Sources of Indoor Particles
Learning Objectives
Students will be able to:
- Identify common sources of indoor particles
- Categorize sources by particle size generated
- Explain how activities affect indoor air quality
- Propose strategies to reduce particle emissions
Where Do Indoor Particles Come From?
Indoor particles come from three main pathways:
Cooking, cleaning, burning
Pollution, pollen, dust
Settled dust kicked up
Major Indoor Sources
Combustion Sources (Highest PM2.5)
| Source | Particle Size | Typical PM2.5 Increase |
|---|---|---|
| Gas stove cooking | 0.1-1 μm | 10-100+ μg/m³ |
| Frying/sautéing | 0.1-2 μm | 50-500+ μg/m³ |
| Candles (burning) | 0.01-0.1 μm | 10-50 μg/m³ |
| Incense | 0.1-1 μm | 100-300+ μg/m³ |
| Wood fireplace | 0.1-1 μm | 50-1000+ μg/m³ |
Cleaning Activities
| Activity | Effect |
|---|---|
| Vacuuming (without HEPA) | Stirs up settled dust; can increase PM for 30+ minutes |
| Sweeping | Major resuspension of settled particles |
| Dusting | Releases particles into air |
| Spray cleaners | Adds chemical aerosols + fragrances |
Paradox: Cleaning makes air dirtier temporarily! Best practice: ventilate well while cleaning.
Human Activity
- Walking: Resuspends settled particles with each step
- Skin cells: We shed millions daily (food for dust mites)
- Clothing: Releases fibers and trapped particles
- Breathing/talking: Exhaled aerosols (0.5-5 μm)
- Personal care products: Sprays, powders, fragrances
The Cooking Problem
Cooking is often the #1 source of PM2.5 in homes:
| Cooking Method | PM2.5 Generated | Risk Level |
|---|---|---|
| Boiling water | Low | Low |
| Steaming vegetables | Low-Medium | Low |
| Baking in oven | Medium | Medium |
| Stir-frying | High | High |
| Deep frying | Very High | Very High |
| Charring/burning food | Extreme | Extreme |
Key factors: Temperature (hotter = more particles), oil (more oil = more particles), duration, ventilation
Outdoor Sources Coming In
How They Enter
- Open windows/doors
- Cracks and gaps in building
- HVAC systems (if unfiltered)
- On clothing and shoes
- On pets
Common Outdoor Sources
- Traffic exhaust
- Industrial emissions
- Wildfire smoke
- Pollen
- Dust storms
Resuspension: The Hidden Problem
Resuspension = When settled particles get kicked back into the air
Major resuspension activities:
- Walking: Each footstep resuspends particles from floors/carpets
- Making beds: Shaking sheets releases dust mites, skin cells, particles
- Sitting on upholstered furniture: Compressing releases trapped particles
- Pets running/playing: Stir up dust from floors
Research finding: A person walking across a carpeted room can increase particle concentrations by 2-10×!
Activity: Source Inventory
Think about your home or school. List particle sources in each category:
| Category | Sources in My Space | Size Category |
|---|---|---|
| Combustion | Mostly PM2.5 | |
| Cooking | PM2.5 + larger | |
| Cleaning | Mixed sizes | |
| Human/pet activity | Mixed sizes | |
| From outdoors | Varies |
Discussion:
- Which sources are controllable vs. uncontrollable?
- What times of day have the most particle sources active?
- How could you reduce particles from each category?
Key Takeaway
Indoor particle sources include combustion (cooking, candles, heating), cleaning activities, human movement, and outdoor air coming in. Cooking is often the biggest source of PM2.5 in homes. Understanding sources is the first step to reducing exposure—we can control many sources through behavior changes, ventilation, and filtration.