Helena Joyce
Air pollution is a serious issue that can have detrimental effects on people's health, the natural world, and the built environment. Measuring air pollution is crucial for understanding its causes and implementing effective regulations to ensure air quality meets legal standards. This process involves collecting and analyzing data on various pollutants, such as gases and particulate matter, to assess their impact on the environment and human health. The methods used for measuring air pollution have evolved over time, ranging from early devices like rain gauges and Ringelmann charts to modern automated technologies that provide real-time pollution measurements. These measurements are then used to generate air quality indexes, such as the Air Quality Index (AQI) or the Air Quality Index values, which help the public understand the air quality in their region and enable authorities to make informed decisions about air pollution control.
| Characteristics | Values |
|---|---|
| Air Quality Index | The higher the number, the worse the air quality. The AQI is split into six different categories that correspond to a different numerical value, color, and level of concern. |
| Air Quality Monitors | Outfitted with sensors designed to detect specific pollutants. Some use lasers to scan particulate matter density in a cubic meter of air, while others rely on satellite imaging to measure energy reflected or emitted by the Earth. |
| Passive Measurement | Passive devices are relatively simple and low-cost. They work by soaking up or otherwise passively collecting a sample of the ambient air, which then has to be analyzed in a laboratory. One of the most common forms of passive measurement is the diffusion tube. |
| Active Measurement | Automated or semi-automated and tend to be more complex and sophisticated than passive devices, though they are not always more sensitive or reliable. They use fans to suck in the air, filter it, and either analyze it automatically or collect and store it for later analysis in a laboratory. |
| Pollutants | Hydrocarbons, ammonia, ground-level ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, nitrogen oxides, and particulate matter. |
What You'll Learn
Passive and active measurement
Air pollution is broadly measured in two ways: passively or actively. Passive devices are relatively simple, small, quiet, inexpensive, and easy to use. They collect samples of ambient air, which are then analysed in a laboratory. Diffusion tubes, fastened to objects like lamp posts, are one of the most common forms of passive measurement. They absorb specific pollutant gases, which are then sent to a laboratory for analysis. Deposit gauges, which are large funnels that collect and drain soot or other particulates into sampling bottles, are another type of passive device. Passive samplers can detect long-term averages, but they are affected by temperature, relative humidity, and air movement. They are also less accurate than active monitors and require longer sampling periods.
Active measurement devices are automated or semi-automated and tend to be more complex and sophisticated than passive devices. They use fans to suck in the air, filter it, and either analyse it automatically or collect and store it for later analysis. Active sensors use either physical or chemical methods. Physical methods measure an air sample without changing it, for example by seeing how much of a certain wavelength of light it absorbs. Chemical methods change the sample through a chemical reaction and measure that. Active sampling uses an air mover (e.g. a pump or blower) to draw air through a substrate or absorbing solution, pump it into a container, or direct it into an in-situ sensor. Most automated air-quality sensors are examples of active measurement, ranging from small handheld devices to large-scale static monitoring stations in urban areas.
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Modern measurement devices
Modern air pollution measurement is largely automated and carried out using many different devices and techniques. These devices range from simple absorbent test tubes known as diffusion tubes to highly sophisticated chemical and physical sensors that give almost real-time pollution measurements, which are used to generate air quality indexes.
One such device is the tapered element oscillating microbalance (TEOM), which is used in modern pollution monitoring stations to measure coarse (PM10) and fine (PM2.5) particulates. The TEOM is based on a glass tube that vibrates more or less as collected particles accumulate on it.
Another modern device for measuring air pollution is the Air Quality Egg, a small, inexpensive, internet-connected air pollution sensor. Such sensors constantly sample particulates and gases and produce moderately accurate, almost real-time measurements that can be analyzed by smartphone apps. Their data can also be used in a crowdsourced way, either alone or with other pollution data, to build maps of pollution over wide areas.
Air pollution is also measured using satellites orbiting the Earth, such as those in the NOAA’s GOES-R (Geostationary Operational Environmental Satellites-R) Series and the Joint Polar Satellite System (JPSS). These satellites collect information about particles in the air, including smoke particles from wildfires, dust from dust storms, urban and industrial pollution, and ash from erupting volcanoes.
