Abstract
Abstract. Light-absorbing impurities (LAIs) deposited in snow have the potential to substantially affect the snow radiation budget, with subsequent implications for snow melt. To more accurately quantify the snow albedo, the contribution from different LAIs needs to be assessed. Here we estimate the main LAI components, elemental carbon (EC) (as a proxy for black carbon) and mineral dust in snow from the Indian Himalayas and paired the results with snow samples from Arctic Finland. The impurities are collected onto quartz filters and are analyzed thermal–optically for EC, as well as with an additional optical measurement to estimate the light-absorption of dust separately on the filters. Laboratory tests were conducted using substrates containing soot and mineral particles, especially prepared to test the experimental setup. Analyzed ambient snow samples show EC concentrations that are in the same range as presented by previous research, for each respective region. In terms of the mass absorption cross section (MAC) our ambient EC surprisingly had about half of the MAC value compared to our laboratory standard EC (chimney soot), suggesting a less light absorptive EC in the snow, which has consequences for the snow albedo reduction caused by EC. In the Himalayan samples, larger contributions by dust (in the range of 50 % or greater for the light absorption caused by the LAI) highlighted the importance of dust acting as a light absorber in the snow. Moreover, EC concentrations in the Indian samples, acquired from a 120 cm deep snow pit (possibly covering the last five years of snow fall), suggest an increase in both EC and dust deposition. This work emphasizes the complexity in determining the snow albedo, showing that LAI concentrations alone might not be sufficient, but additional transient effects on the light-absorbing properties of the EC need to be considered and studied in the snow. Equally as imperative is the confirmation of the spatial and temporal representativeness of these data by comparing data from several and deeper pits explored at the same time.
Highlights
The deposition of light-absorbing impurities (LAI) in snow influences the radiation budget and can cause enhanced melting via snow darkening (Warren and Wiscombe, 1980)
As the glaciers are situated at a relatively low altitude, they are more likely to be exposed to black carbon (BC) than other Himalayan glaciers at a higher altitude, as BC has been shown to decrease with altitude in other parts of the Himalayas (e.g., Kaspari et al, 2014; Ming et al, 2013; Yang et al, 2015)
Reported airborne BC mass absorption cross section (MAC) values are lower than what we found for the two soot standards
Summary
The deposition of light-absorbing impurities (LAI) in snow influences the radiation budget and can cause enhanced melting via snow darkening (Warren and Wiscombe, 1980). The potential impact of LAI on snow and ice makes the Himalayas a region of special interest It contains numerous glaciers which are in a general state of recession, contrasting patterns have been reported in different areas (e.g., Bolch et al, 2012; Kääb et al, 2012). The use of filters can provide a practical logistics advantage for the collection of LAI in remote locations, as it is difficult to maintain the necessary frozen chain for the snow samples from the field to the laboratory for analysis. Our Himalayan observations are further compared to samples from Arctic Finland for their LAI content
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