8.3 Indoor Air Quality and Health

Indoor Air Pollutants

People spend roughly 90% of their time indoors, and indoor air can be 2 to 5 times more polluted than outdoor air. That makes indoor air quality one of the most direct environmental health concerns you'll encounter in this course. This section covers the major indoor pollutants, how they affect health, and what can be done about them.

Radioactive and Fibrous Contaminants

Radon is a colorless, odorless radioactive gas produced by the natural decay of uranium in soil and rock. It seeps into buildings through cracks in foundations and tends to accumulate in basements and lower floors. Radon is the second leading cause of lung cancer in the United States (after smoking), and the risk is even higher for people who smoke.

Asbestos refers to a group of naturally occurring fibrous minerals that were widely used in construction materials before the health risks became clear. In older buildings, you can find it in insulation, floor tiles, and roofing materials. Asbestos is dangerous when disturbed, because inhaling the tiny fibers can cause serious lung diseases, including mesothelioma (a cancer of the lung lining) and asbestosis (chronic scarring of lung tissue). Intact, undisturbed asbestos is generally not a hazard.

Chemical and Biological Pollutants

Formaldehyde is a volatile organic compound (VOC) emitted by many household products, including pressed wood furniture, adhesives, and certain fabrics. It causes eye, nose, and throat irritation at low concentrations, and long-term exposure may increase cancer risk.

Mold grows wherever there's excess moisture and releases spores into the air. It thrives in bathrooms, basements, and anywhere with water damage or high humidity. Mold spores trigger allergic reactions and respiratory problems, and they can make asthma significantly worse.

Secondhand smoke is a mixture of harmful chemicals released by burning tobacco products. It contains over 7,000 chemicals, at least 70 of which are known carcinogens. Non-smokers exposed to secondhand smoke face increased risk of heart disease, lung cancer, and respiratory problems.

Health Effects

Sick Building Syndrome

Sick building syndrome (SBS) describes a situation where occupants of a building experience health symptoms that seem linked to time spent in that building but can't be traced to a single specific cause. The key indicator is that symptoms improve after leaving the building.

Common symptoms include:

• Headaches, dizziness, and nausea
• Eye, nose, or throat irritation
• Fatigue and difficulty concentrating
• Skin irritation or rashes

SBS is tricky to diagnose because multiple factors usually contribute at once. These include poor ventilation (not enough fresh air coming in), chemical contaminants from off-gassing building materials or office equipment, and biological contaminants like bacteria and mold growing in poorly maintained HVAC systems.

Long-Term Health Impacts

Short-term irritation is one thing, but chronic exposure to indoor air pollutants can lead to serious conditions:

• Respiratory diseases like asthma and chronic obstructive pulmonary disease (COPD)
• Cardiovascular problems linked to long-term particulate matter exposure
• Increased cancer risk from pollutants like radon and asbestos

Vulnerable populations face the highest risks. Children, the elderly, and people with pre-existing health conditions are more susceptible to indoor air pollution. The COVID-19 lockdowns brought extra attention to this issue, as people spent even more time indoors than usual.

Mitigation Strategies

Ventilation Improvements

Ventilation is the exchange of indoor air with outdoor air, and it's the single most effective way to reduce indoor pollutant concentrations. It works by diluting contaminants with fresh air and removing excess moisture that encourages mold growth.

There are two main types:

• Natural ventilation uses windows, doors, and other openings to allow air movement.
• Mechanical ventilation uses fans and ductwork to actively circulate and filter air.

Strategies to improve ventilation include:

1. Increasing outdoor air intake in HVAC systems
2. Installing exhaust fans in kitchens and bathrooms (where moisture and cooking fumes concentrate)
3. Using demand-controlled ventilation, which adjusts airflow based on occupancy levels or $CO_2$ concentration

Air Purification Technologies

When ventilation alone isn't enough, air purifiers can remove specific contaminants. The main technologies work differently depending on the type of pollutant:

• HEPA filters capture particles as small as 0.3 microns with 99.97% efficiency. These are effective against dust, pollen, mold spores, and some bacteria.
• Activated carbon filters adsorb gases and odors, making them useful for VOCs like formaldehyde.
• UV-C light inactivates microorganisms such as bacteria and viruses by damaging their DNA.

When choosing an air purifier, consider the room size, the specific pollutants you're targeting, and noise levels. Regular filter replacement is essential for the device to keep working properly.

A few additional methods worth knowing:

• Photocatalytic oxidation breaks down VOCs using a catalyst activated by light.
• Ionizers generate charged particles that attract and remove airborne contaminants.
• Ozone generators should be used with caution. While they can neutralize some pollutants, ozone itself is a respiratory irritant and can be harmful at high concentrations.