Science fiction movie where oxygen mask is needed when raining

This is a movie or TV show I saw at a friend’s house around 1990. The scene I remember shows a man on a street when it is about to start raining (or maybe some kind of gas is coming). For some reason people need a gas mask or oxygen mask to survive when it rains. An old lady doesn’t have one and the man offers to share his. I think it was in a future setting where this was just a normal weather event. I think this scene may have been near the beginning of the movie/show. This is all I remember, and I could be wrong  about any of the details. It’s been bugging me for years. Someone please help.

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