The Indoor Environment

1. The Indoor Environment GISAT 112

2. Overview of the Indoor Environment • Amount of time spent indoors… • Health and safety risks: accidents, food, water, air… • Emphasis here on indoor air quality* • Pollutants, sources, effects • Effects of indoor-outdoor air exchange *but not in the workplace

3. Activity PatternsSource: EPA, Exposure Factors Handbook, August 1997

4. Pollutants • Gases • Inorganic: CO, NOx, SOx, radon…. • Organic: formaldehyde, pesticides, “VOCs”…. • Particles • Inorganic: combustion aerosols, “dust”…. • Organic: spray aerosols, cooking smoke, ETS… • Biogenic: bacteria, fungi, spores, dander, antigens….

5. National Emissions vs. ExposuresExample: Benzene

6. Health Risk RISK = TOXICITY x EXPOSURE • Where toxicity is a measure of adverse health effect per unit mass of pollutant • And exposure is a measure of the mass of pollutant breathed over a period of time

7. Volume of Air Breathed • Typically, about 15 - 20 m3/day • i.e., the volume of a small bedroom • More for athletes in action • Less for couch potatoes and children • About 20 kg per day • For comparison: food and water- ~2 kg/day each

8. Effects • Odor • Irritation of mucous membranes • Lung damage • Infection • Asthma • Cancer • Other systemic effects

9. Worker Productivity

10. Radon in the home • What is Radon? • What are the properties of Radon? • Where does it come from? • How does it get into the house?

11. What is Radon? • Radon (chemical symbol Rn) is a naturally occurring radioactive gas found in soils, rock, and water throughout the U.S. • Radon causes lung cancer, and is a threat to health because it tends to collect in homes, sometimes to very high concentrations. • It has numerous different isotopes, but radon-220, and -222 are the most common. What's an isotope? Source: US EPA

12. Isotopes • A given element might exist in different forms – “isotopes” – with differing numbers of neutrons • If they have the same number of protons, they are the same element • But their weight is different because of the neutrons • Example: Hydrogen, Deuterium, Tritium

13. E.g.: Carbon 14

14. What are the properties of radon? • Radon is a noble gas, which means it is essentially inert, and does not combine with other chemicals. • Radon is a heavy gas, which accounts for its tendency to collect in basements. • It has no color, odor, or taste. • Radon-222 is produced by the decay of radium, has a half-life of 3.8 days, and emits an alpha particle as it decays to polonium-218, and eventually to stable lead. • Radon-220, is the decay product of thorium – it is sometimes called thoron, has a half-life of 54.5 seconds and emits an alpha particle in its decay to polonium-216. What's an alpha particle? Source: US EPA

15. Where does Rn come from?Radon Precursors and Progeny (Masters, Figure 7.54)

16. How does Radon get into the house? • Radon is “pumped” into your house by the heating system • Inhalation exposure • A smaller source can be well water pumped into your house • Inhalation and ingestion exposure Source: US EPA

17. Radon Level If 1,000 people who smoked were exposed to this level over a lifetime... The risk of cancer from radon exposure compares to... WHAT TO DO:Stop smoking and... 20 pCi/L About 135 people could get lung cancer 100 times the risk of drowning Fix your home 10 pCi/L About 71 people could get lung cancer 100 times the risk of dying in a home fire Fix your home 8 pCi/L About 57 people could get lung cancer Fix your home 4 pCi/L About 29 people could get lung cancer 100 times the risk of dying in an airplane crash Fix your home 2 pCi/L About 15 people could get lung cancer 2 times the risk of dying in a car crash Consider fixing between 2 and 4 pCi/L 1.3 pCi/L About 9 people could get lung cancer (Average indoor radon level) (Reducing radon levels below 2 pCi/L is difficult.) 0.4 pCi/L About 3 people could get lung cancer (Average outdoor radon level) (Reducing radon levels below 2 pCi/L is difficult.) Note: If you are a former smoker, your risk may be lower. Radon Risk if You Smoke Source: www.epa.gov/iaq/radon/riskcht.html

18. Radon Level If 1,000 people who never smoked were exposed to this level over a lifetime... The risk of cancer from radon exposure compares to... WHAT TO DO: 20 pCi/L About 8 people could get lung cancer The risk of being killed in a violent crime Fix your home 10 pCi/L About 4 people could get lung cancer Fix your home 8 pCi/L About 3 people could get lung cancer 10 times the risk of dying in an airplane crash Fix your home 4 pCi/L About 2 people could get lung cancer The risk of drowning Fix your home 2 pCi/L About 1 person could get lung cancer The risk of dying in a home fire Consider fixing between 2 and 4 pCi/L 1.3 pCi/L Less than 1 person could get lung cancer (Average indoor radon level) (Reducing radon levels below 2 pCi/L is difficult.) 0.4 pCi/L Less than 1 person could get lung cancer (Average outdoor radon level) (Reducing radon levels below 2 pCi/L is difficult.) Note: If you are a former smoker, your risk may be higher. Radon Risk if You Never Smoked Source: www.epa.gov/iaq/radon/riskcht.html

19. Indoor Air Pollutants(from Miller, Env.Sci., 9th ed., and EPA)

20. Indoor Biocontaminants • The previous diagram leaves out a major class of indoor pollutants, sometimes generally referred to as “biocontaminants”. • Examples: fungi, bacteria, viruses, spores, animal dander, pollen, insect fragments, dust mites. • Microbial contaminants thrive in or on moist materials. • Control by preventing leaks and high-moisture areas; cleaning regularly; and air cleaning if necessary.

