Helena Joyce
Air pollution is a critical global issue, threatening human health and contributing to climate change, biodiversity loss, and waste. With 99% of the global population breathing unclean air, according to the World Health Organization, addressing air pollution is a priority. Measuring pollution levels is the first step in combating this crisis. Various methods and tools are employed to quantify air pollution, such as the Air Quality Index (AQI), which serves as a yardstick, with higher values indicating increased pollution and health risks. Satellites, ground instruments, and air quality monitors provide data on particle pollution, ozone levels, and other pollutants. The AQI, with its color-coded categories, helps warn the public about dangerous air pollution levels, allowing people to take protective measures. Additionally, organizations like UNEP promote international cooperation and provide technical support to enhance air quality monitoring and management worldwide.
| Characteristics | Values |
|---|---|
| Air Quality Index (AQI) | A numerical system that measures the level of air pollution in a given region. The higher the number, the worse the air quality. |
| AQI Range | 0 to 500. |
| AQI Values | 50 or below: good air quality; over 300: hazardous air quality. |
| AQI Categories | Green and Yellow: safe for everyone; Orange: unhealthy for sensitive groups; Red and Purple: unhealthy for everyone; Maroon: emergency conditions. |
| Pollutants Tracked | Ozone (smog), particle pollution, and four other major air pollutants. |
| Data Sources | Governmental, crowd-sourced, and satellite-derived air quality monitors. |
| Databases | UNEP and IQAir's real-time air pollution exposure calculator, which uses AI to calculate population exposure. |
| Monitoring Initiatives | UNEP's deployment of low-cost sensors in Kenya, Costa Rica, Ethiopia, and Uganda. |
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What You'll Learn
Air Quality Index (AQI)
The Air Quality Index (AQI) is a tool developed by the US Environmental Protection Agency (EPA) to communicate information about outdoor air quality and health. It is a numerical system that measures the level of air pollution in a given region, with a higher number indicating worse air quality and a greater health concern. The AQI runs from 0 to 500, with an AQI value of 50 or below representing good air quality, and an AQI value over 300 representing hazardous air quality. Values at or below 100 are generally considered satisfactory, while values above 100 indicate unhealthy air quality for certain sensitive groups of people, becoming unhealthy for everyone as the values increase.
The AQI is established for five major air pollutants regulated by the Clean Air Act: ground-level ozone, airborne particles, carbon monoxide, PM2.5, and nitrogen dioxide. These pollutants are measured through ambient air quality monitoring and stationary source emissions monitoring. Ambient air quality monitoring compares current atmospheric conditions with historical data and clean air standards, while stationary source emissions monitoring measures emissions data at individual stationary emissions sources.
The AQI values are colour-coded, with each category corresponding to a range of index values. For instance, an AQI value of 50 may be colour-coded as green, indicating good air quality, while a value of 300 may be colour-coded as purple or maroon, indicating hazardous air quality.
Air quality databanks process readings from governmental, crowd-sourced, and satellite-derived air quality monitors to produce an aggregated AQI reading. These databases may weigh data differently based on reliability and the type of pollution measured. For example, the UNEP and IQAir developed a real-time air pollution exposure calculator that combines global readings from validated air quality monitors in 6,475 locations across 117 countries, prioritising PM2.5 readings.
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Monitoring stations
One of the critical measurements that monitoring stations focus on is PM2.5, which refers to particulate matter with a diameter of 2.5 micrometres or less. These fine particles can be inhaled and absorbed into the bloodstream, posing significant health risks, including stroke, heart disease, lung disease, and cancer. As per the World Health Organization, air pollution, largely driven by PM2.5, causes approximately 7 million premature deaths annually, highlighting the importance of closely monitoring and regulating these harmful pollutants.
There are two primary types of monitoring approaches: ambient air quality monitoring and stationary source emissions monitoring. Ambient air quality monitoring involves collecting and analysing samples of ambient air pollutants. This type of monitoring helps evaluate the current state of the atmosphere by comparing it to historical data and clean air standards. It provides a broad overview of the air quality in a specific area. On the other hand, stationary source emissions monitoring focuses on individual stationary sources of emissions, such as facilities, manufacturing plants, and processes. This type of monitoring collects data on emission levels and performance, allowing operators to ensure compliance with regulatory requirements and take corrective actions if necessary.
In Europe, monitoring stations are classified based on criteria for macro- and microscale siting, with specific guidelines for data reporting. For most pollutants, stations are expected to report more than 75% of valid data in a year, with a minimum data capture of 90% set for compliance purposes. These stations play a crucial role in providing the data necessary for governments and organisations to address the air pollution crisis and implement effective strategies to improve air quality.
The data collected by monitoring stations is aggregated and processed to generate air quality indices, such as the Air Quality Index (AQI) used by the U.S. Environmental Protection Agency. The AQI provides a numerical representation of air pollution levels, with higher values indicating worse air quality and potential health concerns. These indices are valuable tools for communicating air quality information to the public and guiding decisions to protect public health and the environment.
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Satellite monitoring
Satellite remote sensing offers several advantages over traditional ground-based monitoring. It provides a more comprehensive view of air pollution by covering vast areas that ground monitors cannot access. Satellites can observe and track climate and air pollution indicators, such as wildfires, dust storms, pollen counts, urban green space, and nitrogen dioxide concentrations. Additionally, satellite data can indicate criteria air pollutants like PM2.5 and NO2, as well as greenhouse gases, including CH4 and CO2.
