Fake news and it doesn't make sense either. Automobiles/trucks, industry, shipping and airlines make up the bulk of the smog elements needed to create it - nitrogen oxides and hydrocarbons reacting in the presence of sunlight. Rain doesn't fix much of anything except maybe on the day it rains - after that, all the elements come back.
Todays cars are cleaner at the tailpipe than the background air after about the first 30 seconds of startup, and industry and the other sources of nitrogen oxides and hydrocarbons have been cleaned up enormously too.
Refer to an accurate source of the facts instead:
Homepage | California Air Resources Board