Soluble, light-absorbing species in snow at Barrow, Alaska

Abstract

As part of the international multidisciplinary Ocean ‐ Atmosphere ‐ Sea Ice ‐ Snowpack (OASIS) program we analyzed more than 500 terrestrial (melted) snow samples near Barrow, AK between February and April 2009 for light absorption, as well as H2O2 and inorganic anion concentrations. For light absorption in the photochemically active region (300–450 nm) of surface snows, H2O2 and NO3− make minor contributions (combined < 9% typically), while HUmic LIke Substances (HULIS) and unknown chromophores each account for approximately half of the total absorption. We have identified four main sources for our residual chromophores (i.e., species other than H2O2 or NO3−): (1) vegetation and organic debris impact mostly the lowest 20 cm of the snowpack, (2) marine inputs, which are identified by high Cl− and SO42− contents, (3) deposition of diamond dust to surface snow, and (4) gas‐phase exchange between the atmosphere and surface snow layers. The snow surfaces, and accompanying chromophore concentrations, are strongly modulated by winds and snowfall at Barrow. However, even with these physical controls on light absorption, we see an overall decline of light absorption in near‐surface snow during the 7 weeks of our campaign, likely due to photo‐bleaching of chromophores. While HULIS and unknown chromophores dominate light absorption by soluble species in Barrow snow, we know little about the photochemistry of these species, and thus we as a community are probably overlooking many snowpack photochemical reactions.

Carbonaceous aerosols recorded in a southeastern Tibetan glacier: analysis of temporal variations and model estimates of sources and radiative forcing

“…Second, we treated all the water-insoluble OC from the ice-core measurements as lightabsorbing brown carbon in the forcing estimation, which also likely results in an overestimation of OC forcing if a significant fraction of OC is non-absorbing. However, the watersoluble part, accounting for about half of OC observed in the Manora peak and northwestern India (Ram et al, 2010;Rajput et al, 2014), can also contribute to some absorption of UV and visible light (Chen and Bond, 2010;Beine et al, 2011). Thus, the absorption by water-soluble OC that was not included in the forcing estimate may compensate for the high bias to some extent.…”

A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

“…Thus the theoretical treatment predicts that the temperature dependence of the layer thickness varies depending on which interactions are dominating (Wettlaufer, 1999;Dash et al, 2006). As a consequence of these predictions in certain cases thickness can behave non-monotonically with respect to temperature and/or impurity level (Benatov and Wettlaufer, 2004;Thomson, 2010;Thomson et al, 2013).…”

The specific surface area and chemical composition of diamond dust near Barrow, Alaska

“…Since the primary focus of the campaign was the chemistry of the Arctic boundary layer and snow close to the Arctic ocean, and since snow reactivity clearly depends on its chemical composition [ Grannas et al , 2007], the DD was also analyzed for aldehydes, mineral and organic ions and some other organic constituents. To help quantify snow photochemistry, we also measured the optical absorption spectra of the water‐soluble reactive chromophores (light absorbing species) contained in snow [ Beine et al , 2011]. It is now well established that H 2 O 2 and the nitrate ion NO 3 − are important snow chromophores [ Dominé and Shepson , 2002].…”