One key technique used by satellites is the measurement of aerosol optical depth or aerosol optical thickness. Satellites determine the concentration of particles (aerosols) in the atmosphere by assessing how much light reaches the Earth's surface and how much is reflected off the aerosols. This measurement is comparable to ground-based measurements using a sun photometer. Tools like NASA's NEO and Giovanni enable users to access and analyze satellite data, such as correlating aerosol optical depth with ground measurements to identify the height of aerosols in the atmosphere.
While satellite remote sensing has revolutionized air pollution tracking, it also has limitations. Ground measurements are still necessary to "ground truth" or calibrate satellite-based estimates, especially for certain exposures like pollen. Furthermore, there are challenges in deriving surface conditions from atmospheric column measurements due to algorithmic limitations. However, ongoing advancements are steadily addressing these uncertainties, making satellite monitoring an increasingly valuable tool for addressing the global air pollution crisis.
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Air pollution calculators
Air pollution is a pressing issue that significantly affects climate change, ecosystems, animals, plants, and human health. To address this, various tools and technologies are used to measure and control air pollution levels. Air pollution calculators are one such tool that helps quantify air pollution and guide the development of effective clean air strategies. These calculators are often specific to particular pollutants and can vary in terms of precision, cost, and size.
One example of an air pollution calculator is the Air Quality Index (AQI) Basics calculator. The AQI is a numerical system developed by the U.S. Environmental Protection Agency (EPA) to communicate about outdoor air quality and health. It consists of six colour-coded categories, each representing a range of index values. An AQI value of 50 or below indicates good air quality, while a value over 300 represents hazardous air quality. The EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act, with each pollutant having a national air quality standard to protect public health.
The AQI calculator allows users to select a pollutant and enter its AQI value. The calculator then provides the concentration level and AQI category, along with information for sensitive groups and health impact statements. For instance, an AQI value of 100 generally corresponds to an ambient air concentration that equals the level of the short-term national ambient air quality standard for protecting public health. Values above 100 indicate unhealthy air quality for certain sensitive groups, progressing to unhealthy levels for everyone as values increase.
In addition to the AQI calculator, there are other specialised calculators available for specific industries and pollutants. For instance, the Minnesota Pollution Control Agency provides air emissions calculators for various sectors, including abrasive blasting, aggregate and mineral processing, boilers and furnaces, coating and auto body facilities, storage tanks, vapor recovery, and woodworking facilities. These calculators help determine potential and actual emissions, maintain compliance records, and assess eligibility for specific permits or exemptions.
Personal pollution sensors, such as Flow by Plume Labs, offer individuals a way to measure indoor air quality and track their exposure to pollutants over time. These sensors use techniques like laser diffraction and conductivity variation measurements to detect fine particles, NO2, and VOCs. By providing personal pollution data, these sensors help individuals protect themselves and their loved ones from harmful air pollutants.
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PM2.5 readings
PM2.5 refers to particulate matter with a diameter of 2.5 micrometres or less. These particles are so small that they can only be seen with a microscope. They are lighter than heavier particles, which means they tend to stay in the air for longer, increasing the chances of humans and animals inhaling them.
PM2.5 particles are a common air pollutant that can impact human health and the environment. They are small enough to be breathed in deeply into the lungs and can even enter the bloodstream. This means that they can have serious health impacts, including adverse effects on the heart and lungs. Studies have found a close link between exposure to PM2.5 and premature death from heart and lung disease. They are also known to trigger or worsen chronic conditions such as asthma, heart attacks, bronchitis and other respiratory problems. Due to their adverse health effects, PM2.5 readings are often included in air quality reports from environmental authorities and companies.
The American Heart Association has warned about the impact of PM2.5 on heart health and mortality. Exposure over a few hours to weeks can trigger cardiovascular disease-related mortality and non-fatal events, and longer-term exposure further increases the risk of cardiovascular mortality. Children, older adults, pregnant women and those suffering from lung and/or heart disease are especially vulnerable to the adverse effects of PM2.5 and should take extra precautions when levels are high.
PM2.5 levels are measured using air quality monitoring equipment, and readings are often included in air quality reports. The Air Quality Index (AQI) is a numerical system that measures the level of air pollution in a area, with a higher number indicating worse air quality. The AQI is calculated using data from governmental, crowd-sourced and satellite-derived air quality monitors, with PM2.5 readings being prioritised.
To reduce exposure to PM2.5 and protect health when levels are high, it is recommended to stay indoors and close all windows and openings that allow polluted air to enter.
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Frequently asked questions
Air pollution is measured using the Air Quality Index (AQI), which is a scale from 0 to 500 that indicates how good or bad the air quality is. The higher the AQI value, the greater the level of air pollution and the greater the health concern.
The AQI has six categories, each represented by a specific colour. Code Green and Yellow indicate the air is generally safe for everyone. Code Orange is unhealthy for sensitive groups, and Code Red and Purple indicate the air is unhealthy for everyone. Code Maroon is a health warning of emergency conditions.
The AQI tracks five major air pollutants: ground-level ozone, airborne particles, carbon monoxide, nitrogen dioxide, and sulphur dioxide. These pollutants pose varying levels of risk to human health and are the main ingredients in smog, which reduces visibility.
Instruments on the ground and satellites orbiting the Earth, such as the Joint Polar Satellite System (JPSS), collect information about particles in the air. These include smoke particles, airborne dust, urban and industrial pollution, and volcanic ash.
You can find daily AQI information for your area from the same sources that provide your weather forecast, such as local radio, TV weather reports, newspapers, or weather apps. The EPA also provides real-time AQI maps at AirNow.gov.
