Which Plants Actually Improve Indoor Air?

Air purifying plants are houseplants that absorb volatile organic compounds, the gases given off by paints, furniture and cleaning products. The idea comes from a NASA study, and the chemistry is real. This guide explains what that study measured, why its results shrink in a home, the plants per room figure the research actually implies, and which species did well in the tests.

What the NASA clean air study measured

The NASA clean air study, published in 1989 by B. C. Wolverton and colleagues, measured how fast potted plants removed benzene, formaldehyde and trichloroethylene from sealed chambers of under a cubic metre. The goal was air cleaning on a space station, where nothing leaves or enters the air.

The results were real. In a sealed box, a single plant pulled measurable amounts of those gases out of the air within 24 hours.

Much of the removal came from the potting mix. Microbes living around the roots broke down a large share of the chemicals, which is why later tests found soil with the leaves cut back still did part of the job.

That doesn't make the work sloppy. It answered the question it was built for, which was whether a closed habitat could use plants as part of its air system. The problem started when the numbers were quoted for homes that were never closed.

The study's popular summary suggested 15 to 18 plants for a home of about 170 square metres. That line is where the air purifying label on houseplants comes from.

Why chamber results shrink in a home

Chamber results shrink in a home because a room isn't sealed. Air leaks in and out through doors, windows and the AC's fresh air intake, typically replacing a room's air somewhere around once an hour. That exchange removes gases far faster than a plant can, so the plant's share becomes too small to measure.

In the chamber, the plant was the only thing removing gases. In a room, it competes with ventilation that moves tens of cubic metres of air an hour.

The arithmetic is simple. A 16 square metre bedroom with a 2.8 m ceiling holds about 45 cubic metres of air. At one exchange an hour, the ventilation clears the whole volume every hour, and a potted plant in the corner has no chance of keeping pace with that.

UAE homes make that gap wider in one sense and narrower in another. Apartments sealed tight for AC exchange air more slowly than a leaky older house. Even so, a sealed Dubai apartment exchanges its air through the AC system hundreds of times faster than a plant absorbs anything.

The plants per room figure the research implies

A 2019 review by Bryan Cummings and Michael Waring, which converted 30 years of chamber results into room terms, found that plants would need to fill 10 to 1,000 per square metre of floor to match the gas removal a normal building already gets from air exchange. The spread reflects how differently each study's plants performed.

Put that into a Dubai bedroom of 16 square metres. The figure implies 160 plants at the low end and 16,000 at the high end.

For a whole home of 170 square metres, the same range is 1,700 to 170,000 plants. The popular suggestion of 15 to 18 plants for that home is between 100 and 10,000 times short of it.

The spread is wide because the chamber studies used different species, pot sizes and gases, and certain plants removed formaldehyde far better than benzene. Even the most favourable result in the review leaves the low end at 10 plants for every square metre.

No one lives in a room with 160 potted plants, and that's the point. The research doesn't say plants remove nothing. It says the amount a normal number of plants removes is lost in the building's own air exchange.

Species that performed well in the chamber tests

In the chamber tests, the species with the highest removal rates included Boston fern, peace lily, spider plant, snake plant, English ivy and dracaena. These results are valid for sealed chambers, and they rank the plants against each other, even though no species reaches the room scale figure above.

Those same species are sound houseplants for UAE apartments, which is the more practical reason to choose them. Spider plant and snake plant tolerate AC dryness, and peace lily copes with low light.

Shop the chamber test species on their merit as houseplants. The air purifying plants collection groups the species from those studies, so the list above can be bought as one set.

FAQ

Readers who have seen the NASA figure quoted for years usually want a straight answer about their own home and about adding more pots. Both appear below, stated with the numbers from the review, and without claims beyond what the tests measured.

Does the NASA study apply to a Dubai apartment?

No, the NASA study does not apply directly to a Dubai apartment, because it tested sealed chambers with no air exchange. An apartment's AC fresh air intake replaces the room air on a timescale of hours, which removes volatile compounds far faster than any realistic number of potted plants.

How many plants would make a measurable difference?

About 10 plants per square metre of floor is the lowest figure the 2019 review gives for matching normal air exchange, which is 160 plants in a 16 square metre room. Anything below that makes a change too small to measure against ventilation in a real home.