It’s a fairly well known generalization in the building industry and beyond that we spend up to 90% of our time indoors, so it seems that most people would agree easily enough that the quality of indoor air matters.  In fact, and according to the EPA, indoor air pollutant levels are 2-5 times higher than outdoor levels  and can even exceed outdoor pollutant levels by up to 100 times.  However, most building occupants and owners don’t take sufficient action to measure or improve indoor air quality, or IAQ, which is confusing and worth discussion. Why does indoor air quality matter?  Put simply, we can do better to prevent health and other effects of poor air quality, and we should take preventative action before there are consequences instead of after when it might be too late to mitigate some or all effects.  Stated more boldly, if you knew you were worsening your health and could do something about it, wouldn’t you? The answer to this question should be a resounding, “Yes.” 

A good first step might be to establish a foundational level of understanding of indoor air quality and why it matters - for builders and building occupants alike.  And more than creating a simple understanding, our goal should be to help lead to some next steps we can all take to make sure everyone can breathe healthier air.  

What is Indoor Air Quality? 

When we think about air quality, many people think of all the pollutants outside, from energy production, manufacturing, vehicles, and general levels of air pollution that they might even observe from visible means like smog or from other irritations that can be sensed from stinging eyes or air passageways.  We often have the idea that going inside will protect us from pollution, especially when a building has air conditioning and ventilation systems.  Heading inside on a hot day, especially with air conditioning, it can sure feel like the air gets better.  But our perceptions can be misleading.  Cooler air isn’t more pure if it’s not properly treated, and air without smell doesn’t provide a guarantee either.  In fact, the air we breathe inside buildings and structures can be as dirty or worse than outdoor air.  Air is often stagnant or is recycled through inadequate systems, possibly carrying and even harboring pollutants.  As we build and renovate ever tighter to increase energy efficiency, building professionals must ensure a structure will have proper ventilation, filtration, and humidity controls to safeguard occupant health.  

Why Does Indoor Air Quality Matter?

Health is a primary reason to address poor indoor air quality.  The health effects of poor air quality can be mild or severe and can appear immediately or gradually over time - and even only much later.  Mild health effects might include eye, nose, throat and lung irritation, coughing, dizziness, headaches, fatigue, increased stress, and/or lack of sleep, digestive problems, and allergy symptoms as a part of or independently of other listed effects, while long term, additional risks include asthma and other respiratory diseases, heart disease, certain cancers, and even death.  Children, the elderly, and people with breathing problems or respiratory diseases are often more susceptible to some of the health effects of poor air.  

Research also indicates that poor and even stale air affects our ability to think creatively and clearly.  Our understanding of air quality and its effects on humans is still developing.  Indeed, the health effects of poor IAQ are often summarized as “Sick Building Syndrome,” a term that has been popular but not exactly and fully defined or understood, for decades.  The effects of poor indoor air are becoming clearer - but with so many potential causes and exposure levels, the exact cause and effect of each contaminant on each occupant is not always clear.  What is clear is that better air quality leads to better health, and a host of other positive outcomes.  

Interestingly in the US, indoor air is not regulated in the same way as outdoor air.  The Environmental Protection Agency (EPA) sets outdoor air pollution levels and the Occupational Safety and Health Administration (OSHA) sets building ventilation standards and regulates specific substances, but there is not an agreed upon set of healthy indoor air quality standards.  California and New Jersey (for public employees only) are the only states to set comprehensive indoor air quality requirements regulating ventilation and the levels of specific pollutants.  OSHA promulgated a set of permissible exposure limits (PELS) for certain substances in 1970, but they have largely not been updated since.  According to the agency’s own information, "OSHA recognizes that many of its permissible exposure limits (PELs) are outdated and inadequate for ensuring protection of worker health.” The agency provides links to California’s PEL tables  that National Institute for Occupational Safety and Health (NIOSH) tables, and information provided by the American Conference of Governmental Industrial Hygienists (ACGIH), a nonprofit organization which generates guidelines (available for a fee) for controlling occupational hazards. None of this information creates a simple, actionable set of information most people or organizations can follow and act upon.  This is likely why most information on improving air quality focuses on the top known pollutants/risks, and general steps that can be taken that will likely ameliorate all related hazards.

