7 Common Air Pollutants that Affect Indoor Air Quality (IAQ)

Human health can be influenced or affected by the quality of indoor air pollutants that may be present in a building or home. Various international agencies continue to update or refine and strictly regulate quantitative air quality standards and guidelines to ensure proper indoor air quality management.

The existence of common indoor air pollutants—such as CO (carbon monoxide), CO₂ (carbon dioxide), NO₂ (nitrogen dioxide), O₃ (ozone), PM (particulate matter), SO₂ (sulfur dioxide), and VOCs (volatile organic compounds)—poses a serious threat to human health, especially over the past two to three decades.

Many studies prove that indoor air pollutants are two to four times more concentrated than outdoor air pollutants: the WHO specifically reported that 4.2 million people died in 2016 because of poor air quality.

Indoor air quality (IAQ) is one of the world’s most precious items, even if it appears neglected. Because of the possibility of having higher concentrations of pollutants inside buildings, IAQ just can’t be ignored.

Apart from causing symptoms, the various kinds of building-associated illnesses that are tied to poor indoor air quality can also lead to tremendous and substantial economic loss. The USA’s EPA (Environmental Protection Agency) once linked $140 billion annual direct medical expenditure to problems resulting from IAQ.

The most common air pollutants that affect indoor air quality (IAQ)

The most common air pollutants that affect IAQ include:

• Ozone (O₃)
• Carbon monoxide (CO)
• Carbon dioxide (CO₂)
• Sulfur dioxide (SO₂)
• Nitrogen dioxide (NO₂)
• Particulate matter (PM)
• Volatile organic compounds (VOCs)

Ozone (O₃ or ground-level ozone), as an air pollutant, originates from chemical reactions between volatile organic compounds (VOCs) and nitrogen dioxide (NO₂) in the presence or midst of sunlight.

Ozone pollution can be worse in both cold and hot environments. Sources of ozone pollution are emissions of gasoline vapors, electric utilities, chemical solvents, etc., and can cause airway narrowing and lung inflammation in people exposed to ozone pollutants.

Carbon monoxide (CO) is a colorless, tasteless, and odorless toxic gas that is released from sources like gas-type water heaters, leaky furnaces and chimneys, furnace backdraft, unvented fuel and gas-type space heaters, tobacco smoke, fireplaces, wood stoves, gas-powered equipment, etc.

Carbon monoxide can cause chest pain, nausea, dizziness, fatigue, reduced brain function, impaired coordination and vision, and flu-like symptoms.

Carbon dioxide (CO₂) is a colorless and odorless anthropogenic air pollutant whose major source in buildings or indoors is the occupant’s or occupants’ individual respiration or respiratory system.

Sulfur dioxide (SO₂) is a colorless gas that has a pungent smell and originates from the combustion of oil, coal, and gas that contains sulfur. Combustion is the leading source of indoor sulfur dioxide concentration. Short-term exposure to sulfur dioxide can cause varying degrees of toxic symptoms, airway inflammation, and respiratory illnesses.

Nitrogen dioxide (NO₂) is a highly reactive gas which is associated with development of ozone and PM2.5 (particulate matter, including microscopic matter that is suspended in water or air and is less than or equal to 2.5 microns [symbol = µm] in diameter).

Nitrogen dioxide mainly gets into the atmosphere from the combustion or burning of fuel and, like sulfur dioxide, can also cause airway inflammation and respiratory symptoms.

Particulate matter (PM) consists of both solid and liquid particles in dust, soil, soot, and air, including organic chemicals, acids, and metals. Particle pollution is categorized based n the following sizes (diameters in micron [symbol = µm]):

• PM10 (2.5 µm to 10 µm)
• PM2.5 (less than 2.5 µm)
• PM1.0 (less than 1.0 µm).

PM10 is any particulate matter, including any microscopic matter that is suspended in water or air and has a diameter between 2.5 µm and 10 µm. PM2.5 has a diameter that is less than 2.5 µm, and PM1.0 has a diameter that is less than 1.0 µm.

PM10 affects the oral and nasal cavities, the upper trachea, the larynx, and the pharynx. PM2.5 and PM1.0 can cause pulmonary infection, alterations in heart rate variability, coagulation, cardiac autonomic function, and generate endothelial and vascular dysfunction.

Volatile organic compounds (VOCs) constitute various types of hazardous organic chemicals that are involved in atmospheric photochemical reactions which are regarded as one of the major contributors to symptoms of sick building syndrome (SBS).

The major sources of indoor VOC include pesticides, aerosol sprays, furnishings, high-emission building materials, dry knitted products, laser printers, and office equipment like copiers.

The USA Environmental Protection Agency (EPA) published a list of hazardous air pollutants and included a total of 187 VOCs. Ethylene, methylene chloride, toluene, benzene, tetrachloroethylene, xylene, formaldehyde, and 1,3-butadiene are the most common indoor VOCs that are major contributors to irritants, human carcinogens, and toxicants.

The total volume of indoor volatile organic compounds (VOCs) concentrations is expressed as “TVOCs” which, in other words, represents the total volume of available/present indoor VOC concentrations.

Acute exposure to indoor TVOCs can cause headaches, nausea, cancer, damage to the liver, central system and kidney, irritation to the throat, eye, and nose, loss of coordination, and respiratory diseases.

Note

It’s important to note that, in addition to the common air pollutants mentioned above, indoor temperature and relative humidity also affect indoor air quality (IAQ).

Fang et al. (1998) noted that when pollution levels are constant, IAQ would drop with any increase in temperature and relative humidity. Berglund and Cain (1989) concluded that the effect of temperature on IAQ was stronger than humidity.

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