What forms when carbon dioxide sulfur dioxide or nitric oxide combine with water in the air?

Separately

Carbon dioxide dissolves in rail water to form a very mild solution of carbonic acid.

This is a NATURAL process and NOT 'acid rain'.

CO2(g) + H2O(l) = H2CO3(aq)

However,

Sulphur dioxide also dissolved in rainwater to form sulphurous acid.

This is NOT a natural process, because the product has a lower pH making it more acidic. Hence 'acid rain'.

SO2(g) + H2O(l) = H2SO3(aq)

Similarly

Nitric Oxide also dissolves in rainwater to form various acids of nitrogen. Again this has a lower pH than natural rainwater, making for acid rain.

NO(g) + H2O(l) = H2NO2(aq) ( Nitrous acid).

NB

Water (rainwater) is a very powerful solvent and will dissolve most solutes.

NNB The oxides of the NON-metals dissolve in water to form acids. Carbon, nitrogen and sulphur are elemental non-metals.