Air Pollution Index: How It's Measured

Air pollution is a critical issue that threatens human health and contributes to climate change, biodiversity loss, and pollution. The Air Quality Index (AQI) is a widely used tool for measuring air pollution and its associated health risks. The AQI is designed to provide information about outdoor air quality and is calculated based on the concentration of various air pollutants, including particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide. These pollutants are monitored by stations worldwide, and the AQI value represents the level of air pollution, with higher values indicating greater pollution and health concerns. Different countries and organizations use variations of the AQI, such as the Air Quality Health Index (AQHI) and the Pollutant Standards Index (PSI), and establish categories to communicate the health risks associated with different levels of air pollution.

The Air Quality Index (AQI) is a scale from 0 to 500, with higher values indicating greater air pollution and health risks

The Air Quality Index (AQI) is a critical tool for communicating about outdoor air quality and associated health risks. It is designed as a yardstick that runs from 0 to 500, with higher values indicating increased air pollution and heightened health concerns. The AQI is colour-coded into six categories, each representing a range of index values and corresponding health risks.

An AQI value of 50 or below signifies good air quality, indicating little to no health risk. People can confidently engage in their usual outdoor activities when the AQI falls within this range. However, as the AQI climbs above 50, the air quality deteriorates, posing varying levels of health risks. Values above 100 indicate unhealthy air quality, initially affecting sensitive groups of people and then progressively impacting everyone as the AQI continues to rise.

The AQI is calculated based on the measurement of several critical air pollutants, including particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) emissions. PM2.5, which refers to particulate matter with a diameter of 2.5 micrometres or less, is of particular concern due to its ability to penetrate deep into the bloodstream when inhaled. It is associated with serious health issues such as stroke, heart disease, lung disease, and cancer.

The AQI values are determined by measuring ambient concentrations of these pollutants, and corresponding health impacts are assessed with input from medical experts. While the AQI typically ranges from 0 to 500, it is important to note that air quality can be indexed beyond 500 when extremely high levels of hazardous air pollution are present.

Various tools and technologies, such as laser particle sensors and air quality monitors, are employed to measure these pollutants and calculate the AQI in real time. These measurements are vital for governments and organisations to address the air pollution crisis, strengthen regulations, and protect the health and well-being of people worldwide.

Six pollutants are measured in the AQI formula, with an AQI number assigned based on the pollutant with the highest value at the time of measurement

The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. It is calculated from the concentrations of various pollutants, including ozone, nitrogen dioxide, sulfur dioxide, PM2.5, and PM10. PM2.5 refers to particulate matter measuring 2.5 microns or less in diameter, which can be carried into the lungs and cause serious health issues. The AQI scale typically runs from 0 to 500, with higher values indicating greater levels of air pollution and associated health risks.

There are six pollutants measured in the AQI formula, and an AQI number is assigned based on the pollutant with the highest value at the time of measurement. These six pollutants are monitored by the United States Environmental Protection Agency (EPA) and include ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The sixth pollutant, lead (Pb), is included in the proposed National Air Quality Index (NAQI) categories, which also consider ammonia (NH3).

The AQI includes six color-coded categories, each corresponding to a range of index values and associated health risks. For instance, an AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality. When AQI values exceed 100, the air quality is considered unhealthy, initially for sensitive groups, and then for everyone as values increase further.

The AQI is a valuable tool for monitoring air quality and protecting public health. It helps individuals understand the current air quality and take appropriate actions to protect themselves, especially for sensitive groups such as the elderly, children, and those with respiratory or cardiovascular issues.

PM2.5 is considered the most hazardous air pollutant, impacting human health and is often used as a legal metric

The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. It is measured on a scale that typically runs from 0 to 500, with higher values indicating greater levels of air pollution and associated health concerns. While the AQI considers various pollutants, PM2.5, or fine inhalable particles with diameters of 2.5 micrometers or less, is recognised as one of the most hazardous air pollutants.

