Modeling the Emission, Transport, and Dispersion of Post-wildfire Dust from Western Sagebrush Landscapes within a Regional Air Quality Framework

Abstract:

Millions of hectares are burned by wildfires each year in the western US. The resulting burn scars are extremely wind erodible surfaces with high loadings of easily entrained ash and soil. Previous work has demonstrated that wind erosion from these burn scars can release large amounts of dust and ash as particulate matter (PM) into the atmosphere, resulting in large impacts on downwind air quality and visibility. Sagebrush-dominated landscapes, where often essentially all vegetation is consumed by the fire, appear to be particularly vulnerable. Climate change predictions indicate more wildfire activity in the western US and, hence, more potential for wind erosion from burn scars. However, these PM sources are not yet accounted for in regional air quality models. Here we describe a modification to the AIRPACT regional air quality modeling framework for simulating the emission, transport and dispersion of PM from post-wildfire burn scars. We present results from a 2012 sagebrush fire in southeast Oregon as a case study. Modeled PM emission rates and downwind concentrations are compared against observations for two major dust events, one which resulted in exceedances of the PM10 National Ambient Air Quality Standard in Boise, Idaho the month after the fire and another which resulted in a significant dust on snow event and subsequent snowmelt in the Owyhee Mountains of southwest Idaho the following spring. Additionally, we present model estimates of annual emissions from all wildfires that occurred in sagebrush landscapes of the western US during the 2012 fire year as an estimate of annual post-fire PM loading potential.