I worked for a while for a researcher who figured out that "run of the mill" air pollution can cause crazy things like heart disease, cancer, allergies, stroke, and lung disease. Imagine that car exhaust and CO2 can cause you to get very ill or worse yet, die just by sitting in your own home. Its enough to worry me. If you want to read more about it look here.
I started reading about air quality while working for him. It turns out air quality inside is worse than air quality outside. You spend a lot of time inside and the comforting thing is that you can actually do something about your indoor air quality. You can leave your windows open and you can use quality air filters. These two small steps will go a long way.
Personally I use rabbit air filters. I got a good deal on my air filter around christmas. However I came across this advertisement for one at Future shop and it should be just as good Link.
Cheap girl wants to live a long and healthy life and part of living a long and health life is spending money to prevent poor health (on nutrition, housing and air quality). You don't have to spend a ton of money on these things, but a little will go a long way.