deployed includes surface meteorological stations (temperature, humidity, wind speed and direction, pressure, solar and net radiation, and soil temperature and humidity profiles); sodars; cloud radars; and turbulent heat and moisture flux systems.
Modeling related research has focused on using high-resolution (4km or less grid spacing) mesoscale models. Science questions addressed are the ability of these models to accurately simulate flow in complex terrain; to correctly follow the growth of the convective boundary layer; and to assess the impact of observations from networks of boundary layer profilers on improving the analyzed wind fields through four-dimensional data assimilation. In campaigns such as CCOS-2000 we collaborated with various air chemistry modelers. Meteorological simulations produced by the PSD boundary layer team are being used by the California Air Resources Board to develop their State Implementation Plan to meet EPA regulations on allowed ozone concentrations. More recently, we have also begun work on using Large Eddy Simulation (LES) models to address issues surrounding turbulent mixing within the boundary layer.
Evaluation of operational and research air quality models is another important area of research. In past field campaigns we have developed a real-time model evaluation web site, which incorporates meteorological observations, surface chemistry observations, and coupled (meteorology + chemistry) air-quality forecast information. Analysis of these data sets has focused on the impact of meteorology on air quality, and especially on the impact of meteorological forecast errors on pollution concentration forecast errors.