Tuesday, August 20, 2013

What’s the Dirt on Snow…and Why You Shouldn’t Eat It

Growing up in NH I remember taking a scoopful of snow and dousing it with maple syrup; watching as the snow would magically become the world’s best, most simple dessert.  Those maple syrup snow desserts were a winter dietary staple through my late teens until I learned what could be in that allegedly white, pure snow.  As part of the NH EPSCoR ‘Ecosystems and Society’ Project my colleagues and I have been analyzing the non-snow components (chemical impurities) found within snowpacks throughout the state.  We also look at how these chemical impurities impact the structure of snow grains and albedo, or the amount of light an object reflects, of snow.  
Maple Syrup Snow Cone
blog.villagevoice.com Robert Sietsema February 2010
The chemical impurity that has garnered the majority of scientific and public attention is black carbon [EPA Information].  Black carbon is emitted into the atmosphere from the incomplete combustion of fossil fuels such as coal burning, diesel engines and forest fires.  Once black carbon is in the atmosphere it can be collected by snow as it falls to the earth or it can become the condensation nuclei [Definition]of snowflakes.  When black carbon is incorporated into the snow it ‘darkens’ the snow color; reducing its reflectivity or albedo.  Once albedo has decreased the snow pack will absorb more of the sun’s energy which causes additional warming and melting.   Both permanent and seasonal snow cover act as a white t-shirt for the earth, reflecting up to 90% of incoming solar energy and acting to cool the earth’s temperature.  However the reflectivity of the t-shirt decreases when chemical impurities, such as black carbon, become incorporated into the snow and thus can cause an increase the region’s overall temperature.  
Albedo data collection.  I am using an Analytical Spectral Device FieldSpec 4 (ASD) to measure the amount of sunlight reflecting off of the snow.  March 2013.  Thompson Farm Pasture, UNH. Photo credit: Luke Barbour.
Daily sampling throughout the 2012-2013 winter season revealed an overall decline in albedo when black carbon as well as other chemical impurity concentrations increased within snowpacks throughout the state.  During periods of rapid melt the albedo decreased by up to 30% over a period of three days while the black carbon increased 12 fold just within the top 5cm of the snowpack!  We have also observed astounding 27 fold increase in black carbon concentration following the blizzard on February 8th – 9th, 2013 (38 cm of new snow).  Understanding the mathematical relationship between an increase in black carbon and decrease in albedo is complex especially with the added factor of how fast snow can settle and increase in density.  For the upcoming 2013/2014 winter we will repeat the snow collection process to gather more data which will help us understand the relationship between albedo and chemical impurities within the snowpack.   

Collection of snow for chemical impurity analysis.  February 2013.  Burley Demeritt Organic Dairy Farm, UNH.
Photo credit: Luke Barbour.
Snow has always been an important climate regulator [Climate Regulator - NASA]because it reflects a great deal of the incoming solar energy back to space.  It is no secret that with shorter winters and more impurity laden snow the effectiveness of snow as a climate regulator could be declining.  The first step to creating cleaner, more reflective snow is to understand how chemical impurities, particularly black carbon, affect albedo within New Hampshire.   Once this relationship is fully understood more effective measures could be taken to preserve our snowpacks and create the white, pure snow so that I along with other NH and New England residents can enjoy the maple syrup snow cones that continuously brought so much joy to the winter season.  

Posted by: Jacqueline Amante, MS Earth Science: Geochemical Systems Student, Institute for the Study of Earth, Oceans and Space, University of New Hampshire

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