How do the various types of clouds affect the atmosphere below them in a polluted environment?
I haven't found proper references yet, but this hasn't gotten an answer yet. To speculation!

Long-lived (non-precipitating) clouds can decrease solar insolation at the surface, reducing convection and mixing below the cloud and increasing pollutant concentrations. If clouds are just a symptom of a high-humidity environment, that can promote the condensation of semi-volatile species into particulates (nitrate, ammonia, some organics) if you don't count phase change as a reaction. Convective storms are associated with a lot of mixing, both within the boundary layer and between the boundary layer and the free troposphere, reducing concentrations.

Without the photolysis or rainout processes, I don't know enough about different cloud types and environments to speculate further. I'm hoping this at least sparks more discussion.