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Volume 16, issue 5
Atmos. Chem. Phys., 16, 3609-3629, 2016
https://doi.org/10.5194/acp-16-3609-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 3609-3629, 2016
https://doi.org/10.5194/acp-16-3609-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 Mar 2016

Research article | 17 Mar 2016

Trapping, chemistry, and export of trace gases in the South Asian summer monsoon observed during CARIBIC flights in 2008

Armin Rauthe-Schöch1, Angela K. Baker1, Tanja J. Schuck1,a, Carl A. M. Brenninkmeijer1, Andreas Zahn2, Markus Hermann3, Greta Stratmann4, Helmut Ziereis4, Peter F. J. van Velthoven5, and Jos Lelieveld1 Armin Rauthe-Schöch et al.
  • 1Max Planck Institute for Chemistry (Otto Hahn Institute), Department of Atmospheric Chemistry, Mainz, Germany
  • 2Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research, Karlsruhe, Germany
  • 3Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
  • 4German Aerospace Center (DLR), Institute for Atmospheric Physics, Oberpfaffenhofen, Germany
  • 5Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands
  • anow at: Goethe University Frankfurt, Institute for Atmospheric and Environmental Sciences, Frankfurt am Main, Germany

Abstract. The CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) passenger aircraft observatory performed in situ measurements at 10–12km altitude in the South Asian summer monsoon anticyclone between June and September 2008. These measurements enable us to investigate this atmospheric region (which so far has mostly been observed from satellites) using the broad suite of trace gases and aerosol particles measured by CARIBIC. Elevated levels of a variety of atmospheric pollutants (e.g. carbon monoxide, total reactive nitrogen oxides, aerosol particles, and several volatile organic compounds) were recorded. The measurements provide detailed information about the chemical composition of air in different parts of the monsoon anticyclone, particularly of ozone precursors. While covering a range of 3500km inside the monsoon anticyclone, CARIBIC observations show remarkable consistency, i.e. with distinct latitudinal patterns of trace gases during the entire monsoon period.

Using the CARIBIC trace gas and aerosol particle measurements in combination with the Lagrangian particle dispersion model FLEXPART, we investigated the characteristics of monsoon outflow and the chemical evolution of air masses during transport. The trajectory calculations indicate that these air masses originated mainly from South Asia and mainland Southeast Asia. Estimated photochemical ages of the air were found to agree well with transport times from a source region east of 90–95°E. The photochemical ages of the air in the southern part of the monsoon anticyclone were systematically younger (less than 7 days) and the air masses were mostly in an ozone-forming chemical mode. In its northern part the air masses were older (up to 13 days) and had unclear ozone formation or destruction potential. Based on analysis of forward trajectories, several receptor regions were identified. In addition to predominantly westward transport, we found evidence for efficient transport (within 10 days) to the Pacific and North America, particularly during June and September, and also of cross-tropopause exchange, which was strongest during June and July. Westward transport to Africa and further to the Mediterranean was the main pathway during July.

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The flying laboratory CARIBIC onboard a passenger aircraft measured trace gases and aerosol particles in the upper tropospheric Indian summer monsoon anticyclone in summer 2008. We used the measurements together with meteorological analyses to investigate the chemical signature of the northern and southern part of the monsoon, the source regions from where the air was entrained into the monsoon and which parts of the world received polluted air that had been chemically processed in the monsoon.
The flying laboratory CARIBIC onboard a passenger aircraft measured trace gases and aerosol...
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