Measurement report: Hydrogen peroxide in the upper tropical troposphere over the Atlantic Ocean and western Africa during the CAFE-Africa aircraft campaign
Authors: Hamryszczak Zaneta , Dienhart Dirk , Brendel Bettina , Rohloff Roland , Marno Daniel , Martinez Monica , Harder Hartwig , Pozzer Andrea , Bohn Birger , Zöger Martin , Lelieveld Jos , Fischer Horst 
Published: May 2023

Abstract. This study focuses on the distribution of hydrogen peroxide
(H2O2) in the upper tropical troposphere at altitudes between 8
and 15 km based on in situ observations during the Chemistry of the Atmosphere: Field Experiment in Africa (CAFE-Africa) campaign conducted in August–September 2018 over the tropical Atlantic Ocean and western Africa. The measured hydrogen peroxide mixing ratios in the upper troposphere show no clear trend in the latitudinal distribution with locally increased levels (up to 1 ppbv​​​​​​​) within the Intertropical Convergence Zone (ITCZ), over
the African coastal area, as well as during measurements performed in
proximity to the tropical storm Florence (later developing into a
hurricane). The observed H2O2 distribution suggests that mixing
ratios in the upper troposphere seem to be far less dependent on latitude
than assumed previously and the corresponding factors influencing the
photochemical production and loss of H2O2. The observed levels of
H2O2 in the upper troposphere indicate the influence of convective
transport processes on the distribution of the species not only in the
tropical but also in the subtropical regions. The measurements are compared
to observation-based photostationary steady-state (PSS) calculations and
numerical simulations by the global ECHAM/MESSy Atmospheric Chemistry (EMAC) model. North of the ITCZ, PSS
calculations produce mostly lower H2O2 mixing ratios relative to
the observations. The observed mixing ratios tend to exceed the PSS
calculations by up to a factor of 2. With the exception of local events, the comparison between the calculated PSS values and the observations indicates enhanced H2O2 mixing ratios relative to the expectations based on PSS calculations in the north of the ITCZ. On the other hand, PSS calculations tend to overestimate the H2O2 mixing ratios in most of the sampled area in the south of the ITCZ by a factor of up to 3. The significant influence of convection in the ITCZ and the enhanced presence of clouds towards the Southern Hemisphere indicate contributions of atmospheric transport and cloud scavenging in the sampled region. Simulations performed by the EMAC model also overestimate hydrogen peroxide
levels particularly in the Southern Hemisphere, most likely due to
underestimated cloud scavenging. EMAC simulations and PSS calculations both
indicate a latitudinal gradient from the Equator towards the subtropics. In
contrast, the measurements show no clear gradient with latitude in the
mixing ratios of H2O2 in the upper troposphere with a slight
decrease from the ITCZ towards the subtropics, indicating a relatively low
dependency on the solar radiation intensity and the corresponding photolytic
activity. The largest model deviations relative to the observations
correspond with the underestimated hydrogen peroxide loss due to enhanced
cloud presence, scavenging, and rainout in the ITCZ and towards the south.