Benchmarking Photolysis Rates with Socrates (24.11): Species for Earth and Exoplanets

Abstract

Using the Socrates photolysis scheme, we present newly calculated photolysis rates under modern Earth atmospheric conditions for species directly relevant to Earth and species relevant to different atmospheric compositions. We compare to a previous photolysis comparison exercise, namely PhotoComp 2011. Overall, we find good agreement between our results and previous work, with discrepancies usually caused by the implementation of temperature or pressure dependent quantum yields and updated cross-section data. We provide a new set of benchmark photolysis rates for additional species both for Solar irradiance and when irradiated by an M dwarf host star. In general, the higher actinic flux at far-UV and shorter wavelengths of the M dwarf compared to the Sun drives increased photolysis rates for reactions with high threshold energies. This work provides an updated set of benchmark results for further studies of photolysis in the Earth's atmosphere and that of other planets.

Figures (26)

• Figure 1: The pressure (Pa) - temperature (K) atmospheric profile from ccmval2010sparc adopted in this work.
• Figure 2: Absorption cross section (cm$^2$ molecule$^{-1}$) against wavelength (nm) for the UV/visible range for O_2 & O_3 (left and right panels, respectively). The illustrative data are from lu2010absorption and yoshino1992high for O_2, and brion1998absorption for O_3 (see Table \ref{['tab:data_sources']} for our full list of data sources).
• Figure 3: Actinic flux (W m$^{-2}$ m$^{-1}$) from Socrates as a function of wavelength (nm) at three different levels, the top-of-atmosphere, upper mid-atmosphere (a pressure of $1$ Pa) and lower mid-atmosphere (at a pressure of $\sim$2400 Pa) corresponding to the ozone layer, shown by the solid blue, green, and magenta lines, respectively.
• Figure 4: O_3 photolysis rates (J) as a function of atmospheric pressure (Pa, top row) and as a function of wavelength (nm, bottom row) for the reactions: $\chem{O_3} \rightarrow \chem{O(^3P)} + \chem{O_2}$ (left column) and $\chem{O_3} \rightarrow \chem{O(^1D)} + \chem{O_2}$ (right column), where O(^3P) is the ground state of atomic oxygen and O(^1D) the first excited state. The rates from the UCI-ref model ccmval2010sparc and Socrates (this work) are shown as the dashed orange, and solid blue lines, respectively (top row). The photolysis spectra (bottom row) are shown for Socrates at TOA (blue) and at $\sim$100 Pa (green).
• Figure 5: O_2 photolysis rates (J) as a function of atmospheric pressure (Pa, top row) and as a function of wavelength (nm, bottom row). Total photolysis rate of O_2 into two atomic O (top left) is shown for comparison of Socrates (blue) to the UCI-ref model (dashed orange). Separate rates for the reactions$\chem{O_2} \rightarrow \chem{O(^3P)} + \chem{O(^1D)}$ (green) and$\chem{O_2} \rightarrow \chem{O(^3P)} + \chem{O(^3P)}$ (blue) are shown for Socrates (top right). The bottom panels show the rates for$\chem{O_2} \rightarrow \chem{O(^3P)} + \chem{O(^1D)}$ (bottom left) and$\chem{O_2} \rightarrow \chem{O(^3P)} + \chem{O(^3P)}$ (bottom right) as a function of wavelength (nm) at the TOA (blue) and for a pressure of $\sim$1 Pa (green) which corresponds to PhotoComp's TOA.