Surface Disordering and Film Formation on Ice Induced by Formaldehyde and Acetaldehyde
journal contributionposted on 18.12.2014, 00:00 by Min H. Kuo, Samar G. Moussa, V. Faye McNeill
Small aldehydes, such as formaldehyde (HCHO) and acetaldehyde (CH3CHO), are known to contribute significantly to the OH and O3 budgets in polar atmospheres via chemical interaction with snow and ice surfaces. However, our understanding of how these small aldehydes interact with ice surfaces is rather limited. In this work, ellipsometry was used to study the interaction of gas-phase HCHO and CH3CHO with ice under partial pressure and temperature conditions akin to polar snowpack interstitial space. Both HCHO and CH3CHO were found to induce surface change consistent with the formation of a disordered interfacial layer (DIL) at temperatures below which no intrinsic DIL is expected to exist (T < 238 K). For HCHO, induced surface disorder showed both temperature and partial pressure dependence. For CH3CHO, temperature seemed to be the dominant factor; a DIL surface transition was observed in the presence of CH3CHO at 223 ± 2 K, in agreement with earlier findings that partitioning behavior of CH3CHO is different above and below this transition temperature. Exposure to HCHO or CH3CHO was also observed to cause the formation of opaque domains on the ice surface, which may correspond to hydrate formation.