Who's Air Quality Guidelines: Selected Indoor Pollutants

The World Health Organization (WHO) has outlined guidelines for indoor air quality to protect public health from the adverse effects of indoor exposure to air pollution. These guidelines are targeted at public health professionals and specialists involved in preventing health risks from environmental exposures. The WHO has identified three main groups of indoor pollutants that are particularly harmful to human health: biological indoor pollutants, such as dampness and mold; pollutant-specific originating from chemical pollution, such as benzene, formaldehyde, and radon; and pollutants from the combustion of indoor fuels, including carbon monoxide. These pollutants can have hazardous effects on human health, especially in large quantities or after prolonged exposure. The guidelines provide recommendations for reducing exposure to these pollutants, promoting better living and working environments, and ensuring access to clean air as a fundamental human right.

Health risks of indoor pollutants

The World Health Organization (WHO) has outlined several potentially harmful organic and inorganic compounds that can have adverse health effects in large quantities or after prolonged exposure. The organization has identified three main groups of indoor pollutants that are particularly damaging to environmental health: biological indoor pollutants, pollutant-specific originating from chemical pollution, and pollutants from the combustion of indoor fuels.

Biological indoor pollutants include bacteria, molds, and fungi that thrive in a moist atmosphere. Indoor chemical pollutants, on the other hand, have more diverse origins and are present in our homes as volatile organic compounds (VOCs) emitted from various products. Examples of such chemical pollutants include benzene, carbon monoxide, formaldehyde, naphthalene, nitrogen dioxide, polycyclic aromatic hydrocarbons (especially benzo[a]pyrene), radon, trichloroethylene, and tetrachloroethylene. These pollutants are known for their hazardousness to health and are often found indoors in concentrations of concern. For instance, trichloroethylene (TCE) has been linked to an increased risk of testicular tumors, with the concentrations of airborne TCE associated with an excess lifetime cancer risk of 1/10,000, 1/100,000, and 1/1,000,000 being 230, 23, and 2.3 μg/m3, respectively.

Additionally, indoor air quality can be influenced by outdoor pollutants, such as sulfur dioxide from vehicle combustion in urban areas. The WHO has also identified particulate matter, including PM2.5 and PM10, as a dangerous group of pollutants that can negatively affect indoor air quality.

To ensure good indoor air quality (IAQ) and maintain human health and well-being, it is crucial to address the sources of these pollutants and implement measures to reduce their presence. This may include improving ventilation, using air conditioning, and installing indoor air quality monitors to detect harmful substances and potential health risks.

Sources and pathways of exposure

The World Health Organization (WHO) has outlined several potentially harmful organic and inorganic substances that can negatively impact health in the Indoor Air Quality (IAQ) standards and guidelines. These substances are present in homes, commercial buildings, and other workplaces and can cause adverse health effects in large quantities or after prolonged exposure.

WHO has identified three main groups of indoor pollutants that are particularly detrimental to environmental health: biological indoor pollutants, such as dampness and mould, which can arise from hundreds of different types of bacteria, moulds, and fungi when there is sufficient moisture in the atmosphere; pollutant-specific chemical pollutants, including Volatile Organic Compounds (VOCs) emitted from purchased products; and pollutants from the combustion of indoor fuels.

The eight specific chemical pollutants highlighted by WHO include benzene, carbon monoxide, formaldehyde, naphthalene, nitrogen dioxide, polycyclic aromatic hydrocarbons (especially benzo[a]pyrene), radon, trichloroethylene, and tetrachloroethylene. These substances are known for their hazardousness to health and are often found indoors in concentrations of concern. For example, carbon monoxide is a common indoor air pollutant that can originate from various sources, such as faulty heating systems, poorly ventilated fireplaces, or the use of certain fuels for cooking or heating.

Indoor air quality can also be influenced by outdoor pollutants, such as sulphur dioxide from vehicle combustion in urban areas, and indoor levels of particulate matter like PM10 and PM2.5, which are usually higher than outdoor levels due to indoor sources. Additionally, ventilation, indoor temperature, and relative humidity play a role in maintaining good indoor air quality and thermal comfort while preventing moisture-related issues such as mould growth.

To ensure good indoor air quality and minimise exposure to harmful pollutants, it is recommended to install an indoor air quality monitor, which can alert individuals when their health is at risk. Additionally, the WHO guidelines provide a uniform basis for protecting public health and reducing exposure to known or potentially hazardous pollutants, targeting public health professionals and specialists involved in building design and the use of indoor materials and products.

Health effects of pollutants

The World Health Organization (WHO) has identified three main groups of indoor pollutants that are particularly harmful to human health: biological indoor pollutants, pollutant-specific chemical pollutants, and pollutants from the combustion of indoor fuels.

