Increasing life-span by indoor air purification…how to best accomplish this?

I live in Houston (where people often have easily 5 years+ maybe 10+ shorter life expectancy due to poor outdoor air quality) and I want to try and achieve several extra years life expectancy by increasing the air quality inside my condo.

Please try to rate in order of air-purification increase per dollar (assuming no allergic reactions) and explain the best ways to use these methods (including how much, what size...) for a 700 sq. foot condo:

1. Using houseplants to clean the air
2. Using "professional grade" electric-powered HEPA filtration systems
3. Running you A/C fans full-blast with the most expensive standard filters you can buy
4. Buying an oxygen generator (note there have been articles about the dangers of overly pure IE over 60% or so pure oxygen...how do you make sure it doesn't become too pure?)

5 to infinity. Any other methods you can think of