Uptake Measurements of Acetaldehyde on Solid Ice Surfaces and on Solid/Liquid Supercooled Mixtures Doped with HNO3 in the Temperature Range 203−253 K

Uptake of acetaldehyde on ice surfaces has been investigated over the temperature range 203-253 K using a coated wall flow tube coupled to a mass spectrometric detection. The experiments were conducted on pure ice surfaces and on liquid/solid ice mixture both doped with nitric acid (0.063, 0.63, and 6.3 wt %). Uptake of acetaldehyde on these surfaces was always found to be totally reversible whatever the experimental conditions were. The number of acetaldehyde molecules adsorbed per surface unit was conventionally plotted as a function of acetaldehyde concentration in the gas phase. Although the amounts of acetaldehyde adsorbed on solid ice surfaces (pure and HNO(3)-doped ice) were approximately similar and rather limited, the number of acetaldehyde molecules taken up on the HNO(3)-doped solid ice/liquid mixtures are significantly higher, up to 1 or 2 orders of magnitudes compared to pure ice surfaces. At 213 K for example and for low concentrations of acetaldehyde (<1 x 10(13) molecule cm(-3)), the amount of acetaldehyde molecules taken up on solid/liquid doped surfaces is 3.3 and 8.8 times higher than those measured on pure ice respectively for 0.063 and 0.63 wt % of HNO(3). The huge quantities of acetaldehyde taken up by liquid-/solid-doped mixtures are likely dissolved in the nonhomogeneous liquid part of the surfaces according to the Henry's law equilibrium. As a consequence, up to about 10% of acetaldehyde may be scavenged by supercooled liquid droplets of convective clouds in the upper troposphere.