the Underestimation of Isorene in Houston during the Texas 2013 DISCOVER-AQ Campaign

Abstract:

This study applies principal component analysis to aircraft data from the Texas 2013 DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) field campaign to characterize isoprene sources over Houston during September 2013. The biogenic isoprene signature appears in the third principal component and anthropogenic signals in the following two. Evaluations of the Community Multiscale Air Quality (CMAQ) model simulations of isoprene with airborne measurements are more accurate for suburban areas than for industrial areas. This study also compares model outputs to eight surface automated gas chromatograph (Auto-GC) measurements near the Houston ship channel industrial area during the nighttime and shows that modeled anthropogenic isoprene is underestimated by a factor of 10.60. This study employs a new simulation with a modified anthropogenic emissions inventory (constraining using the ratios of observed values versus simulated ones) that yields closer isoprene predictions at night with a reduction in the mean bias by 56.93%, implying that model-estimated isoprene emissions from the 2008 National Emission Inventory are underestimated in the city of Houston and that other climate models or chemistry and transport models using the same emissions inventory might also be underestimated in other Houston-like areas in the United States.