Air Pollution Measurement: How Is It Done?

Air pollution is a pressing global issue, with 99% of the world's population breathing unclean air, according to the World Health Organization. It is therefore imperative that air pollution levels are measured to help governments and countries identify hotspots and take targeted action to protect human and environmental well-being. Air pollution is measured in Air Quality Index (AQI) values, which are calculated using data from governmental, crowd-sourced, and satellite-derived air quality monitors. Modern air pollution measurement is largely automated and carried out using various devices and techniques, from simple diffusion tubes to highly sophisticated chemical and physical sensors that provide near real-time pollution measurements.

The Air Quality Index (AQI)

The AQI is divided into six color-coded categories, each corresponding to a different level of health concern. The color-coding makes it easy for people to quickly determine whether the air quality is reaching unhealthy levels in their communities. When the AQI is above 100, the air quality is considered unhealthy for certain sensitive groups of people, and as the AQI value increases, it becomes unhealthy for everyone. For each pollutant, an AQI value of 100 corresponds to an ambient air concentration that equals the level of the short-term national ambient air quality standard for the protection of public health.

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. Air quality monitors are equipped with sensors designed to detect specific pollutants, with some using lasers to scan particulate matter density in a cubic meter of air, and others relying on satellite imaging to measure energy reflected or emitted by the Earth.

Passive and active measurement

Air pollution levels can be measured through active and passive monitoring methods. Active measurement methods involve the use of specialised equipment and trained personnel to collect real-time data on air pollutant concentrations. Passive measurement, on the other hand, relies on the natural accumulation of pollutants on collection devices, which are then analysed in a laboratory setting.

Satellite monitoring

Satellites can observe and measure the concentration of particles (aerosols) in the atmosphere by detecting the amount of light that reaches the surface of the Earth and how much is reflected off the pollutants. This measurement is called Aerosol Optical Depth (AOD) or Aerosol Optical Thickness (AOT). The data is then compared to ground measurements to determine if the pollution is near the surface or high in the atmosphere.

AOD is a measure of light extinction (scattering and absorption) by atmospheric aerosols, which enables it to predict ambient PM2.5 concentrations. PM2.5 refers to fine soot, which is one of the most harmful air pollutants. While satellites can provide valuable data on PM2.5, they do not directly measure it. Scientists are working to convert the broader measurements of aerosols into PM2.5 estimates using models and data from ground monitors.

Despite the benefits of satellite monitoring, it is important to note that ground measurements are still necessary for calibrating satellite-based estimates. Limitations in algorithms and the inherent difficulties in accessing and interpreting observational data present challenges that need to be addressed to fully realise the potential of satellite monitoring for air pollution measurement.

Air pollution calculators

Air pollution is typically measured using the Air Quality Index (AQI), which is divided into six colour-coded categories, each corresponding to a different level of health concern. An AQI of 50 or below is generally considered safe, while readings above 100 are deemed unhealthy. Satellites orbiting the Earth, such as the Joint Polar Satellite System (JPSS), monitor the particle pollution in our atmosphere, providing measurements of particle pollution and ground-level ozone. These satellites can also measure carbon monoxide, which is associated with poor air quality resulting from wildfires.

Air quality databanks process readings from governmental, crowd-sourced, and satellite-derived air quality monitors to produce an aggregated AQI reading. In 2021, the United Nations Environment Programme (UNEP), in collaboration with IQAir, developed the first real-time air pollution exposure calculator, which combines global readings from over 6,400 locations in 117 countries. This database prioritises PM2.5 readings and uses artificial intelligence to calculate each country's population exposure to air pollution on an hourly basis.

Air quality monitors are equipped with sensors designed to detect specific pollutants, such as PM2.5, PM10, ground-level ozone, nitrogen dioxide, and sulfur dioxide. Some monitors use lasers to scan particulate matter density, while others rely on satellite imaging to measure energy reflected or emitted by the Earth.

While the AQI is a useful tool for communicating air quality and associated health risks, it is important to note that it does not provide a complete picture of air pollution. Other factors, such as climate and transport, can influence pollutant concentrations and their impacts on human health and the environment.

Air quality monitors

Satellite Systems

Satellite systems, such as NOAA's GOES-R series and the Joint Polar Satellite System (JPSS), play a crucial role in monitoring air quality. These satellites collect data on particle pollution, smoke particles from wildfires, dust storms, urban and industrial pollution, volcanic ash, and ground-level ozone. The high-resolution measurements provided by these satellites help track the movement of aerosols and monitor air quality on a global scale.

Government and Organisation-led Initiatives

Governments and organisations also contribute to air quality monitoring through initiatives such as AirNow, which provides an easy-to-use air quality meter based on zip codes or postal codes. Additionally, organisations like PurpleAir offer real-time air quality monitoring by deploying sensors that measure particulate pollution (PM2.5), temperature, humidity, and pressure. These sensors provide accurate and affordable data, empowering individuals and communities to make informed decisions about their air quality.

Low-Cost Indoor Air Quality Monitors

In recent years, low-cost indoor air quality monitors have gained popularity. These devices use sensors to detect and monitor specific air pollutants, such as particulate matter (PM), carbon dioxide, and environmental factors like temperature and humidity. While they may not detect all pollutants, they provide a simple and quick way for users to assess their indoor air quality and take necessary actions to improve it.

Despite the advancements in air quality monitoring, challenges remain. According to the World Health Organization, 99% of the global population breathes unclean air, highlighting the urgency for governments to strengthen air quality regulations and monitoring capacities. Additionally, regions like Africa, Central Asia, and Latin America face sparse air quality monitoring, impacting the ability to address air pollution in these areas effectively.

In conclusion, air quality monitors are vital tools that provide valuable insights into the state of our air. By utilising a combination of satellite systems, government initiatives, and low-cost indoor monitors, we can better understand and address air pollution, ultimately improving human and environmental well-being.

Frequently asked questions