Greta Jimenez
Air pollution is a pressing issue that significantly impacts human health and the environment, and scientists and governments are working to address it through various means. Measuring air pollution is a critical step in understanding and mitigating its effects, and this process involves collecting and analysing data on air quality. This data is used to create air quality indexes (AQI) that provide information about the level of pollution and the associated health risks. There are various methods for collecting this data, including passive devices such as diffusion tubes and deposit gauges, as well as more active, automated methods that use physical or chemical techniques to measure air samples. These measurements help identify pollution hotspots and inform targeted actions to protect and improve environmental and human well-being.
| 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 Categories | Green (0-50) — Good; Yellow (51-100) — Moderate; Orange (101-150) — Unhealthy for Sensitive Groups; Red (151-200) — Unhealthy |
| Passive Measurement Devices | Diffusion tubes, deposit gauges, rain gauges, Ringelmann charts, soot and dust collectors |
| Active Measurement Devices | Automated or semi-automated devices that use physical or chemical methods to analyze air samples |
| Air Quality Monitors | Sensors designed to detect specific pollutants, using lasers or satellite imaging |
| Pollutants Monitored | PM2.5, PM10, ground-level ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide |
| Databases | UNEP and IQAir developed a real-time air pollution exposure calculator using data from 6,475 locations in 117 countries |
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What You'll Learn
Air quality monitoring: sensors, satellites, and lasers
Air quality sensors are essential for measuring and studying pollutants that can harm public health and the environment. There are various ways to measure air pollution, including using sensors, satellites, and lasers.
Sensors
There are many types of air quality sensors, including government-operated ground-level and satellite-based sensors, as well as low-cost commercially available sensors that can be mounted on bicycles, cars, trucks, and drones. These low-cost sensors use lasers to estimate the number and size of particles passing through a chamber and meters to estimate the amount of gas passing through the sensor. Technological improvements have led to smaller, more affordable sensors with new capabilities, such as better satellite-based sensors that can help close gaps in pollution monitoring and research.
Satellites
The U.S. federal agencies have long operated satellites with sensors that monitor air quality to understand weather patterns and inform research. Satellites have become essential tools for tracking weather events and improving daily weather forecasts. For example, satellites can easily track the evolution of aerosols released into the atmosphere from dust storms and wildfires, which can react to form particles and ozone.
Newer satellite-based sensors offer better data for monitoring air quality, which is useful for monitoring rural areas and pollution transport. Multiple sensors can be deployed in a network to track the formation, movement, and variability of pollutants and improve the reliability of measurements.
Satellite remote sensing provides data on air quality, filling in spatial gaps in ground monitoring resources. There are numerous satellite data that can indicate criteria air pollutants (e.g. PM2.5 and NO2) and greenhouse gases (e.g. CH4 and CO2).
Lasers
Air quality monitors are equipped with lasers that scan particulate matter density in a cubic meter of air.
Air Quality Monitoring
Air quality databanks process readings from governmental, crowd-sourced, and satellite-derived air quality monitors to produce an aggregated Air Quality Index (AQI) reading. The U.S. Environmental Protection Agency's AQI is a numerical system that measures the level of air pollution in a given region. The higher the number, the worse the air quality. The AQI is split into six categories, each with a different numerical value, color, and level of concern.
UNEP and IQAir developed the first real-time air pollution exposure calculator in 2021, which combines global readings from validated air quality monitors in 6,475 locations in 117 countries, territories, and regions.
Addressing Air Pollution
Air pollution significantly affects climate change and slowly destroys ecosystems, animals, and plants. It also has a tremendous impact on human health and well-being. According to the World Health Organization, 99% of the global population breathes unclean air, and air pollution causes 7 million premature deaths annually. PM2.5 poses the greatest health threat and is often used as a metric in legal air quality standards. Governments must strengthen air quality regulations, including monitoring capacity, to address the air pollution crisis.
