When we think of air quality, we often think about news stories discussing thick smog or blazing forest fires. These headlines are eye-catching, and the issues they deal with are important.

But perhaps we’d better understand air quality if we pictured less dramatic settings, like offices, living rooms, and cars. That’s because a vast majority of all the air we breathe is indoor air.

Nowadays, people spend 86% of their time indoors, a number which jumps to an astonishing 93% when including transit and commute times. And, with the current pandemic, these numbers are likely even higher. Clearly, indoor air quality is important enough to warrant its own special examination.

Woman coughing.
The effects of poor indoor air quality can be immediately felt (Source)

What Causes Bad Air Indoors?

You might think that the same pollutants that affect the outdoors affect the indoors—and you wouldn’t be incorrect. Many environmental pollutants, like particulate matter (e.g. PM2.5 and PM10), CO2, SO2, CO, and NO2 are problematic both indoors and out. And air travels frequently between the indoors and outdoors, circulating whatever particles it contains, which means that the distinction can become a bit blurry. However, some pollutants are far more likely to cause problems indoors. 


Perhaps the most famous example of an indoor air pollutant is asbestos. Up until the 1970s, asbestos was used in a variety of products, particularly in construction materials. In 1997, after discoveries about its negative health impacts, the U.S. Consumer Product Safety Commission banned asbestos usage in wallboards. From that point on its usage began to decrease and face increasingly stringent regulations. While this has gone a long way to help prevent asbestos-related mesothelioma and other lung conditions, it’s still necessary to monitor asbestos levels and remove any asbestos found. And there’s more of it out there than you think—in fact, it was only recently discovered that several steam pipes in a New York City bus depot had been pumping out asbestos filled air for decades.


Another major indoor air pollutant is mold. Whenever there’s water damage to a building, there’s a good chance that building will suffer from mold issues; it’s estimated that 10% of all U.S. buildings suffer from mold pollution. Like asbestos, mold can cause its fair share of problems, including asthma, allergies, and headaches. Due to its prevalence and health impacts, it’s necessary to consider mold levels when understanding indoor air quality. 


One of the most concerning indoor-centric air pollutants is radon. Radon is a colorless, odorless, radioactive gas which seeps into buildings from surrounding soil and rock, and which can cause cancer. Fortunately, many states don’t have to deal with it, as radon deposits are located primarily in the Northeast and upper Midwest. And, while still dangerous, monitoring requirements have greatly helped reduce risks—29 states require disclosure on the sale of a house, and 23 have mandates that new construction be radon resistant.

Volatile Organic Compounds (VOCs)

While we might not be aware of their name, we’ve all come into contact with another pollutant that’s particularly concerning indoors: Volatile Organic Compounds, or VOCs. VOCs are organic compounds that disperse into the air, causing problems like coughing, asthma, and eye irritation. Essentially, most things giving off indoor “fumes” are really giving off VOCs—paint, cigarette smoke, adhesives, new mattresses, and more. According to the EPA, VOCs are consistently higher indoors than outdoors. In some cases, they can be over 10 times higher! 

Indoor Air Quality and Health

Dust particles floating in a sunbeam.
High levels of dust are more prevalent indoors than out (Source)

Besides having different pollutants than outdoor air, indoor air actually has more pollutants. One EPA study found that the dozen most common organic pollutants were 2 to 5 times more prevalent indoors. This means that indoor air is really far more detrimental to health than you’d expect. Let’s take a look at some of the ways in which unhealthy indoor air impacts people.

The most common issue caused by indoor air pollution is the general irritation of the body’s various soft tissues. This can include rhinitis and nasal congestion, coughing, eye irritation, and even nosebleeds. Generally, some form of irritation is likely occurring when people complain of being allergic to bad indoor air. While not usually life-threatening in and of themselves, these issues can severely decrease one’s quality of life.

Perhaps the most common serious health consequence of polluted indoor air is asthma. Indoor asthma triggers include dust mites, pet dander, VOCs, and indoor smoke, though these are just a few of the causes. A recent literature review further established the relationship between indoor air and asthma, finding that indoor environments almost certainly impact asthma outcomes, and that some of the most harmful contaminants include “coal and biomass combustion, microbes, and tobacco.” Low indoor air quality is a big part of the reason that, in the U.S., a staggering “7.7 percent of adults and 8.4 percent of children have asthma.”

By far the worst widespread health impact of poor indoor air quality is cancer, particularly of the lungs. Persistent damage to any body part is a major risk factor, and, in the case of poor indoor air quality, the respiratory tract and lungs are continually irritated. There are over 223,000 lung cancer deaths annually, and many of these are due to indoor air quality. All this is not to mention the carcinogenic impacts of poor indoor air on the nose, mouth, and throat.

For still more information on the health impacts of poor indoor air quality, you can look to the EPA primer on the topic, which delves into a fuller list of potential health impacts, and also includes helpful suggestions for diagnosis and recovery. But what’s even more surprising are the effects that indoor air can have on mental, not just physical, performance.

Indoor Air Quality and Cognition

A group of students studying in a library.
Students and employees who enjoy better indoor air quality are more productive (Source)

Focus is important—it allows us to direct our attention, absorb information, and work for extended periods of time. But it’s extremely hard to focus in locations with poor indoor air quality.

