Learning Forum

[Ramesh Chandra Mishra]

I am trying to model NOx -ozone phototchemistry which invoves following equations:

How can I include these for volumetric reactions(problem arises especially beacause of O becauses all the other species can be included in materials). Also how can some know the rate exponent, pre-exponential factor and activation energy?

[Rob]

You may need to create another species for "O". The reaction mechanism you've found in literature should also give you the various rates etc, otherwise you'll need to find a source of data. 

[Ramesh Chandra Mishra]

How do I include photolysis equation (first equation)? Since its not a thermal process and involves photodissociation, no activation energy and other constants are required. So how do i input the first equation?

[Rob]

There is an energy effect, but it may be slight.  What does the literature say about the effect? Can you consider hv as a catalyst species? 

[Ramesh Chandra Mishra]

That is the issue. Its not clearly specified. The only reason I need to use this equation is because it gives atomic oxygen as a product which is used in the second equation to form ozone. If I ignore this equation, there is no source of "O" left. In literature they have only made an assumption that generation rate of O (FIRST EQUATION)=consumption rate of O(SECOND EQUATION)

[Rob]

So that step is rate limiting? In other words, if you don't get that bit right the rest of the results will be questionable. If you can find a production rate you could use a source term?

[Ramesh Chandra Mishra]

Probably. Because if I dont get it right, ozone formation will be in question.

[Rob]

Yes, we can help with how, but rates etc are something you need to find or work out. 

[Ramesh Chandra Mishra]

Thanks Rob. Please let me know how can i include the photolysis reaction . Please note that this reaction does not require any reaction rate like the other 2 reactions. Rather it requires the photolysis rate .

[Rob]

There is still a reaction or rate effect. So, it's a case of understanding the mechanism/physics. I don't have an answer for atmospheric chemistry (I'm a CFD specialist with reasonable real-world experience), so need you to propose the real phyics which I can then suggest modelling options from. 

A source term for O radical from NO2 could simply be a source/sink term based on species concentration. But you'd need to define the rate or material creation maths.