Air Pollutants: What's Lurking In Your Indoor Air?

Particulate matter, often written as PM, is a mixture of chemical species composed of solids and aerosols. It is made up of tiny pieces of dust, dirt, soot, smoke, droplets of liquid, and other pollutants. PM can be released from a variety of sources, including cooking, combustion activities, household products, and hobbies. Outdoor PM can also enter indoor spaces through doors, windows, ventilation systems, and small cracks, causing indoor PM levels to exceed outdoor levels. Exposure to PM, especially PM2.5, has been linked to adverse health effects, including respiratory and cardiovascular diseases, cancers, and premature death. Therefore, it is important to identify and remove sources of indoor pollutants, improve ventilation, and upgrade filters to reduce particulate matter and improve indoor air quality.

Outdoor air pollution can enter buildings

One way outdoor air pollution enters buildings is through openings such as doors and windows. When these are left open, outdoor pollutants can easily infiltrate indoor spaces. Additionally, small cracks and crevices in building structures can also allow outdoor PM to enter. This includes “leakiness” in building foundations, where pollutants such as radon, volatile chemicals, and outdoor particles can infiltrate. Even when doors and windows are closed, outdoor air can still enter through natural ventilation, driven by factors like outdoor climate and weather conditions.

Another entry point for outdoor air pollution is through ventilation systems. Mechanical ventilation, which includes the use of fans or air handling systems, can inadvertently draw in outdoor pollutants. While ventilation is important for maintaining good indoor air quality, it can also introduce outdoor particles and gases. Ground-level ozone, for example, can enter buildings through ventilation processes and react with chemicals in building materials to create harmful byproducts. This can have serious health implications, triggering asthma symptoms and causing respiratory problems.

The design and construction of buildings also play a role in the infiltration of outdoor air pollution. The air exchange rate, or the rate at which outdoor air flows into a building, is influenced by the building's design, construction, and operating parameters. Infiltration occurs through openings, joints, and cracks in walls, floors, and ceilings, as well as around windows and doors. Weather conditions can further impact the air exchange rate, as occupants may be more likely to keep windows closed during cold or warm seasons, affecting natural ventilation.

Lastly, outdoor air pollution can be inadvertently carried into buildings by people. When entering a building, pollutants from the outdoors can be brought in on shoes and clothing. This includes soils, dusts, and other particles that adhere to these surfaces. Therefore, it is important to consider not only the building's structure and ventilation but also the role of occupants in potentially introducing outdoor air pollution into indoor spaces.

Cooking, combustion activities, and household products

Cooking is a significant source of indoor particulate matter (PM), which can have severe health effects, including cardiovascular disease and lung cancer. Frying with vegetable oils, for example, can produce a large number of particles and organic gases. Deep frying, stir-frying, stewing, and boiling are all cooking methods that release particulate matter, with deep frying producing the most. Gas stoves also generate higher concentrations of particles than electric rings and grills.

The use of household products, such as cleaning products, air fresheners, oil diffusers, and aerosol sprays, can also release particulate matter. These products emit gaseous pollutants that can react to form secondary particles.

Combustion activities, such as smoking tobacco, burning candles or incense, and using fireplaces, oil furnaces, or fuel-burning space heaters, release particulate matter. Fossil fuels, such as carbon, hydrogen, nitrogen, sulfur, and oxygen, produce pollutants during combustion, including carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen dioxide (NO2), and particulate matter.

Particulate matter (PM) is a general term for a mixture of solid particles and liquid droplets found in the air. These particles vary in size, with larger particles (PM10) being inhalable and capable of causing adverse health effects, and finer particles (PM2.5) being more harmful and capable of entering the lungs and causing lung disease. Exposure to PM2.5 has been linked to premature death, especially in individuals with chronic heart or lung diseases, and reduced lung function growth in children.

Smoking tobacco, burning candles, and incense

Smoking Tobacco

Tobacco smoke contains more than 5000 chemical substances, about 98 of which are proven to cause cancer, and many others that are yet to be identified. The particulate matter emitted when a cigarette is smoked is highly carcinogenic. Tobacco smoke affects multiple organ systems and leads to a large number of complications and diseases, such as cancer and asthma. Second-hand smoke exposure is extraordinarily high in enclosed spaces and poses a particular threat to the health of vulnerable individuals such as children and the elderly.