One study showed that, in office buildings “the performance of simulated office work could be significantly increased by removing common indoor sources of air pollution, such as floor-coverings.” Another found that adding a $1000 air filter produced equivalent academic improvement to reducing class size by one-third. A comprehensive review of literature reached similar conclusions, and found that “ventilation rates in new and existing schools often do not meet the minimum ASHRAE guidelines,… It is clear that programs should be put in place to ensure that all schools provide necessary ventilation.” When we aren’t supplying our bodies with high quality air, we suffer the consequence cognitively.

The impact of indoor air quality on cognition isn’t just a function of pollutants, though. It also depends on so-called “weather characteristics”, like temperature and humidity.

According to OSHA, the optimal indoor temperature range for an office is from 68 to 77 degrees Fahrenheit, with men typically preferring colder offices and women warmer ones. Recent studies have actually suggested that warmer temperatures might be best—one found that the error rate of typists increased from 10 percent to 25 percent when the temperature was lowered from 77 to 68 degrees Fahrenheit. While the preferred range of temperatures is problematically large, and the office temperature debate rages on, it’s safe to say that the ideal temperature should at least be somewhere around this range.

Humidity must also be tightly controlled for productivity and comfort. The ideal range is between 30% to 50%. Any more and people run the risk of feeling sweaty and sticky, and any less and the air can become uncomfortably dry. In either case, it’s hard to work or even to enjoy being inside. When trying to improve productivity and learning, it’s important that both temperature and humidity are considered.

Finally, when trying to understand the full impact of indoor air quality on health, It’s also important to note the psychological impacts of poor indoor air quality. After all, the above health and performance effects are not isolated. Rather, they come along with increases in distraction, anxiety, and irritation. These are noteworthy, negative impacts in and of themselves. And there are second level repercussions when employees or students feel anxious about going to the office or school, as quality of life suffers even when at home. Fortunately, the opposite is also true. When people are comfortable and able to enjoy clean air, they’re able to be more productive—and, more importantly, be healthy.

Causes and Solutions 

Mold on the corner of a cieling.
Mold is a frequent cause of poor indoor air quality (Source)

Poor air quality can be diagnosed through the presence of pollutants—but to truly understand indoor air quality, it’s vital to consider the sources of these pollutants.

Some sources are environmental, such as the quality of the outdoor air which permeates a building, or the levels of radon in nearby soil and rock. These are among the most difficult environmental factors to control for—after all, it’s difficult to control the outdoors.

However, paying attention to the outdoor environment can help. For instance, studies have shown that closing windows during days with low levels of outdoor air quality can significantly reduce respiratory-related hospitalizations (this applies particularly to areas with nearby wildfires). Or, in another case, planting trees can reduce CO2 levels, which might stem from a nearby road.

Another major source of poor indoor air quality is bad ventilation. In older homes and buildings, around 60% of ventilation comes naturally through attics, gaps near windows, and other sources. However, older buildings frequently have issues with closed or blocked vents themselves. And while newer buildings may have better ventilation systems, they’re also more likely to have less natural airflow. Recently, poor ventilation was even suspected to have contributed to the high levels of Covid-19 seen in nursing homes. Studies have shown that improving ventilation results in a direct improvement in health.

A final major source of poor indoor air quality can be attributed to individual decisions. Decisions like whether to smoke, how frequently to clean, and whether to keep pets all impact indoor air quality. Fortunately, when we understand common pollutants and sources, we can begin to make decisions that lead to happier and healthier lives.

Sometimes, it can be hard to know exactly what is contributing to poor air quality. This is the reason for the term “sick building syndrome,” which has been increasingly used in recent years. Certain buildings have such poor indoor air quality that staying in them for prolonged periods of time can cause people to report feelings of illness, even when no specific diagnosis can be made. Sick building syndrome is an area of burgeoning scientific resource, as it can be a real issue for those living or working in affected spaces. 

Monitoring Indoor Air Quality

An array of air quality monitors on a dresser.
Several of the most common indoor air quality monitors (Source)

There are three major parts of improving indoor air quality: diagnosing an issue, addressing the cause, and testing the solution. Air quality monitoring is an important part of the process.

For instance, if you suspected that a persistent runny nose was due to high levels of dust in the air, you might monitor for PM10 and PM2.5 in order to see whether levels were actually high. If it seemed like they were, you could invest in a deep carpet clean, air filtration system, or even hypoallergenic flooring. And if you did this and still had a problem, you could test again to sanity-check what was going on!

Vaughn’s excellent post on a recent experiment is an excellent example of the importance of monitoring indoor air quality. Temperature, air pressure, humidity, and CO2 levels were measured across a variety of office buildings in New York City. The findings were informative, and concerning: Buildings were outside of the ideal temperature range for comfort concerning 43% of the time and had unsafe CO2 levels 17% of the time. Only one building maintained a proper humidity range across the monitoring period. However, now that data has been gathered from these buildings, they can take steps to improve their indoor air quality.

However, the world of air quality monitoring—including indoor air quality monitoring—can feel confusing. There’s a lot to consider: what parameters to measure, what power source you will use, and what accuracy and range you need. In one of my previous posts, I examine these aspects of air quality monitoring more thoroughly, and discuss several sensors that can help with indoor air quality monitoring. 

Ultimately, understanding indoor air quality monitoring is worth the learning curve, because indoor air is important! After all, that’s the air we most frequently breathe.

Monitoring Your Air

Hopefully, you now feel more familiar with some of the environmental pollutants, issues, causes, and solutions specific to indoor air. If you’re interested in learning even more about your indoor air—and improving the health and wellbeing of yourself, your family, or your community—please don’t hesitate to reach out! Our team can help you get set up with our no-code monitoring platform, so that you can begin discovering more about your air today. 

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