Indoor Air Quality Index (IAQI): Measure, Understand and Act

Indoor Air Quality Index (IAQI) simplifies complex pollutant data into a single score so you can quickly gauge indoor safety and act to protect occupants. This guide explains how IAQI is calculated, which pollutants matter, and practical steps to improve indoor air in homes and public buildings. Read on to learn more.

Understanding indoor air quality

Indoor air quality (IAQ) is a gauge of how clean and safe the air inside buildings—homes, offices, schools—is for breathing. It matters because we spend about 90% of our time indoors, and that air can directly affect our health and how comfortable we feel.

Indoor air is often loaded with dust, pet dander, mold spores, smoke, chemical fumes from cleaners and paints, carbon dioxide from people and appliances, radon gas, and fine particles from cooking or outdoor pollution. These come from sources like combustion (gas stoves, heaters), building materials and furniture, cleaning products, outdoor air, and everyday human activity.

Proper ventilation means a steady flow of fresh outdoor air to dilute and remove indoor pollutants. You also want to balance humidity—aim for roughly 30-50%. Too much moisture encourages mold and bacteria growth, while very dry air can irritate your respiratory system.

Heating, ventilation, and air-conditioning (HVAC) systems help control the indoor air environment, but they only work well if cared for regularly. Replace filters and service systems as needed to reduce pollutants and prevent mold or bacteria from spreading.

So paying attention to ventilation, humidity, and HVAC maintenance goes a long way toward healthier indoor air.

What is the Indoor Air Quality Index (IAQI)

The IAQI is a straightforward gauge designed to answer the everyday question: 'Is the air inside this building clean or polluted?' It distills complex pollutant readings into a simple scale that anyone can understand at a glance, communicating risk levels without jargon.

You’ll find categories like Good, Moderate, Polluted, Very Polluted, and Severely Polluted. Those descriptive labels help people decide whether to open a window, run a fan, or take more substantial action.

IAQI focuses on the pollutants that matter most indoors – carbon dioxide (CO₂), volatile organic compounds (VOCs), particulate matter (PM), and sometimes formaldehyde – because those influence comfort and health. High CO₂ levels can make a room feel stuffy and leave you sluggish; VOCs are everywhere from paints to cleaners to new furniture.

It differs from outdoor indices like the EPA’s AQI by honing in on indoor-specific issues. CO₂ and VOCs are ubiquitous inside homes, offices, and classrooms but rarely top the list for outdoor air measures.

IAQI refreshes rapidly, often using very short averaging windows (like one-minute averages). That near-real-time feedback lets occupants spot problems as they arise and respond immediately.

The developers took inspiration from the familiar concept behind the EPA’s outdoor AQI but adapted it for indoor life – where pollutant levels change fast and different substances take priority. The result is a practical, easy-to-read guide for breathing a little easier inside.

How the IAQI works

Think of the IAQI – Individual Air Quality Index – as a score for a single pollutant. It tells you how polluted the air is for one substance, such as ground-level ozone (O₃), carbon monoxide (CO), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), or particulate matter (PM₂.5 or PM₁₀).

It starts with a measurement: the pollutant’s concentration in the air. That measurement gets compared to national ambient air quality standards, which specify maximum safe concentrations over set averaging times (for example, 1 hour or 24 hours). Next, a formula converts the measured concentration into an IAQI value. The formula scales the concentration between breakpoints – those are the concentration thresholds tied to index values. In short, the number you get reflects where the pollutant sits on the health-risk scale.

You can calculate an IAQI for each pollutant independently. Then, to report a single, easy-to-understand number to the public, officials use the highest IAQI among all measured pollutants for that day and area. In other words, the worst offender sets the overall AQI.

IAQI values also map to familiar categories: Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and Hazardous. That labeling helps people quickly grasp risk and decide whether they should take precautions.

Pollutants that affect indoor air quality

Our indoor air can be surprisingly hazardous. Here’s a quick, plain-language guide to the most common indoor pollutants, where they come from, and what they can do to your health.

1. Asbestos: A fibrous mineral once widely used in insulation and fireproofing. Tiny asbestos fibers can cause lung cancer, mesothelioma, and other serious diseases if inhaled.

2. Biological pollutants: Living or once-living things such as bacteria, viruses, mold spores, dust mites, pollen, pet dander, and bits of insects. They can cause allergies, asthma attacks, lung infections, and other breathing problems.

3. Carbon monoxide (CO): A colorless, odorless gas produced by burning fuel (gas, wood, charcoal, kerosene, propane) without enough oxygen. CO stops oxygen getting into your tissues, causing headaches, dizziness, nausea, and at high levels, death.

