Acetaldehyde in the Alaskan subarctic snowpack

F Domine,A.-S Taillandier,S Houdier,W R Simpson

doi:10.5194/acp-10-919-2010

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 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.

Highlights

Snow is a complex multiphase medium consisting of ice crystals, interstitial air, atmospheric particles scavenged by precipitating snow or deposited by wind, and possibly liquid water and vegetal debris (Domine et al, 2008; Grannas et al, 2007)
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
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

Summary

Introduction

Snow is a complex multiphase medium consisting of ice crystals, interstitial air, atmospheric particles scavenged by precipitating snow or deposited by wind, and possibly liquid water and vegetal debris (Domine et al, 2008; Grannas et al, 2007). F. Domine et al.: Acetaldehyde in the Alaskan subarctic snowpack et al, 2002; Guimbaud et al, 2002; Hutterli et al, 1999; Jacobi et al, 2002; Sumner and Shepson, 1999). Domine et al.: Acetaldehyde in the Alaskan subarctic snowpack et al, 2002; Guimbaud et al, 2002; Hutterli et al, 1999; Jacobi et al, 2002; Sumner and Shepson, 1999) Among this last class, we focus our attention on aldehydes, which are intermediates in hydrocarbon oxidation processes that play a central role in atmospheric chemistry (Lary and Shallcross, 2000; Shepson et al, 1996). In polar regions, aldehydes contribute significantly to the OH budget (Yang et al, 2002), and they react with bromine atoms, terminating chains of reactions that destroy ozone in the polar marine boundary layer during the spring (Barrie et al, 1988; Grannas et al, 2002)

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Conclusion