1
Engage
Emission Rates and Concentrations
Duration
50 minutes
Type
Engage
Standards
HS-PS3-1, HSF-LE.A.1
Learning Objectives
Students will be able to:
- Define emission rate and distinguish from concentration
- Perform unit conversions for mass emission rates
- Set up mass balance equations for indoor spaces
- Calculate how source strength affects indoor concentrations
- Identify common indoor PM sources and their emission rates
The Big Question
"If we know how much particulate matter a source emits per minute, can we predict the concentration in a room?"
Emission Rate vs. Concentration
Emission Rate (E)
- Mass released per unit time
- Units: ug/min, mg/h, kg/day
- Property of the SOURCE
- Does not depend on room size
Concentration (C)
- Mass per unit volume of air
- Units: ug/m3, mg/m3
- Property of the ENVIRONMENT
- Depends on room size, ventilation, removal
The Mass Balance Equation
The fundamental equation for indoor particle dynamics:
V dC/dt = E + Q*Cout*P - Q*C - kd*V*C
| Term | Meaning | Units |
|---|---|---|
| V dC/dt | Rate of change of mass in room | ug/h |
| E | Indoor emission rate | ug/h |
| Q*Cout*P | Infiltration from outdoors | ug/h |
| Q*C | Loss by ventilation | ug/h |
| kd*V*C | Loss by deposition | ug/h |
Common Indoor PM Emission Sources
| Source | PM2.5 Emission Rate | Duration |
|---|---|---|
| Candle burning | 100-300 ug/min | Hours |
| Gas stove cooking | 500-2000 ug/min | 30-60 min |
| Cigarette | 10,000-14,000 ug/cigarette | 5-10 min |
| Incense | 200-500 ug/min | 30-60 min |
| Vacuum cleaning | 50-200 ug/min | 15-30 min |
Activity: Emission Rate Calculations
Problem Set
- Unit conversion: Convert an emission rate of 500 ug/min to mg/h and g/day.
- Simple buildup: A 50 m3 sealed room (no ventilation or deposition) has a source emitting 100 ug/min. What is the concentration after 1 hour? After 2 hours?
- Why is this unrealistic? Why would real concentrations be lower than your calculated values?
Key Takeaway
Emission rates quantify how fast sources release particles, while concentration describes the resulting air quality. The mass balance equation relates these quantities through room volume, ventilation, and deposition. Understanding this fundamental relationship is essential for predicting and controlling indoor particle levels.