if/ there/ be/ much/ exhaust fume/ air/ more/ people/ cope/ respiratory problem//.

If there is too much exhaust fume in the air, more and more people will cope with respiratory problem.

If there will be too much exhaust fume in the air, more and more people will cope with respiratory problem.

If there are too much exhaust fume in the air, more and more people will cope with respiratory problem.

If there was too much exhaust fume in the air, more and more people will cope with respiratory problem.