Introduction to Air Quality Sensors
Learning Objectives
Students will be able to:
- Identify different types of air quality sensors and what they measure
- Explain why we need sensors to monitor air quality
- Read and interpret basic sensor displays
- Describe the difference between CO2 and PM2.5 sensors
Why Do We Need Sensors?
You can't manage what you can't measure.
Most air quality problems are invisible. We can't see CO2, PM2.5, or most pollutants. Our noses can only detect some problems (like smoke or strong odors). Sensors give us objective, numerical data about what's really in the air.
Types of Air Quality Sensors
CO2 Sensors
What they measure: Carbon dioxide concentration in parts per million (ppm)
Why it matters: CO2 is a proxy for ventilation—high CO2 means stale air and possible buildup of other pollutants
Common devices: Aranet4, CO2.click, Temtop
PM2.5 Sensors
What they measure: Particle concentration in micrograms per cubic meter (μg/m³)
Why it matters: PM2.5 is the most health-relevant pollutant—directly linked to respiratory and cardiovascular effects
Common devices: PurpleAir, IQAir, AirVisual
How Do These Sensors Work?
| Sensor Type | Technology | How It Works |
|---|---|---|
| CO2 (NDIR) | Non-dispersive infrared | CO2 molecules absorb specific wavelengths of infrared light; more absorption = higher concentration |
| PM2.5 (Optical) | Laser light scattering | Particles scatter laser light; sensor counts scattering events to estimate particle count and size |
Reading Sensor Displays
CO2 Display
This reads 847 parts per million—for every million molecules of air, 847 are CO2.
PM2.5 Display
This reads 12 micrograms per cubic meter—the mass of PM2.5 particles in each cubic meter of air.
What's Normal? Reference Values
| Measure | Good | Moderate | Poor |
|---|---|---|---|
| CO2 | <800 ppm | 800-1500 ppm | >1500 ppm |
| PM2.5 | <12 μg/m³ | 12-35 μg/m³ | >35 μg/m³ |
Note: Outdoor CO2 is about 420 ppm. Any reading above that is due to indoor sources (mainly breathing).
Activity: Sensor Exploration
If you have a CO2 sensor available:
- Note the current reading in the classroom
- Have everyone breathe toward the sensor—what happens?
- Open a window or door—what happens over time?
- Take the sensor outside—what reading do you get?
Discussion Questions:
- Why does the reading go up when people breathe near it?
- Why does opening a window lower the reading?
- What would you expect the reading to be in an empty room?
Key Takeaway
Air quality sensors let us measure what we can't see. CO2 sensors tell us about ventilation, while PM2.5 sensors measure harmful particles. By using sensors, we can get objective data about air quality and make informed decisions about how to improve it. In this unit, you'll learn to collect, analyze, and act on sensor data.