Maria C. Zatko

East Antarctic sea ice in spring: spectral albedo of snow, nilas, frost flowers and slush, and light-absorbing impurities in snow

Abstract Spectral albedos of open water, nilas, nilas with frost flowers, slush, and first-year ice with both thin and thick snow cover were measured in the East Antarctic sea-ice zone during the Sea Ice Physics and Ecosystems eXperiment II (SIPEX II) from September to November 2012, near 65°S, 120°E. Albedo was measured across the ultraviolet (UV), visible and near-infrared (nIR) wavelengths, augmenting a dataset from prior Antarctic expeditions with spectral coverage extended to longer wavelengths, and with measurement of slush and frost flowers, which had not been encountered on the prior expeditions. At visible and UV wavelengths, the albedo depends on the thickness of snow or ice; in the nIR the albedo is determined by the specific surface area. The growth of frost flowers causes the nilas albedo to increase by 0.2–0.3 in the UV and visible wavelengths. The spectral albedos are integrated over wavelength to obtain broadband albedos for wavelength bands commonly used in climate models. The albedo spectrum for deep snow on first-year sea ice shows no evidence of light-absorbing particulate impurities (LAI), such as black carbon (BC) or organics, which is consistent with the extremely small quantities of LAI found by filtering snow meltwater. Estimated BC mixing ratios were in the range 0.1–0.5 ng of carbon per gram of snow.

The magnitude of the snow-sourced reactive nitrogen flux to the boundary layer in the Uintah Basin, Utah, USA

Reactive nitrogen (Nr = NO, NO2, HONO) and volatile organic carbon emissions from oil and gas extraction activities play a major role in wintertime ground-level ozone exceedance events of up to 140 ppb in the Uintah Basin in eastern Utah. Such events occur only when the ground is snow covered, due to the impacts of snow on the stability and depth of the boundary layer and ultraviolet actinic flux at the surface. Recycling of reactive nitrogen from the photolysis of snow nitrate has been observed in polar and midlatitude snow, but snow-sourced reactive nitrogen fluxes in mid-latitude regions have not yet been quantified in the field. Here we present vertical profiles of snow nitrate concentration and nitrogen isotopes ( 15N) collected during the Uintah Basin Winter Ozone Study 2014 (UBWOS 2014), along with observations of insoluble light-absorbing impurities, radiation equivalent mean ice grain radii, and snow density that determine snow optical properties. We use the snow optical properties and nitrate concentrations to calculate ultraviolet actinic flux in snow and the production of Nr from the photolysis of snow nitrate. The observed 15N(NO 3 ) is used to constrain modeled fractional loss of snow nitrate in a snow chemistry column model, and thus the source of Nr to the overlying boundary layer. Snow-surface 15N(NO 3 ) measurements range from 5 to 10 ‰ and suggest that the local nitrate burden in the Uintah Basin is dominated by primary emissions from anthropogenic sources, except during fresh snowfall events, where remote NO x sources from beyond the basin are dominant. Modeled daily averaged snow-sourced Published by Copernicus Publications on behalf of the European Geosciences Union. 13838 M. Zatko et al.: Snow-sourced reactive nitrogen flux in the Uintah Basin Nr fluxes range from 5.6 to 71⇥ 107 molec cm 2 s 1 over the course of the field campaign, with a maximum noontime value of 3.1⇥ 109 molec cm 2 s 1. The top-down emission estimate of primary, anthropogenic NO x in Uintah and Duchesne counties is at least 300 times higher than the estimated snow NO x emissions presented in this study. Our results suggest that snow-sourced reactive nitrogen fluxes are minor contributors to the Nr boundary layer budget in the highly polluted Uintah Basin boundary layer during winter 2014.

Effects of postdepositional processing on nitrogen isotopes of nitrate in the Greenland Ice Sheet Project 2 ice core

Records of ice core nitrate and its isotopes hold the potential to assess past atmospheric conditions regarding NOx and oxidant levels. However, relating such records to past atmospheric conditions requires a site-specific understanding of the postdepositional processing of snow nitrate. We report δ15N(NO3−) records from the Greenland Ice Sheet Project 2 (GISP2) ice core over major climate transitions. Model calculations and comparison with records of parameters influencing UV-driven postdepositional processing of snow nitrate suggest that the observed variability in GISP2 δ15N(NO3−) over major climate transitions is primarily driven by changes in the degree of postdepositional loss of snow nitrate. Estimates of the fractional loss of snow nitrate is (16–23)% in the Holocene and (45–53)% in the glacial period, suggesting a (41 ± 32)% lower nitrate depositional flux to Greenland during the glacial period relative to the Holocene.