# UKCA Chemistry and Aerosol Tutorial 8

## What you will learn in this Tutorial

In this tutorial you will learn how the wet deposition of chemical species is handelled in UKCA. You will then add-in the wet deposition of one of your new tracers.

Task 8.1: Add in wet deposition for BOB, using the following values:

${\displaystyle \ k(298)\ }$ ${\displaystyle \ -\left({\Delta H}/R\right)\ }$ ${\displaystyle \ k(298)}$ for the 1st dissociation ${\displaystyle \ -\left({\Delta H}/R\right)}$ for the 1st dissociation ${\displaystyle \ k(298)}$ for the 2nd dissociation ${\displaystyle \ -\left({\Delta H}/R\right)}$ for the 2nd dissociation
${\displaystyle \ 0.21\times 10^{+06}\ }$ ${\displaystyle \ 0.87\times 10^{+04}\ }$ ${\displaystyle \ 0.2\times 10^{+02}\ }$ ${\displaystyle \ 0.0\ }$ ${\displaystyle \ 0.0\ }$ ${\displaystyle \ 0.0\ }$

Note: If you were unable to successfully complete Task 7.1, then please take a copy of the h job from the Tutorial experiment (Tutorial: solution to Task 7.1 - add new dry deposition) and work from there, as this will allow you to only make the changes required for this task. Please also make a new branch and merge-in branch fcm:um_br/dev/luke/vn8.4_UKCA_Tutorial_Solns/src at revision number 14711 to allow you to proceed.

The formulation used in UKCA is described in Giannakopoulos (1999)[1]. This scheme uses the following formula to calculate the effective Henry's Law coefficient

${\displaystyle H_{eff}=k\left(298\right)\exp \left(-{\frac {\Delta H}{R}}\left[\left({\frac {1}{T}}\right)-\left({\frac {1}{298}}\right)\right]\right)}$

where ${\displaystyle k\left(298\right)}$ is the rate constant at 298K.

During this tutorial you will be tasked with adding the wet deposition of one of your new tracers.

References

1. Giannakopoulos, C., M. P. Chipperfield, K. S. Law, and J. A. Pyle (1999), Validation and intercomparison of wet and dry deposition schemes using 210Pb in a global three-dimensional off-line chemical transport model, J. Geophys. Res., 104(D19), 23761–23784, doi:10.1029/1999JD900392.

## Turning on Wet Deposition for a Species

### Chemistry Scheme Specification

Within the UKCA code, whether a species is wet deposited or not is controlled in the ukca_chem_scheme.F90 file. In the chch_defs_scheme array there are lines like

chch_t( 10,'HONO2     ',  1,'TR        ','          ',  1,  1,  0),  & !  10 DD: 7,WD: 4,
chch_t( 11,'H2O2      ',  1,'TR        ','          ',  1,  1,  0),  & !  11 DD: 8,WD: 5,


Where the 1 in the 7th column turns on wet deposition of that species (being 0 otherwise). You will need to change the 0 to a 1 for the species that you wish to now wet deposit.

### Setting Henry's Law values

In the ukca_chem_scheme.F90 the parameters required to calculate ${\displaystyle H_{eff}}$ are held in the henry_defs_scheme array, and has format

 ${\displaystyle \ k(298)\ }$ ${\displaystyle \ -\left({\Delta H}/R\right)\ }$ ${\displaystyle \ k(298)}$ for the 1st dissociation ${\displaystyle \ -\left({\Delta H}/R\right)}$ for the 1st dissociation ${\displaystyle \ k(298)}$ for the 2nd dissociation ${\displaystyle \ -\left({\Delta H}/R\right)}$ for the 2nd dissociation

Columns 3 and 4 are used if the species dissociates in the aqueous phase. In this case, ${\displaystyle H_{eff}}$ is further multiplied by a factor of

${\displaystyle 1+{\frac {k(aq)}{H^{+}}}}$

where

${\displaystyle k(aq)=k\left(298\right)\exp \left(-{\frac {\Delta H}{R}}\left[\left({\frac {1}{T}}\right)-\left({\frac {1}{298}}\right)\right]\right)}$

and column 3 contains the values of ${\displaystyle k(298)}$ and column 4 contains the value of ${\displaystyle -{\Delta H}/R}$. Similarly, if the species dissociates a second time then a further factor of ${\displaystyle 1+k(aq)/H^{+}}$ is applied, where this value of ${\displaystyle k(aq)}$ is calculated from the values of ${\displaystyle k(298)}$ and ${\displaystyle -{\Delta H}/R}$ in columns 5 and 6.

Note: As with the 2D dry deposition values in depvel_defs_scheme, the order of henry_defs_scheme also assumes that the values are in the same order as the species (that wet deposit) in the chch_defs_scheme array.

Examples for this array are

0.2100E+06, 0.8700E+04, 0.2000E+02, 0.0000E+00, 0.0000E+00, 0.0000E+00,&   !    4  HONO2
0.8300E+05, 0.7400E+04, 0.2400E-11,-0.3730E+04, 0.0000E+00, 0.0000E+00,&   !    5  H2O2


### Increase the value of JPDW

Similar to when adding dry deposition of a species you will need to increase the size of the JPDW counter. This is done with a hand-edit, the value of JPDW being set in the CNTLATM file in your \$HOME/umui_jobs/jobid directory.