Transport Simulations of Carbon Monoxide and Aerosols from Boreal Wildfires during Arctas Using WRF-Chem

The Weather Research and Forecasting Model (WRF) was developed by the National Center for Atmospheric Research as the next generation mesoscale meteorology model. The inclusion of a chemistry module (WRF-Chem) allows transport simulations of chemical and aerosol species such as those observed during NASA's Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) during 2008. The ARCTAS summer deployment phase during June and July coincided with large boreal wildfires in Saskatchewan and Eastern Russia. One of the most important aspects of simulating wildfire plume transport is the height at which emissions are injected. WRF-Chem contains an integrated one-dimensional plume rise model to determine the appropriate injection layer. The plume rise model accounts for thermal buoyancy associated with fires and the local meteorological stability. This study compares results from the plume model against those of more traditional injection methods such as filling the planetary boundary layer or a layer 3-5 km above ground level (AGL). Fire locations are satellite-derived from the GOES Wildfire Automated Biomass Burning Algorithm (WF_ABBA) and the MODIS thermal hotspot detection. Two preprocessing methods for these fires are compared: the prep_chem_sources method included with WRF-Chem, and the Naval Research Laboratory's Fire Locating and Monitoring of Burning Emissions (FLAMBE). Satellite products from the AIRS, MISR and CALIOP sensors provide data for verifying the simulations. Observed near-source plume heights from MISR's stereo-height product are compared with the plume rise model's simulated injection heights. Long range plume transport is evaluated qualitatively in the horizontal using AIRS's total column carbon monoxide product. Qualitative vertical evaluation uses CALIOP's high vertical resolution and aerosol identification algorithm. Horizontal plume structures are further tested quantitatively using an object-based methodology. The plume rise model produces the best agreement with satellite-observed injection heights. Filling the planetary boundary layer or the 3-5 km AGL layer with emissions exhibit less agreement with the observational plume heights. Results indicate that WRF-Chem can accurately transport chemical plumes throughout the ten-day simulation. However, differences in injection heights produce different transport pathways. Small differences in injection height are ameliorated when synoptic scale features such as warm conveyor belts quickly loft the emissions to higher altitudes. In scenarios where large scale lofting is delayed, the plume rise simulations creates the most accurate simulated plumes.