JPL 00-3 Heterogenous Chemistry Section Addenda and Errata

JPL-003 Heterogenous Chemistry Section Addenda and Errata

Figure 3 - Recommended Reactive Uptake Coefficients

For ease of reproduction by those implementing the halogen activation model presented in the Appendix on pages 57-62, the g_o values for the reactions presented in Figure 3 assumed a fresh sulfuric acid aerosol surface (i.e., as stated on page 45, the reacto-diffusive length, = 0, for each reaction is assumed to be small, this is equivalent to setting, = 0 for the ClONO₂ and HOCl reactions in the model.) Also as stated on page 45, p_HCl is assumed to be much greater than p_ClONO2.

While the assumption of a negligible l for the HOCl + HCl reaction is chemically unreasonable for stratospheric aerosols, it has the advantage that it avoids the necessity to specify a representative aerosol radius. The second assumption avoids the necessity of specifying a ClONO₂ partial pressure. Ross Salawitch of JPL has pointed out that those implementing the heterogeneous model and checking it against the uptake coefficients presented in Figure 3 could easily miss or misinterpret the assumptions on page 45. Furthermore, the relative g_os presented in Figure 3 for the reactions of ClONO₂ and HOCl with HCl are unrealistic for normal stratospheric conditions.

To address these concerns the model has been exercised for a 50 mbar case assuming 5ppmv of water vapor and 2 ppbv of HCl, as before, but with 0.1 ppbv of ClONO₂and an aerosol diameter of 10^-5 cm (0.1 mm). These new results, which primarily effect the plots for g_os for the ClONO₂ and HOCl with HCl reactions, are displayed in Figure 3a, below. The plots for the N₂O₅and BrONO₂hydrolysis reactions are unchanged (i.e. the calculation assumes that = 0 for these reactions).

Water Activity Parameterizations

The parameterization for calculating the activity of water, aw, in sulfuric acid aerosols in the chlorine activation model is adopted from Tabazadeh et al. [307] and presented in Table A-1 on page 58. A simpler approximation for estimating aw is noted below Table A-2 on page 59; this approximation is presented for convenience, but is not used in the chlorine activation model implementation.

F_HClTypographical Error

The expression in the middle column of the last row of Table A-4 on page 62 contains a typographical error:

F_HOCl should be F_HCl.

Reference Typographical Error

The Robinson et al. references [270] and [272] are the same work. The year of publication listed in [270] is incorrect, it should be 1997 not 1996. Call out to these two references on pages 49 and 53, 57 will be consolidated in future editions.

Figure 3a. Recommended reactive uptake coefficients as a function of temperature for key stratospheric heterogeneous processes on sulfuric acid aerosols. For ClONO₂ and HOCl species, the aerosol diameter used in the calculation is 10^-5 cm, a characteristic value in the stratosphere. Because the current uptake models for N₂O₅ and BrONO₂ hydrolysis do not provide the information about the reacto-diffusive length ( = 0 ), the aerosol diameter used in the calculation is assumed to be much larger than their reacto-diffusive length (i.e. = 0 for N₂O₅ and BrONO₂ is set to be zero).

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