title: Adsorption and hydrolysis of alcohols and carbonyls on ice at temperatures of the upper troposphere.
abstract: The uptake of gaseous ethanol, 1,1,1-trifluoroethanol, acetone, chloral (CCl(3)CHO), and fluoral (CF(3)CHO) on ice films has been investigated using a coated-wall flow tube at temperatures 208-228 K corresponding to the upper troposphere (UT), with a mass spectrometric measurement of gas concentration. The uptake was largely reversible and followed Langmuir-type kinetic behavior, i.e., surface coverage increased with the trace gas concentration approaching a maximum surface coverage at a gas phase concentration of N(max) ∼ (2-4) × 10(14) molecules cm(-3), corresponding to a surface coverage of ∼30% of a monolayer (ML). The equilibrium partition coefficients, K(LinC), were obtained from the experimental data by analysis using the simple Langmuir model for specific conditions of temperature and concentration. The analysis showed that the K(LinC) depend only weakly on surface coverages. The following expressions described the temperature dependence of the partition coefficients (K(LinC)) in centimeters, at low coverage for ethanol, trifluoroethanol, acetone, chloral, and fluoral: K(LinC) = 1.36 × 10(-11) exp(5573.5/T), K(LinC) = 3.74 × 10(-12) exp(6427/T), K(LinC) = 3.04 × 10(-9) exp(4625/T), K(LinC) = 7.52 × 10(-4) exp(2069/T), and K(LinC) = 1.06 × 10(-2) exp(904/T). For acetone and ethanol the enthalpies and entropies of adsorption derived from all available data showed systematic temperature dependence, which is attributed to temperature dependent surface modifications, e.g., QLL formation. For chloral and fluoral, there was an irreversible component of uptake, which was attributed to hydrate formation on the surface. Rate constants for these surface reactions derived using a Langmuir-Hinshelwood mechanism are reported.
authors.affiliation: Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK.
authors.forename: Angela
authors.initials: A
authors.lastname: Symington
authors.forename: Lay May
authors.initials: LM
authors.lastname: Leow
authors.forename: Paul T
authors.initials: PT
authors.lastname: Griffiths
authors.forename: R Anthony
authors.initials: RA
authors.lastname: Cox
mesh_terms: D000079:Acetaldehyde / Q000031:analogs & derivatives* / Q000737:chemistry; D000096:Acetone / Q000737:chemistry*; D000327:Adsorption; D001272:Atmosphere / Q000737:chemistry; D002697:Chloral Hydrate / Q000031:analogs & derivatives* / Q000737:chemistry; D000431:Ethanol / Q000031:analogs & derivatives / Q000737:chemistry*; D006868:Hydrolysis; D007053:Ice; D013499:Surface Properties; D013696:Temperature
chemical_list: D007053:Ice; D000096:Acetone; D000431:Ethanol; D002697:Chloral Hydrate; C019120:trifluoroacetaldehyde hydrate; C021100:trichloroacetaldehyde; D000079:Acetaldehyde