You can measure air quality using consumer-grade monitors, free government tools like the EPA’s Air Quality Index, or professional testing services. The right approach depends on whether you’re checking outdoor pollution levels, monitoring indoor air in your home or office, or investigating a specific concern like mold or chemical exposure. Each method tracks different pollutants and offers different levels of accuracy.
What You’re Actually Measuring
Air quality isn’t a single number. It’s a collection of measurements for different pollutants, each with its own health thresholds. The most commonly tracked include:
- PM2.5 and PM10: Tiny particles from combustion, dust, smoke, and industrial activity. PM2.5 particles are smaller than 2.5 micrometers, small enough to reach deep into your lungs and bloodstream. This is typically the most important outdoor pollutant to track.
- Carbon dioxide (CO2): A marker of how well a room is ventilated. Outdoor air sits around 380 to 500 ppm. The American Society of Heating, Refrigerating and Air-Conditioning Engineers recommends keeping indoor levels below 1,000 ppm. At that level, researchers have observed moderate decreases in decision-making performance, with more substantial impairment at 2,500 ppm. Crowded classrooms, conference rooms, and aircraft cabins regularly hit several thousand ppm.
- Volatile organic compounds (VOCs): Gases released by cleaning products, paint, furniture, building materials, and cooking. Measured in parts per billion (ppb) or micrograms per cubic meter. The LEED green building standard sets a guideline of 500 µg/m³, roughly equivalent to 108 ppb. A study of 32 retail stores found that all but one exceeded that threshold, with an average indoor reading of 271 ppb.
- Carbon monoxide, ozone, and nitrogen dioxide: Tracked primarily in outdoor air by government monitoring networks, though carbon monoxide from gas stoves and heaters is also an indoor concern.
Check Outdoor Air Quality for Free
The fastest way to measure outdoor air quality is to use the EPA’s Air Quality Index, available at AirNow.gov or through dozens of weather apps. The AQI converts raw pollution data into a color-coded scale from 0 to 500. For PM2.5 specifically, a 24-hour average of 0 to 9.0 µg/m³ rates as “Good” (AQI 0 to 50). Readings of 9.1 to 35.4 µg/m³ are “Moderate” (AQI 51 to 100). Once you cross 35.5 µg/m³, the air becomes “Unhealthy for Sensitive Groups,” and above 55.5 µg/m³ it’s considered “Unhealthy” for everyone.
These numbers come from government monitoring stations that use high-precision instruments. The EPA designates specific equipment as “Federal Reference Methods” or “Federal Equivalent Methods.” Most stations measure PM2.5 using beta attenuation monitors, which pass a stream of radiation through collected particles and calculate their mass based on how much radiation gets absorbed. These instruments cost tens of thousands of dollars and undergo rigorous certification. The data they produce is the gold standard for air quality measurement.
If the nearest government station is far from your location, community networks like PurpleAir fill in the gaps with thousands of low-cost sensors. These give you hyperlocal readings, sometimes block by block, but with less precision than official stations.
Consumer Monitors for Indoor Air
Home air quality monitors range from about $80 to $300 and typically measure PM2.5, CO2, VOCs, temperature, and humidity. Popular options include devices from Aranet, AirThings, IQAir, and Temtop. What you choose depends on which pollutants matter most to you. If ventilation is your main concern (home office, bedroom, classroom), prioritize a monitor with a reliable CO2 sensor. If you’re worried about wildfire smoke or cooking particles, focus on PM2.5 accuracy.
These devices use different sensor technologies depending on the pollutant. For particles, they shine a laser beam through a small chamber. When a particle drifts through the beam, it scatters the light in all directions. A photodetector placed at an angle picks up these flashes of scattered light. The brightness of each flash corresponds to the particle’s size, and by counting flashes over time, the sensor estimates concentration. It’s the same basic principle as professional instruments, just with less precise optics and airflow control.
For CO2, the most accurate consumer monitors use non-dispersive infrared (NDIR) sensors. These work by shining infrared light through a small tube of air. CO2 absorbs infrared light at a specific wavelength (4.26 micrometers), so the sensor calculates concentration based on how much light gets absorbed. NDIR sensors offer good long-term stability and accuracy, typically within plus or minus 30 ppm plus 5%. If a monitor doesn’t specify the sensor type for CO2, it may use a cheaper estimated method that’s far less reliable.
VOC sensors in consumer devices are broader and less specific. They detect a general class of chemicals but can’t tell you which particular compounds are present. For that level of detail, you’d need professional lab analysis.
How Accurate Are Low-Cost Sensors?
Consumer-grade sensors are useful for spotting trends and relative changes, but they can be significantly off in absolute terms. A study comparing low-cost monitors against EPA reference instruments in Dallas found mean average percentage errors for PM2.5 ranging from 29% to 132% even after calibration. At the median, calibrated sensors were within about 4% of the reference reading, which sounds great, but the averages tell a different story: mean differences of around 24% were common, and individual readings could be wildly off during unusual conditions.
This means your $150 monitor is good at telling you “air quality just got noticeably worse” or “opening the window improved things.” It’s less reliable for determining whether you’re at exactly 12 µg/m³ versus 8 µg/m³. For most home users, tracking relative changes and spotting spikes is what matters anyway.
Getting Better Results From Your Monitor
Where and how you place your monitor affects accuracy. Keep it away from direct sources of pollution like stoves, candles, or open windows where gusts can overwhelm the sensor. Place it at breathing height, roughly where your head would be while sitting or sleeping, and give it at least a foot of clearance from walls.
Some monitors allow manual calibration. For CO2 sensors, a common approach is to place the device outdoors in fresh, well-mixed air for 10 to 15 minutes and set that reading as your baseline (outdoor CO2 is roughly 420 ppm currently). For particle sensors, calibration against a known reference is harder to do at home, but some manufacturers offer correction factors for specific conditions like wildfire smoke or high humidity, which can cause sensors to read high because water droplets scatter light just like particles do.
Calibration should happen in stable environmental conditions, away from temperature swings or direct sunlight. If your monitor has been sitting unused for months, give it 24 hours of continuous operation before trusting the readings, as some sensors need time to stabilize.
Professional Indoor Air Quality Testing
If you suspect a specific problem (mold, radon, formaldehyde from new construction, or unexplained symptoms in a building), professional testing gives you lab-verified results that a consumer monitor can’t match. An industrial hygienist or certified air quality professional will visit your space, collect air samples, send them to a lab for analysis, and provide a detailed report with recommendations.
Professional testing typically runs $75 to $150 per hour, with total costs for a standard residential assessment averaging $292 to $585 in the U.S. That usually covers the site visit, sample collection, lab analysis, and the written report. Specialized tests for asbestos, mold species identification, or comprehensive VOC panels may cost more.
This level of testing makes sense when you need actionable evidence, whether for a health investigation, a real estate transaction, a landlord dispute, or post-renovation clearance testing. For ongoing daily monitoring, a consumer device is more practical.
A Simple Approach for Most People
If you’re just getting started, check AirNow.gov or a weather app for your local outdoor AQI. That takes 30 seconds and tells you whether it’s a good day to exercise outside or open your windows. For indoor air, a monitor with an NDIR-based CO2 sensor and a laser particle counter covers the two most actionable measurements. Watch for CO2 climbing above 1,000 ppm (a sign you need more ventilation) and PM2.5 staying above 12 µg/m³ indoors (a sign your filtration or ventilation needs attention). Those two numbers alone will tell you more about your air than most people ever learn.