Article

Journal of Atmospheric Chemistry

, Volume 15, Issue 3, pp 215-234

First online:

The distribution of light nonmethane hydrocarbons over the mid-Atlantic: Results of the Polarstern cruise ANT VII/1

  • R. KoppmannAffiliated withInstitut für Atmosphärische Chemie, Forschungszentrum Jülich GmbH
  • , R. BauerAffiliated withInstitut für Atmosphärische Chemie, Forschungszentrum Jülich GmbH
  • , F. J. JohnenAffiliated withInstitut für Atmosphärische Chemie, Forschungszentrum Jülich GmbH
  • , C. PlassAffiliated withInstitut für Atmosphärische Chemie, Forschungszentrum Jülich GmbH
  • , J. RudolphAffiliated withInstitut für Atmosphärische Chemie, Forschungszentrum Jülich GmbH

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Abstract

During the cruise ANT VII/1 (September/October 1988) of the German research vessel Polarstern the latitudinal distributions of several nonmethane hydrocarbons were measured over the Atlantic between 45°N and 30°S by in-situ gas chromatography.

On the average, the highest mixing ratios of ethane, propane, i- and n-butane, ethene and acetylene were observed in the Northern Hemisphere around 40° N and just north of the intertropical convergence zone, respectively. South of the equator, a bulge in the mixing ratios of ethane and acetylene was observed indicating aged biomass burning emissions. This observation coincided with enhanced tropospheric ozone found in this region at this season. On the average ethane and acetylene mixing ratios were around 500 and 100 ppt, respectively, whereas the levels of the other NMHC were in the range of some ppt up to 100 ppt.

compared with the results of the cruise ANT V/5 (March/April, 1987), the ethane mixing ratios in September/October proved to be a factor of 3 lower in the Northern Hemisphere and a factor of 2 higher in the Southern Hemisphere, probably due to seasonal effects. Possible causes are the higher OH radical concentrations in summer, which result in a faster removal of ethane or stronger emission from biomass burning which also peaks in the dry season.

The relative pattern of the hydrocarbons just north of the ITCZ was very similar for both measurement series. In this region, the NMHC were advected by long-range transport from the continent, whereas generally the ocean itself acts as a major NMHC source. This is supported by the results of a balance calculation between oceanic emissions and atmospheric removal rates.

Key words

Hydrocarbons carbon monoxide marine atmosphere Atlantic hydrocarbon budgets