What Is Indoor Air Quality

Indoor air quality is not a single number. It is a picture of how clean and comfortable the air inside a building is, based on the levels of various pollutants alongside temperature and humidity. It is shaped by everything from how a building was constructed to what is happening inside it at any given moment.

A common assumption is that homes are clean environments because they look tidy. The problem is that most indoor pollutants are completely invisible. Carbon dioxide, fine particles and volatile organic compounds cannot be seen, yet their levels can shift dramatically within minutes. Cooking dinner, lighting a candle or simply having a few people in a room with the windows closed is enough to drive a measurable change in air quality.

Unlike outdoor air, which disperses across open spaces, indoor air recirculates through enclosed rooms. Without adequate ventilation, pollutants build up gradually, often without anyone noticing until levels have been elevated for some time.

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Poor indoor air quality rarely announces itself as one obvious problem. It tends to show up as a collection of things: persistent headaches, low energy despite a reasonable night’s sleep, difficulty concentrating or a dry throat that keeps coming back.

For people with asthma, allergies or respiratory conditions, poor air quality often makes existing symptoms worse. But it is not just about people who are already sensitive. Research in offices and classrooms has found that better ventilation and lower CO₂ levels are consistently linked to improved concentration and cognitive performance. The air quality in a meeting room or a child’s bedroom can have a direct and practical effect on how well people think.

The encouraging part is that most indoor air quality problems have practical solutions. You do not need to rebuild your home. Better ventilation habits, understanding which activities drive pollutant levels up, and knowing what is actually happening through monitoring are often enough to make a real difference.

Several factors shape the air inside any building:

• Ventilation: Fresh outdoor air dilutes indoor pollutants. The less air movement a space has, the more pollutants accumulate over time.
• Occupancy: Every person in a room exhales CO₂ and moisture. A family spending an evening in a well-sealed sitting room will raise CO₂ levels faster than most people expect.
• Cooking: Gas hobs, ovens, frying and grilling all release particles and combustion gases. PM2.5 levels during cooking frequently exceed typical outdoor air quality readings.
• Cleaning products: Many sprays, air fresheners and solvents release volatile organic compounds — the familiar clean smell of some products is often VOCs.
• Furniture & building materials: MDF and certain adhesives emit formaldehyde and other VOCs. Off-gassing is typically highest in newer homes and after renovations.
• Outdoor air: Traffic emissions, pollen, wildfire smoke and industrial pollution can enter through open windows, structural gaps and HVAC systems.
• Temperature & humidity: Both affect comfort directly, and humidity has a significant effect on mould growth.

Pets: Pet dander and hair add to airborne particle levels.

The BREATHE Airmonitor Plus monitors eight parameters. Each tells you something different about your indoor environment:

The health effects of poor indoor air quality depend on which pollutants are present, at what concentrations, and for how long people are exposed to them.

CO₂ itself is not a toxin at the concentrations found in homes, but elevated CO₂ indicates that fresh air is not circulating adequately. When ventilation is poor, other pollutants tend to accumulate alongside it. Most people will recognise the heavy, stuffy feeling in a crowded or poorly ventilated room. That feeling has measurable effects on alertness and cognitive function.

Fine particles are a more direct health consideration. PM2.5 particles are small enough to reach deep into the lungs and, with sustained or repeated exposure at higher concentrations, have been associated with respiratory and cardiovascular effects in population studies. PM2.5 is produced by cooking, candles, wood fires and smoking, and also enters from outdoor air.

TVOCs and formaldehyde can contribute to eye and throat irritation, headaches and general discomfort, particularly in poorly ventilated spaces or in newer buildings where off-gassing from materials is still active.

Children, older adults and people with existing respiratory or cardiovascular conditions are generally more affected by poor indoor air quality than healthy adults, though the effects are rarely absent in any group when exposures are prolonged.

These values are general guidance for consumer environments. Specific guidance for occupational, medical or educational settings may differ. The published version of this guide will cite relevant WHO, EPA and ASHRAE standards.

Different pollutants require entirely different sensor technologies, which is why a single measurement cannot capture the full picture of what is happening indoors.

CO₂ is most accurately measured using non-dispersive infrared (NDIR) sensors, which detect CO₂ by measuring how much infrared light the gas absorbs. Particulate matter is measured using laser particle counters, which detect particles by the way they scatter a beam of light. VOCs and formaldehyde each require dedicated gas sensors.

Consumer devices that combine multiple sensors in one unit give a far more useful picture than single-parameter monitors. Indoor conditions change constantly. Cooking can raise PM2.5 levels within two minutes; CO₂ builds slowly over the course of an evening in an occupied room. Continuous monitoring captures these changes in a way that occasional spot readings cannot.

1. Reduce sources where possible. Use lower-VOC paints and cleaning products, have gas appliances serviced regularly and avoid burning candles in poorly ventilated rooms.
2. Ventilate regularly. Opening windows, even briefly, dilutes indoor pollutants faster than most other actions. In newer airtight homes, mechanical ventilation becomes more important.
3. Use extractor fans. Running kitchen and bathroom extractors while cooking and showering removes moisture and combustion products at the source before they spread through the home.
4. Manage humidity. Keeping relative humidity between 40 and 60 percent reduces mould risk and maintains comfortable conditions.
5. Replace filters regularly. HVAC filters, air purifiers and mechanical ventilation systems all need routine filter changes to function correctly.
6. Monitor what is actually happening. Data from a continuous air quality monitor will often reveal problems you had not anticipated, and confirms when changes are working.
7. Consistent, small improvements tend to produce better long-term outcomes than occasional large interventions.