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In order to investigate the effects of convection on the OH-oxidation potential and trace gas composition in the Upper Troposphere (UT), the 'Chemistry of the Atmosphere Field Experiment–Africa' (CAFE–Africa) was conducted in August 2018. The intense solar radiation in the tropics leads to the formation of a pronounced low-pressure region, the intertropical convergence zone (ITCZ). The southeasterly trade wind transports air influenced by biomass burning from southern African into the ITCZ, where they mix with emissions of volatile organic compounds (VOC), and through strong convection they get uplifted into the UT. During such transport, electrification can occur leading to formation of large amounts of NOX and HOX, which ultimately leads to intensified oxidation of boundary layer air masses during transport and with the UT itself. The High Altitude and Long Range (HALO) aircraft was used to investigate the effects of convection on OH mixing ratio (MXR) and the OH oxidation potential. The CAFE-Africa measurement data show that the effects of convection on OH-MXR and OH oxidation potential are more pronounced over continental areas when compared to maritime areas. The measured OH-MXR increases from 0.24(±0.09) pptv in the boundary layer to 1.07(±0.42) pptv in the continental outflow range at altitudes of 13.0-13.5 km. In the averaged maritime data set, there is not a pronounced altitude band, in which convective effects are observed, but a general increase between 12–15 km in OH-MXR of 0.52(±0.26) pptv. OHbudgets were also calculated for the air masses in the UT. We found that the OH-Production Rate (PR) in the continental influence is 12.27(±3.6)·105 molec cm-3s-1, which exceeds the maritime OH-PR by a factor of three. In both air mass types, the largest source of OH is the secondary formation via the HO2+NO channel. For an in-depth investigation of convective effects, OH-reactivity within the UT was parameterized. OH removes VOCs faster than CO, so the CO/VOC ratio should be higher within the fresh convected air masses. Conversely, aged air masses, should be dominated by CO-reactivity. The air masses were separated into fresh-convective and aged air masses, based on the larger reactivity. Convective air masses show in average an increase in OH-PR of 40-50%, which results from an increase in OH production via HO2+NO. In the continental airmass, this is caused by an increase in the NO-MXR. For maritime convective air in the UT however, NO does not increase. In this case there is an increase in HO2 transported to the UT with an origin in the marine boundary layer. Additionally there is an increase in H2O2 during marine convection that further increases OH-PR. Finally, the OH-recycling probability was calculated for the UT data. The OH-recycling probability can be interpreted as a measure of the stability of the prevailing oxidation potential. Low primary and high secondary OH-PR lead to a trend that deviates from that described in the literature. Under normal conditions H2O2 is considered as a secondary OH source. However, investigation of the recycling probability showed, that in order to analyze the OH-recycling probability in the UT, parts of H2O2 must be considered as a primary OHsource if it is transported into the UT by convection and its origin lies in another chemical system
