Laboratory Studies of Photochemistry in Antarctic Snow and Ice

Our US NSF-funded project had two major parts: (1) measuring the quantum yields
for photolysis of nitrite (NO2-), nitrous acid (HNO2), and hydrogen peroxide
(HOOH) using laboratory ices, and (2) measuring the wavelength-dependent light
absorption by soluble species in snow samples from Dome Concordia and Summit,
Greenland. The laboratory photolysis work is not included in this database but
can be found in publications cited in the reference section of this metadata.
The second part of our work (the measurements of light absorption by soluble
snow chemical species) is included in this database and was recently submitted
to the Journal of Geophysical Research (C. Anastasio and T. Robles, Light
absorption by soluble chemical species in Arctic and Antarctic snow). This
work is summarized below.

Using a liquid core waveguide spectrophotometer we have quantified the very low
light absorbance of dissolved chromophores (light absorbing species) in
filtered samples of melted polar snows. Light absorption coefficients at 280
nm span the ranges of 0.005 - 0.029 m^-1 and 0.002 - 0.037 m^-1 for samples
from Summit, Greenland and Dome Concordia, Antarctica, respectively.
Absorption coefficients decrease with increasing wavelength and also decrease
with increasing depth in the snow pack. At both sites nitrate (NO3-) and HOOH
together account for approximately half of the summed light absorption
coefficients for wavelengths of 280 nm and above; the remaining ~ 50% of light
absorbance is due to unknown, probably organic, chromophores. Based on our
light absorption measurements and modeled actinic fluxes, we calculate that the
rates of sunlight absorption by soluble chromophores in surface snows are
approximately (1 - 4) 10^11 and (3 - 10) 10^11 photons cm^-3 s^-1 during
summer at Summit and Dome C, respectively. Approximately 50 - 90% of this
sunlight absorption is due to unknown chromophores, while the remainder is due
to hydrogen peroxide and nitrate. Although we do not know quantum yields for
the photochemical reactions of the unknown chromophores, their large
contribution to the rate of sunlight absorption suggests that they play an
important role in the photochemistry of polar snowpacks.