An increase in pollution does in fact affect cloud formation. If the pollutants are aerosolized they reflect the suns light and cloud cover increases, if they absorb it clouds are dissipated.
Some pollutants(chemicals) mix in with the clouds and form atmospheric molecules that form things like acid rain. The level of cloud cover plays a role in the atmospheric temperature which in turn affects other things like humidity and moisture. In order for clouds to form there must be sufficient amounts of moisture in the air. On a clear sunny day there is very little moisture in the air. Conversely, on a cloudy day, increased levels of moisture are present.