Biological indoor pollutants arise from different types of bacteria, moulds, and fungi when there is sufficient moisture in the atmosphere. Indoor mould growth can also be a consequence of poor ventilation, which is linked to higher energy consumption and climate change considerations. Dampness and mould were the focus of WHO guidelines published in 2009.

Indoor chemical pollutants have more diverse origins and are present in our homes as volatile organic compounds (VOCs) emitted from products we purchase. The WHO has identified eight specific chemical pollutants that negatively impact indoor air quality, including benzene, formaldehyde, and nitrogen dioxide. These pollutants are known for their hazardousness to health and are often found indoors in concentrations of concern. For example, nitrogen dioxide and carbon dioxide contribute to health problems, and carbon monoxide can be hazardous in large quantities or after long periods of exposure.

Pollutants from the combustion of indoor fuels, such as polycyclic aromatic hydrocarbons, can also be harmful. Additionally, indoor air quality can be affected by outside pollutants, such as sulfur dioxide from road vehicle combustion in urban areas, and particulate matter (PM) from both indoor and outdoor sources. The WHO has set guideline values for PM2.5, a particularly dangerous group of pollutants.

The health effects of these pollutants can range from respiratory issues to more severe consequences, such as increased cancer risk. For example, the WHO has proposed a unit risk estimate of 4.3 × 10−7 (μg/m3)−1 for indoor air quality, based on increased testicular tumours in rats. The guideline values for pollutants are based on comprehensive scientific evidence and are intended to provide a uniform basis for protecting public health from adverse effects.

Air quality monitoring

The World Health Organization (WHO) has outlined several potentially harmful organic and non-organic substances that can negatively impact health in indoor spaces. These substances can be found in homes, commercial buildings, and other workplaces. WHO's indoor air quality (IAQ) guidelines are targeted at public health professionals and specialists involved in preventing health risks from environmental exposures.

The WHO has identified three main groups of indoor pollutants that are particularly damaging to environmental health: biological indoor pollutants, such as dampness and mould; chemical pollutants, including volatile organic compounds (VOCs); and pollutants from the combustion of indoor fuels, such as carbon monoxide.

To ensure good IAQ, buildings often rely on heating, ventilation, and air conditioning (HVAC) systems, which can lead to higher energy consumption. Therefore, a balance between energy use, optimum IAQ, and thermal comfort is essential. The WHO guidelines provide a uniform basis for protecting public health from the adverse effects of indoor air pollution and recommend eliminating or minimising exposure to hazardous pollutants.

Additionally, understanding air pollution particle size and the characteristics of semi-volatile organic compounds (SVOCs) can help individuals improve their environmental health by knowing how to avoid or reduce exposure to these pollutants. The WHO guidelines provide valuable information on specific pollutants, including their sources, exposure pathways, health effects, and risk evaluations, empowering individuals to make informed decisions to protect their health and well-being.

Energy efficiency and IAQ

Energy efficiency and indoor air quality (IAQ) are often considered unrelated, with energy efficiency being an environmental concern and IAQ a matter of occupational health. However, they are closely intertwined, and a balance between the two is essential for the health and productivity of building occupants.

The relationship between energy efficiency and IAQ is complex and multifaceted. While energy efficiency measures can positively impact IAQ, there is also a risk that they may negatively affect it. For example, a 2022 Swedish study found that energy-saving measures in "airtight buildings" without mechanical ventilation can impair IAQ and increase hazardous chemicals and radon levels.

On the other hand, smart buildings with advanced Internet of Things (IoT) solutions can improve both energy efficiency and IAQ. IoT enables a network of interconnected HVAC-related technologies, including sensors and detectors, which, combined with artificial intelligence (AI) and machine learning (ML), can automatically adjust the HVAC system to optimise ventilation and energy efficiency.

To ensure that energy efficiency measures do not compromise IAQ, it is crucial to address IAQ at the beginning of retrofit and weatherization projects. This includes proper inspection, diagnostic testing, and the removal or isolation of indoor air pollutant sources. By integrating IAQ protections into energy efficiency projects, greater energy savings can be achieved, and public health can be protected.

Additionally, smart HVAC solutions can play a pivotal role in improving both IAQ and energy efficiency. During the COVID-19 pandemic, the focus on infection mitigation strategies highlighted the importance of increased ventilation, filter efficiency, and ultraviolet energy. These measures not only improve IAQ but also reduce HVAC energy consumption, demonstrating that energy efficiency and IAQ can coexist and mutually benefit health and the environment.

Frequently asked questions