The Effects of Drought on Predictions of Air Quality in Texas: Vegetation and Biogenic Hydrocarbons

Abstract:

Biogenic hydrocarbons, primarily isoprene and monoterpenes, are important precursors for tropospheric ozone and secondary organic aerosol formation. Annual biogenic emissions in Texas ranked first within the continental United States in the 2011 National Emission Inventory. In recent years, the effects of drought in Texas have been among the most severe in the southern United States; during 2011, more than 80% of the state was under exceptional drought. Understanding the effects of drought on vegetation and biogenic emissions is important as the state concurrently faces requirements to achieve and maintain attainment with the National Ambient Air Quality Standard (NAAQS) for ozone in several large metropolitan areas. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) has been utilized extensively for the estimation of biogenic emissions on global and regional scales. This research investigates the interannual variability in leaf area index and isoprene and monoterpene emissions estimates from MEGAN in eastern Texas climate regions with diverse climatology and land cover. In MEGAN, the adjustment to emissions from a standardized set of environmental conditions is determined using a multiplication of individual activity factors for leaf age, soil moisture, and the canopy environment. The research also interprets and quantifies differences in environmental activity factors between years with extreme to exceptional drought and average to above average precipitation in eastern Texas and identifies influences on biogenic emissions estimates from MEGAN.