Physically based modeling of atmosphere‐to‐snow‐to‐firn transfer of H₂O₂ at South Pole

Abstract

Quantitative interpretation of ice core chemical records requires • detailed understanding of the transfer processes that relate atmospheric concentrations to those in the snow, firn, and ice. A unique, 2 year set of year-round surface snow samples at South Pole and snow pits, with associated accumulation histories, were used to test a physically based model for atmosphere-to-firn transfer of H202. The model, which extends our previous transfer modeling at South Pole into the snowpack, is based on the advection-dispersion equation and spherical diffusion within representative snow grains. Required physical characteristics of the snowpack, such as snow temperature and ventilation, were estimated independently using established physical models. The surface snow samples and related model simulations show that there is a repeatable annual cycle in H202 in the surface snow at South Pole. It peaks in early spring, and surface snow concentration is primarily determined by atmospheric concentration and temperature, with some dependence on grain size. The snow pits and associated model simulations point out the importance of accumulation timing and annual accumulation rate in understanding the deposition and preservation of H202 and 5•80 at South Pole. Long-term snowpack simulations suggest that the firn continues to lose H202 to the atmosphere for at least 10-12 years (•3 m) after burial at current South Pole temperatures and accumulation rates. Paper number 98JD00460. 0148-0227 / 98 / 98 J D-00460509.00 Unlike aerosols, volatile species such as hydrogen peroxide, formaldehyde, and organic acids are reversibly incorporated in the snow because a fraction of the deposited mass of these species cycles between the atmosphere and snow as precipitation ages and as surface and near-surface conditions change [Bales et al., 1992; McConnell et al., 1997c]. H202, which is important because of its photochemical role, has been relatively well studied and is also seen as a good model compound for understanding reversible deposition in general [Bales and Wolff, 1995]. Models of chemical transfer, or transfer functions, are most readily formulated in the forward direction, that is, atmosphere-to-snow-to-firn-to-ice, and can help lead to an understanding of the underlying physical processes [Waddington et al., 1996; McConnell et al., 1997c]. In an example of a forward model, McConnell et al. [1997b] developed a lumped parameter model to simulate H202 concentrations in a snow pit given photochemical modeled estimates of the atmospheric concentration of H202 and a priori knowledge of the timing of snow accumulation from automatic depth gauges. The empirical model was used to simulate three snow pits at Summit, Greenland, each spanning the same period of summer 1994 to summer 1995. To define model parameters, simulations were objectively compared to the three pit concentration profiles. The results indicated that the preserved H202 profile is strongly dependent on snow accumulation rate and timing but the model 10,561 1-17, 1996. M. R. Albe...

Contrasting atmospheric boundary layer chemistry of methylhydroperoxide (CH<sub>3</sub>OOH) and hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) above polar snow

“…4c, d) and confirms previous work that physical atmosphere-snow exchange needs to be included in such a H 2 O 2 firn model (McConnell et al, 1998). In contrast to H 2 O 2 , MHP firn air concentrations show in general a decline with depth, starting right at the surface on 15 April or at 0.4 m depth as during the second experiment (Fig.…”

Modelling the physical multiphase interactions of HNO<sub>3</sub> between snow and air on the Antarctic Plateau (Dome C) and coast (Halley)

“…Hutterli et al, 2003;Bock et al, 2016). The distribution of hydrogen peroxide, H 2 O 2 , and formaldehyde, HCHO, within the snowpack has been estimated using a physical air-snow and firn trans-fer model which included temperature-driven air-ice uptake and release (Hutterli et al, 2003;McConnell et al, 1998 Bock et al (2016) to describe the concentration of NO − 3 in the skin layer at Dome C, East Antarctic Plateau. Bock et al (2016) proposed that the skin layer snow nitrate concentration at Dome C is determined by thermodynamic equilibrium ice solubility on the grain surface followed by solidstate diffusion during winter.…”

1-D Air-snowpack modeling of atmospheric nitrous acid at South Pole during ANTCI 2003

“…Understanding the transfer processes is essential to snow chemistry. To the best of the authors' knowledge, models for investigating snow chemistry to date only include hydrogen peroxide by McConnell et al (1998) and formaldehyde by Hutterli et al (1999). They use parameterizations to relate gas concentrations in the ice to those in the firn air (Domine et al, 2007).…”

“…Trace gas concentrations are also affected by in situ chemistry production/loss and gas/liquid exchange. We model interstitial HONO using the combination of one-dimensional advection-dispersion equation by McConnell et al (1998) and multiphase model by Sportisse and Djouad (2000):…”