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Preprints
https://doi.org/10.5194/acp-2020-93
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-93
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  19 Feb 2020

19 Feb 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Impact of the South Asian monsoon outflow on atmospheric hydroperoxides in the upper troposphere

Bettina Hottmann1, Sascha Hafermann1, Laura Tomsche1,a,b, Daniel Marno1, Monica Martinez1, Hartwig Harder1, Andrea Pozzer1, Marco Neumaier2, Andreas Zahn2, Birger Bohn3, Helmut Ziereis4, Jos Lelieveld1, and Horst Fischer1 Bettina Hottmann et al.
  • 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, 55128, Germany
  • 2Karlsruhe Institute of Technology, Karlsruhe, 76021, Germany
  • 3Forschungszentrum Jülich GmbH, Jülich, 52425, Germany
  • 4German Aerospace Center, Institute of Atmospheric Physics, Oberpfaffenhofen, 82234, Germany
  • anow at: NASA Langley Research Center, Hampton, VA 23681, USA
  • bnow at: Universities Space Research Association, Columbia, MD 21046, USA

Abstract. During the OMO (Oxidation Mechanism Observation) mission, trace gas measurements were performed onboard the HALO (High Altitude LOng range) research aircraft in summer 2015 in order to investigate the outflow of the south Asian summer monsoon and its influence on the composition of the Asian Monsoon Anticyclone (AMA) in the upper troposphere over the eastern Mediterranean and the Arabian Peninsula. This study focuses on in situ observations of hydrogen peroxide (H2O2) and organic hydroperoxides (ROOH), as well as their precursors and loss processes. Observations are compared to steady state calculations of H2O2, methyl hydroperoxide (MHP) and inferred unidentified hydroperoxide (UHP) mixing ratios. Measurements are also contrasted to simulations with the general circulation ECHAM/MESSy for Atmospheric Chemistry (EMAC) model. We observed enhanced mixing ratios of H2O2, MHP and UHP in the AMA relative to the northern hemispheric background. Highest concentrations for H2O2 and MHP were found in the southern hemisphere outside the AMA, while for UHP, highest concentrations were found within the AMA. In general, the observed concentrations are higher than steady-state calculations and EMAC simulations. Especially in the AMA, EMAC underestimates the H2O2 and ROOH mixing ratios. Longitudinal gradients indicate a pool of hydroperoxides towards the center of the AMA, most likely associated with upwind convection over India. This indicates main contributions of atmospheric transport to the local budgets of hydroperoxides along the flight track, explaining strong deviations to steady-state calculations which only accounts for local photochemistry. Deviations to EMAC simulations are most likely due to uncertainties in the scavenging efficiencies for individual hydroperoxides in deep convective transport to the upper troposphere, corroborated by a sensitivity study. It seems that the observed excess UHP is excess MHP transported to the west from an upper tropospheric source related to convection in the summer monsoon over South-East Asia.

Bettina Hottmann et al.

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Bettina Hottmann et al.

Bettina Hottmann et al.

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Short summary
During OMO we observed enhanced mixing ratios of hydroperoxides (ROOH) in the Asian Monsoon Anticyclone (AMA) relative to the background. The observed mixing ratios are higher than steady-state calculations and EMAC simulations, especially in the AMA, indicating atmospheric transport of ROOH. Deviations to EMAC are likely due to uncertainties in the scavenging efficiencies. Longitudinal gradients indicate a pool of ROOH towards the center of the AMA, associated with upwind convection over India.
During OMO we observed enhanced mixing ratios of hydroperoxides (ROOH) in the Asian Monsoon...
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