21. There’s Money in Mold(from the Raleigh News and Observer, 12-20-01)

22. Regulations • Outdoor Air • SOx, NOx, CO, Ozone, Particles, Pb • Hazardous air pollutants (189/33) • Indoor Air • Codes: ventilation, combustion devices • Asbestos removal • Product labeling (e.g., carpets) • Toxic substance warnings (e.g., in CA) • Smoking bans • Radon (guidelines for acceptable levels; testing required by some States when houses sold)

23. Ventilation Terminology • Natural ventilation • Infiltration and exfiltration occur by natural driving forces (temperature differences, wind) • Mechanical ventilation • Air forced into or exhausted from buildings by fans • Dilution ventilation: dilute indoor-generated pollutants below thresholds • Exhaust ventilation: extract high-concentration pollutants or moisture

24. Ventilation Rates • Ventilation rates are often expressed as air exchange rates, in air changes per hour (ACH) air flow rate ÷ room volume = ACH [hr-1] • For example, a 300 m3 house through which 150 m3/hr of air is entering via infiltration (and exiting via exfiltration) is experiencing an ACH of 0.5 hr-1 due to natural ventilation

25. How Air Pollutants Move • By (molecular) diffusion • Kinetic activity • Relevant for gases, very fine particles • By convection • Pollutants carried by air that moves by temperature differences (warm air rises…) • Pollutants carried by air that is mechanically driven, or wind-driven • By settling • Force of gravity pulls airborne particles downward • Relevant for particles larger than about 1 μm diameter

26. Volatility and Evaporation • Some liquid materials (and a few solid ones) are relatively volatile. • This means that at about room temperature, these materials—or some of their constituents—tend to evaporate. • During evaporation, molecules escape from a liquid and become gaseous (vapors). • Volatile organic compounds (VOCs) are particularly common air contaminants, and many synthetic materials inside buildings emit them.

27. Concentrations Can Be Highly Variable

28. Mass (or Material) Balances • Consider the RATE of material flow • Draw a boundary around system • e.g. a bathroom sink • In the simplest form: Input – Output = Accumulation • More generally: Input – Output + Generation – Consumption = Accumulation • Or: I – O + G – C = A

29. This is the “volumetric flow rate” of the system Mass Balance Example • How many ACH are needed to keep the concentration of formaldehyde at or below 10 μg/m3 in a 2.5 x 4 x 30 m room, if there is a constant source of 50 μg/h in the room? (Assume complete mixing and steady-state.) • So for I – O + G – C = A: I = 0 μg/h (assuming clean air coming in) O = (10 μg/m3)(Volume*ACH) = (10 μg/m3)(300 m3)(ACH) G = 50 μg/h C = 0 μg/h (assuming nothing in the room eats formaldehyde!) A = 0 μg/h (assuming steady state) • So I – O + G – C = A simplifies to O = G 0 0 0

30. Mass Balance Example (cont’d) O = G (10 μg/m3)(300 m3)(ACH) = 50 μg/h = /h 1.7 x 10-2

31. Air Exchange and Ventilation • Ventilation: exchange of indoor and outdoor air • Diagram below is from an IAQ modeling tool. Values represent airflows between rooms and between indoors and outdoors. • Let’s look at a simple mass balance around a room…

32. Mass Balance Example • A room with a volume of 25 m3 contains a source of pollutant “P” that emits P at 120 micrograms per hour. • Air flows into this room (from adjacent rooms and/or the outdoors) at 20 m3 per hour. Air flows out at the same rate. • The air flowing into the room contains a small amount of P…10 μg/m3. • Assume that the source has been in the room long enough to bring the concentration of P up to a steady value. • Assume there are no reactions that destroy P and no surfaces in the room that adsorb it. • Run a mass balance, then calculate the concentration of P in the room.

33. Mass Balance for a Pollutant Room volume = 25 m3 20 m3/h 20 m3/h Pin = 10 μg/m3 Poll. Gen = 120 μg/h Pout = ? μg/m3 Output = Input + Generation – Consumption – Accumulation So 20•Pout = 20•Pin + 120 – 0 – 0 = 200 + 120 = 320 μg/h Therefore, under steady conditions 320 μg/h of P is flowing out of the room. The concentration coming out is 320 μg/h ÷ 20 m3/h = 16 μg/m3. If the air in the room is well-mixed, that is also the concentration in the room.