Opened 13 days ago

Last modified 12 days ago

#317 new Enhancement

Correct OH reaction coefficients for SO2, CO

Reported by: hcpxvi Owned by:
Priority: minor Milestone:
Component: FP other Version: FLEXPART 10.4
Keywords: OH, CO, SO2 Cc:


I note first that I am actually using the dev branch, but I think this is the same in Flexpart V10.x

Currently, the amounts of SO2 and CO in Flexpart do not decay via reaction with OH. This is because the variables POHCCONST and POHDCONST in the files SPECIES_xxx are set to a negative value. The user cannot turn on the reaction with OH just by removing the - signs because the absolute values are placeholders, used for all species where reaction with OH is not enabled. (If you cluelessly remove the - signs for SO2, it decays far too fast.)

I would be very grateful if someone could supply me with the correct values for POHCCONST, POHDCONST and POHNCONST for SO2 (and, less urgently, CO). The ideal thing would be for the correct values to go into the SPECIES_xxx files supplied with Flexpart. But I would be happy for now to get the values as a reply in this ticket --- I can easily put them into SPECIES_xxx myself. (This would also leave the values where a person searching the web could find them.)

If no-one knows the right values and I manage to dig suitable ones out of the literature I shall add them to this ticket.

Change History (1)

comment:1 Changed 12 days ago by hcpxvi

Progress so far on the SO2+OH reaction:

  • The rate constant for SO2+OH has a complex dependence on temperature and pressure (eqs 3--4 of Sun et al. (2022)) which cannot be boiled down to equation 13 of Pisso et al.(2019)
  • A very simple approach is to identify the pressure and temperature range at which most of your SO2 is located and choose a suitable value of k1 from the table in the supplement to Sun et al. (2022) ( ) You can then edit SPECIES_023, setting POHCCONST to that value and set both POHDCONST and POHNCONST to 0.0 . Setting POHCCONST=4.8e-13 gives reasonable results for the SO2 observed after the HT-HH eruption, which was all in the mid-stratosphere.
  • I suspect that it is not possible to give values of POHCCONST, POHDCONST and POHNCONST for SO2 which are reasonable for all altitudes and express the temperature dependence correctly.
  • An ideal enhancement for the distant future would be for Flexpart to implement eqs. 3 and 4 of Sun et al. (2022), but this would require a change to the SPECIES_xxx format to include the five parameters which go into those equations.
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