Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-7177-2006 http://www.atmos-chem-phys-discuss.net/6/7177/2006/ http://www.atmos-chem-phys-discuss.net/6/7177/2006/acpd-6-7177-2006.html http://www.atmos-chem-phys-discuss.net/6/7177/2006/acpd-6-7177-2006.pdf 7177 7205 2006-07-28 Processes controlling the concentration of hydroperoxides at Jungfraujoch Observatory, Switzerland S. J. Walker M. J. Evans A. V. Jackson M. Steinbacher C. Zellweger J. B. McQuaid Institute for Atmospheric Science, School of the Earth and Environment, University of Leeds, Leeds, UK Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory for Air Pollution/Environmental Technology, 8600 Dübendorf, Switzerland An automated, ground-based instrument was used to measure gas-phase hydroperoxides at the Jungfraujoch High Altitude Research Station as part of the Free Tropospheric EXperiment (FREETEX) during February/March 2003. A nebulising reflux concentrator sampled ambient air twice hourly, prior to on-site analysis by HPLC speciation, coupled with post-column peroxidase derivatisation and fluorescence detection. Hydrogen peroxide (H₂O₂) concentrations reached up to 1420 pptv over the 13-day period with a mean of 206±261 pptv (± one standard deviation). Methyl hydroperoxide (CH₃OOH) reached up to 921 pptv with a mean of 76±96 pptv. No other organic hydroperoxides were detected. The lack of an explicit diurnal cycle suggests that hydroperoxide concentrations are chiefly influenced by transport processes rather than local photochemistry at this mountainous site. We find elevated concentrations of H₂O₂ in air masses originating from the south-west indicative of higher concentrations of HO_x due to more active photochemistry. Air which has been recently polluted exhibits low H₂O₂ concentration due to a combination of suppression of HO₂ by NO_x and deposition. We also conclude that despite being at a high alpine site, the vast majority of the air observed was extensively influence by the boundary layer during our campaign (diagnosed from high CO concentrations and the high NO_x to NO_y ratio) resulting in deposition of H₂O₂ to the surface and hence reduced H₂O₂ concentrations. The concentrations of H₂O₂ sampled here are consistent with previous box modelling studies of hydroperoxides which invoked a depositional sink.