Acid rain equation

Guys, acid rain. Teachers are disagreeing:

2SO2 + O2 ---> 2SO3 (sulphur trioxide)

THEN
SO3 + H2O ---> H2SO4

[OR]

SO2 + H2O ---> H2SO3 (sulphurous acid)

THEN
H2SO3 is oxidised to H2SO4

So, sulphur trioxide intermediate, or sulphurous acid intermediate?