Abstract
We examine the capability of the Global Modeling Initiative (GMI) chemistry and transport model to reproduce global mid-tropospheric (618hPa) O(3)-CO correlations determined by the measurements from Tropospheric Emission Spectrometer (TES) aboard NASA's Aura satellite during boreal summer (July-August). The model is driven by three meteorological data sets (fvGCM with sea surface temperature for 1995, GEOS4-DAS for 2005, and MERRA for 2005), allowing us to examine the sensitivity of model O(3)-CO correlations to input meteorological data. Model simulations of radionuclide tracers ((222)Rn, (210)Pb, and (7)Be) are used to illustrate the differences in transport-related processes among the meteorological data sets. Simulated O(3) values are evaluated with climatological ozone profiles from ozonesonde measurements and satellite tropospheric O(3) columns. Despite the fact that three simulations show significantly different global and regional distributions of O(3) and CO concentrations, all simulations show similar patterns of O(3)-CO correlations on a global scale. These patterns are consistent with those derived from TES observations, except in the tropical easterly biomass burning outflow regions. Discrepancies in regional O(3)-CO correlation patterns in the three simulations may be attributed to differences in convective transport, stratospheric influence, and subsidence, among other processes. To understand how various emissions drive global O(3)-CO correlation patterns, we examine the sensitivity of GMI/MERRA model-calculated O(3) and CO concentrations and their correlations to emission types (fossil fuel, biomass burning, biogenic, and lightning NO(x) emissions). Fossil fuel and biomass burning emissions are mainly responsible for the strong positive O(3)-CO correlations over continental outflow regions in both hemispheres. Biogenic emissions have a relatively smaller impact on O(3)-CO correlations than other emissions, but are largely responsible for the negative correlations over the tropical eastern Pacific, reflecting the fact that O(3) is consumed and CO generated during the atmospheric oxidation process of isoprene under low NO(x) conditions. We find that lightning NO(x) emissions degrade both positive correlations at mid-/high- latitudes and negative correlations in the tropics because ozone production downwind of lightning NO(x) emissions is not directly related to the emission and transport of CO. Our study concludes that O(3)-CO correlations may be used effectively to constrain the sources of regional tropospheric O(3) in global 3-D models, especially for those regions where convective transport of pollution plays an important role.