Analysis of the Observations From the GABRIEL Field Campaign (Surinam, October 2005) Using two Global Atmospheric Chemistry Models

We present a comparison of the detailed set of measurements taken by aircraft over Surinam during October 2005 for the GABRIEL (Guyanas Atmosphere-Biosphere exchange and Radicals Intensive Experiment with the Learjet) campaign with the Offline Chemistry-Transport Model MATCH-MPIC and the Chemistry-Climate Model EC-HAM5/-MESSy1, and examine the sensitivity of the comparisons to various model parameters. Both models underestimate the high concentrations of OH radical observed during the campaign, although ECHAM5/MESSy1 better captures the range of values observed. MATCH-MPIC also performs more poorly in the planetary bounday layer compared with ECHAM5/MESSy1, where MATCH-MPIC also underestimates the high humidities observed during the campaign. Both models simulate HO2 radical concentration well in the free troposphere and the marine boundary layer, and underestimate it in the terrestrial boundary layer. Our initial analysis indicates that MATCH-MPIC performs particularly well in simulating several episodes of biomass burning influence observed during the campaign, which are not reproduced well by ECHAM5/MESSy1. Sensitivity studies with biomass burning emissions and tagged CO tracers indicate that biomass burning in Africa contributes substantially to background CO over Surinam while episodes of high CO mixing ratio correspond with South American biomass burning.