Photochemistry of Pollutants in Snow and Ice

This project is currently funded by the National Science Foundation (CAREER), Division of Atmospheric Sciences, #0547435. 

The Background:

Once considered to be a pristine area, far removed from the reach of anthropogenic pollutants, it is now recognized that significant long-range transport of contaminants such as heavy metals, SO_x, and persistent organic pollutants reaches the Arctic.  Volatile contaminants from lower latitudes can reach the Arctic through a process known as global distillation.  Contaminants evaporate from warmer lower latitudes and condense out in the colder air of high latitudes.  This phenomenon explains why more volatile species such as polychlorinated biphenyls travel to the highest latitudes, while less volatile contaminants (like DDT) stay relatively close to their source region.  This phenomenon is illustrated in the figure below, which shows the concentration of lindane (a pesticide) measured in surface waters increasing from the tropics to the poles as a result of global distillation (Arctic Monitoring and Assessment Programme, 1998).

Many of these pollutants have toxic effects to living organisms.  Many POPs are also listed as possible carcinogens by agencies such as the Environmental Protection Agency and European government agencies. Undoubtedly, the concerns over negative health effects provide an impetus for the study of the environmental fate of persistent organic pollutants and the potential for transformation of these pollutants into more, or less, toxic compounds.  This is particularly important in Arctic regions where indigenous peoples depend on higher trophic level food sources.  

Our Interests:

In recent years it has become apparent that the frozen surfaces of polar regions are highly reactive.  Photochemical processes (i.e. sunlight driven) drive the production of a variety of compounds within snow and ice, including halogens, carbonyl compounds, alkyl halides and others.  What happens to the anthropogenic (man-made) pollutants that deposit with the frozen precipitation, however, is largely unknown.  Photochemical transformations of anthropogenic organic contaminants in ice have been observed, although published information regarding these processes is scant.  Our research goal is to understand these processes better.

WHY SHOULD WE CARE???

Transformations of anthropogenic organic pollutants in snow and ice could have vast implications for atmospheric chemistry processes, contaminant transport and ecosystem health.  The polar regions are unique in the fact that they sit in darkness during winter, until a slow sunrise leads to 24-hour sunlit conditions.  Pollutants deposited in the dark winter will have the opportunity to build-up until the polar sunrise, when photochemical processes are fueled by 24-hours of continuous irradiance from the sun.    Upon snowmelt, contaminants (or their photochemical byproducts) present in accumulating snow will be transferred with melt water to the terrestrial/aquatic environment underlying the snowpack or could be revolatilized into the atmosphere.  In the case of ocean surfaces, a complicating factor is that sea-ice may be several years old before melting, allowing for both significant photochemical reaction time and opportunity to collect contaminants by both wet and dry deposition.  However, the melt process will be relatively quick compared to the timescale of contaminant accumulation, resulting in a “surge” of toxic chemicals into the overlying atmosphere or surrounding environment (or potentially reduced toxicity species if photochemistry converts the deposited contaminant into a more benign compound).  Because the indigenous populations in the Arctic rely primarily on subsistence living, these contaminants will work their way up the food chain and eventually make their way into humans.  Already, negative effects are being evidenced in Arctic wildlife - so ecosystem health is at risk as we speak.  We need to better understand the processes that affect POPs - and potentially what compounds they are turning into - if we are to have any chance of mitigating the potential negative impacts of these pollutants.

It is thus apparent that studies of photochemical processes of organic pollutants in ice and snow are urgently needed to 1.) better understand the wide range of pollutants that could be subject to photochemical degradation in ice and snow 2.) better understand the mechanisms responsible for degradation and 3.) fully characterize the products produced.  Armed with this information, we can then better understand the impacts that surface photochemistry might have on the overlying atmosphere and surrounding ecosystem, and how future climate change might impact such processes.

The Plan:

Our planned research activities will include laboratory experiments to:

• determine the photochemical behavior of a variety of pollutants in frozen water media (snow and ice)

• determine if other chemicals present in the snow or ice can affect the chemistry (e.g. photosensitizers)

• determine how the rates of reaction and mechanisms vary between liquid and frozen water

A component of the research will also involve field work in the Arctic environment.  Here we will study:

• Does the degradation we observe in the laboratory experiments occur under natural environmental conditions?

• How does the rate of degradation vary with the depth of snow or ice?

• Are the products we identify found in natural environmental samples (snow, air, runoff, etc)?

Pollutants we will study include PCBs, brominated flame retardants, chlorinated pesticides, hexachlorobenzene, among others.

Publications/Presentations:

Enhanced aqueous photochemical reaction rates after freezing. Grannas, AM; Bausch, AR; Mahanna, KM.  Journal of Physical Chemistry A, 111, 11043-11049, 2007. 

Organic Pollutants in the Arctic: Investigations of Photochemical Reactivity in Liquid Water and Ice.  M.S. Thesis, Ashley Sprenkle, May 2007.

American Geophysical Union Fall Meeting. “Photochemical degradation of organic pollutants in liquid water and ice.”  A. Sprenkle and A. Grannas, December 2006. (Poster)

American Chemical Society Northeast Regional Meeting. "Photochemical generation of OH radicals in snow and ice." J. Cebollero, A. Grannas, October 2006. (Poster)

American Chemical Society Northeast Regional Meeting.  "Photochemistry in the quasi-liquid layer of ice." A. Bausch, A. Grannas, K. Mahanna, October 2006. (Poster)

American Chemical Society Northeast Regional Meeting.  "Photochemical degradation of organic pollutants in liquid water and ice." A. Sprenkle and A.Grannas, October 2006. (Talk)

American Chemical Society Northeast Regional Meeting. "Environmental implications of snow and ice photochemistry." A. Grannas, October 2006. (Talk)

American Chemical Society (Philadelphia Section) Graduate/Undergraduate Poster Session. "Probing Photochemistry in the Quasi-Liquid Layer: Laboratory Studies and Implications."  K.M. Mahanna, V.M. Greis, A.M. Grannas, January 2006.  Kendell received a Philadelphia Section Undergraduate Poster Award for her presentation.

American Geophysical Union Fall Meeting.  "Photochemical Degradation of Persistent Organic Pollutants in Snow and Ice."  V.M. Greis, K.M. Mahanna, A.M. Grannas, December 2005.  (Poster)

American Geophysical Union Fall Meeting. "Probing Photochemistry in the Quasi-Liquid Layer: Laboratory Studies and Implications."  K.M. Mahanna, V.M. Greis, A.M. Grannas, December, 2005. (Talk)

Last updated 3/18/09

Disclaimer: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.