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Air pollution calculators: measuring AQI and health risks
Air pollution is a pressing issue that significantly affects climate change and ecosystems, and has a tremendous impact on human health and well-being. According to the World Health Organization, 99% of the global population breathes unclean air, which causes approximately 7 million premature deaths annually.
Air pollution calculators are vital tools that enable public health officials to address this crisis by providing data on specific pollutants. These calculators use air quality databanks that process readings from governmental, crowd-sourced, and satellite-derived air quality monitors. The data is aggregated to produce an Air Quality Index (AQI) reading. The AQI is a numerical system that measures the level of air pollution in a given region. Developed by the U.S. Environmental Protection Agency (EPA), the AQI is designed to communicate information about outdoor air quality and associated health risks.
The AQI is divided into six color-coded categories, each indicating a different level of health concern. The categories are as follows:
- Green (0-50) - Good: Air pollution poses little to no risk.
- Yellow (51-100) - Moderate: Air quality is acceptable, but some individuals with heightened sensitivity may be at risk.
- Orange (101-150) - Unhealthy for Sensitive Groups: People with sensitivities may experience negative health effects, but the general public is less likely to be affected.
- Red (151-200) - Unhealthy: The general public may experience health effects, and those with sensitivities may face more serious consequences.
- Purple (201-300) - Very Unhealthy: Health warnings of emergency conditions. The entire population is likely to be affected, with significant discomfort and respiratory effects.
- Maroon (300+) - Hazardous: Health alert and emergency conditions. Everyone may experience more serious health effects.
It is important to note that the AQI values are general guidelines, and specific health risks may vary depending on individual sensitivities and the type of pollutant.
By utilizing air pollution calculators and understanding the AQI categories, public health officials can implement strategies to mitigate air pollution and protect the well-being of the public.
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Passive measurement: diffusion tubes and deposit gauges
Passive measurement techniques, such as diffusion tubes and deposit gauges, are simple and cost-effective methods used to monitor air pollution, particularly gas-phase pollutants. These techniques are valuable tools for assessing both indoor and outdoor air quality and identifying areas of high or low pollution concentrations.
Diffusion tubes are small, pencil-shaped glass tubes filled with a chemical reagent that reacts with specific airborne pollutants. This reaction produces a coloured stain, with the intensity of the colour indicating the concentration of the pollutant. These tubes are passive dositubes that utilise the natural diffusion of gases to measure the time-weighted average (TWA) gas concentrations over extended periods. They are especially useful for measuring high concentrations of gaseous pollutants, such as carbon monoxide, hydrogen sulphide, nitrogen dioxide, sulfur dioxide, and benzene, commonly found in industrial settings.
Diffusion tubes are advantageous due to their simplicity, low cost, and ease of use. They do not require electrical power, calibration, or maintenance, making them accessible for a variety of applications. Additionally, they can be placed in areas where workers are present, providing valuable data on individual exposure to pollutants.
However, one limitation of diffusion tubes is their lower limit of detection, which may not be sensitive enough for measuring very low concentrations of certain pollutants, such as nitrogen dioxide. In such cases, more sophisticated instruments may be required.
Deposit gauges, another passive measurement technique, have also played a significant role in the history of air pollution monitoring. In the early 20th century, Irish physician and environmental engineer John Switzer Owens advanced the use of deposit gauges to measure air pollution. This work, along with events like the Great Smog of London in 1952, led to a turning point in environmental awareness and the implementation of stricter pollution control measures.
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Active measurement: automated and semi-automated devices
Air pollution measurement is broadly categorised into two types: passive and active. Passive devices are simple, low-cost solutions that collect ambient air samples, which are then analysed in a laboratory. Active measurement devices, on the other hand, are automated or semi-automated, and they tend to be more complex and sophisticated than passive devices. These devices use fans to draw in air, which is then filtered and analysed either immediately or stored for later laboratory analysis.
