The NOAA-EPA Air Quality Forecast (AQF) system is based on the coupling of North American Mesoscale (NAM) meteorological model (currently, WRF-NMM) and the Community Multiscale Air Quality (CMAQ) atmospheric chemistry transport model, wherein CMAQ is driven by the meteorological data from the NAM. An experimental AQF system (AQFX) was introduced by employing the same vertical coordinate system of NAM, i.e. the hybrid ċ-P coordinate, in CMAQ governing equations and calculations. This updated system provides more accurate representation of the 3-D meteorological fields and reduce mass inconsistency errors in chemistry/transport calculations.

Lateral boundary conditions (LBC) constitute a key input parameter in regional air quality model calculations. To represent the possible influence of stratospheric intrusions on the simulated 3-D ozone (O3) distributions, the initial NAM-CMAQ configurations explored the use of the Global Forecast System (GFS) as a possible source of lateral boundary conditions. However, this approach resulted in an overestimation of O3 concentration in the upper free-troposphere and thus the surface O3 concentration in certain meteorological condition (e.g. tropopause folding).

Potential Vorticity (PV) has been shown to be strongly correlated with O3 concentrations in the upper troposphere. In this study, we will use AQFX to explore the use of PV to specify O3 concentrations in the top-most CMAQ layer (~100mb). Model calculations with the default LBCs and the PV configurations are compared to analyze the relative merits of the two approaches. Model simulations of 3-D O3 distributions will be compared with ozonesonde measurements during 2006 from the IONS network.

Disclaimer: The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. This work constitutes a contribution to the NOAA Air Quality Program. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.