Although the COVID pandemic helped reinvigorate air quality concerns as a topic of recent public conversation, the concerns are not new.  Indoor air quality first came to mainstream public awareness in the mid and later 20th century, primarily with regard to fossil fuel combustion concerns (focused at first on outdoor pollution) smoking bans, and radon scares.  Public health officials and a small group of building scientists have been studying causes, effects, and solutions in the decades since, but often with insufficient recognition.  These experts already knew we can take steps to improve indoor air quality. Now it’s up to the rest of us to learn and take action.  

Source: Visual Capitalist

What are Top indoor Air Pollutants, and Causes?

The types, causes, and amounts of indoor air pollution vary widely.  Some pollutants are generated on site, while others make their way into our buildings.  Sometimes, pollutants are brought into a space through ventilation or other occupant-related actions, while at other times they might leach into a space through cracks in walls, floors, ceilings, or openings.  Some pollutants are temporary, such as someone building a fire or smoking while others are constant, such as the chemicals that may leak out of a finish or material. 

Common Indoor Air Pollutants include:

• Biological contaminants such as bacteria; viruses; animal and insect dander, saliva and urine; dust mites; pollen; mold, mildew  and exhaled carbon dioxide (CO2)
• Dust and other particulates
• Chemicals from cleaning and other maintenance supplies, such as pesticides
• Chemicals that “offgas,” or leach into the air from furniture, and other building materials and products 
• Materials that are inherently toxic, such as asbestos and lead
• Radon and other soil gasses
• Pollutants from fossil fuel combustion inside buildings, such as natural gas from cooking, heating, water heating, and fireplaces.  These include carbon monoxide (CO), nitrogen dioxide (NO2), fine and ultra fine particles, polycyclic aromatic hydrocarbons (PAHs), and formaldehyde
• Additional equipment emissions, such as from printers, copiers and computers
• Chemicals from personal care products
• Cigarette smoke
• Air pollutants, including some of the items listed above, brought or allowed into the built environment from the outside environment 

Many indoor air pollutants are chemicals known as volatile organic compounds (VOCs).  VOCs are commonly known as cancer-causing chemicals and as elements that combine with other chemicals to form ground-level ozone, or smog.  VOCs are generated from manufacturing, gasoline and diesel exhaust, and from many fossil-fuel containing products.  VOCs evaporate or “off gas" from many building materials and household items, often more when they are newer.  VOCs can also offgas over time.  Common VOCs include acetone, methanol, benzene, ethanol, toluene and formaldehyde.  If your new carpeting has a strong smell, you are likely breathing VOCs. 

Particulate Matter (PM), or particulates are fine particles such as dust, ash, or smoke, that are light enough to be suspended in the air. A number often follows the PM to indicate the size in microns of the particles.  Particles PM 10 or larger, such as salt or sand, are often stopped from entering the respiratory tract by the body’s defenses (infographic).  PM 2.5 particles are 2.5 microns or smaller, which means they are about 30 times smaller than a human hair.  These super fine particles can lodge in the lungs or even in the bloodstream, and can cause both short and long term health effects.  Indoor sources of PM 2.5 include cooking, fireplaces, space heaters, smoking, and appliance combustion. Many building related professionals are involved in activities which involve working in environments with a great deal of dust and other particulate matter, and should take precautions to protect themselves.  

Bacteria and viruses travel the air on tiny droplets when people sneeze, cough, or even breathe.  Poor air circulation and crowded conditions aid these pathogens in spreading and worsening infectious diseases, from the common cold to COVID-19.    

Dampness breeds mold and mildew.  Though mold is everywhere, mold does not grow at harmful levels without excessive moisture.  Dampness can cause problems and can promote other pollutants, even without the presence of mold.  