Burning Candles

Burning candles can release particulate matter into the air, which can be made up of tiny pieces of soot and smoke.

Burning Incense

Incense burning is a religious ritual commonly practised in many cultures and is popular among older adults. Incense is made up of a mixture of fragrance materials and herbal, wood, and adhesive powder. When incense is burnt, pollutants, including particulate matter, carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen dioxide, volatile organic compounds, aldehydes, and polycyclic aromatic hydrocarbons, are released into the air. The amount of PM generated by incense can be up to 4.5 times that of cigarettes. Incense smoke is associated with carcinogenicity, increased cardiovascular mortality, and respiratory conditions. Studies have also demonstrated the capacity of incense smoke to induce oxidative stress and inflammation, which may lead to significantly reduced vascular nitric oxide levels and increased levels of inflammatory mediators, promoting vascular dysfunction.

To reduce particulate matter and improve indoor air quality, it is important to identify and remove the source of the pollutant. Other methods include upgrading the furnace filter to a higher MERV rating, preferably 13 or higher, and ventilating the space by getting fresh air, filtering the air, and improving airflow.

Particles from biological sources, like pollen and mould

Particulate matter, or PM, is a mixture of many chemical species composed of solids and aerosols. It includes small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. These particles vary widely in size, shape, and chemical composition. They may contain inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the earth's crust.

PM10 and PM2.5 are two types of particulate matter classified based on size. Larger particulate matter is called PM10, and much finer particulate matter is called PM2.5. PM2.5 is the most harmful to human health. It is associated with the greatest proportion of adverse health effects related to air pollution, both in the United States and worldwide. Short-term exposures to PM10 have been linked to worsening respiratory diseases, while long-term exposure to PM2.5 has been associated with premature death, particularly in people with chronic heart or lung diseases.

Mould, or mold, is a fungus that reproduces through spores. These spores are typically 3 to 40 microns in size and are released into the air for reproduction. If they encounter a suitable environment, they develop into new mould. Mould spores can be found indoors, particularly in humid environments, and are known allergens that can trigger allergic reactions and respiratory problems.

To reduce exposure to these biological particles, it is recommended to keep windows closed during high pollen days and periods of high outdoor air pollution. Upgrading to higher-efficiency filters in heating, ventilation, and air conditioning (HVAC) systems can also help capture and reduce the presence of these particles in indoor air. Portable air cleaners and proper ventilation are additional measures to improve indoor air quality.

Health effects of particulate matter exposure

Particulate matter is a mix of tiny solid and liquid particles in the air. These particles can be released indoors through activities such as cooking, smoking, burning candles or incense, using fireplaces, and using household cleaning products. They can also enter indoor spaces from outdoors through doors, windows, and small cracks.

When particulate matter is inhaled, it can have significant health effects, especially when the particles are smaller in size. Fine particulate matter, known as PM2.5, is defined as particles with a diameter of 2.5 microns or less. These particles are so small that they can reach deep into the respiratory tract and lungs, causing irritation and damage to the alveoli walls. This can lead to short-term health effects such as eye, nose, throat, and lung irritation, coughing, sneezing, a runny nose, and shortness of breath.

Long-term exposure to PM2.5 has been linked to more severe health consequences. Studies have associated it with increased mortality, particularly in individuals with chronic heart or lung diseases. It has also been linked to reduced lung function growth in children and an increased risk of heart attacks. Additionally, long-term exposure to particulate matter has been associated with an increased risk of strokes, coronary heart disease, respiratory diseases, and lung cancer.

People with existing heart and breathing problems, pregnant women, children, and older adults are more vulnerable to the health effects of particulate matter exposure. It is essential to take measures to reduce indoor particulate matter, such as improving ventilation, using air filters, and avoiding indoor activities that generate high levels of particulate matter.

While indoor sources contribute significantly to particulate matter exposure, it is important to recognize that outdoor sources, such as vehicle exhaust, wildfires, and industrial emissions, also play a significant role in indoor particulate matter levels. Therefore, staying indoors may not always provide complete protection from particulate matter exposure.

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