UKCA & UMUI Tutorial 8

Adding Wet Deposition

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

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

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

References

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.

Henry's Law Specification Definition

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 $H_{eff}$ are held in the henry_defs_scheme array, and has format

k(298)

-{\Delta H}/R

k(298)

for the 1st dissociatation

-{\Delta H}/R

for the 1st dissociatation

k(298)

for the 2nd dissociatation

-{\Delta H}/R

for the 2nd dissociatation

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

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

where

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

In this case, columns 3 and 4 contain the values of $k(298)$ and $-{\Delta H}/R$ used in the above formula. Similarly, if the dissasociates a second time then a further factor of $1+k(aq)/H^{+}$ , where $k(aq)$ is calculated from the values of $k(298)$ and $-{\Delta H}/R$ 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.

! The following formula is used to calculate the effective Henry's Law coef,
! which takes the affects of dissociation and complex formation on a species'
! solubility (see Giannakopoulos, 1998)
!
!       H(eff) = K(298)exp{[-deltaH/R]x[(1/T)-(1/298)]}
!
! The data in columns 1 and 2 above give the data for this gas-aqueous transfer,
!       Column 1 = K(298) [M/atm]
!       Column 2 = -deltaH/R [K-1]
!
! If the species dissociates in the aqueous phase the above term is multiplied by
! another factor of 1+{K(aq)/[H+]}, where
!       K(aq) = K(298)exp{[-deltaH/R]x[(1/T)-(1/298)]}
! The data in columns 3 and 4 give the data for this aqueous-phase dissociation,
!       Column 3 = K(298) [M]
!       Column 4 = -deltaH/R [K-1]
! The data in columns 5 and 6 give the data for a second dissociation,
! e.g for SO2, HSO3^{-}, and SO3^{2-}
!       Column 5 = K(298) [M]
!       Column 6 = -deltaH/R [K-1]

Written by Luke Abraham 2013