Is Air a Scam

Should I buy an air purifier? Or should I make one?

Probably. There is a long history of studies looking at air filtration, and the good news is that the technology works to drastically improve indoor air quality. If you’re able to buy an air filter, look for a HEPA air purifier that will grab more than 99.97 percent of tiny 0.3 micron particles in the air.

These purifiers work by forcing air through a tiny mesh that captures smoke, allergens and pollen, but make sure to check the square footage coverage on the product. Buying a purifier that cleans a 200-square-foot space and putting it in a 400-square-foot room won’t give you good results, said Deborah Bennett, an environmental health researcher at the University of California at Davis School of Medicine.

If you live in an area with chronically poor air quality because of pollution, it’s probably a good idea to invest in a purifier.

Another evidence-based method of cleaning air is to filter house air through an HVAC system set to recirculate. Smoke and other particulates will get sucked into the house filter and pushed through the system.

Just make sure those are clean and have a high Minimum Efficiency Reporting Value — often called the MERV rating. The rating shows a filter’s ability to capture larger particles between 0.3 and 10 microns, so a higher rating means the system can grab a larger share of particles.

If an off-the-shelf air purifier is out of your budget and your house doesn’t have an HVAC system, you can make your own air purifier for about $30 by taping a square furnace filter (again, with a MERV rating of 12 or higher) to the front or back of a box fan.

Just like a commercial air purifier, the fan sucks air through the filter,and pushes out clean air on the other side. Semi-scientific tests of these D.I.Y. systems showed that they removed about 80 percent of the pollution particles from a room.

They work best for short windows of time, say when a massive smoke plume moves in and parks over a city for a week.In the long run, the fan’s motor is likely to overheat or clunk out.

In order for these systems to work, they are likely to be noisy, the experts say.It’s the same idea as a range hood over your stove (which you should also use when cooking,to cut down on compounds flying into the air you’re breathing): Noise is annoying,but it matters because it means that air is being moved around.

Let’s backtrack: How do I figure out the indoor air risk in my home?

Your indoor air risk depends on the outdoor air quality, which can be monitored with apps,how much flow there is between indoor and outdoor (newer, energy-efficient houses tend to have very little air circulation with the outdoors), and the activities that happen inside your home.

Consider cooking, which creates a lot of compounds, especially when using a gas stove, as well as cleaning. Experts suggest opening windows to flush out cleaning products as producers of compounds that you may not want to be breathing in.

Can boiling herbs improve air quality?

No. The idea is that increasing the humidity of a room with poor air quality will encourage particles to drop out of the sky and fall down like rain, but that’s not how the physics works, said Christopher Cappa, an environmental engineer at the University of California at Davis.

In fact, it can have an irritating effect. “In general, wildfire smoke particles don’t like water very much so they’re not going to grow effectively unless you make your house into a cloud — and that’s not going to happen,” Dr. Cappa said.

Ultrafine particles, which can enter your bloodstream and even your brain, are going to hang out in the air unless pushed or sucked away, so humidity won’t change their location. “Even if you grow them by making it more humid, it might actually make them stay in the air longer,” he said.

If I fill my home with plants, will that clean my air?

Not on any meaningful scale. There have been studies that looked at how plants decrease so-called V.O.C.s (volatile organic compounds) in the air, but those studies were done in very controlled conditions — not in homes that have complex air environments.

According to an analysis of 196 plant experiments published last year in the Journal of Exposure Science & Environmental Epidemiology, you’d need 10 to 1,000 plants per square meter of a building in order to achieve the same air exchange that most buildings already have with outdoor air.

“I like plants — plants feel good,” said Richard Corsi, an air quality researcher at Portland State University.“But to physically measure a change in air quality, you essentially would be living in a jungle. And you’d have other problems with humidity and mold.”

Plants simply are too passive to make a meaningful difference in air quality, Dr. Cappa said. “One of the things to think about with filters or moving air around: You’re really doing something active to move the air around to move it through,” he said. “If you don’t have anything actively moving around, it’s going to take quite a while to change anything.”

Will candles or essential oils help air quality?

No, and they actually do the opposite. So-called clean-burning candles will emit more compounds into the air. The problem is the flame, Dr. Corsi said. The wax and scenting agents get heated up but they only burn for a millisecond, so there’s no chance for complete combustion because the time is so short.

“You start to combust things but you don’t finish combusting them, so you get all these strange intermediate compounds from scenting agents,” Dr. Corsi said. Some of those can be toxic or irritating.

For essential oils, the problem is similar: They are emitting compounds into the air that can react with the complex existing air chemistry to create irritating offshoots.

“There is no evidence that suggests that the oils improve air quality,” said Tanvir Khan, an air quality engineer and researcher at the Florida Solar Energy Center, part of the University of Central Florida. “Other pollutants, like ozone, which comes from outside to inside, can react with V.O.C.s to create secondary pollutants which are harmful.”

Can negative ions change my air quality?

No. Negative ion filters are sometimes compared with HEPA air filters, but they’re not very effective. They work by shooting negative ions into the air, which causes particles to stick to your walls or floor, taking them out of the air.

They do emit ozone, and many people associate ozone as a clean smell — it’s the smell you get after a lightning storm. The problem is that ozone is an irritant, and negative ion filters have a low flow rate; they don’t move the air around enough to make a difference (back to: noisy is better). A couple of studies have found that most ion generators created a lot of ions — hooray! — but had no noticeable effect on pollen, mold or bacterial counts beyond reductions that an air-conditioner provided.

Another version of negative ions that is even more passive is a Himalayan salt lamp. They are “natural ionizers,” but there is no evidence that they work to improve air quality.