World Health Organization Guidelines

This page summarizes the World Health Organization's (WHO) position and guidelines concerning indoor air quality (IAQ), drawing from various WHO publications issued between 1987 and 2023.

The World Health Organization (WHO) plays a crucial role in establishing global air quality guidelines to protect public health from the adverse effects of air pollution. Recognizing that air pollution is the single biggest environmental threat to human health, the WHO has been periodically issuing evidence-based recommendations since 1987.

WHO's Stance on Indoor Air Quality

Clean air is recognized by WHO as a basic requirement for human health and wellbeing. Since people spend a significant portion of their time indoors, indoor air quality is a critical determinant of health. WHO emphasizes that indoor air pollution is a major cause of morbidity and mortality worldwide. Problems like dampness, mould, and emissions from building materials, consumer products, and combustion activities (heating, cooking) contribute substantially to this burden.

WHO's primary aim in issuing air quality guidelines is to provide a basis for protecting public health from the adverse effects of air pollution and for eliminating or reducing hazardous air contaminants to a minimum. These guidelines are intended to inform risk management decisions, particularly in setting standards, but are not standards in themselves. National authorities must consider these guidelines within the context of local environmental, social, and economic conditions. WHO stresses that efforts should always be made to keep air pollution levels as low as practically achievable.

The WHO guidelines cover various indoor pollutants such as particulate matter, volatile organic compounds (VOCs), mold, and radon, offering comprehensive strategies to mitigate these risks.

Evolution of WHO Air Quality Guidelines

WHO's concern with air pollution dates back decades. Key milestones relevant to IAQ include:

1987: Air Quality Guidelines for Europe

This first edition assessed 28 chemical contaminants, recognizing the importance of indoor air quality and including pollutants often found indoors. It established different approaches for non-carcinogens (threshold-based guideline values) and carcinogens (risk estimation).

2000: Air Quality Guidelines for Europe (Second Edition)

This edition updated the previous guidelines, reflecting new scientific data and risk assessment methodologies. It expanded the list of pollutants and included a dedicated section on indoor air pollutants like environmental tobacco smoke (ETS), man-made vitreous fibres, and radon. The applicability of guidelines to both indoor and outdoor air (except where specified) was maintained.

2005: Global Update (AQG 2005)

Focused on particulate matter (PM), ozone (O3​), nitrogen dioxide (NO2​), and sulfur dioxide (SO2​), providing updated guideline levels applicable globally and in all environments, including indoors. It introduced the concept of interim targets for PM, ozone, and SO2​ as steps for highly polluted areas.

2009: WHO Guidelines for Indoor Air Quality: Dampness and Mould

Addressed biological contaminants, concluding that sufficient evidence links dampness and mould to respiratory symptoms, allergies, and asthma exacerbation. Due to the complexity of microbial exposures, it recommended preventing/minimizing dampness and microbial growth rather than setting numerical limits for biological agents.

2010: WHO Guidelines for Indoor Air Quality: Selected Pollutants

Provided specific guideline values or risk estimates for nine key indoor pollutants: benzene, carbon monoxide (CO), formaldehyde, naphthalene, nitrogen dioxide (NO2​), polycyclic aromatic hydrocarbons (PAHs), radon, trichloroethylene (TCE), and tetrachloroethylene.

2014: WHO Guidelines for Indoor Air Quality: Household Fuel Combustion

Focused specifically on the significant health risks from burning solid fuels and kerosene in households, providing emission rate targets (ERTs) for stoves and fuels needed to meet WHO AQG levels for PM2.5​ and CO. It strongly discouraged the household use of unprocessed coal and kerosene.

2021: WHO Global Air Quality Guidelines

Provided updated, lower AQG levels for PM2.5​, PM10​, O3​, NO2​, SO2​, and CO, based on a substantial increase in evidence showing adverse health effects at lower concentrations than previously understood. It retained the concept of interim targets and added good practice statements for specific PM types like black carbon/elemental carbon (BC/EC), ultrafine particles (UFP), and sand/dust storm particles.

Policy and Implementation

WHO guidelines provide a crucial scientific foundation for developing national air quality standards, although they are not legally binding in themselves. The transition from these international guidelines to enforceable national standards necessitates careful consideration of local contexts, including technical feasibility, socioeconomic factors, and political decisions regarding acceptable risk levels and the protection of vulnerable populations. Serving as critical references, the guidelines, including any interim targets, allow countries to benchmark progress, evaluate the effectiveness of air quality management strategies, shape global health policy, advocate for cleaner indoor environments, and ultimately drive legislative changes and policy measures to mitigate air pollution and improve public health.

Effective air quality management requires:

• Monitoring: Assessing current air quality levels.
• Source control: Reducing emissions from major sources like traffic, industry, household fuel combustion, and building materials. For indoor air, this includes using low-emission materials, proper venting of combustion appliances, and controlling activities like smoking.
• Ventilation: Ensuring adequate exchange between indoor and outdoor air to dilute indoor pollutants and control humidity, while considering the quality of outdoor air and energy efficiency.
• Policy integration: Addressing air quality across sectors (health, energy, environment, transport, housing) and involving multiple stakeholders.
• Public awareness and communication: Informing the public about risks and protective measures.