Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: Volume 1. Inorganic compounds

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Abstract

Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed. A different version of this compilation/evaluation, which will be updated when new data become available, is uploaded online (https://sites.google.com/site/mingjintang/home/diffusion).

Figures

  • Figure 1. Influence of gas phase diffusion on the effective uptake coefficients (defined as γeff / γ , the ratio of the effective uptake to the true uptake coefficient) as a function of the true uptake coefficient. N2O5, with a diffusion coefficient of 0.085 cm2 s−1 at 760 Torr and 296 K and an average molecular speed of 24 096 cm s−1, is used as the representative trace gas for the calculations. (a) Uptake onto spheric particles with different diameters at 760 Torr and 296 K; (b) uptake onto the wall of a cylindrical flow tube (inner diameter: 2.0 cm) at 296 K and at different pressures.
  • Table 1. Dimensionless diffusion volumes of molecules and atoms of atmospheric interest. Data are taken from Table 11-1 of Reid et al. (1987).
  • Table 2. Summary of preferred diffusivities of atmospheric reactive trace gases in air at 296 K. Several trace gases without recommended diffusivities are also listed to highlight the necessity of further measurements.
  • Table 3. Summary of measured diffusivities of HNO3 and NH3, and comparison with the estimated values.
  • Table 4. Summary of measured diffusivities of NO, NO2, NO3, N2O5 and HONO, and comparison with the estimated values.
  • Table 5. Summary of measured diffusivities of SO2, SO3, H2SO4, O3, OH, HO2 and H2O2, and comparison with the estimated values.
  • Table 6. Summary of measured diffusivities of halogen species, and comparison with the estimated values.
  • Figure 2. Temperature dependence of the diffusivity of OH radicals in air: comparison of measured diffusivity (Liu et al., 2009, black solid curve, left y axis) with estimated values (black dashed curve, left y axis). The ratios of estimated diffusivities to the measured ones (red curve, right x axis) are also plotted as a function of temperature.

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Tang, M. J., Cox, R. A., & Kalberer, M. (2014). Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: Volume 1. Inorganic compounds. Atmospheric Chemistry and Physics, 14(17), 9233–9247. https://doi.org/10.5194/acp-14-9233-2014

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