Air Quality Index: Pollution Measurement

Air pollution is a pressing issue that affects human health and the planet. It refers to the release of pollutants into the air, such as smog, soot, greenhouse gases, and hazardous chemicals. To address this issue, it is crucial to measure the level of pollution in the air, which is done through various methods and devices. The Air Quality Index (AQI) is a commonly used metric that functions similarly to a thermometer, indicating changes in pollution levels. Satellites, sensors, and monitors are also employed to collect data on air quality, with the data being used to create maps of pollution levels. These measurements help identify the causes of air pollution, enabling the implementation of regulations and interventions to improve air quality and protect public health.

The Air Quality Index (AQI)

Air quality is measured using the Air Quality Index (AQI). The AQI works similarly to a thermometer, ranging from 0 to 500. However, instead of measuring temperature, the AQI reflects changes in the amount of pollution in the air.

The AQI tracks five major air pollutants, with ground-level ozone and airborne particles being the two pollutants that pose the greatest risk to human health. These particles can include smoke particles from wildfires, airborne dust from storms, urban and industrial pollution, and volcanic ash. The AQI is calculated by measuring the concentration of air pollutants over a specified period, typically using ground instruments and satellites orbiting the Earth.

The AQI consists of six categories, each associated with a specific colour code and health advisory. When the air quality is generally safe for everyone, the AQI is indicated as Code Green or Yellow. Code Orange represents unhealthy air quality for sensitive groups, including children, the elderly, and individuals with heart and lung diseases. Code Red and Purple indicate that the air is unhealthy for everyone, while Code Maroon signifies emergency conditions.

The AQI values reflect air quality management objectives aimed at reducing emissions, and the index is used to provide health advice and guidance. For instance, the Air Quality Health Index (AQHI) uses a scale of 1 to 10+ to indicate the level of health risk associated with local air quality. The AQHI offers advice on protecting one's health during different levels of air pollution and suggests behavioural changes to reduce environmental footprints.

The AQI is an essential tool for monitoring and managing air pollution, which has become a significant environmental and health concern globally. According to the World Health Organization (WHO), air pollution is responsible for millions of premature deaths annually, with 99% of the world's population living in areas that do not meet the WHO's air quality guidelines.

Satellite monitoring

The Sentinel-5P (S-5P) satellite, for example, is capable of monitoring and tracking pollutants in great detail. It can detect major pollution sources and the direction contaminants travel once released into the atmosphere. With its advanced resolution and processing speed, the S-5P can create maps in near real-time, benefiting environmentalists, air traffic control, and other industries.

In the United States, satellite data has been instrumental in assessing compliance with the Clean Air Act's National Ambient Air Quality Standards (NAAQS). By utilizing satellite observations, researchers can identify areas with high pollution levels that may have been missed by ground monitors. This is especially important as air pollution concentrations can vary significantly over short distances.

Satellite observations have also been used globally to track air quality and identify pollution hotspots, transboundary pollution sources, and episodic events such as forest fires and dust storms. The wide spatial coverage of satellite remote sensing helps address data gaps resulting from vast geographies.

However, challenges exist in satellite monitoring. These include the technical capacity to interpret large volumes of data accurately and the lack of infrastructure to store and process it. Nonetheless, satellite technology is a valuable tool for monitoring air pollution and can be used to complement ground-based monitoring stations.

Wearable sensors

The development of wearable sensors has democratized access to air quality data, allowing citizens to actively participate in scientific research and environmental justice campaigns. For example, the AirCasting platform, developed by HabitatMap, utilizes data from wearable sensors to map out air pollution levels across the USA. Hundreds of campaign groups have used this data to call for improvements in their local areas and educate students about environmental pollution. Additionally, community-based organizations and libraries are making these sensors increasingly accessible to the public, fostering a growing desire to monitor personal environments and engage in scientific research.

One such wearable sensor is the AirBeam, which is available through community-based organizations and libraries. The AirBeam sensor measures air quality and displays the data on the AirCasting platform, enabling users to visualize pollution levels in their area. Other examples of wearable sensors include the Atmotube PRO, a portable indoor and outdoor air quality tracker that detects fine particles and volatile organic compounds, and personal air quality monitors designed to be carried on a keychain or necklace.

Static monitors

Air pollution is a serious issue that affects human health and the planet. To monitor and address this issue, static monitors are employed to measure the level of pollution in the air. These devices, also known as air quality monitors, play a crucial role in assessing and managing air quality.

One of the essential sensors in a static monitor is the PM2.5 sensor, which detects fine particulate matter. Particulate matter, or PM, is a common proxy indicator for air pollution and is known to have negative health impacts. It is composed of various substances, including sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water. Static monitors with PM2.5 sensors help individuals and organizations track the levels of these harmful particles in the air.

In addition to PM2.5 sensors, static monitors can also incorporate additional sensors to detect other pollutants. For instance, some monitors may include sensors for PM1 and PM10, providing a more comprehensive assessment of particulate pollution. Moreover, for indoor air quality monitoring, volatile organic compounds (VOCs) sensors are particularly important as VOCs tend to pose a greater threat in enclosed spaces.

Furthermore, static monitors may also offer sensors for carbon dioxide (CO2) and radon, enhancing their ability to detect a wider range of pollutants. While carbon monoxide-specific monitors and smoke detectors have long been used to protect human health, static monitors that include CO sensors provide a more comprehensive view of indoor air quality.

It is important to acknowledge that static monitors have limitations. They may not detect all pollutants, and their effectiveness can vary. The cost of a static monitor does not always indicate superior performance, as factors like additional features, display quality, housing, and sensor types influence the price. Nonetheless, static monitors remain a valuable tool for individuals, organizations, and communities seeking to understand and address local air quality issues.

Air pollution sensing systems

The Air Quality Index (AQI) is a commonly used metric for measuring air quality. It functions similarly to a thermometer, providing a scale from 0 to 500 to indicate changes in pollution levels. The AQI categorises air quality into six colour-coded levels, ranging from safe air to emergency conditions. This index is an essential tool for communicating health risks to the public.

To gather data on air pollution, a range of sensing systems are employed. These include ground-based instruments and satellites orbiting the Earth. Satellites like the GOES-R Series and the Joint Polar Satellite System (JPSS) monitor particle pollution and provide measurements of aerosols and gases like carbon monoxide. These satellite systems offer valuable data on a global scale.

In addition to satellite technology, ground-based air quality sensors (AQS) play a crucial role in air pollution sensing. These sensors can be part of large sensor networks established by organisations like the World Meteorological Organization (WMO) and national governments. For instance, India's National Air Quality Monitoring Programme (NAMP) utilises a network of 703 AQ stations across 307 cities and towns to monitor major pollutants. These ground-based sensors can provide real-time data on specific pollutants, which is then analysed to generate insights and alerts for the public.

Furthermore, smart sensor networks, such as the Global Environment Monitoring System for Air (GEMS Air) by the United Nations, contribute to air pollution sensing. These networks combine manual and automatic monitoring sensors, including wireless sensor networks (WSN) and community sensor networks (CSN), to assess air quality at both global and regional levels.

Overall, air pollution sensing systems provide critical information for understanding and mitigating the impacts of air pollution. By measuring various ambient parameters and pollutants, these systems help track the environmental health of different areas, ensuring optimal conditions for human health and ecological well-being.

Frequently asked questions