Fresh air. Sure, New York's much cleaner than when we were children (remember the black soot that used to collect on the outside windowsill?), but this is still not a city where you want to sleep under an open window.
Try this: if you live near Broadway on the Upper West Side, sit on the benches in the middle of broadway with a clean white piece of paper on your lap and see what happens to it in just 15 minutes. It's not appetizing.
We recommend using air purifiers at home, and have found that cheaper models with regular filter changing are just as good as the super duper expensive models.
We like the design and size of the Bionaire's LC series. It comes with a HEPA filter and carbon filter, an ionizer and either 2 or 3 speeds. It will accomodate room sizes from 100 sq. ft. to 208 sq. ft., and prices run from $13 to $80 (ATTENTION: These models are being discontinued and won't be available for too long. Bionaire (800-363-3479) has some, as do these online retailers. We still think it's worth it. The filters will still be available and the new ones are more expensive). MGR