Calculations of in-snow NO₂and OH radical photochemical production and photolysis rates: A field and radiative-transfer study of the optical properties of Arctic (Ny-Ålesund, Svalbard) snow

Abstract

[1] Depth-integrated production rates of OH radicals and NO 2 molecules from snowpacks in Ny-Ålesund, Svalbard, are calculated from fieldwork investigating the light penetration depth (e-folding depth) and nadir reflectivity of snowpacks during the unusually warm spring of 2006. Light penetration depths of 8.1, 11.3, 5.1, and 8.2 cm were measured for fresh, old, marine-influenced, and glacial snowpacks, respectively (wavelength 400 nm). Radiative-transfer calculations of the light penetration depths with reflectivity measurements produced scattering cross sections of 5.3, 9.5, 20, and 25.5 m 2 kg −1 and absorption cross sections of 7.7, 1.4, 3.4, and 0.5 cm 2 kg −1 for the fresh, old, marineinfluenced, and glacial snowpacks, respectively (wavelength 400 nm). Photolysis rate coefficients, J, are presented as a function of snow depth and solar zenith angle for the four snowpacks for the photolysis of H 2 O 2 and NO 3 − . Depth-integrated production rates of hydroxyl radicals are 1270, 2130, 950, and 1850 nmol m −2 h −1 (solar zenith angle of 60°) for fresh, old, marine-influenced, and glacial snowpacks, respectively. Depth-integrated production rates of NO 2 are 32, 56, 11, and 22 nmol m −2 h −1 (solar zenith angle of 60°) for the fresh, old, marine-influenced, and glacial snowpacks, respectively. The uncertainty of repeated light penetration depth measurement was determined to be ∼20%, which propagates into a 20% error in depth-integrated production rates. A very simple steady state hydroxyl radical calculation demonstrates that a pseudo first-order loss rate of OH radicals of ∼10 2 -10 4 s −1 is required in snowpack. The snowpacks around Ny-Ålesund are thick enough to be considered optically infinite.Citation: France, J. L., M. D. King, J. Lee-Taylor, H. J. Beine, A. Ianniello, F. Domine, and A. MacArthur (2011), Calculations of in-snow NO 2 and OH radical photochemical production and photolysis rates: A field and radiative-transfer study of the optical properties of Arctic (Ny-Ålesund, Svalbard) snow,

The effect of measurement geometry on recording solar radiation attenuation in snowpack (e-folding depth) using fibre-optic probes

“…The data in Figure 1 are the result of a single experiment and are within the 20% repeatability uncertainty previously recorded for the repeated measurement of e-folding depth using an inferior instrument (France and others, 2011b). Thus we can conclude that the geometry of measuring efolding depth may not be important and provides limited experimental evidence to disagree with the inference of Warren and others (2006).…”

Influence of grain shape on light penetration in snow

“…First, 60 cm long horizontal holes with the same diameter as the fibers are prepared at approximately 5 cm intervals from the surface to a maximum depth of 30 cm (a guiding support is used to ensure their horizontality). At greater depth, light entering the snowpack from the pit face perturbs the internal radiation field (Bohren and Barkstrom, 1974;Warren et al, 2006;France et al, 2011b). The holes are made in the sun direction in order to avoid shading by the operator.…”

“…Performing accurate irradiance measurements is difficult since the introduction of sensors perturbs the medium (Dunkle and Bevans, 1956;Giddings and LaChapelle, 1961) and repeat experiments demonstrate uncertainties of ∼ 20 % as a result of measurement error and natural variability of snow (France et al, 2011b;. The few attempts to reproduce irradiance measurements, using radiative transfer models with the spherical assumption, failed (Sergent et al, 1987;Meirold-Mautner and Lehning, 2004).…”

“…Earlier studies dealt with broadband irradiance profiles (O'Neill and Gray, 1972;Fukami et al, 1985) so that general features were retrieved (such as the increase of broadband e-folding depth with depth) but no quantitative information on grain shape can be inferred. Studies with spectrally resolved measurements include the works of Grenfell and Maykut (1977) in the Arctic, Beaglehole et al (1998) in Antarctica, Perovich (2007) on mid-latitude seasonal snow, France et al (2011a) in Antarctica, France et al (2011b) in Svalbard and France et al (2012) in Alaska. Spectral diffuse reflectance and asymptotic flux extinction coefficient were measured or deduced from measurements.…”

Simulation of black carbon in snow and its climate impact in the Canadian Global Climate Model

“…If there is no snowfall (F s = 0) then the effective radius remains constant. We use z s = 25 cm as the maximum depth of the surface snow layer in parameterisations of snow grain size, corresponding to a typical depth of solar penetration in snow (France et al, 2011). If the depth of snowpack is shallower than 5 cm, the effective radius is kept constant.…”