Wall loss of semi-volatile organic compounds in a Teflon bag chamber for the temperature range of 262–298 K: mechanistic insight on temperature dependence

Abstract

Abstract. ​​​​​​​Teflon bag chambers have long been used for investigating atmospheric chemical processes, including secondary organic aerosol formation. The wall-loss process of gas-phase species in Teflon bag chambers has typically been investigated at around room temperature. Recent laboratory studies started employing Teflon bag chambers at sub-273 K conditions for simulating wintertime and upper-tropospheric environments. However, temperature dependence in vapor-wall-loss processes of semi-volatile organic compounds (SVOCs) in a Teflon bag chamber has not been well investigated. In this study, we experimentally investigated wall-loss processes of C14–C19 n-alkanes in a 1 m3 Teflon bag for the temperature range of 262 to 298 K. Enhanced wall losses of the tested n-alkanes were observed following the decrease in temperature. For instance, 65 %​​​​​​​ of C14 n-alkane was lost to the wall 15 h after injection at room temperature, while the corresponding value was 95 % at 262 K. The experimental data were analyzed using a two-layer kinetic model, which considers both absorption of gas-phase species to the surface layer of the Teflon wall and diffusion to the inner layer. The experimental data demonstrated that absorption of gas-phase species by the surface layer was enhanced at lower temperatures. The temperature dependence in absorption was well accounted for using the equilibrium-dissolution model of organic compounds to the Teflon surface by considering reduced saturation vapor pressure at lower temperatures. On the contrary, diffusion of n-alkanes from the surface to the inner layer slowed down at reduced temperatures. Mechanistic studies on these processes will need to be conducted in the future to quantitatively predict the influence of temperature-dependent wall-loss processes of SVOCs on laboratory experimental results.