Uptake of Gas-Phase Species by 1-Octanol. 1. Uptake of α-Pinene, γ-Terpinene, p-Cymene, and 2-Methyl-2-hexanol as a Function of Relative Humidity and Temperature

With use of a droplet train apparatus, the uptake by 1-octanol of gas-phase α-pinene, γ-terpinene, p -cymene, and 2-methyl-2-hexanol was measured as a function of relative humidity and temperature (263−293 K). 1-Octanol was selected as a surrogate for hydrophobic oxygenated organic compounds found in tropospheric aerosols. The mass accommodation coefficients (α) of γ-terpinene, p -cymene, and 2-methyl-2-hexanol obtained from these measurements exhibit negative temperature dependences. The upper and lower values of α at 265 and 290 K, respectively, are as follows: for γ-terpinene 0.12 and 0.076; for p -cymene 0.20 and 0.097; and for 2-methyl-2-hexanol 0.25 and 0.11. The uptake of α-pinene is solubility limited, yielding values for the product HD l 1/2 for α-pinene in 1-octanol ( H = Henry's law constant, D l = liquid-phase diffusion coefficient). With use of estimated values of D l the Henry's law constant is obtained as ln H (M/atm) = −(6.59 ± 1.16) + (3.80 ± 0.31) × 10 3 / T . The presence of water vapor does not affect the uptake of the above organic gas-phase species. Uptakes of the gas-phase species benzene, H 2 O, SO 2, and H 2 S were also studied and were found to below the detection limit of the droplet apparatus. This implies that the uptake coefficient for these species is less than 10 -3 for trace gas/liquid droplet interaction times up to 1.5 × 10 -2 s.