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Indoor Air Pollution: You Can't See It, but It's in Your Home

The facts of indoor air pollution can sound daunting to anyone concerned about healthy air quality. The U.S. Environmental Protection Agency has reported testing homes where indoor air is 100 times more polluted than the air outdoors. Before you run for the door, however, realize that the actual average level of indoor pollutants is more in the range of two to five times the concentration of pollutants outdoors. The increase in indoor pollution is directly related to advances on another environmental front: energy efficiency. Older, less efficient homes used to “breathe.” Ventilation with fresh outdoor air happened naturally through cracks and gaps in the structure and building materials, diluting indoor air pollutants. However, heating and cooling was also lost from these homes and energy consumption was high. As architects and builders have designed and constructed homes to be more air-tight and conserve energy, the reduction of natural ventilation has caused indoor air pollution to accumulate and concentrate.

Why Indoor Air Quality is Important

The average person takes about 28,000 breaths per day. Eighty percent of these are at home. The possibility of exposure to pollutants elsewhere is to some extent a risk we choose to accept. However, while you may be able to make some choices that reduce exposure to outdoor pollution, there’s little you can do to avoid a high level of air pollution if it exists inside your own home. In the closed-loop design of a typical central air and heating system, indoor air is continuously circulated throughout the living spaces in the home. Pollutants that have their source in certain areas, such as the kitchen, are eventually dispersed throughout the entire house. Closing doors to particular rooms and even the use of individual room air cleaners provide only limited effectiveness. In a home with toxic air, wherever the air goes, the pollution follows.

The consequences of exposure to indoor air pollution vary according to the predominant pollutants and individual sensitivity of occupants. They can also be divided into two categories:

Immediate effects. These include mostly irritants and annoyances. They may result from just one exposure or many.  Hay fever or allergy-like symptoms are common, including eye, nose and throat irritation, headaches and generalized fatigue. In an individual predisposed to asthma, exposure to indoor air pollution may trigger an episode. Immediate symptoms resulting from indoor air pollution often depend upon the individual sensitivity of occupants. However, repeated exposure to high concentrations can sensitize even those with no previous history of reactions.

Long-term effects. Years of daily exposure to indoor pollutants may result in illnesses that are disabling or even fatal. These may include chronic respiratory obstruction, heart disease and cancer. The lesson from these hazards is that, even if symptoms are not apparent on a day-to-day basis, effects that compromise health may show up after an extended time span.

What’s in the Air?

The components of indoor air pollution in residences are fairly standard. Most occur spontaneously and aren’t related to poor housekeeping. Some you can see or smell, while some are invisible and provide no clues beyond unexplained physical discomfort. Indoor air pollution may originate outdoors then concentrate inside, or it may result from interior causes.  

  • Common dust. It’s the inorganic stuff you can see floating around and also accumulating on surfaces inside the house. Dust is constantly being stirred up, circulated throughout the air and then gradually settling again. While some dust is made up of dirt and sand from the outdoors, most of it actually has an indoor source. Ingredients in the dust recipe include skin flakes shed by humans, insect waste, pet dander, lint from carpets, drapes and bedding, dead dust mites, and carbon soot produced by stoves or furnaces.
  • Organic matter. Living microorganisms are also small enough to remain buoyant and populate household air. Microscopic mold spores and pollen may surge into a house by the millions every time an exterior door or window is opened. Once inside, these invisible contaminants multiply and thrive, adding to the toxic concentration in interior air. Mold spores find moisture sources and establish permanent colonies, often in unseen locations.
  • Fumes. Many indoor sources emit fumes that add to the air pollution load. Simple cooking with natural gas may increase indoor humidity and also emit fumes that contain combustion byproducts and gases such as nitrogen dioxide. Components of cigarette smoke contain many toxic fumes. Also, wooden building materials like flooring contain glues that gradually off-gas chemical vapors into the interior environment. Carpets and other materials can release volatile organic compounds such as formaldehyde that have known health hazards.
  • Bacteria and viruses. The smallest of airborne pathogens are those most likely to transmit communicable diseases and respiratory infections. These contaminants thrive in specific environments according to the indoor temperature and humidity. While bacteria tends to spread in warmer, moist air, viruses – including colds and flu – prefer cooler, drier air.

