Evaluation of NCEP Atmospheric Models for Driving Air Quality Prediction

Operational air quality predictions for the United States (U. S.) are provided by National Air Quality Forecasting Capability (NAQFC). NAQFC provides nationwide operational predictions of ozone and particulate matter. Predictions are produced twice per day (at 06 and 12 UTC cycles) at 12 km resolution and 1 hour time intervals through 48 hours and distributed at http://airquality.weather.gov. The NOAA National Centers for Environmental Prediction (NCEP) operational North American Mesoscale (NAM) 12 km weather predictions is used to drive the Community Multiscale Air Quality (CMAQ) model. Higher resolution operational NWP models have recently been introduced as part of the NCEP model suite. These include the NAM CONUS Nest (4 km horizontal resolution) and the Fire Weather nest (1.33 km for smaller domains) run four times per day through 60 hours and the High Resolution Rapid Refresh (HRRR, 3 km) run hourly out to 15 hours. This paper will evaluate the impact of higher resolution models for capturing boundary layer and orographic flows important for driving air quality prediction. The NWP models will be evaluated against standard and mesonet fields averaged for various regions for August 2014 and December 2014. The Updated Real-time Mesoscale Analysis (URMA) will also be used for evaluations. URMA adjusts a background meteorological field to the nearby observations using the two dimensional version of the NCEP variational Global Statisical Interpolation (GSI) assimilation system. Such diagnostic downscaled meteorological analyses and predictions that account for complex terrain and coastal effects are often used to drive air pollution models on local scales. Large errors in ozone prediction are often found around the Los Angeles Basin in the summer months while using the operational 12 km NAM – CMAQ system. This presentation overviews the NCEP mesoscale analysis and prediction systems (e.g.: NAM and its high resolution nests, HRRR, RTMA). An evaluation of meteorological fields important to air quality modeling (eg: near surface winds, temperatures, moisture and boundary layer heights, cloud cover) will be reported on for the NAM, NAM nests and Downscaled predictions for the Los Angeles basin. The meteorological performance will be presented along with errors in the operational NAM-CMAQ system to evaluate the correlation between ozone error and the ability of the mesoscale model to resolve local flows influenced by the complexity of surrounding topography.