Air–water interface equilibrium partitioning coefficients of aromatic hydrocarbons

The single equilibration technique was used to determine the equilibrium partitioning coefficients (pc) of an air–water interface for target aromatic volatile organic compounds (VOCs), including benzene, toluene and ethylbenzene. The tested liquid concentrations (CL) of VOC ranged from 0.5 to 20 mg/l, and the temperatures (Tw) of the solutions were 300, 305, 310 and 315 K, respectively. The pc values were calculated using the gaseous concentrations (Cg*) of aromatic hydrocarbons in equilibrium with the aqueous phase and the formula pc=(Cg*/CL). The heats of VOC of liquid and gaseous phase transfer (ΔHtr) in pure water, and the highly linear regression relationship (with squared correlation coefficients, R2, from 0.900 to 0.999) between (lnCg*) and (1/Tw) are also evaluated. Experimental results indicated that the pc values of the target VOC components increase with Tw but, in contrast, are not significantly affected by CL in pure water. However, pc of more soluble compounds, like iso-propanol and methyl ethyl ketone, have been evaluated to be significant with CL in the earlier investigation. Finally, the co-solute effect on pc is also evaluated in this work, as determining pc of the aromatic hydrocarbons by using aqueous ethanol (in a volume ration of 1–15%) as solutes.