Though we may be able rely on governmental agencies to at least address some sources of outdoor pollution, dealing with pollutants in indoor air is left up to the individual homeowner. While complete elimination of all indoor air pollution is not cost-efficient, control and reduction is very doable. Methods to reduce indoor air pollution can be reduced to two basic approaches: reducing indoor sources of air pollution and lowering the concentration of pollutants that do accumulate in the air.

  • Common methods such as regular dusting with electrostatic cloths can reduce the level of dust on surfaces that will continuously be stirred up in the air.  Lint and dust emitted by carpeting can be reduced by frequent vacuuming.
  • Locate and remove sources of indoor mold growth. Areas that accumulate damp air such as attics and crawl spaces are friendly environments for mold growth. Mold may also grow on damp surfaces of HVAC equipment such as the air conditioner evaporator coil located in the air handler.
  • Make sure any household appliances or heating equipment that utilizes combustion is inspected annually and given regular preventive maintenance to eliminate combustion byproducts such as soot or hazardous fumes such as carbon monoxide.
  • Keep pets clean and brush long-haired pets outdoors only. Where there are individuals particularly sensitive to pet dander, it may be necessary to limit pets to certain areas of the house.
  • Refrain from smoking cigarettes indoors, particularly when children are present.
  • When using cleaning supplies, paints or other potentially toxic substances, follow manufacturer’s directions, provide adequate ventilation, and only purchase limited amounts of these products so storage of excess can be avoided.

Mechanical Filtration And Air Cleaners

Mechanical filters range from the standard flat-panel filter installed in your heating and cooling system to whole-house units. Air cleaners and purifiers include electrostatic cleaners that utilize ionization to remove particulates and ultraviolet lights that neutralize living microorganisms. Here’s a rundown of how these household accessories work:

MERV Ratings

Standard furnace or A/C filters are rated on the MERV (minimum efficiency reporting value) scale ranging from 1 to 16; the higher the MERV numeral, the more efficient the filter. Filters above 16 are considered HEPA medical-grade filtration. The fiberglass panel “thowaway” filters often supplied as standard equipment with a furnace or A/C are usually rated from MERV 1 to 4. These filters are not useful for much more than removing large inorganic dust particles. At the upper range of the scale, HEPA filters above 16 remove particulates down to the size of virus particles, but obstruct airflow so much they’re not appropriate for the average residential HVAC system, unless serious system modifications are made. Whole-house filters in the MERV range of 8 to 12 provide the best compromise of filter efficiency with optimum airflow. These filters installed directly in your return air duct filter all the air in the house as it circulates through the ductwork multiple times per day. Incorporating pleated cotton or polyester media, they remove airborne particulates down to a size of approximately 1 micron, including all dust and most common microorganisms including mold spores and pollen.

Air Cleaners

Electronic air cleaners are available in whole-house or single-room portable models. These units use the power of ionization to charge neutral airborne particulates with a positive or negative charge as they pass through an electronic grid. Once charged, airborne particulates are attracted to any surface with the opposite charge. As the airflow passes through a series of positive- and negatively-charged collector plates, charged particles are removed from the air and captured by the plates. These units typically incorporate mechanical pre-filters to remove the largest dust particles that are less affected by ionization.

UV Lamps

Ultraviolet lamps help control living contaminants such as mold spores, pollen and bacteria. Exposure to ultraviolet (UV) light neutralizes these pathogens by destroying their capacity to reproduce. Installed inside ductwork, a UV lamp tube continuously exposes the airflow to germicidal UV light to neutralize microorganisms. UV lamps may also be positioned to shine on the A/C or heat pump's indoor coil and condensate pan to prevent mold and bacteria growth, which is another source of contamination in household air.

For more information about controlling air pollution in the Chicago area, contact us today at

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