Ozone and Snow

Research

Destruction of ozone within polar snowpack was first reported based on measurements taken at Summit, Greenland in 2000. Some of our team members were along on that research trip. Those first observations demonstrated that the destruction of ozone was strongly correlated with sunlight intensity, and negatively correlated with nitrogen oxides. We followed up on these findings with additional, much more detailed observations at Summit, the South Pole, and Colorado that confirmed the first results and further explored the dependencies of ozone losses in snow.

Snow sparkles in Greenland near the instrument tower. Our team is investigating how, driven by sunlight, ozone is created and destroyed between snow and air. Photo by Brie Van Dam.

Ozone levels decrease with depth within the snowpack, and the intensity of sunlight accelerates the reduction, indicating a photochemical reaction. A previous study showed that, on average, at noon during summer only 10% of the ambient ozone was preserved at 1 meter depth, while up to 90% was preserved during April as a result of the less intense springtime sunshine. The mechanism driving this ozone destruction in the snow is not yet well understood.

All of the electrical cables and sample tubing are brought from the undersnow lab through this insulated and heated arctic pipe, the top of which is shown here. Keeping the cables and tubing at a roughly constant temperature is important to ensure better-quality signals from the equipment. Photo by Brie Van Dam.

Since the snowpack is permeable, air moves between the atmosphere and the snowpack, through diffusion, convection, and (most importantly) wind pumping driven by pressure fluctuations as wind flows over the snow surface. The result is a loss of ozone from the near-surface air, with the loss increasing as wind speed and sunlight increase.

However, snowpack photochemistry also results in the release of nitrogen oxides, which catalyze photochemical formation of ozone in the above-snow atmosphere, and releases hydrogen oxide precursors that increase the rate of photochemical ozone production. The result can be significant net ozone formation in the air above the snow.

Because ozone is simultaneously destroyed in the snow and created above the snow, the impact of snowpack processes on the ozone in the troposphere as a whole is complex. For this project, we are going to look very closely at these processes, making many sets of observations at various levels above the snow surface. We hope that our work will not only help us understand ozone fluxes in snow better, but will be incorporated in global climate models that can better simulate the impact that changes in snow- and ice-cover and permafrost extent have upon tropospheric ozone.