THIS SENTENCE IS CORRECT, ISN'T IT? ANOTHER WAY TO REWRITE?

As the vehicle emits smoke into the air. the source of air pollution might be serious gradually

The sentence is incorrectly written. The subject-verb agreement / placement is not correct. The sentence structure is also not correct. You have the start of the second sentence in lowercase when that should be in uppercase. The thought that can be identified by the reader, but it will take about 2 readings for an English Native Language speaker / reader to understand what you are trying to say.

A better way to have written this sentence would have been:

1. Air pollutiion may become more serious over time as vehicles continously emit smoke into the air.
2. As vehicles continously emit smoke into the air, over time, air pollution becomes a more serious problem.