Ensemble air quality forecasts over the Lower Fraser Valley, British Columbia: a summer 2004 case study

Preliminary results of an AQ ensemble forecast system will be presented. The system includes the Community Multiscale Air Quality Model (CMAQ), driven by the Fifth-Generation NCAR / Penn State Mesoscale Model (MM5) and the Mesoscale Compressible Community Model (MC2). CMAQ is run with a resolution of 12 and 4 km.

The different meteorological input fields from MM5 and MC2, as well as the fact that different ensemble members run at different resolutions lead to different parcel trajectories, allow the ensemble to filter out some of the unpredictable components of the weather. The resulting ensemble air-quality forecast has benefits similar to the well-proven ensemble weather forecasts; namely, more skillful forecasts further into the future.

The spatial domain considered in the simulation includes the Lower Fraser Valley (LFV) of British Columbia. The AQ data used to test the system performance are provided by Environment Canada and the Greater Vancouver Regional District. The daily operational runs include both the AQ ensemble forecasts as well as the verification runs against surface AQ observations. Results for the months of June and July 2004 will be presented.