Active sensors use either physical or chemical methods for measurement. Physical methods, such as photometers and digital cameras, measure an air sample without changing it, for example by measuring how much of a certain wavelength of light it absorbs. The most commonly used methods of measuring light pollution fall under this category. Chemical methods, such as gas chromatography and flame ionization, change the sample through a chemical reaction and then measure the result.
Most automated air-quality sensors are examples of active measurement. These sensors range from small handheld devices to large-scale static monitoring stations in urban areas. Small, inexpensive, portable, and sometimes wearable internet-connected air pollution sensors, such as the Air Quality Egg and PurpleAir, constantly sample particulates and gases and produce moderately accurate, almost real-time measurements that can be analysed by smartphone apps.
Public places such as busy railway stations sometimes have active air quality monitors permanently installed to measure levels of nitrogen dioxide and other pollutants. Some static monitors are designed to give immediate feedback on local air quality through colour-coded lights. Large, expensive, static street-side monitoring stations are also used by local authorities to constantly sample various pollutants commonly found in urban air. These stations make up metropolitan monitoring systems such as the London Air Quality Network and the Automatic Urban and Rural Network (AURN).
In addition to the above, autonomous mobile robots equipped with atmospheric composition analysers are being used to control the concentration of emissions of harmful industrial substances into the atmosphere and measure the concentration of carbon dioxide. These robots can access uninhabited areas and provide round-the-clock monitoring of vast territories, including measurements during the day and night, and send data online. They are also more affordable and provide greater detail than stationary monitoring stations.
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Regulatory requirements: EPA standards and WHO guidelines
Regulatory requirements for pollution measurement are informed by standards and guidelines from organisations such as the EPA and WHO. The EPA, or the US Environmental Protection Agency, plays a key role in regulating and monitoring air pollution in the US. The Clean Air Act (CAA) requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants ("criteria" air pollutants) that can harm public health and the environment. These criteria air pollutants include carbon monoxide, ground-level ozone, lead, nitrogen oxides, particulate matter, and sulfur dioxide. The EPA also regulates toxic air pollutants from industrial sources, such as mercury, polychlorinated biphenyls (PCBs), benzene, and volatile organic compounds (VOCs).
The EPA quantifies two main types of monitoring: Ambient Air Quality Monitoring and Stationary Source Emissions Monitoring. The former involves measuring ambient air pollutant samples to compare current air quality with historical data and clean air standards. The latter focuses on measuring emissions data at individual stationary emission sources. The EPA also provides information about emissions levels, sources of greenhouse gases, and options for reducing emissions.
The EPA's Clean Air Markets Division (CAMD) runs programs aimed at reducing air pollution from power plants, addressing issues like acid rain, ozone depletion, particle pollution, and interstate transport of air pollution. Additionally, the EPA establishes New Source Performance Standards (NSPS) for newly constructed sources or those undergoing significant upgrades. These standards include equipment specifications, operation requirements, and measurement guidelines.
The World Health Organization (WHO) has also recognised the global air quality crisis, reporting that 99% of the world's population breathes unclean air, leading to approximately 7 million premature deaths annually. PM2.5, or particulate matter with a diameter of 2.5 micrometres or less, is a significant pollutant that poses a grave health risk when inhaled. The WHO's guidelines on air quality standards emphasise the urgent need for governments to strengthen air quality regulations and monitoring capacities to address this crisis.
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Frequently asked questions
Measuring air pollution is the first step. This is done by collecting and measuring the components of air pollution, notably gases and particulates.
Some of the earliest devices used to measure pollution include rain gauges (in studies of acid rain), Ringelmann charts for measuring smoke, and simple soot and dust collectors known as deposit gauges.
Modern methods of measuring pollution include active and passive devices. Passive devices are simple and low-cost, collecting samples of ambient air to be analysed in a laboratory. Active devices are automated or semi-automated, using fans to suck in air, filter it, and analyse it immediately or store it for later analysis.
