Possible ways to clean indoor air a little.

Prompted partly by reading info such as: ‘According to an article in “Heart,” the journal of the British Cardiac Society: “Epidemiology has clearly shown a link between increases in particulate air pollution and deaths and admissions caused by heart failure, myocardial infarction [heart attack] and arrhythmia.”‘, from a CNN item, which I posted to thread on forum here: Hong Kong Suffers Chronic Air Pollution.

It seems there may be two ways to reduce indoor pollution: using filters/purifiers (machines), and using houseplants (which can act as natural filters/purifiers).

Update, June 2022: now also important that ventilation and use of HEPA or equivalent filters can reduce concentrations of any Covid in indoor air, and hence reduce risk of transmission.

Cleaning Pollutants from Indoor Air

Air Purifiers and HEPA Air Filters

Google produces heaps of results on filters and purifiers for cleaning air; but – by scanning thro results listings – seems many of these are aimed at selling these machines, so might wonder how credible their info is.

Mechanical Filters – especially HEPA

Reading info that seems unbiased, it appears the best type of filters to use are HEPA – high-efficiency particulate air filters. which are the name suggests are mechanical filters that remove particulates.
“To qualify as a “true HEPA” filter, a device must be able to capture at least 90 percent of all particles 0.3 microns or more in diameter that enter it.” – Air Filter and Purifier FAQ, by Asthma and Allergy Foundation of America. See also HEPA on Wikipedia.
– so if you aim to buy a filter, check it meets this criterion.
Also need a good air circulation rate.

Seems it’s not fully certain that such filters lead to health benefits, but are indications the can be worthwhile. For instance:

Summary of a paper in Science magazine includes:

“high-efficiency particulate-air (HEPA) filtration of ambient air significantly reduced heritable mutation rates at repetitive DNA loci in laboratory mice housed outdoors near a major highway and two integrated steel mills. These findings implicate exposure to airborne particulate matter as a principal factor contributing to elevated mutation rates in sentinel mice and add to accumulating evidence that air pollution may pose genetic risks to humans and wildlife.”
Reduction of Particulate Air Pollution Lowers the Risk of Heritable Mutations in Mice

There is lots of info from the American Lung Association at Factors to Consider Before Using/Buying an Air Cleaner. Looks at effectiveness, with info including:
A study conducted at the University of Maryland assessed the effectiveness of commercially available air cleaners on tobacco smoke in a room. The study tested five HEPA filters and one electrostatic precipitator. The precipitator and four of the five HEPA units removed more than 99% of the particles present in the air within 60 minutes. The remaining HEPA unit removed 90% of the airborne particles in the room

Also summarises some studies on health impacts of air cleaners.
In study on tobacco smoke (maybe roughly similar to smog from smoky vehicles, factories etc): The air cleaner significantly reduced the concentration of particles and nicotine. The air cleaner reduced symptoms of headache, rhinorrhea, and minimum cross sectional area of the nasal passage. Symptoms of nasal congestion, nasal irritation, and measured mid-nasal volume were not altered. These data indicate that a portable room air cleaner can significantly reduce, although not eliminate, the acute response to a relatively high concentration of tobacco smoke in healthy subjects with a history of symptoms associated with ETS exposure.

A Danish study reported in February 2008 found swift benefits from using HEPA filter, for elderly people living by a highway:

“Our main finding was a significant improvement in the function of small finger blood vessels after reduction of indoor air particles. This effect most likely indicates a general improvement in the function of the inner lining of small vessels, including those supplying the heart,” Dr. Steffen Loft, of the Institute of Public Health in Copenhagen, said in a prepared statement.

Abnormal function of the inner lining of small vessels is known to be a predictor of dangerous or possibly fatal cardiovascular events.

HEPA filtration removed about 60 percent of the ultrafine, fine and coarse air particles in homes, according to researchers, and was associated with an 8.1 percent improvement in individual microvascular function (MVF).

“This suggests that indoor air filtration represents a feasible means of reducing cardiovascular risk,” he said.

HEPA filters may improve cardiovascular health

Air Purifiers using Ozone

There are also some air purifiers that generate ozone as means of removing some pollutants.

However, doesn’t look like these are too great. According to US Environmental Protection Agency:

When inhaled, ozone can damage the lungs. Relatively low amounts of ozone can cause chest pain, coughing, shortness of breath and, throat irritation. It may also worsen chronic respiratory diseases such as asthma as well as compromise the ability of the body to fight respiratory infections.

…

Available scientific evidence shows that, at concentrations that do not exceed public health standards, ozone is generally ineffective in controlling indoor air pollution.
“Ozone Generators that are Sold as Air Cleaners: An Assessment of Effectiveness and Health Consequences”

Houseplants as Air Filters

There is info on Internet saing that plants can clean air. Seems they can help, but not readily coping with volumes of air in rooms that aren’t sealed from outside world.

Article Living filter: do houseplants really improve indoor air? [link now defunct] includes:
former EPA Indoor Air Division Director Robert Axelrad’s primary complaint. He said that NASA’s studies did little to simulate the air changes of a typical home or office. “Our calculations indicate that a much higher density of plants would be required (hundred of plants in the typical house) to achieve these results,” writes Exelrad.

At “Indoor Air Pollution: An Introduction for Health Professionals”, learn:
As a practical means of pollution control, the plant removal mechanisms appear to be inconsequential compared to common ventilation and air exchange rates. In other words, the ability of plants to actually improve indoor air quality is limited in comparison with provision of adequate ventilation.