PM2.5 is a component of particulate matter (PM), which encompasses a mixture of solid particles and liquid droplets in the air. These fine particles result from emissions, primarily the combustion of gasoline, oil, diesel fuel, or wood, and secondary chemical reactions in the atmosphere. PM2.5 is of particular concern due to its ability to penetrate deep into the lungs and potentially enter the bloodstream.

The adverse health impacts of PM2.5 exposure are well-documented. Short-term exposures of up to 24 hours have been linked to increased hospital admissions for heart and lung issues, acute and chronic bronchitis, asthma attacks, emergency room visits, and respiratory symptoms. Long-term exposure to PM2.5 has been associated with premature death, especially in individuals with chronic heart or lung diseases, and impaired lung development in children.

The World Health Organization's Global Burden of Disease Project identifies PM2.5 as the air pollutant with the greatest proportion of adverse health effects, both in the United States and worldwide. This fine particulate matter is also a significant contributor to reduced visibility, causing haze in many areas, including national parks and wilderness regions.

Due to its detrimental effects on human health, PM2.5 is often used as a legal metric for air quality standards. Regulatory bodies, such as the Environmental Protection Agency (EPA) in the United States, establish standards and regulations to reduce PM2.5 emissions and protect public health. The measurement of PM2.5 levels is crucial for assessing air quality, guiding policy decisions, and mitigating the health risks associated with this hazardous pollutant.

Countries like Mexico, Singapore, and South Korea use different indices to report air quality

The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For instance, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. The AQI is divided into six colour-coded categories, each corresponding to a range of index values.

Singapore's National Environment Agency (NEA) uses a variant of the Pollution Standards Index (PSI), which was devised by the United States Environmental Protection Agency. The PSI gives a score for air pollution based on the density of six pollutants: PM2.5, PM10, carbon monoxide, ozone (O3), nitrogen dioxide (NO2), and sulphur dioxide (SO2). In 2019, Singapore's average PM2.5 concentration was 19 µg/m³, which exceeded the World Health Organisation's recommended target of 10 µg/m³.

South Korea also uses the Air Quality Index (AQI). At the end of 2020, the city of Jeungpyeong had a US AQI reading of 97, which was classified as "Moderate." The main source of air pollution in South Korea is fossil fuel combustion, with China's burning of coal contributing to at least 50% of the PM2.5 particulates in the country's air. Additionally, dust blown in from China's western deserts and Inner Mongolia impacts South Korea's air quality.

Real-time air pollution exposure calculators and maps provide up-to-date information on air quality for various locations worldwide

The Air Quality Index (AQI) is a yardstick that runs from 0 to 500, with higher values indicating greater levels of air pollution and health concerns. Various countries and organisations have adopted their own AQIs, with the specific pollutants measured and the scale used varying between them. For example, the US AQI is divided into six colour-coded categories, with an AQI value of 50 or below representing good air quality, and a value over 300 indicating hazardous conditions.

In 2013, Hong Kong introduced the Air Quality Health Index (AQHI), which considers four air pollutants: ozone, nitrogen dioxide, sulfur dioxide, and particulate matter. China's Ministry of Environmental Protection (MEP) monitors the daily pollution levels in 163 of its major cities, measuring the levels of six atmospheric pollutants. Singapore, on the other hand, uses the Pollutant Standards Index (PSI), while South Korea uses the Comprehensive Air-quality Index (CAI).

To address the issue of varying AQIs, a common definition of the AQI has been established, allowing government agencies worldwide to submit real-time air monitoring data. Websites like WAQI.info provide real-time air quality data for over 10,000 stations in more than 80 countries. The GAIA air quality monitor used by WAQI.info measures PM2.5 and PM10 particle pollution, considered one of the most harmful types of air pollution. Users can access historical air pollution data for specific cities by clicking on flags displayed on the map.

In addition to maps, real-time air pollution exposure calculators have been developed to enhance air quality monitoring. On 7 September 2021, the United Nations Environment Programme (UNEP), in collaboration with Swiss air quality technology company IQAir, launched the first real-time air pollution exposure calculator. This calculator aims to support global efforts to improve air quality and, in turn, enhance health and the environment.

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