31 Aug 2023
 | 31 Aug 2023
Status: this preprint is currently under review for the journal AMT.

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

Longkun He, Wenli Liu, Yatai Li, Jixuan Wang, Mikinori Kuwata, and Yingjun Liu

Abstract. Teflon bag chambers have long been used for investigating atmospheric chemical processes, including secondary organic aerosol formation. 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 well been investigated. In this study, we experimentally investigated wall-loss process 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 hours after injection at room temperature, while the corresponding value was 95 % at 262 K. The experimental data were analyzed using the two-layer kinetic model, which considers both absorption of gas phase species to the surface layer of Teflon wall and diffusion to the inner layer. The experimental data demonstrated that absorption of gas phase species by the surface layer enhanced at lower temperature. The temperature dependence in absorption was well accounted using the equilibrium dissolution model of organic compounds to the Teflon surface by considering reduced saturation vapor pressure at lower temperature. On the contrary, diffusion process of n-alkanes from the surface to inner layer slowed down at reduced temperature. Hence the relative importance of the surface and inner layers on wall-loss process changes with temperature. 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.

Longkun He et al.

Status: open (until 12 Oct 2023)

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  • RC1: 'Comment on amt-2023-187', Anonymous Referee #1, 18 Sep 2023 reply
  • RC2: 'Comment on amt-2023-187', Anonymous Referee #2, 25 Sep 2023 reply

Longkun He et al.


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Short summary
We experimentally investigated vapor wall loss of n-alkanes in a Teflon chamber across a wide temperature range. Increased wall loss was observed at lower temperatures. Further analysis suggests that lower temperature enhances partitioning of n-alkanes to surface layer of Teflon wall but slows their diffusion into inner layer. The results are important for quantitative analysis of chamber experiments conducted at low temperatures, simulating wintertime or under upper tropospheric conditions.