Reply To: Specify reactions in Fluent

[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.