Just because the air outside is polluted like crazy doesn't mean you need to live in a toxic indoor environment.

http://www.alive.com/4239a12a2.php?subject_bread_cramb=630

http://www.nachi.org/indoorair.htm

http://www.ext.vt.edu/departments/envirohort/articles/misc/plntclar.html

http://www.montgomerycountymd.gov/content/dep/greenman/cleanairplants.pdf

Difficulty level:  Easy. 

Time: Almost none

Cost: Negligible