A less common but deadly risk related to systems which rely on water is Legionellosis, or Legionnaires Disease, caused by Legionella, a bacteria that grows in slow or still water.  Legionella can become aerosolized by spraying water or mist from evaporative cooling towers that are untreated for microbial contaminants.  Proper design, and inspection and maintenance of plumbing and cooling systems, both residential and commercial, will limit the growth and spread of this bacteria.  Legionnaires Disease was in the news more recently with concern about water systems that had been stagnant due to COVID office closures.  

Allergens such as dust mites, pests, insects, plants, mold, and chemicals trigger an immune system response, or allergic reaction, in a percentage of the population.  Allergies can be mild, or life threatening. Onsite fossil fuel combustion has also been linked to significant increases in childhood asthma rates. In one study, children in homes with gas stoves had a 42% increased risk of experiencing asthma symptoms. 

Carbon monoxide (CO) is one of the toxic byproducts of fossil fuel combustion. CO is an odorless, tasteless gas that can be deadly when not properly vented or in the event of a leak.  It’s worth noting that carbon monoxide detectors are readily, commercially available, and are required in many jurisdictions.  Cooking and heating with natural gas also produces nitrogen dioxide (NO2), sulfer dioxide, polycyclic aromatic hydrocarbons, VOCs and particulate matter. Studies have shown homes with gas stoves have 50% to 400% higher average NO2 levels, often exceeding recommended outdoor limits of toxic chemicals.    

Carbon dioxide (CO2) is a great example of an indoor pollutant many people never consider as a risk, as this chemical is a byproduct of a normal activity like breathing. However, in a tight or poorly ventilated space, perhaps in a meeting or classroom, it’s not a coincidence that many people become sleepy over time.  The average room is 800 ppm or parts per million of CO2, where outdoor levels might be more like 400 ppm. Exhaled air is about 4% CO2 and builds up in small or poorly ventilated spaces.  While the full effects of elevated CO2 levels are not fully understood, even at 1000 ppm, decision making can deteriorate, and even further at 2,500 ppm.  Headaches, and lethargy, impaired cognitive function have been linked to CO2 exposure in the short term, also causally linked to absenteeism as a result.  CO2 levels in interior spaces are rising as one related concern as tighter buildings mean pollutants must be diluted and exhausted for optimal health, comfort, and productivity.  

Radon is a silent, natural gas that enters buildings and is the #2 cause of lung cancer in the United States, behind smoking.  Fortunately, there are now reliable tests and mitigation systems that can simply collect and exhaust radon.  If more people tested for radon and mitigated, this could easily be a healthy building and indoor air quality success story.     

Some materials are inherently toxic, such as asbestos and lead.  Left undisturbed, these materials do not likely affect air quality, although it might be worth addressing them for other reasons.  However, these materials are often encapsulated or otherwise treated so that people will not breathe in disturbed particles or come into direct contact with the materials.  When disturbed, such as by construction or deteriorating conditions on site, these materials can be inhaled or ingested.  

Sadly and again, we don’t know everything there is to know yet about indoor air quality and the chemicals we breathe, and even touch.  Consumers often assume that everything purchased has been rigorously safety tested, but out of 80,000+ chemicals in circulation, only a very small % have been tested (reported as 1% in 2013 senate testimony). The average person is exposed to well over 100 chemicals per day, and we have a lot yet to learn about these long-term exposures.  But the good news is that we can take steps to significantly improve our air, regardless of understanding even more about the consequences of unhealthy air.  

Benefits of Improving Indoor Air Quality

Rather than only focusing on reducing negative consequences, another way to look at the reasons for improving air quality is to think about bringing positive benefits to building occupants.  Aprilaire has identified 8 Basic Benefits of Healthy Air:

1. Reduce Illness
2. Eliminate Pests 
3. Alleviate Allergies
4. Make Buildings more Pet-Friendly
5. Improved Sleep
6. Increased Energy Efficiency
7. Increased Building Value
8. Lower Stress Levels

With regard to work spaces, several studies have also linked better air quality with more creativity and productivity.  In a 2015 study by Joseph Allen and his colleagues,  volunteers in a well ventilated office performed 61% better with well-ventilation conditions, and 101% better under optimal ventilation. In a subsequent study, the same team found that professionals in well renovated, ventilated buildings scored 26.4% higher than those in unimproved buildings.  The employees also reported health improvements.  One study used the Air Quality Index, although it’s primarily an outdoor measure, to measure a 5-6% productivity gain when air pollutants are rated as good (AQI of 0 to 50) compared to when they are measured as unhealthy (AQI of 150-200).  One company reports that six work days are lost per year per every ten employees due to poor air quality, not to mention that employee attraction and retention could be related to workplace conditions, not to mention potential effects of perceived building conditions on employee sourcing and retention. 

