Surface layer ozone dynamics and air-snow interactions at Summit, Greenland. Spring and summer ozone exchange velocity and snowpack ozone: The complex interactions.

摘要

In recent decades, the Arctic has witnessed startling environmental changes prompting concerns about the Arctic climate system, which in turn, could amplify climate change on a global scale. In recent years, studies have provided evidence that important chemical gas exchanges occur between the polar snowpack and the atmosphere, and that sunlit snow is one of the most photochemically- and oxidatively-active regions of the entire troposphere.; The overarching goal of this research is to study the interaction of atmospheric ozone with the permanent snowpack based on flux-tower measurements at Summit, Greenland. The ozone exchange [Ve(O3)] above the snow surface is not a simple constant value as climate models assume, but is highly dependent on environmental conditions (e.g., solar radiation, wind speed, atmospheric stability) and on the snowpack chemistry (e.g., nitrogen oxides, formaldehyde).; Throughout the spring, positive and negative values for Ve(O3) were observed and vertical flux divergence was negligible. During the summer, Ve(O3) exhibited a noticeable diurnal variation, where statistically significant downward/positive Ve(O3) occurred in the afternoon hours (starting around solar noon). A distinct vertical flux divergence with height also occurred during the same period, suggesting ozone production above the snow.; Meanwhile, snowpack ozone concentration showed a distinct diurnal depletion/recovery cycle, much stronger during summer than spring. This cycle, primarily affected by solar radiation penetrating the upper snowpack layer, indicates that photochemical ozone loss mechanisms are likely active and their intensities are season-dependent. In addition, the seasonal change in temperature gradients showed that the snowpack is dramatically more affected than the atmosphere itself, leading to speculation on (a) chemistry occurring in the quasi-liquid layer around snow grains and (b) thermal gas adsorption/desportion.; While the dynamics of snowpack ozone and surface layer ozone should be correlated, the complex dynamical processes are not yet clearly identifiable. Nonetheless, these analyses showed that (a) snowpack ozone is depleted by either photochemical and/or physical processes and (b) atmospheric ozone above the snow surface possibly results from the peroxy-nitrogen cycle.