Acetaldehyde in the Alaskan subarctic snowpack

Abstract

Abstract. Acetaldehyde is a reactive intermediate in hydrocarbon oxidation. It is both emitted and taken up by snowpacks and photochemical and physical processes are probably involved. Understanding the reactivity of acetaldehyde in snow and its processes of physical and chemical exchanges requires the knowledge of its incorporation mechanism in snow crystals. We have performed a season-long study of the evolution of acetaldehyde concentrations in the subarctic snowpack near Fairbanks (65 • N), central Alaska, which is subjected to a vigorous metamorphism due to persistent elevated temperature gradients in the snowpack, between 20 and 200 • C m −1 . The snowpack therefore almost entirely transforms into depth hoar. We have also analyzed acetaldehyde in a manipulated snowpack where temperature gradients were suppressed. Snow crystals there transformed much more slowly and their original shapes remained recognizable for months. The specific surface area of snow layers in both types of snowpacks was also measured. We deduce that acetaldehyde is not adsorbed onto the surface of snow crystals and that most of the acetaldehyde is probably not dissolved in the ice lattice of the snow crystals. We propose that most of the acetaldehyde measured is either trapped or dissolved within organic aerosol particles trapped in snow, or that acetaldehyde is formed by the hydrolysis of organic precursors contained in organic aerosols trapped in the snow, when the snow is melted for analysis. These precursors are probably aldehyde polymers formed within the aerosol particles by Correspondence to: F. Domine (florent@lgge.obs.ujf-grenoble.fr) acid catalysis, but might also be biological molecules. In a laboratory experiment, acetaldehyde-di-n-hexyl acetal, representing a potential acetaldehyde precursor, was subjected to our analytical procedure and reacted to form acetaldehyde. This confirms our suggestion that acetaldehyde detected in snow could be produced during the melting of snow for analysis.

Classification of clouds sampled at the puy de Dôme (France) based on 10 yr of monitoring of their physicochemical properties

“…Samples were frozen until quantification of carbonyls, which was done once a year. Previous works highlighted the full recovery of carbonyls after samples were frozen, since they are analyzed right after their thawing (Domine et al, 2010;Houdier et al, 2011). In cloud droplets, carbonyl compounds (in particular formaldehyde) form adducts with dissolved SO 2 .…”

Organics in environmental ices: sources, chemistry, and impacts

“…Carbonyls larger than HCHO, such as acetaldehyde, acetone, glyoxal and methylglyoxal have been measured in polar snow (Houdier et al, 2002;Domine et al, 2010Domine et al, , 2011Douglas et al, 2012), at concentrations somewhat lower but of the same order of magnitude as those of HCHO. In the case of acetone, Houdier et al (2002) note that the measured concentrations are much too high to be explained by adsorption, and that the size of the molecule makes incorporation into the ice crystalline lattice unlikely.…”

Organics in environmental ices: sources, chemistry, and impacts

“…Carbonyls larger than HCHO, such as acetaldehyde, acetone, glyoxal and methylglyoxal have been measured in polar snow Domine et al, 2010Domine et al, , 2011Douglas et al, 2012), at concentrations somewhat lower but of the same order of magnitude as those of HCHO. In the case of acetone, Houdier et al (2002) note that the measured concentrations are much too high to be explained by adsorption, and that the size of the molecule makes incorporation into the ice crystalline lattice unlikely.…”

“…They suggest instead that acetone is incorporated into organic particles contained in the snow. In the case of acetaldehyde, Domine et al (2010) (Yamamoto et al, 1976;Moore et al, 1995), it is unlikely that they would form a solid solution with ice. Methanol and formic acid deserve further study, especially given that they have been measured in snowpack interstitial air and/or in melted snow samples (Legrand and Deangelis, 1995;Boudries et al, 2002;Dibb and Arsenault, 2002).…”

“…For example, Domine et al (2010) pointed out that acetaldehyde may be produced during the melting of snow samples prior to analysis, e.g., from precursors in organic aerosols trapped in the snow. This could clearly interfere with the measurement of free aldehydes in snow.…”