Convective transport of hydroxyl and hydroperoxyl precursors to the upper troposphere

Tropospheric photochemistry point models are unable to capture the vertical structure of HOx (HO and HO2), important atmospheric oxidants in the troposphere. Specifically, the models underestimate HOx levels in the upper troposphere. Convective vertical motion has been proposed as a mechanism to transport HOx precursors, hydrogen peroxide (H2O2), methylhydroperoxide (CH3OOH), and formaldehyde (CH2O), into the upper troposphere where they are photolyzed to form HOx. Using a convective influence product which incorporated air mass back trajectories and GOES water vapor images, marine tracers methyl iodide and bromoform, and continental tracers tetrachloroethene and dichloromethane where identified as excellent tracers for convective influence in the upper troposphere. Furthermore, the ratio of H2O2 to CH3OOH was shown to detect convection over marine regions due to the preferential removal of H 2O2 by precipitation or reactions with SO2 in cloud droplets. These in-situ convective tracers were used to identify convected air masses throughout the South Pacific. Enhancements up to a factor of 2 were identified in convective outflow during the Northern Hemisphere autumn. However, during the spring, peroxide enhancements were not observed due to excessive wet removal of H2O2 and lower CH3OOH boundary layer mixing ratios. Convective enhancements of CH2O were also not observed. In addition to transport in convective systems in the tropics, subtropical transport with CH3OOH levels up to 1 ppbv were observed in the mid-latitudes. These results show that vertical transport in convective systems is a source of HOx precursors to the upper troposphere and is important in regions where the background troposphere is dry. Furthermore, the impact of convective transport of HOx precursors is not isolated to the tropics, but is important globally