The EPA has compiled a list of available literature also shows measurable benefits to students from improved air quality.  Positive outcomes from improving ventilation and maintenance procedures include improved test scores, health outcomes and drastically reduced absenteeism.  Surprisingly, over 50% of US schools, where almost 60 million people spend a large part of their day, need repairs in order to be considered in even “good” condition.  As reported by the EPA, schools that are current on maintenance have a higher daily attendance by 4 to 5 students per 1000, and a lower annual dropout rate by 10 to 13 students per 1000. Proper room temperature, humidity, and ventilation, all have a positive correlation to better test scores as well.  

How Do You Know if You Have Poor Indoor Air Quality?

There isn't one single measure or score measure for indoor air quality, but there are steps we can all take to improve and monitor indoor air quality generally and for specific substances, from simple and maybe even obvious, to more complex actions and those that require a professional.  If you find some of these ideas seem obvious to you, make sure you can check those boxes.  (If all of these actions were so obvious and always implemented, indoor air would likely be less of a problem.)    

On your own, first use your senses to check your building and also yourself.

• Do you experience headaches, nausea, dizziness, or breathing difficulties inside a built space? Do you feel better when you are not inside a particular building?  If so, do the symptoms come back when you reenter the building? 
• Do you see any visible problems like mold or mildew?
• Do you note any leaks or flooding, or see standing water?
• Is the space particularly humid? 
• Do you smell strong or chemical type smells?
• Do you see any stored chemical items like paints or solvents?  
• Are there any spilled chemicals?
• Are pesticides regularly used onsite?

Any of these situations, symptoms, or conditions can contribute to poorer indoor air quality and should be investigated or improved.  Obviously, safety is the foremost concern - do not attempt to repair or address any concern you are not qualified to address.  

One question to ask if you experience health concerns or perceive chemical smells is whether you recently installed any newer furniture or carpeting?  Have you painted recently?  You may want to investigate the chemical content of these items and check for VOCs, and then check with the manufacturer to understand any risks, and also to check with an HVAC professional to understand your options for mitigating the chemicals.  Generally speaking if you smell a strong chemical type smell, you are likely breathing something your body would prefer not to intake.  

If possible, you can also hire a building performance expert, a professional with building science training who takes a whole building perspective in evaluating building design and performance, including mechanical systems,  as well as occupant health and comfort.  A building performance expert addresses energy efficiency and sustainability, and health and comfort.  These professionals investigate the causes of problems such as moisture and mold, and yes even potentially harmful odors. They work on all types of structures and can work with building professionals or directly with building occupants.  Services provided include energy and other audits, design and consulting, certification advising and/or verification, and health, safety and security automation and monitoring systems.  

On your own or with the advice of a professional, you can learn more about the pollutants in your home or work space by using an air quality monitor.  After measuring indoor air quality at various times and conditions, you can make informed decisions about whether and how to improve your air quality.  

There is currently not an official agreed upon measure for indoor air quality, but given this omission, it does appear that many organizations and in fact many air quality monitor manufacturers make use of the Air Quality Index, or AQI  created by the EPA since 1976 and intended for outdoor use.  (Other AQI’s can be used as well.) The AQI reports a score from 0 to 500, where a higher number indicates a greater level of pollution.  50 or better is considered satisfactory air quality posing little to no risk, where the health risk is raised for everyone at a level of 200 or higher.  Above 300 is considered an emergency condition.  The AQI measures for 5 major pollutants:

• Ground-level ozone
• PM2.5 and PM 10 particle pollution
• Carbon monoxide
• Sulfur dioxide
• Nitrogen oxide 

A complication is that the EPA selected pollutants of concern in outdoor environments and set levels accordingly.  While it’s not necessarily bad to say that indoor levels should not be higher, it might be easy to argue levels inside buildings should be lower, and that different pollutants might be of more concern indoors, or just that more pollutants should be monitored.  This leaves individuals and organizations without clear guidance.  