4. Nitrogen dioxide (NO2): A gas mainly released by burning fuels, such as from gas stoves or wood heaters. It irritates the lungs, worsens asthma, and reduces lung function.

5. Particulate matter (PM): Tiny particles of solids or liquids—dust, smoke, soot, or droplets—suspended in the air. These particles can get deep into your lungs and bloodstream, increasing heart and lung disease risk.

6. Formaldehyde: A chemical found in some building materials, furniture, and household products. It causes eye, nose, and throat irritation, triggers allergies, and may cause cancer.

7. Pesticides: Chemicals used to kill insects and rodents. They can stay in indoor air and on surfaces, posing health risks that include neurological effects and cancer.

8. Radon: A naturally occurring radioactive gas that can enter buildings through the soil. Long-term exposure increases lung cancer risk.

9. Lead: Often found in old paint and the dust it creates. Lead exposure causes serious neurological damage, especially in children.

10. Secondhand smoke: Smoke from burning tobacco products contains many harmful chemicals. It irritates the respiratory system and increases the risk of respiratory and other diseases.

11. Volatile organic compounds (VOCs): Gases released from paints, cleaning products, air fresheners, and many household items. Short-term exposure causes headaches, nausea, and dizziness; long-term exposure can damage the liver, kidneys, or central nervous system.

    
    

Knowing the common indoor pollutants helps you take simple steps—like ventilating, using exhaust fans, testing for radon, keeping smoking outdoors, and choosing low-emission products—to reduce exposure and protect your health.

Ventilation, temperature and humidity influences

Ventilation controls how much outdoor air replaces indoor air – and that has a big effect on IAQ. When rooms don’t get enough fresh air, pollutants build up. That buildup raises the risk of breathing problems, allergic reactions, and infections.

Temperature plays a less obvious but important role. Warmer indoor air speeds the release of chemicals from building materials, furniture, and household products – think of how formaldehyde off-gasses from pressed wood as temperatures rise. In other words: Heat can push more pollutants into the air you breathe.

Humidity matters too – but in opposite ways depending on whether it’s high or low. When indoor humidity climbs above about 60%, mold, dust mites, and other microbes thrive. Those pests and spores often trigger asthma and allergies. But when humidity falls below roughly 30%, it dries out your mucous membranes, which irritates your respiratory tract and makes it easier for viruses to spread.

The takeaway? Keeping ventilation adequate, temperatures moderate, and humidity in a comfortable middle range helps reduce these risks. Small steps – like opening windows, using exhaust fans, and running a dehumidifier or humidifier when needed – can go a long way toward making your indoor air healthier.

Health effects of poor indoor air

Ever walked into a stuffy room and immediately felt a headache or itchy eyes? That’s poor indoor air quality causing immediate symptoms like that—and with continued exposure, it can contribute to longer‑term health problems.

Immediate health effects

Poor indoor air can cause a surprising range of immediate symptoms. You might notice sore, itchy eyes or a scratchy throat soon after walking into a room. Headaches, dizziness, fatigue, and nausea also show up quickly for some people.

Breathing problems are common. Irritated airways can trigger coughing, wheezing, chest tightness, or shortness of breath. Those signs often make existing conditions—like asthma, bronchitis, and other chronic lung diseases—worse.

Certain indoor pollutants affect the nervous system. Carbon monoxide and volatile organic compounds (VOCs) can cause headaches, weakness, confusion, and more tiredness than you’d expect.

Everyday household allergens matter too. Dust mites, mold, pet dander, tobacco smoke, and cockroach droppings are common triggers for asthma attacks and allergic reactions.

Indoor air can affect more than your lungs. Short-term exposure to ozone or fine particles may raise blood pressure and increase blood-clotting risk, which can put strain on the heart even in otherwise healthy adults.

You’ve probably heard the term “sick building syndrome.” It’s used to describe a group of symptoms people develop while inside certain buildings and then feel better after they leave. Poor indoor air quality is usually the culprit.

Some people are more vulnerable than others. Children, older adults, anyone with asthma or lung disease, and people with cardiovascular conditions tend to feel these effects more quickly and more severely.

Long-term health risks

We often think about the air inside our homes in terms of comfort – is it stale, stuffy, or too dry? But the quality of indoor air can affect your health in numerous, serious ways.

Chronic exposure to common indoor pollutants such as dust mites, mold, pet dander, environmental tobacco smoke, fine particles, and combustion byproducts can trigger or worsen asthma and COPD. These exposures also cause bronchial irritation and inflammation, and in some cases, pneumonia.

Radon gas, a common indoor pollutant, is a well-established human carcinogen and the second leading cause of lung cancer.

