Can a global model chemical mechanism reproduce NO, NO2, and O3 measurements above a tropical rainforest?
1Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
2National Centre for Atmospheric Science (NCAS), University of York, Heslington, York, YO10 5DD, UK
3Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
4National Centre for Atmospheric Science�Climate, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
5Centre for Ecology and Hydrology Edinburgh, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK
6The University of Edinburgh, School of Chemistry, Joseph Black Building, West Mains Road, Edinburgh, EH9 3JJ, UK
7Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
8School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
*now at: NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO, 80501, USA
**now at: Department of Chemistry, University of Reading, Whiteknights, Reading, RG6 6AH, UK
Abstract. A cross-platform field campaign, OP3, was conducted in the state of Sabah in Malaysian Borneo between April and July of 2008. Among the suite of observations recorded, the campaign included measurements of NOx and O3–crucial outputs of any model chemistry mechanism. We describe the measurements of these species made from both the ground site and aircraft. We examine the output from the global model p-TOMCAT at two resolutions for this location during the April campaign period. The models exhibit reasonable ability in capturing the NOx diurnal cycle, but ozone is overestimated. We use a box model containing the same chemical mechanism to explore the weaknesses in the global model and the ability of the simplified global model chemical mechanism to capture the chemistry at the rainforest site. We achieve a good fit to the data for all three species (NO, NO2, and O3), though the model is much more sensitive to changes in the treatment of physical processes than to changes in the chemical mechanism. Indeed, without some parameterization of the nighttime boundary layer-free troposphere mixing, a time dependent box model will not reproduce the observations. The final simulation uses this mixing parameterization for NO and NO2 but not O3, as determined by the vertical structure of each species, and matches the measurements well.