Ice‐oxyhydrocarbon interactions in the troposphere

Both surface and volume uptake can contribute to the removal of tropospheric gases by ice‐phase precipitation and cloud particles. These processes were evaluated by depositing ice in the presence of several gaseous oxyhydrocarbons and analyzing the chemical composition of the deposit. Acetone, methanol, ethanol, n‐propanol, n‐butanol, tert‐butanol, cyclohexanol, and toluene were tested. Volume uptake appears to be the dominant process, and results are presented as temperature‐dependent volume uptake coefficients. When extrapolated to 0°C, the volume uptake coefficients are at least a factor of two smaller than predictions based on gas partitioning into liquid water. Volume uptake coefficients at −10°C are 5–2 mol m −3 Pa −1 for the alkanols (i.e., 5 × 10 2 –2 × 10 2 mol L −1 atm −1 ), 0.8 mol m −3 Pa −1 for acetone, and 0.01 mol m −3 Pa −1 for toluene. Further, our analysis indicates that the alkanols weaken water‐water bonding when incorporated into ice. This assertion is based on the positive temperature dependence of the alkanol volume uptake coefficients and is corroborated by indirect estimates of the effect of the alkanols on ice saturation vapor pressure. Since the observed volume uptake coefficients do not exceed the 10 mol m −3 Pa −1 threshold proposed by Crutzen and Lawrence [2000], our results indicate that the incorporation of the studied compounds into vapor‐deposited ice is not a substantial atmospheric removal process.