Estimating the Spread in Future Fine Dust Concentrations in the Southwest United States

Abstract

AbstractThis work examines how environmental variables previously shown to be correlated with dust emissions (temperature, vapor pressure deficit, relative humidity, precipitation, soil moisture, wind speed, and leaf area index [LAI]) explain historical variability in observed fine dust concentrations in the southwestern United States. We quantify fine dust concentrations in the U.S. Southwest dust season, March through July 1995 through 2015, using fine iron measurements from the Interagency Monitoring of Protected Visual Environments network as a dust proxy. We use Coupled Model Intercomparison Project Phase 5 (CMIP5) output to estimate how environmental variables that drive dust concentrations may change in the future. The majority of CMIP5 models that simulate LAI, a quantity anticorrelated with dust concentrations, show increasing LAI in the Southwest United States in the 21st century. Based on linear estimates of how dust concentrations respond to changes in LAI, increases in LAI could result in reduced dust concentrations in the future. However, when environmental variables are selected objectively using lasso regression, LAI is not selected in favor of other variables. When using a linear combination of objectively selected environmental variables, we estimate that future Southwest dust season concentrations will increase by 0.24 μg m−3 (12%) by the end of the 21st century for RCP 8.5. This estimated increase in fine dust concentration is driven by decreases in relative humidity, precipitation, and soil moisture and buffered by decreased wind speeds.