Enhanced vapor wall loss of intermediate volatility alcohols at elevated relative humidity

A series of experiments was conducted to investigate the role of water vapor in enhancing vapor wall loss of intermediate volatility alcohols ranging from C₄-C₉ terminal aliphatic alcohols, aromatic alcohols, and diols. In the first of two types of experiments, a constant alcohol concentration (2.48 ± 1.48 ppmv) was introduced along with a dilution reference (DR) while chamber relative humidity (RH) was varied from dry (~3%) to a maximum of ~40%. Alcohol gas phase concentrations in the inlet manifold and chamber were monitored throughout each experiment by on-line gas chromatography with flame ionization detection. Wall loss was parameterized in each case using the dilution ratio (i.e., ratio of inlet to chamber concentration) for the alcohol relative to that for the DR. Dilution ratios uniformly increase across the range of investigated alcohols as chamber RH is increased but varied considerably among the different alcohols. In the second type of experiment, RH was held constant and chamber concentrations of 1-nonanol were varied as the chamber was spun up to steady state and back down. The rate of decay of 1-nonanol concentration differs between dry and ~25% suggesting that RH can also influence reversibility of RH-enhanced wall losses. Finally, a model was used to simulate wall loss processes for each investigated alcohol. Measurements and model output were overall in close agreement indicating that gas-wall partitioning is strongly linked to RH.