Influence of summertime deep convection on formaldehyde in the middle and upper troposphere over Europe

[1] We present HCHO measurements performed during the Upper Tropospheric Ozone: Processes Involving HOx and NOx (UTOPIHAN) II aircraft campaign over central-western Europe and the northwestern Mediterranean region in 2003 and 2004. We compare these with box model and three-dimensional (3-D) chemistry-transport model results for “background” and “convective” conditions. Generally, we obtain good agreement between the model and measurement data, although the 3-D model tends to underestimate HCHO near the tropopause, whereas the box model tends to slightly overestimate HCHO for the background case. Sensitivity simulations indicate that the most important factors determining HCHO concentrations are the abundances of NO, reactive hydrocarbons (e.g., isoprene), CH3OOH, CH3OH, and acetone and also the level of irradiance. In the middle and upper troposphere the most important HCHO production term is the reaction of CH3O2 with NO (68 ± 10%, including a contribution of 38 ± 7% from CH4 oxidation), followed by the destruction of CH3OOH by OH and photolysis (14 ± 2%), and the reaction of CH3OH with OH (14 ± 8%). HCHO loss is dominated by photolysis rather than by the reaction with OH, except in the upper tropospheric convective case, where the loss by OH contributes about 50%. Our measurements furthermore indicate that convective transport of H2O2 can be very efficient.