Difference between revisions of "UKCA & UMUI Tutorial 6"

Revision as of 12:36, 21 June 2013

Adding new Chemical Reactions

UKCA currently uses two different methods of defining the chemical reactions solved in the model. The first is a backward Euler solver, and is used for the RAQ and StdTrop chemistry schemes where the solver itself is created by a code-writer. The second makes use of the ASAD chemical integration software package, and is used for the CheT/TropIsop, CheS/Strat, and CheST/StratTrop chemistry schemes. ASAD can use many different solvers, although currently it uses symbolic Newton-Raphson solver. In this tutorial we will only consider the ASAD framework, as this is easily extended by a user.

ASAD considers four different types of chemical reactions: bimolecular reactions, trimolecular reactions, heterogeneous reactions, and photolysis reactions.

Biomolecular Reactions

For most bimolecular reactions, it is sufficient to provide the $k_{0}$ , $\alpha$ , and $\beta$ coefficients that are used to compute the rate coefficient $k$ from the Arrhenius expression

$k=k_{0}\left({\frac {T}{300}}\right)^{\alpha }{\textrm {exp}}\left({\frac {-\beta }{T}}\right)$

The bimolecular reactions are defined in the ukca_chem_scheme.F90 routines using the ratb_t Fortran type specification, and are held in arrays. At the end of this routine the ratb_defs_scheme array is created from these, and if that scheme is selected in UKCA these reactions are copied across into the master ratb_defs array.

To format of this ratb_t type is

ratb_t('Reactant 1','Reactant 2','Product 1 ','Product 2 ','Product 3 ',&
'Product 4 ',   $k_{0}$ ,   $\alpha$ ,   $\beta$ , Fraction of Product 1 produced, Fraction of Product 2 produced, Fraction of Product 3 produced, Fraction of Product 4 produced), &

Where the fraction of a product can be set to 0.000 if this functionality does not need to be used, i.e. the fraction is 1.0.

The specifications of the induvidual reactions are done as, e.g.

ratb_t('OH        ','C5H8      ','ISO2      ','          ','          ',& ! B144 
'          ',  2.70E-11,  0.00,   -390.00, 0.000, 0.000, 0.000, 0.000), & ! B144 IUPAC2009   
...
ratb_t('OH        ','HCl       ','H2O       ','Cl        ','          ',& ! B159 
'          ',  1.80E-12,  0.00,    250.00, 0.000, 0.000, 0.000, 0.000), & ! B159 JPL2011

The first reaction in these examples takes its kinetic data from IUPAC. Going to this website, this reaction is defined here.

Written by Luke Abraham 2013

@@ Line 23: / Line 23: @@
  '<span style="color:purple">Product 4 </span>',  <math>k_{0}</math>,  <math>\alpha</math>,  <math>\beta</math>, <span style="color:blue">Fraction of Product 1 produced</span>, <span style="color:red">Fraction of Product 2 produced</span>, <span style="color:green">Fraction of Product 3 produced</span>, <span style="color:purple">Fraction of Product 4 produced</span>), &
+Where the fraction of a product can be set to 0.000 if this functionality does not need to be used, i.e. the fraction is 1.0.
 The specifications of the induvidual reactions are done as, e.g.