FAST-JX v7.0 photolysis mechanism

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NOTE: Page under construction

FAST-JX v7.0 has been introduced into GEOS-Chem v10-01, along with the UCX chemistry mechanism, by Sebastian Eastham (MIT).

Overview

This update is being tested in the 1-month benchmark simulation v10-01c.

Sebastian Eastham incorporated Fast-JX v7.0a into the GEOS-Chem UCX mechanism. From Eastham et al. (2014):

GEOS-Chem uses a customized version of the Fast-JX v6.2 photolysis rate solver (Wild et al., 2000), which efficiently estimates tropospheric photolysis. The customized version uses the wavelength bands from the older Fast-J tropospheric photolysis scheme and does not consider wavelengths shorter than 289 nm, assuming they are attenuated above the tropopause. However, these high-energy photons are responsible for the release of ozone-depleting agents in the stratosphere. The standard Fast-JX model (Prather, 2012) addresses this limitation by expanding the spectrum analyzed to 18 wavelength bins covering 177–850 nm, extending the upper altitude limit to approximately 60 km. We therefore incorporate Fast-JX v7.0a into GEOS-Chem UCX. Fast-JX includes cross-section data for many species relevant to the troposphere and stratosphere. However, accurately representing sulfur requires calculation of gaseous H2SO4 photolysis, a reaction which is not present in Fast-JX but which acts as a source of sulfur dioxide in the upper stratosphere. Based on a study by Mills (2005), the mean cross-section between 412.5 and 850 nm is estimated at 2.542 × 10−25 cm2. We also add photolysis of ClOO and ClNO2, given their importance in catalytic ozone destruction, using data from JPL 10-06 (Sander et al., 2011). Fast-JX v7.0a includes a correction to calculated acetone cross sections. Accordingly, where hydroxyacetone cross-sections were previously estimated based on one branch of the acetone decomposition, a distinct set of cross sections from JPL 10-06 are used.
The base version of GEOS-Chem uses satellite observations of total ozone columns when determining ozone-related scattering and extinction. The UCX allows either this approach, as was used for the production of the results shown, or can employ calculated ozone mixing ratios instead, allowing photolysis rates to respond to changes in the stratospheric ozone layer.

Input files for FAST-JX v7.0

  1. FJX_spec.dat: Fast-J X-sections, to replace jv_spec.dat (GEOS-Chem v9-02 and earlier versions) and spec2008.dat (Fast-JX v6.2 implementation)
  2. FJX_j2j.dat: Links GEOS-Chem chemical species to Fast-JX species, to replace ratj.d
  3. jv_spec_mie.dat: Aerosol optical properties at 5 wavelengths

Major changes

Previous issues that have now been resolved

In this section we discuss issues that have been recently fixed in the implementation of FAST-JX v7.0:

Reactivation of bromine species photolysis for tropospheric simulation

This update will be tested in the 1-month benchmark simulation v10-01c.

Sebastian Eastham wrote:

Bromine species photolysis should probably be reactivated in the tropospheric version – given that it was online in the pre-UCX version, we may as well keep it online. Doing so is just a question of removing the 'x' in the FJX_spec.dat file for the relevant species.

In FJX_spec.dat change the following lines from:

BrO   x300 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00  J10
           0.000E+00 0.000E+00 0.000E+00 5.620E-19 1.202E-18 2.008E-18
           3.239E-18 4.520E-18 5.064E-18 5.809E-18 7.350E-19 0.000E+00
BrNO3 x200 0.000E+00 0.000E+00 5.484E-19 7.245E-19 3.702E-18 3.475E-18  J10
           3.182E-18 2.978E-18 5.304E-19 6.086E-19 4.489E-19 1.963E-19
           1.584E-19 1.307E-19 1.110E-19 8.033E-20 3.377E-20 1.270E-21
BrNO3 x300 0.000E+00 0.000E+00 8.026E-19 1.071E-18 5.166E-18 4.190E-18  J10
           3.467E-18 3.039E-18 5.567E-19 5.989E-19 4.528E-19 2.098E-19
           1.705E-19 1.425E-19 1.207E-19 8.648E-20 3.716E-20 1.445E-21
HOBr  x300 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00  J10
           0.000E+00 0.000E+00 1.324E-19 2.011E-19 2.202E-19 2.196E-19
           1.726E-19 1.367E-19 1.157E-19 1.125E-19 6.197E-20 2.755E-21

to:

BrO    300 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00  J10
           0.000E+00 0.000E+00 0.000E+00 5.620E-19 1.202E-18 2.008E-18
           3.239E-18 4.520E-18 5.064E-18 5.809E-18 7.350E-19 0.000E+00
BrNO3  200 0.000E+00 0.000E+00 5.484E-19 7.245E-19 3.702E-18 3.475E-18  J10
           3.182E-18 2.978E-18 5.304E-19 6.086E-19 4.489E-19 1.963E-19
           1.584E-19 1.307E-19 1.110E-19 8.033E-20 3.377E-20 1.270E-21
BrNO3  300 0.000E+00 0.000E+00 8.026E-19 1.071E-18 5.166E-18 4.190E-18  J10
           3.467E-18 3.039E-18 5.567E-19 5.989E-19 4.528E-19 2.098E-19
           1.705E-19 1.425E-19 1.207E-19 8.648E-20 3.716E-20 1.445E-21
HOBr   300 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00 0.000E+00  J10
           0.000E+00 0.000E+00 1.324E-19 2.011E-19 2.202E-19 2.196E-19
           1.726E-19 1.367E-19 1.157E-19 1.125E-19 6.197E-20 2.755E-21

--Melissa Sulprizio 13:33, 14 May 2014 (EDT)

Error in reducing wavelength bins for tropospheric simulation

This update will be tested in the 1-month benchmark simulation v10-01c.

Sebastian Eastham wrote:

In fast_jx_mod, specifically RD_XXX, there is a transformation to reduce 18 cross sections to 12. Since bin 18 now corresponds to bin 12 and so on, the wavelengths are moved within the cross section array QQQ. However, the 12-bin capability is rarely used (if ever), so when Fast-JX was extended to allow cross sections with 1 or 3 sets of data, the 12 and 8 bin codes were not updated accordingly. This results in very large cross sections for acetone at long wavelengths, because the shorter wavelength data is being used instead.
I've notified Michael Prather - he did not know about this bug and is putting together a fix ASAP. I've written my own fix in the meantime, which results in the acetone cross sections matching much more closely, at least between the two v10-01c versions.

--Melissa Sulprizio 10:39, 12 May 2014 (EDT)

References