An air quality monitor is one answer to beginning to understand the air and pollutants particular to your home, office, or other indoor environment.  Actually, a monitor is more of a step and not a final answer; the devices help you measure quality at various times and conditions, and then they provide information you can use to make decisions about whether you need to work to improve your air.  

Air quality monitors might be judged on:

• What is measured
• Accuracy 
• Ease of use
• Interface 
• Battery operated (and length of charge), or plug in 
• Size
• Price
• Wireless capacity
• Notifications, if applicable 

What do air quality monitors measure?  Biological, chemical and particle contaminants, conditions, and comfort factors include:

• VOCs 
• PM1, PM2.5, PM 10 
• Formaldehyde 
• CO2
• CO
• NO2
• Ozone
• Humidity
• Air pressure
• Temperature
• Ambient Light
• Ambient Noise
• Radon (often separate)

All air quality monitors are not the same, and what they measure varies.  The prices range from well under $100 to several hundred dollars.  It is worth taking the time to pick a monitor or even a set of monitors you feel will help understand your particular conditions.  If you do not feel qualified or are simply overwhelmed by this complex set of risks, you can work with a professional to pick the right monitoring equipment and placement ,and to get some advice about understanding initial readings and indications.  This equipment will continue to evolve, especially as first adopters continue to unearth bugs and make recommendations, and measurements, what is measured, and even the explanation of what this all means should continue to greatly improve.  

What Steps Can be Taken to Improve Indoor Air Quality?

Ventilation and filtration are among the obvious, major areas to optimize for healthy indoor air, but there are also other important factors to consider.  Why make our systems work harder due to preventable other problems we can reduce or eliminate?  Ideally, all of the following steps can be taken to the extent they are reasonably possible. Obviously, all indoor spaces are different, and solutions require different levels of time, energy, and also investment.  

