What are the trends in indoor air quality and their effects on human health?

On average, Americans spend approximately 90 percent of their time indoors
1. Indoor concentrations of certain pollutants are typically 2 to 5 times higher than typical outdoor concentrations.
2. People who are generally most vulnerable to the adverse effects of pollution (eg, the very young, the elderly, those with cardiovascular or respiratory disease) tend to spend more time indoors.
3. Indoor concentrations of some pollutants have increased in recent decades due to energy efficient building construction (when adequate mechanical ventilation is lacking to ensure adequate air exchange) Insecticides, and household cleaners.

Contaminants and Sources
Typical pollutants include:
• Combustion by-products such as carbon monoxide, particulate matter and ambient tobacco smoke.
• Substances of natural origin, such as radon, pet dander, and mold.
• Biological agents such as mold.
• Pesticides, lead and asbestos.
• Ozone (from some air purifiers).
• Various VOCs from various products and materials.

Most pollutants that affect indoor air quality come from inside buildings, but some also come from outside.
• Indoor sources (sources within the building itself). Combustion sources in indoor environments, including tobacco, wood and coal heating and cooking appliances, and fireplaces, release harmful combustion byproducts such as carbon monoxide and particulate matter directly into the indoor environment. Cleaning supplies, paints, pesticides, and other commonly used products introduce many different chemicals, including volatile organic compounds, directly into indoor air. Building materials are also potential sources, either through degraded materials (for example, asbestos fibers released from building insulation) or from new materials (for example, chemical offgassing from pressed wood products). Other substances in indoor air are of natural origin, such as radon, mold, and pet dander.

• Outdoor sources: Outdoor air pollutants can enter buildings through open doors, windows, ventilation systems, and structural cracks. Some pollutants enter indoors through building foundations. Radon, for example, forms underground when naturally occurring uranium in rocks and soil decays. Radon can then enter the building through cracks or gaps in the structure. Harmful fumes from chimneys can re-enter homes, polluting the air in homes and communities. In areas where groundwater or soil is contaminated, volatile chemicals can enter buildings through the same process. Volatile chemicals in water systems can also enter indoor air when building occupants use water (e.g. showering, cooking). Finally, when people enter buildings, they may inadvertently bring in dirt and dust from outside on their shoes and clothing, as well as pollutants that cling to these particles.

Other Factors Affecting Indoor Air Quality
In addition, several other factors can affect indoor air quality, including air exchange rates, outdoor climate, weather conditions, and occupant behavior. The air exchange rate with the outside is an important factor in determining the concentration of indoor air pollutants. The rate of air exchange is influenced by the design, construction and operating parameters of the building and is ultimately a function of infiltration (air flows into the structure through openings, joints and cracks in walls, floors and ceilings and around doors and windows), natural ventilation (air flows through open flow through windows and doors) and mechanical ventilation (air is forced into the room or out of the room by a ventilation device such as a fan or air handling system).

Outdoor climate and weather conditions as well as occupant behavior can also affect indoor air quality. Weather conditions can affect whether building occupants open or close windows and whether they use air conditioners, humidifiers or heaters, all of which affect indoor air quality. Certain climate conditions can increase the likelihood of indoor moisture and mold growth without proper ventilation or air conditioning controls.

Impact on human health
Health effects associated with indoor air pollutants include:
• Irritating to eyes, nose and throat.
• Headaches, dizziness and fatigue.
• Respiratory disease, heart disease and cancer.

The link between some common indoor air pollutants (eg radon, particulate pollution, carbon monoxide, Legionella) and health effects is well established.
• Radon is a known human carcinogen and the second leading cause of lung cancer.

Carbon monoxide is poisonous, and short-term exposure to elevated levels of carbon monoxide in the indoor environment can be fatal.

Legionnaires' disease, a type of pneumonia caused by exposure to Legionella bacteria, is associated with buildings with poorly maintained air conditioning or heating systems.

Many indoor air pollutants -- dust mites, mold, pet dander, environmental tobacco smoke, cockroach allergens, particulate matter, etc. -- are "asthma triggers," meaning some asthmatics may experience asthma attacks after exposure.
While adverse health effects have been attributed to certain pollutants, scientific understanding of some indoor air quality issues is still evolving.

One example is "sick building syndrome," which occurs when building occupants experience similar symptoms after entering a particular building, which lessen or disappear after they leave the building. These symptoms are increasingly attributed to various building indoor air properties.

Researchers have also been studying the relationship between indoor air quality and important issues traditionally considered unrelated to health, such as student performance in the classroom and productivity in professional settings.

Another developing area of research is the design, construction, operation and maintenance of "green buildings" for energy efficiency and improved indoor air quality.

ROE Index
Although much is known about the wide range of indoor air quality problems and associated health effects, only two national indicators of indoor air quality based on long-term and qualitative data are currently available: radon and serum cotinine(a measure of tobacco smoke exposure. Index.)

For various reasons, ROE metrics cannot be developed for other indoor air quality issues. For example, there is no nationwide monitoring network that routinely measures air quality within a statistically valid sample of homes, schools, and office buildings. This does not mean that nothing is known about the wide range of indoor air quality issues and related health effects. Instead, information and data on these issues can be gleaned from government publications and scientific literature. These data are not presented as ROE indicators because they are not nationally representative or do not reflect issues over a sufficiently long time period.