In desperate need of help - Vague Pronouns

English as a Second Language English Vocabulary, Grammar and Idioms
1

When the car hit a tree, it made a terrible noise.

The car made a terrible noise as it crashed into a tree.

Air pollution normally increases along with population growth. This increasing pollution is a big problem for many cities.

Air pollution normally increases along with population growth. This is a big problem for many cities.

I’m thinking the second option on the first pair and the first option on the second pair due to both options clearly displaying what the TRUE co-reference is within the statements. I’m really hoping for verification to my train of thought on this one.

2

I agree. Though the second sentence could be improved by using a comma instead of a period:
Air pollution normally increases along with population growth, presenting a big problem for many cities.