The harm isn’t limited to the lungs. Numerous studies have found strong links between indoor air pollution and increased risk of ischemic heart disease and stroke. Researchers have also identified suggestive associations with other cancers, including nasopharyngeal, laryngeal, and cervical cancers.

Household air pollution is hazardous during pregnancy as well – it’s been linked to low birth weight, stillbirth, and other pregnancy complications. And emerging research suggests possible impacts on the brain, with inflammation and oxidative stress from indoor pollutants potentially contributing to cognitive decline and neurological disease.

Taken together, the evidence makes it clear that indoor air quality matters profoundly – not just for your respiratory health but for your cardiovascular, reproductive, and neurological well-being as well.

Applications of IAQI in monitoring and decision making

The Individual Air Quality Index (IAQI) is based on measurements of the most common pollutants – PM2.5, PM10, carbon monoxide, nitrogen dioxide, sulfur dioxide, and ozone – taken at local air quality monitoring stations. Those raw measurements get converted into a simple index so people can quickly grasp how clean or dirty the air is.

The IAQI values fall into color-coded bands that range from Good (green) to Hazardous (maroon). Each band signals different health risks, and the friendly labels make it easy to see at a glance when the air could be harmful.

Those categories matter most for people who are more vulnerable: kids, older adults, pregnant people, and anyone with asthma, other lung problems, or heart disease. When the index climbs into the unhealthy range, those groups will have a higher chance of breathing-related symptoms or complications.

Public agencies use the IAQI to guide decisions, too. Officials issue health advisories, postpone or modify outdoor events, roll out pollution-control measures, or recommend wearing masks when levels spike. The clear colors and numbers help authorities act fast and communicate risk.

You can use the IAQI the same way. Check the index before planning time outside. On bad-pollution days, consider postponing vigorous outdoor exercise, staying indoors, or running a HEPA air purifier at home. Those small choices add up to less exposure and better health.

IAQI in public facilities for vulnerable groups

Public facilities rely on the Indoor Air Quality Index (IAQI) to keep a finger on the pulse of indoor pollution and safeguard the most vulnerable among us: children, older adults, people with respiratory conditions, and communities with fewer resources. Here’s how IAQI monitoring helps:

• It catches harmful pollutants. IAQI tracking detects dangerous contaminants like particulate matter, carbon monoxide, radon, mold, and allergens that can trigger asthma attacks and other respiratory problems. Spotting these threats early makes a real difference.

• It translates technical data into simple scores anyone can understand. When the numbers show air quality slipping, managers and occupants can act fast – increase ventilation, limit use of a space, or close an area temporarily until conditions improve.

• It highlights where help is needed most. Because lower-income communities often face worse indoor air, IAQI data guides where to focus support. Facility operators use those readings to prioritize repairs, upgrade ventilation, or direct resources to sites serving disadvantaged groups.

In short, IAQI provides clear, actionable information that keeps public spaces healthier and helps target support where it’s needed most.

Emerging technologies and research in IAQI

Modern buildings are increasingly fitted with real-time air quality monitors that tie directly into smart ventilation systems, so the air gets cleaner automatically when problems appear. At the same time, compact smart sensors for homes are popping up everywhere, giving people an easy way to track their indoor air health.

Outside, networks of sensors measure several pollutants and let authorities pinpoint sources by comparing readings across locations – essentially triangulating the problem. Meanwhile, new robotic tools equipped with cameras are making duct cleaning faster and more thorough than old manual methods.

Standards are catching up too: ASHRAE’s 241 (expected 2026) will formally bring pathogen control for indoor air into building codes. Researchers are also refining test methods for active air-cleaning technologies used in occupied spaces, such as duct-mounted purifiers and reactive air or surface treatments.

On the data side, AI – from neural networks to natural language processing – helps sift through huge sensor datasets. That work improves forecasts, reveals likely pollution sources, and supports smarter, more personalized indoor-environment control. Together, these advances make air quality easier to monitor, understand, and manage.

Community initiatives and regulatory guidance

Love My Air Wisconsin (LMA WI), a school-based program funded by the EPA with $500,000 over three years, will install air quality sensors in Milwaukee Public Schools, targeting neighborhoods with high asthma rates.

The National Institute of Environmental Health Sciences (NIEHS) supports community-engaged research and education, enabling residents to take part in studies and learn from the results.

The EPA plays a dual role as regulator and supporter: it provides funding, technical assistance, and educational materials; it also offers practical guidance on cutting pollution sources, estimating the benefits of various actions, and sharing tools communities can use to reduce local air-quality risks.

Finally, many stakeholders are pushing to institutionalize air-quality monitoring and reporting in schools and community organizations. Making these procedures routine helps ensure consistent data collection and clearer, faster responses when problems arise.