Abstract
Abstract. Atmospheric hydroperoxides (ROOH) were measured at Summit, Greenland (72.97° N, 38.77° W) in summer 2003 (SUM03) and spring 2004 (SUM04) and South Pole in December 2003 (SP03). The two dominant hydroperoxides were H2O2 and CH3OOH (from here on MHP) with average (±1σ) mixing ratios of 1448 (±688) pptv, 204 (±162) and 278 (±67) for H2O2 and 578 (±377) pptv, 139 (±101) pptv and 138 (±89) pptv for MHP, respectively. In early spring, MHP dominated the ROOH budget and showed night time maxima and daytime minima, out of phase with the diurnal cycle of H2O2, suggesting that the organic peroxide is controlled by photochemistry, while H2O2 is largely influenced by temperature driven exchange between the atmosphere and snow. Highly constrained photochemical box model runs yielded median ratios between modeled and observed MHP of 52%, 148% and 3% for SUM03, SUM04 and SP03, respectively. At Summit firn air measurements and model calculations suggest a daytime sink of MHP in the upper snow pack, which decreases in strength through the spring season into the summer. Up to 50% of the estimated sink rates of 1–5×1011 molecules m−3 s−1 equivalent to 24–96 pptv h−1 can be explained by photolysis and reaction with the OH radical in firn air and in the quasi-liquid layer on snow grains. Rapid processing of MHP in surface snow is expected to contribute significantly to a photochemical snow pack source of formaldehyde (CH2O). Conversely, summer levels of MHP at South Pole are inconsistent with the prevailing high NO concentrations, and cannot be explained currently by known photochemical precursors or transport, thus suggesting a missing source. Simultaneous measurements of H2O2, MHP and CH2O allow to constrain the NO background today and potentially also in the past using ice cores, although it seems less likely that MHP is preserved in firn and ice.
Highlights
Atmospheric hydroperoxides (ROOH) contribute significantly to the tropospheric oxidizing capacity either directly as hydrogen peroxide (H2O2) or indirectly as HOx radical and ozone precursors in the remote and upper troposphere (Barth et al, 2007; Grannas et al, 2007, and references therein)
Averaging 2-h binned data of the 1-m gas phase concentrations over the entire field seasons confirmed the presence of a diurnal cycle of H2O2 at Summit, Greenland (Bales et al, 1995) during summer 2003 and during the spring season 2004 with maxima occurring between 13:00 and 17:00 (01:00 and 03:00) solar time and amplitudes of 760 and 137 pptv, respectively
Dividing the spring 2004 season into three subsequent 10day periods revealed that during the spring transition from dark to 24-h sunlit conditions the diurnal cycles of H2O2 and MHP evolved in very different ways (Table 1, Fig. 2)
Summary
Atmospheric hydroperoxides (ROOH) contribute significantly to the tropospheric oxidizing capacity either directly as hydrogen peroxide (H2O2) or indirectly as HOx radical and ozone precursors in the remote and upper troposphere (Barth et al, 2007; Grannas et al, 2007, and references therein). The spatial and temporal variability of atmospheric oxidants including ROOH and the role of heterogeneous chemistry are still poorly constrained Frey et al.: Atmospheric hydroperoxides above polar snow fluxes across the snow-air interface with important implications for atmospheric oxidant concentrations at regional and possibly global scales (Domineand Shepson, 2002; Grannas et al, 2007)
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