Investigating the photo-oxidative and heterogeneous chemical production of HCHO in the snowpack

Environmental context. Snowpacks present a surprisingly active environment for photochemistry, leading to sunlight-induced oxidation of deposited organicmatter and the subsequent emission of a variety of photochem-ically active trace gases. We seek to address questions regarding the ultimate fate of organic matter deposited onto snow in the remote regions of the world. The work is relevant to atmospheric composition and climate change. Abstract. We investigate snowpack fluxes of formaldehyde (HCHO) into the South Pole boundary layer using steady-state photochemical models. We study two chemical sources of HCHO within the snowpack. First, we study chemical production of HCHO from the processing of methyl hydroperoxide (CH3OOH): photolysis, reaction with the hydroxyl radical (OH), and by an acid catalysed rearrangement. Assuming surface layer concentration effects for acidic solutes, we show that the acid catalysed production of HCHOwithin ice could contribute a non-negligible source to the snowpack HCHO budget. This novel source of HCHO complements existing explanations of HCHO fluxes based on physical emission of HCHO from snow. Secondly, we investigate HCHO production from the oxidation of organic matter (OM) by OH within snow to explain observed fluxes of photochemical origin from the South Pole snowpack. This work shows that laboratory-derived photochemical production rates of HCHO and our standard model are inconsistent with field observations, which has implications for the distribution of OM relative to oxidants within ice particles. We resolve thi