• Heating, Ventilation and Air Conditioning (HVAC) 
  • Be sure to design, maintain, and operate ventilation systems properly.  Consult an HVAC professional for all HVAC related decisions and actions.  Systems must be designed and sized correctly, regularly services, and operated properly, which includes being in working operation.  
  • Bringing in sufficient outside/fresh air is important to ensuring high quality indoor air conditions.  Even opening a window can help improve air quality, though a quality ventilation system which includes proper filtration is often the best option.  And opening windows is not recommended with outdoor air quality is low.  Fresher air reduces, or dilutes, both inorganic pollutants as well as those generated by occupants, such as carbon dioxide 
  • Proper filtration is key, but note that you can’t just “stick" a more efficient filter on an existing system, as you can cause other problems, like an air pressure drop, and even system stress or failure.  Install a high efficiency filter, ideally Minimum Efficiency Reporting Value (MERV) 13 or higher, which can trap even smaller particles including viruses, but only with the advice/approval of a qualified professional.  MERV 13 filters are 85% efficient at removing particles in the 1-3 micron range, and 90% efficient at the 3-10 micron range.  COVID-19 particles are typically 1-4 microns in size, which is one reason these filters have become a hot topic. (How many more people have now even heard the term MERV?)
  • Air vents should be open and not blocked by items or furniture 
  • Spot Ventilation: It’s important to be able to exhaust pollutants properly, such as using a fan to remove cooking exhaust, bathroom steam, or workspace chemicals
  • Proper Maintenance of HVAC and plumbing with regard to slow or standing water in systems
    • Legionnaire’s Disease is preventable, and it’s a disaster when it strikes.  Proper and regular maintenance is essential to protect lives. 
  • Humidity Control:
    • Keep humidity ideally between 30% - 60%, or 40% - 50% if possible to prevent moisture build up.  Make sure to also ventilate attics and crawl spaces.  Clean all humidifier appliances regularly.  Dry any water-damaged carpets and building materials immediately, or consider replacing these items.  Repair leaks immediately.  Do not finish basements unless proper ventilation and heat, and leak control/drainage are assured.  
• Cleaning and Maintenance
  • Regular and effective cleaning will help lower indoor air pollution, as cleaning helps manage dust, dust mites, pollens, animal dander, and other allergens.  Make sure to use vacuums with a HEPA or better filter so that you are not recirculating dust and other particulate matter, or use a central vacuum if possible.  Proper maintenance includes maintaining HVAC equipment on a regular basis.  
  • Less or no toxic cleaning products should ideally be used 
  • Note that minimal clutter helps those who are cleaning to clean more efficiently, in any environment 
• Choose Healthier Materials
  • Choose building materials that do not give off or give off lower potential cancer-causing volatile organic compounds, or VOCs.  For some products, low-VOC items may require more research to find, but products like paint have come a long way and are readily available with low and even commonly no-VOCs. Rate It Green was literally created to help people discuss and share information about more sustainable and healthy building products and services, and there are also a number of databases that can help with this research from a more technical perspective. Many product categories are still developing - buying these emerging leading edge products is a key way to encourage responsible manufacturers to keep making and selling these better products.  Several top green building certifications verify product health, including VOC levels.  
• Integrated pest management should be employed to reduce the levels of toxic pollutants 
• Do not store chemicals in areas people will inhabit 
• Work to limit or prohibit the use of chemicals that emit odors or particles, and really work to reduce or eliminate all hazardous materials 
• Don’t use odor-masking chemicals or air fresheners generally 
• Areas with vehicle and other exhaust should be separate and ventilated separately from occupied indoor spaces 
• Gas appliances should be fully vented
• Do not burn wood inside, if possible 
• Do not mask odors - Instead, find the cause of the odor 
• Smoking should not be permitted
• Test for radon
• Test for inherently hazardous substances such as lead and asbestos
• Check all machinery for unhealthy emissions 
• Work to isolate and minimize sources of dust and other particles, such as construction work 
• Fix leaks and address standing water immediately 
• Enclose process, containers, or areas where chemicals are being used, so the chemicals never enter the air people breathe 
• Wear proper protective equipment (PPE) as needed or required 

These definitions, risks, and ideas for action are really just a start on a journey for all of us to learn how to improve air quality in our homes, schools, healthcare facilities, workplaces, and in all built environments.  We know that poor air is bad for our health and limits our potential to some extent, and we do have some solid ideas on how to do better.  But we still have a lot to learn about the specifics, and how to set easy to use and clear standards of what is acceptable and what we can do to make sure everyone can benefit from this knowledge.  How will we achieve better indoor air quality for everyone, in our home cities and states and countries, and across the globe?  Can we get everyone to the same level of understanding?  Do we need to, or should we focus on steps we should take, and if so, do we start with low hanging fruit?  What is the best way to have the biggest impact as soon as possible?

We welcome your clarifications, comments, and feedback. Are there additional risks we have not included, more information we can provide, examples you’d like to share about successes from measuring or taking steps to improve air quality?   We also invite your articles, discussions, blog posts, events, news, stories, and viewpoints in your own posted content?  Share your expertise, or ask a question.  'Not a member?  It's (relatively) easy, and FREE!  Add your voice, and help us bring sustainable and healthy building information to more people and organizations.  
 

Additional Information:

Introduction to Indoor Air Quality -  EPA
Particulate Matter Basics - EPA
American Lung Association - Clean Air  
This scientist says cleaning indoor air could make us healthier - and smarter - ScienceMag.org
It’s Time to Care about Healthy Air - Aprilaire
Evidence from Scientific Literature about Improved Academic Performance – EPA
Think Those Chemicals Have Been Tested? - New York Times
https://www.globalindoorhealthnetwork.com/statistics

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• Keywords : Healthy Building, Health, Air Quality, Indoor Air Quality, Ventilation, Humidity, Filtration

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