Vapor wall loss of semi-volatile organic compounds in a Teflon chamber

We have investigated the vapor wall loss of semi-volatile organic compounds (SVOCs) in a Teflon smog chamber. We studied the vapor wall loss of seven SVOCs with known saturation concentrations, including alkanes (hexacosane, pentacosane, docosane, eicosane, and d₆₂-squalane), an organic acid (oleic acid), and a polyol (levoglucosan) in single-component and binary-component (organic) systems, using ammonium sulfate (AS) seeds to constrain the particle wall loss. We coated inorganic particles with SVOCs and measured the loss of organics from those particles to constrain the wall losses, observing loss rates proportional to the saturation concentrations of the SVOCs. The loss rate of oleic acid mixed with d₆₂-squalane was proportional to its mole fraction in the mixture. Our results show that the vapor wall-loss rates of SVOCs are significant, quasi-irreversible, and proportional to the SVOC vapor concentrations. The vapor wall-loss rate constant of the SVOCs that we studied in the CMU chamber is 3.8 ± 0.3 h⁻¹; this is comparable to values in other chambers with similar surface area to volume ratios. Our results are also consistent with a relatively high mass accommodation coefficient for SVOCs, α_org > 0.1.