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 To cite this version: S. J. Walker, M. J. Evans, A. V. Jackson, M. Steinbacher, C. Zellweger, et al.. Processes controlling the concentration of hydroperoxides at Jungfraujoch Observatory, Switzerland. Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2006, 6 (4), pp.7177-7205. hal-00302033 HAL Id: hal-00302033 https://hal.archives-ouvertes.fr/hal-00302033 Submitted on 28 Jul 2006 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Atmos. Chem. Phys. Discuss., 6, 7177–7205, 2006 Atmospheric www.atmos-chem-phys-discuss.net/6/7177/2006/ Chemistry ACPD © Author(s) 2006. This work is licensed and Physics 6, 7177–7205, 2006 under a Creative Commons License. Discussions Hydroperoxides at Jungfraujoch Observatory Processes controlling the concentration S. J. Walker et al. of hydroperoxides at Jungfraujoch Title Page Observatory, Switzerland Abstract Introduction Conclusions References S. J. Walker1, M. J. Evans1, A. V. Jackson1, M. Steinbacher2, C. Zellweger2, and 1 J. B. McQuaid Tables Figures 1Institute for Atmospheric Science, School of the Earth and Environment, University of Leeds, Leeds, United Kingdom J I 2Swiss Federal Institute for Materials Science and Technology (Empa), Laboratory for Air J I Pollution/Environmental Technology, 8600 Dubendorf,¨ Switzerland Back Close Received: 6 June 2006 – Accepted: 11 June 2006 – Published: 28 July 2006 Correspondence to: A. V. Jackson ([email protected]) Full Screen / Esc Printer-friendly Version Interactive Discussion EGU 7177 Abstract ACPD An automated, ground-based instrument was used to measure gas-phase hydroper- oxides at the Jungfraujoch High Altitude Research Station as part of the Free Tro- 6, 7177–7205, 2006 pospheric EXperiment (FREETEX) during February/March 2003. A nebulising reflux 5 concentrator sampled ambient air twice hourly, prior to on-site analysis by HPLC speci- Hydroperoxides at ation, coupled with post-column peroxidase derivatisation and fluorescence detection. Jungfraujoch Hydrogen peroxide (H2O2) concentrations reached up to 1420 pptv over the 13-day Observatory period with a mean of 206±261 pptv (± one standard deviation). Methyl hydroperox- S. J. Walker et al. ide (CH3OOH) reached up to 921 pptv with a mean of 76±96 pptv. No other organic 10 hydroperoxides were detected. The lack of an explicit diurnal cycle suggests that hy- droperoxide concentrations are chiefly influenced by transport processes rather than Title Page 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 HOx Abstract Introduction due to more active photochemistry. Air which has been recently polluted exhibits low Conclusions References 15 H2O2 concentration due to a combination of suppression of HO2 by NOx and depo- sition. We also conclude that despite being at a high alpine site, the vast majority of Tables Figures the air observed was extensively influence by the boundary layer during our campaign (diagnosed from high CO concentrations and the high NOx to NOy ratio) resulting in J I deposition of H2O2 to the surface and hence reduced H2O2 concentrations. The con- 20 centrations of H2O2 sampled here are consistent with previous box modelling studies J I of hydroperoxides which invoked a depositional sink. Back Close 1 Introduction Full Screen / Esc Hydroperoxides play an important role in gas-phase free radical chemistry of the at- Printer-friendly Version mosphere and in the aqueous-phase chemistry of acid precipitation. Hydroperoxides Interactive Discussion 25 such as hydrogen peroxide (H2O2) and methyl hydroperoxide (CH3OOH) are produced through the self-reaction of peroxy radicals (hydroperoxy, HO2 and organic peroxy, EGU 7178 RO2) (e.g. Lee et al., 2000). These peroxy radicals are intimately linked to ozone pro- duction and loss, leading to hydroperoxides being a key diagnostic of the chemical ACPD state of the atmosphere. The chemistry of the O , HO and RO is summarized in x x x 6, 7177–7205, 2006 Fig. 1. H2O2 is also a major oxidant of SO2 in clouds (Penkett et al., 1979) so along- 5 side O3 and OH, its measurement is needed to assess the oxidative capacity of the atmosphere. Hydroperoxides at Previous analyses of H2O2 and CH3OOH observations have identified key physical Jungfraujoch and chemical processes controlling their concentration (e.g. Heikes et al., 1987). As Observatory shown in Fig. 1, the production of H2O2 is controlled by the abundance of HO2, which S. J. Walker et al. 10 shows sensitivity to HOx (OH and HO2) production, loss and recycling. Formation of peroxy radicals is predominantly through the photo-oxidation of carbon