Here is a list of plants NASA investigated and found improved home air quality:

■ English ivy (Hedera helix);

■ spider plant (Chlorophytum comosum)

■ golden pothos (Epipremnum aureum)

■ peace lily (Spathiphyllum "Mauna Loa")

■ Chinese evergreen (Aglaonema modestum);

■ bamboo or reed palm (Chamaedorea sefritzii);

■ snake plant (Sansevieria trifasciata);

■ heartleaf philodendron (Philodendron scandens "oxycardium");

■ selloum philodendron (Philodendron selloum);

■ elephant ear philodendron (Philodendron domesticum);

■ red-edged dracaena (Dracaena marginata);

■ cornstalk dracaena (Dracaena fragrans "Massangeana");

■ Janet Craig dracaena (Dracaena deremensis "Janet Craig");

■ Warneck dracaena (Dracaena deremensis "Warneckii"); and

■ weeping fig (Ficus benjamina).

Many of these houseplants are used in the Las Vegas casinos because they adapt to such low light conditions. NASA recommends that you use 15 to 18 good-sized houseplants in 6- to 8-inch diameter containers in an average 1,800-square-foot house.

Researchers also found soil and roots helped remove airborne pollutants. They found soil microorganisms become more efficient at absorbing pollutants when they were exposed to the roots and soil. And when NASA removed the plants' lower leaves for more soil surface contact, it increased the houseplants' effectiveness at removing pollutants.