Dry Deposition Estimates in Texas during Drought Years

Abstract:

Severe drought has been a recurring phenomenon in the southwestern United States. Most climate models suggest that droughts will become more frequent in the future as climate changes in response to increased concentrations of greenhouse gases and other radiative forcing species in the atmosphere. Drought-induced changes in natural and anthropogenically managed and cultivated land cover systems have the potential to affect air quality. Dry deposition refers to the process by which trace gases and particulates in the atmosphere are transferred to the Earth’s surface, including to soil, vegetation, and water, in the absence of precipitation. It is a primary physical removal mechanism for ozone during the warm spring through early fall seasons in Texas. As the state endeavors to achieve and maintain attainment with the National Ambient Air Quality Standards (NAAQS) for ozone, it is important to understand the impacts of drought conditions on estimates of dry deposition. This research explores the interannual variations in predicted dry deposition velocities and component surface resistances of ozone in eastern Texas during 2006-2011, including years with severe to exceptional drought conditions (e.g. 2011) as well as years with average to above average precipitation patterns (e.g. 2007). Two widely used dry deposition algorithms that have been incorporated within the Comprehensive Air Quality Model with Extensions (CAMx), the photochemical grid model used to support air quality planning efforts in Texas, are used in offline simulations.