Air Quality Assessment
Learning Objectives
Students will be able to:
- Interpret the Air Quality Index (AQI) scale and its health categories
- Identify which pollutants are measured in AQI calculations
- Analyze air quality scenarios and recommend appropriate responses
- Apply unit knowledge to assess real-world air quality situations
The Air Quality Index (AQI)
The Air Quality Index (AQI) is a standardized scale from 0 to 500 that tells you how clean or polluted the air is and what health effects might be of concern.
Think of it like a thermometer for air pollution!
AQI Categories
| AQI Range | Category | Color | Health Message |
|---|---|---|---|
| 0-50 | Good | Green | Air quality is satisfactory |
| 51-100 | Moderate | Yellow | Acceptable; sensitive individuals may have minor issues |
| 101-150 | Unhealthy for Sensitive Groups | Orange | Sensitive groups (asthma, elderly, children) may be affected |
| 151-200 | Unhealthy | Red | Everyone may begin to experience health effects |
| 201-300 | Very Unhealthy | Purple | Health alert: everyone may experience serious effects |
| 301-500 | Hazardous | Maroon | Health emergency: entire population affected |
Pollutants Measured in AQI
The AQI is calculated separately for each of these five pollutants, and the highest value becomes the reported AQI:
Fine particles
Coarse particles
Ground-level ozone
Nitrogen dioxide
Carbon monoxide
Note: SO2 (sulfur dioxide) is also measured but less common in most areas. CO2 is NOT included in AQI—it affects climate but isn't directly toxic at normal outdoor levels.
Indoor vs. Outdoor AQI
Important Distinction
The official AQI measures outdoor air quality only! Indoor air often has different pollutant levels:
Indoor can be WORSE when:
- Poor ventilation traps pollutants
- Cooking, cleaning, burning candles
- New furniture off-gassing VOCs
- Many people in closed space (CO2)
Indoor can be BETTER when:
- Good HVAC filtration running
- Air purifiers in use
- Windows closed during wildfire
- No indoor pollution sources active
Scenario Analysis Activity
For each scenario, identify the likely pollutant(s), estimate relative air quality, and recommend actions:
Scenario 1: Wildfire Smoke
Your city has an outdoor AQI of 185 due to wildfire smoke from 100 miles away. Your school has old windows that don't seal well and no air filtration.
- Primary pollutant: (PM2.5)
- Indoor air quality likely: (Also poor - smoke seeps in)
- Recommendations: (Close windows anyway, run portable air purifiers/CR boxes, limit outdoor activities)
Scenario 2: The Science Lab
Students are using markers and glue for a project. The room has no windows open and feels stuffy. Some students complain of headaches.
- Primary pollutants: (VOCs from markers/glue, elevated CO2)
- Problem: (Poor ventilation + pollution sources)
- Recommendations: (Open windows, turn on fan, use low-VOC products)
Scenario 3: Hot Summer Day
It's 95°F and sunny. The outdoor AQI is 135 with ozone as the primary pollutant. Should the PE class have outdoor activities?
- Primary pollutant: (Ground-level ozone)
- AQI category: (Orange - Unhealthy for Sensitive Groups)
- Recommendations: (Move activities indoors or to early morning, reduce intensity, watch for symptoms)
Scenario 4: The Cafeteria
The school cafeteria uses gas stoves. During lunch prep, there's visible steam and cooking odors. No exhaust hood is running.
- Primary pollutants: (NO2, CO, PM2.5 from cooking)
- Problem: (Combustion products not being vented)
- Recommendations: (Turn on exhaust hood, open windows, consider electric alternatives)
Reading Air Quality Data
Practice interpreting this data from an indoor air quality monitor:
| Time | CO2 (ppm) | PM2.5 (μg/m³) | Activity |
|---|---|---|---|
| 8:00 AM | 450 | 8 | Room empty, windows closed overnight |
| 9:00 AM | 850 | 12 | 25 students arrived |
| 10:00 AM | 1,400 | 15 | Full class, no ventilation |
| 10:30 AM | 900 | 10 | Windows opened |
| 12:00 PM | 1,100 | 45 | Lunch - cooking in adjacent room |
Analysis Questions:
- What caused the CO2 to rise from 8 AM to 10 AM?
- What effect did opening windows have?
- Why did PM2.5 spike at noon?
- What would you recommend for this classroom?
Unit 1 Review: What We've Learned
Lesson 1: Air Composition
78% N2, 21% O2, ~1% Ar, 0.04% CO2
Lesson 2: Concentration (ppm)
1% = 10,000 ppm; small amounts can have big effects
Lesson 3: Diffusion
Gases spread from high to low concentration; temperature speeds it up
Lesson 4: Indoor Pollutants
CO2, CO, VOCs, PM2.5, radon - sources and health effects
Lesson 5: Chemical Reactions
Combustion creates pollutants; NOx + VOCs + sun = ozone
Lesson 6: Air Quality Assessment
AQI scale, 0-500, color-coded health categories
Unit 1 Complete!
You now understand the chemistry of air—what it's made of, how pollutants spread and react, and how to assess air quality. This foundation prepares you for the rest of the IAQ curriculum: learning about particles and health in more detail, working with air sensors, and eventually building your own air purifier!