Indoor Air Pollution: What's Making Us Sick?

Indoor air pollution is a serious threat to human health, causing millions of deaths each year. It is caused by a variety of factors, including outdoor air pollution, human activities within buildings, such as smoking, burning solid fuels, and cooking, as well as inadequate ventilation. In developing countries, the indoor burning of solid fuels like wood, coal, and dung releases harmful pollutants, including fine particulate matter and carbon monoxide, impacting air quality and human health. Indoor air pollution can cause a range of health issues, including respiratory diseases, heart disease, cognitive deficits, and cancer. It is important to identify the sources and concentrations of indoor air pollutants and devise strategies to improve indoor air quality.

Inadequate ventilation

Ventilation is the process of exchanging indoor and outdoor air. Inadequate ventilation occurs when there is insufficient outdoor air entering indoor spaces, leading to a concentration of pollutants. This can be due to the design and construction of buildings, which may be intentionally built to minimise the infiltration of outdoor air. Infiltration is when outdoor air enters through openings, joints, and cracks in walls, floors, and ceilings, as well as around windows and doors. Natural ventilation, which occurs through open windows and doors, can also be limited, especially in energy-efficient homes that are relatively airtight. As a result, indoor air can become stagnant, and pollutant levels can rise rapidly.

Mechanical ventilation devices, such as outdoor-vented fans, can help remove indoor air pollutants from specific rooms, such as bathrooms and kitchens. However, these may not be sufficient in buildings with poor overall ventilation. Additionally, mechanical ventilation may not always be an option, especially in areas with limited access to electricity or financial resources.

The impact of inadequate ventilation is more severe in developing countries, where solid fuels like wood, coal, and dung are burned indoors for cooking and heating. This practice releases harmful pollutants, including fine particulate matter and carbon monoxide. Women and children, who typically spend more time near the domestic hearth, are at a higher risk of exposure to these pollutants.

Furthermore, indoor air pollution due to inadequate ventilation can be exacerbated by human activities such as smoking, burning solid fuels, cooking with inefficient stoves, and using chemical cleaning products. These activities release toxins and fine particles that can penetrate deep into the lungs and enter the bloodstream. Prolonged exposure to these pollutants can have detrimental effects on health, especially for vulnerable populations such as children, older adults, and individuals with pre-existing health conditions.

Outdoor air pollution entering indoors

Outdoor air pollution can enter indoor spaces through a variety of pathways, leading to a buildup of pollutants that can severely impact human health. This process, known as infiltration, occurs when outdoor air flows into buildings through openings, joints, and cracks in walls, floors, and ceilings, as well as around windows and doors. Infiltration is driven by air temperature differences and wind, with indoor temperatures and higher humidity levels contributing to increased infiltration.

In addition to infiltration, natural ventilation through open windows and doors also allows outdoor air pollution to enter indoor spaces. Mechanical ventilation devices, such as outdoor-vented fans and air handling systems, play a role in exchanging indoor and outdoor air. However, inadequate ventilation can be detrimental as it may not bring in enough outdoor air to dilute indoor emissions or carry indoor pollutants out effectively.

Outdoor ground-level ozone and other gases, such as nitric oxide, can enter indoor spaces through ventilation processes. These pollutants can further react with chemicals in building materials, creating harmful byproducts. Research has linked indoor ozone from outdoor sources to adverse health effects, including asthma symptoms, respiratory problems, and impaired lung function.

The use of polluting fuels and technologies, such as solid fuels for cooking and heating, contributes to both indoor and outdoor air pollution. Inefficient combustion processes release toxic chemicals like formaldehyde and lead, which accumulate indoors, especially in poorly ventilated dwellings. Additionally, residential cooking with natural gas produces NOx and other air pollutants, leading to higher indoor levels of NO2 compared to outdoor levels.

The impact of outdoor air pollution entering indoor spaces is significant, as individuals spend a large proportion of their time indoors. The interaction between indoor and outdoor pollutants is influenced by human behavior and the surrounding environment. Therefore, addressing both indoor and outdoor sources of pollution is crucial to minimizing their impact on human health and the environment.

Polluting fuels and technologies

The World Health Organization (WHO) has identified indoor air pollution as the world's largest single environmental health risk. This is largely due to the burning of polluting fuels such as wood, animal dung, charcoal, agricultural waste, and kerosene in open fires or inefficient stoves in and around the household.

In developing countries, solid fuels such as wood, coal, and dung are often burned indoors for cooking and heating. This releases harmful pollutants, including fine particulate matter and carbon monoxide, which can cause a variety of health problems, including respiratory infections, asthma, heart disease, and cancer. The use of polluting fuels and technologies also requires significant time for cooking on inefficient devices and gathering and preparing fuel.

Worldwide, around 2.1 billion people still cook using solid fuels and kerosene in open fires and inefficient stoves. Most of these people are poor and live in low- and middle-income countries, where access to clean fuels and technologies is limited. Income is a strong determinant of energy access and types of fuel sources. As incomes rise, households tend to transition from traditional solid fuels to cleaner non-solid fuels such as ethanol and natural gas.

The WHO has issued guidelines for indoor air quality and household fuel combustion, recommending against the use of solid fuels, unprocessed coal, and kerosene for indoor cooking. Clean fuels, as defined by the WHO, include solar, electricity, biogas, liquefied petroleum gas (LPG), natural gas, and alcohol fuels. These fuels and technologies have been shown to reduce household air pollution and protect health.

In addition to the transition to cleaner fuels, advances in technology also play a crucial role in combating indoor air pollution. Sensors and intelligent home systems can now detect and monitor indoor air quality, triggering ventilation systems to maintain healthy air conditions. Nanotechnology is also being developed to remove indoor contaminants on a molecular level, offering even more precise methods for tackling indoor air pollution.

Tobacco smoke

ETS has been categorized as a human carcinogenic agent, causing lung cancer, cardiovascular disease (e.g. heart disease and stroke), and respiratory diseases. It can also trigger more frequent and severe asthma attacks and cause reproductive issues, such as low birth weight. There is no known safe level of exposure to ETS, and even exposure to secondhand smoke can cause illness and premature death.

The impact of tobacco smoke on indoor air quality is significant. The concentration of pollutants from tobacco smoke can be much higher indoors, as new engine models and lead-free fuels have reduced particulate matter emissions from car exhausts. A controlled experiment found that the air pollution emitted by cigarettes was 10 times greater than diesel car exhaust, with environmental tobacco smoke particulate matter reaching levels 15 times higher than those measured outdoors.

Indoor spaces where smoking occurs, such as homes or cafes, can experience a buildup of ETS, leading to poorer indoor air quality. This is especially true if air filters are not regularly cleaned or replaced. While ventilation, filtration, and air cleaning techniques can reduce secondhand smoke indoors, they do not eliminate it.

The best way to improve indoor air quality in spaces where smoking has occurred is to avoid smoking indoors altogether. Stopping smoking indoors can prevent further buildup of ETS and allow the space to air out over time.

Radon

The World Health Organization (WHO) has developed guidelines for indoor air quality, including recommendations for radon levels. Radon concentration indoors can be measured with a small passive detector or a do-it-yourself test kit. If elevated levels of radon are detected, a mitigation system can be installed to collect and vent the gas outdoors, reducing indoor radon levels.

The use of energy-efficient homes can also contribute to indoor radon levels. These homes tend to be relatively airtight, causing the air inside to become stagnant and pollutant levels to rise rapidly. Inadequate ventilation can further increase indoor radon levels by not bringing in enough outdoor air to dilute indoor sources of radon and by not carrying indoor radon outdoors.

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