Contrasting atmospheric boundary layer chemistry of methylhydroperoxide (CH3OOH) and hydrogen peroxide (H2O2) above polar snow

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Frey, M. M., Hutterli, M. A., Chen, G., Sjostedt, S. J., Burkhart, J. F., Friel, D. K., Bales, R. C.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Greenland; South Pole; South pole
• Online Access: https://doi.org/10.5194/acp-9-3261-2009; https://www.atmos-chem-phys.net/9/3261/2009/

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 H 2 O 2 and CH 3 OOH (from here on MHP) with average (±1σ) mixing ratios of 1448 (±688) pptv, 204 (±162) and 278 (±67) for H 2 O 2 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 H 2 O 2 , suggesting that the organic peroxide is controlled by photochemistry, while H 2 O 2 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 1–5×10 11 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 (CH 2 O). 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 H 2 O 2 , MHP and CH 2 O 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.