Role of convection in determining the budget of odd hydrogen in the upper troposphere

This paper presents a model study of the changes in upper tropospheric HOx (= OH + HO2) due to upward convective transport of surface pollutants. The model used is a three-dimensional global Lagrangian tropospheric chemistry transport model of 70 chemical species and 150 reactions including nonmetha ne hydrocarbon chemistry. It is driven by meteorological data from the U.K. Meterological Office with a 6 hour time resolution. We find that the effec t of convection is to increase upper tropospheric (300-200 hPa) HOx globall y by over 50%. The effect is greatest over the tropical continents where co nvection and VOC emissions from vegetation are colocated. The convection of isoprene, and hydroperoxides has the greatest effect. Convecting formaldeh yde and acetone has a lesser effect. The contribution from isoprene depends more on the convection of its degradation products than the convection of isoprene itself. The upper tropospheric HOx budget is shown to be very sens itive to the model implementation of convective wet deposition.