Minimizing chemical pollution from airport de-icing

A changing climate could mean milder winters, so that many cold countries may be headed for more days with temperatures hovering near the freezing point. More precipitation in the winter months is also a distinct possibility. On top of this, winter temperatures may become even more variable. In short, those near-zero conditions so difficult to deal with could become more common.

De-icing adds to pollution

Airports use chemicals to de-ice airplanes and keep runways free of ice. From a pollution standpoint, what would happen if airports had to use even greater amounts of de-icing chemicals each winter? Using funding from the research programme on Climate Change and Impacts in Norway (NORKLIMA) at the Research Council of Norway, researchers from the division for Soil and Environment at the Norwegian Institute for Agricultural and Environmental Research (Bioforsk) have been searching for answers to this question, in collaboration with scientists in the US and the UK.

Helen French, who works at Bioforsk in addition to her position as associate professor at the Norwegian University of Life Sciences (UMB), headed the research project Pollution risks and water management at airports and roads in a changing climate, which received funding under the NORKLIMA programme. Her project studied the pollution situation at Oslo Gardermoen Airport in particular.

Highest chemical usage at temperatures near zero

A statistical model for Oslo Gardermoen Airport indicated that more wind, more precipitation and more flights -- combined with low temperatures -- resulted in increased usage of de-icing chemicals on the airplanes.

"At Oslo Gardermoen Airport, temperatures near the freezing point are those that entail the greatest use of chemicals," says Dr French. Although current winter temperatures are typically well below freezing, "if the climate warms, the airport will likely need to increase its use of chemicals."

Groundwater at risk

The airport is situated above Norway's largest groundwater deposit, and there are fears that pollution from the airport could seep into the groundwater. Several factors play a role in this process:

"The amount of chemicals applied is of course an important factor," continues Dr French. "But another key aspect is the volume of water transporting those chemicals down into the ground. This is what determines the seepage rate and the dilution process."

The project's field studies showed that chemicals used at airports can be broken down before reaching the groundwater, depending partly on how deep-lying the groundwater reservoirs are.

The researchers carried out field tests, modelling and statistical analyses of historical data to calculate the extent of pollution stemming from chemical de-icing in the period 1999-2009 based on the airport's current climate.

Soil bacteria to the rescue

"Plants' uptake of water and evaporation throughout the summer helps to keep water up in the soil. The bacteria in the soil can then break down the chemicals," explains Dr French.

It was previously thought that the bulk of airport chemicals washed away with the spring meltwater, which would mean a greater risk of groundwater pollution in frost-heavy years.

But measurements taken of snow along the Oslo runways showed that, fortunately, the chemicals melt out of the snow cover during the winter and infiltrate the soil before the spring thaw. This gives the soil a greater role in the process of breaking down the chemicals.

Among the cleanest

Thanks to the comprehensive research findings and a stronger focus on environmental impacts, pollution at the Oslo airport is now monitored far more closely than airports in many other places around the world.

"Roughly 80 per cent of the chemicals used in de-icing airplanes at Oslo Gardermoen Airport is collected and put to good use at a nearby wastewater treatment facility," concludes Dr French. "Ten per cent gets dispersed along the runways, and ten per cent is carried off on the planes. In this respect, Oslo Gardermoen Airport may be the world's best."