Air quality monitors have become increasingly affordable and accessible. But do you need one? And if so, what should it measure? Let's look at when monitoring is useful and its limitations.
What Consumer Monitors Measure
PM2.5 (Particulate Matter)
Fine particles under 2.5 microns. This is the most useful metric for most people. Good monitors provide reasonably accurate PM2.5 readings. Shows effects of cooking, cleaning, outdoor pollution, and air purifier effectiveness.
CO2 (Carbon Dioxide)
Indicates ventilation quality. Useful for understanding if your space is well-ventilated. Levels rise when rooms are occupied with poor airflow.
Temperature and Humidity
Basic environmental readings. Humidity is useful for comfort and for understanding conditions that affect allergens and mold.
VOCs (Volatile Organic Compounds)
Consumer VOC sensors are typically non-specific—they detect "something" but can't tell you what. Less useful than you might expect. Readings can be triggered by harmless substances.
When Monitoring Makes Sense
Understanding Your Baseline
A monitor can show you what your typical air quality looks like, when it's worse (cooking? rush hour? overnight?), and whether interventions help.
Verifying Air Purifier Effectiveness
If you're running an air purifier, a PM2.5 monitor can show whether it's actually reducing particles. Useful for validating your investment.
Identifying Problem Activities
Monitoring reveals how much cooking, cleaning, or other activities affect air quality. This helps prioritize where to focus improvement efforts.
Wildfire Season
During smoke events, knowing indoor vs outdoor levels helps you decide when to seal up versus ventilate.
When Monitoring Isn't Necessary
- If you don't plan to act on the information
- If you're satisfied with your air quality
- If it will cause anxiety without improving outcomes
- If you already know your air quality is poor and need to address it regardless
A monitor is a tool for information, not a solution by itself.
Choosing a Monitor
Prioritize PM2.5
This is the most actionable metric. Look for monitors with laser-based PM sensors, which are more accurate than simpler optical sensors.
CO2 Is Useful
If ventilation is a concern, CO2 monitoring helps you understand when to open windows or improve airflow.
Be Skeptical of VOC Readings
Consumer VOC sensors aren't very informative. They're included in many monitors but the readings are difficult to interpret meaningfully.
Consider Data Logging
Monitors that record data over time help you see patterns. When does air quality spike? Does it correlate with activities?
Limitations to Understand
Not Laboratory Accurate
Consumer monitors are approximate. They're useful for trends and relative comparisons, not precise measurements. Don't expect medical-grade accuracy.
Placement Matters
Readings near a window, in direct sunlight, or next to a pollution source will differ from room averages. Placement affects what you see.
Calibration Drift
Some sensors drift over time and may need calibration or replacement. Accuracy can degrade.
VOC Sensors Are Limited
Most consumer VOC sensors can't distinguish between harmful and harmless compounds. A spike might be from cooking, cleaning products, or nothing concerning.
Practical Use Tips
- Place at breathing level, away from direct pollution sources
- Give new monitors time to stabilize (hours to days)
- Focus on trends over time rather than single readings
- Compare before/after interventions rather than worrying about absolute numbers
- Don't obsess—checking once or twice a day is sufficient