Cryosphere - Soot in Snow
Extensive research on soot in snow and snow grain size has been carried out in the Polar Regions. However, in North American prairie snowpacks, a lack of observations addressing the effect of soot in snow on snow albedo causes uncertainty to the overall global effect that this parameter has on climate. Measurements in freshly fallen prairie snowpacks in Northwestern Iowa and Central Texas were collected from February 28- March 5, 2007 and April 6, 2007, respectively. A second field campaign was conducted in northwestern Iowa from February 8 -11, 2008.
Several types of sites were sampled to measure soot in snow concentrations including: frozen lakes with minimal human impact, agricultural fields impacted by agricultural dust, human impacted sample sites, and multi-day monitoring locations. Measurements recorded at all site locations include: snow samples, temperature, density, and grain size. Snow reflectance and snow radiance was collected at a subset of the sites with an ASD VNIR Spectroradiometer (350 - 1500 nm).
Snow impurity, consisting of light-absorbing particulate matter, was measured by filtering meltwater through a nuclepore 0.4 micrometer filter. Filters were examined using a photometer to measure mass impurity concentration. Preliminary soot observations indicate prairie snow pack concentrations ranging from 1 ngC/g to 236 ngC/g with an average of 61.4 ngC/g. These measurements are within range of previously published values in the Arctic and can lower snow albedo. As expected, spectral albedo was found to decrease with increasing impurities. Differences in soot concentration were observed between the two snowfall events in Iowa. The central Texas event had higher soot concentrations than both Iowa snowfalls.
In addition to measuring snow impurities, in 2008 six samples were collected for a preliminary study of organic contaminants present in these snowpacks. Four of the sites were located in agricultural fields, one in a wildlife refuge and the last in downtown Spirit Lake. Each of the six snow samples was analyzed for a suite of organic compounds including chlorinated benzenes, hexachlorocyclohexanes, chlordanes, pesticides, DDT and PCBs. With few exceptions, detectable levels of all organic compounds were present in all of the samples. Total PCB concentrations were found to be between 27 and 51 ng L-1 with the downtown site and a site located immediately adjacent to a rural road both having concentrations in excess of 50 ng L-1. Total DDT concentrations were found to range between 0.19 and 1.84 ng L-1. A variety of pesticides were also detected with the town site typically elevated over the agricultural sites.