monoxide (CO) and volatile organic compounds (VOC), by the OH radical (detailed in Lightfoot et al., Title Page 1992). A second significant source is from formaldehyde (CH2O), which undergoes photolysis and reaction with OH to produce HO2. Abstract Introduction 15 Air-masses rich in NOx tend to show lower H2O2 concentrations as peroxy radicals Conclusions References oxidise NO to NO2 rather than self-reacting to form H2O2 (Tremmel et al., 1993; Penkett et al., 1995) and total radical loadings are suppressed by HNO3 production through the Tables Figures reaction of OH with NO2 radicals (Poppe et al., 1993). According to Lee et al. (2000), substantial suppression of hydroperoxide production occurs at NO concentrations ex- J I 20 ceeding 100 pptv. In contrast, it is calculated that NO concentrations below 3 to 20 pptv are needed for hydroperoxide production to dominate (Reeves and Penkett, 2003; J I Crutzen and Zimmermann, 1991; Finlayson-Pitts and Pitts, 1986). Such low concen- Back Close trations of NO can only be found in very remote regions of the troposphere lacking NOx sources. Full Screen / Esc 25 Lower concentrations of H2O2 are observed in air masses exposed to the ground or clouds due to dry and wet deposition (e.g. Kleinman, 1986; Heikes et al., 1987; Printer-friendly Version Chandler et al., 1988; Gallagher et al., 1991). Rapid loss of gaseous H2O2 into clouds 4 −1 Interactive Discussion is due to a high Henry’s law coefficient of H2O2(HH2O2 is 7.73×10 M atm at 298 K, Sander et al., 2003) and rapid oxidation of S(IV) species to S(VI) within the aqueous EGU 7179 phase. Other important H2O2 and CH3OOH sinks are their reaction with OH radicals and photolysis at ultraviolet wavelengths generating OH and in the case of CH3OOH, ACPD OH and CH O. 3 6, 7177–7205, 2006 The aim of this paper is to investigate the impact of these chemical and physical pro- 5 cesses on the concentration of H2O2 and CH3OOH at a remote mountainous site and to understand the usefulness of H2O2 observations as a diagnostic of the atmospheric Hydroperoxides at compositional system. Jungfraujoch Observatory 2 Experimental S. J. Walker et al. 2.1 Site description Title Page 10 The observations are from the FREE Tropospheric EXperiment (FREETEX) that took place in February to March 2003 at the Sphinx Observatory, Jungfraujoch High Alti- Abstract Introduction tude Research Station (7.98◦ E, 46.55◦ N) (subsequently referred to as JFJ) situated Conclusions References at 3580 m above mean sea level (a.m.s.l.). There have been three previous FREE- TEX campaigns in 1996, 1998 and 2001 at this site (Zanis et al., 1999, 2000a, b, Tables Figures 15 2003; Carpenter et al., 2000). The Sphinx Observatory resides in a saddle between the two alpine summits, Jungfrau (4155 m a.m.s.l.) to the south-west and Monch¨ J I (4099 m a.m.s.l.) to the north-east, in the Swiss Alps. This leads to mainly north- westerly and southerly air masses reaching the station. The site characteristics are J I described in Zellweger et al. (2003). The observatory is usually thought to be located in Back Close 20 the lower free troposphere (FT) in winter and early spring but can experience planetary boundary layer (PBL) air (Carpenter et al., 2000), especially in the summer when con- Full Screen / Esc vection is enhanced (Baltensperger et al., 1997; Lugauer et al., 1998, Zellweger et al., 2003). The high altitude site is thought to experience few local emission sources, and Printer-friendly Version therefore can offer ideal conditions for long-term sampling of free tropospheric air. The Interactive Discussion 25 JFJ is incorporated in the Swiss National Air Pollution Monitoring Network (NABEL), which is maintained by EMPA Dubendorf¨ on behalf of the Swiss Federal Office for the EGU 7180 Environment (FOEN). Among other species, NO, NO2,O3 and CO are measured rou- tinely and are available with a time resolution of 30 min. All meteorological parameters ACPD are measured by the Federal Office of Meteorology and Climatology (MeteoSwiss). 6, 7177–7205, 2006 Due to the importance of monitoring long-term trends of gaseous and aerosol param- 5 eters in the free troposphere, the JFJ station has been incorporated into the Global Atmosphere Watch (GAW) program of the World Meteorological Organization (WMO) Hydroperoxides at as a Global GAW Station. Jungfraujoch Observatory 2.2 Method for hydroperoxide sample collection and analysis S. J. Walker et al. Sample collection took place at the Sphinx laboratory between the 27 February and 10 the 12 March 2003. Figure 2 shows a schematic diagram of the analytical system.