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Air Quality Index
Air pollution is a complex issue, with many different components contributing to poor air quality. Air quality is measured using the Air Quality Index (AQI), a numerical system that tracks five major air pollutants. The higher the AQI number, the worse the air quality.
The AQI is split into six colour-coded categories, each with a corresponding level of health concern. These categories are: Green (0-50) for good air quality; Yellow (51-100) for moderate air quality; Orange (101-150) for unhealthy air quality for sensitive groups; Red (151-200) for unhealthy air quality; Purple (201-300) for very unhealthy air quality; and Maroon (301-500) for hazardous air quality. When AQI values are above 100, air quality is considered unhealthy for certain sensitive groups of people, and as the AQI values increase, it becomes unhealthy for everyone.
The AQI is calculated using data from instruments on the ground and satellites orbiting the Earth, such as the NOAA’s GOES-R and JPSS series of satellites. These satellites monitor particle pollution in the atmosphere, including smoke particles from wildfires, airborne dust during dust and sandstorms, urban and industrial pollution, and ash from volcanic eruptions. The data collected by these satellites helps to provide real-time information on air quality standards, which is essential for public health officials to understand the current air quality, predict future trends, and develop strategies to improve health conditions.
Additionally, air pollution calculators allow for a more specific analysis, where public health officials can input a pollutant and its AQI level and receive information on concentration levels, corresponding categories, and the potential impact on sensitive groups. This detailed information is crucial for public health officials to make informed decisions and take appropriate actions to address air pollution and protect public health.
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WHO air quality database
The World Health Organization (WHO) has been monitoring air quality and updating its air quality database since the 1970s. The database is crucial for raising awareness about air pollution and its health risks, as well as for calculating global exposures and the resulting burden of disease.
The 2022 WHO air quality database status report includes data from approximately 6743 human settlements, a significant increase from the 1102 settlements in its first publication in 2011. However, the majority of these settlements are in high- and middle-income countries, with more than 90% located in regions like China, Europe, India, and North America. This indicates that air quality monitoring is lacking in many low- and middle-income countries, particularly in Africa, Central Asia, and Latin America.
The WHO air quality database utilises official data sources, which can be challenging to access and assess due to variations in monitoring methods and governing bodies. Nonetheless, the data plays a vital role in informing the health sector about air quality discussions and facilitating multisectoral engagement of United Nations agencies. By following the 2021 WHO air quality guidelines, countries can take targeted action to reduce the harmful effects of air pollution on human health and the environment.
The database includes measurements of various pollutants, with a focus on PM2.5, which refers to particulate matter with a diameter of 2.5 micrometres or less. These fine particles pose a significant health threat as they can be inhaled and absorbed into the bloodstream, contributing to illnesses such as stroke, heart disease, lung disease, and cancer. By tracking and reducing exposure to PM2.5, governments can make substantial progress in improving air quality and protecting public health.
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Mobile measurement platforms
MMPs offer a dynamic perspective on air quality by utilising vehicles such as cars, buses, and drones to collect data across different locations. This mobility allows for high-resolution spatial and temporal measurements, capturing variations in pollutant concentrations that stationary monitoring sites may miss. The flexibility of MMPs enables comparisons between diverse areas, such as urban centres, rural regions, and transportation corridors, providing a comprehensive understanding of air pollution.
One notable example of MMP utilisation is the Aclima, Inc. mobile measurement and data acquisition platform, which equipped Google Street View cars with research-grade instruments. This project, conducted in California between 2016 and 2017, successfully demonstrated the effectiveness of MMPs in quantifying spatial variations in air pollutant concentrations over short periods, even as brief as two weeks.
The advantages of MMPs extend beyond their mobility. They serve as mobile laboratories, providing on-site analytical capabilities and high-quality data. This data aids in identifying "hotspots" of elevated pollutant concentrations, informing compliance testing, and indicating potential contributing sources within communities. MMPs also facilitate the study of atmospheric processes, leading to a deeper understanding of air pollution dynamics.
Furthermore, MMPs contribute to public health and awareness. By making air quality information more accessible, individuals can potentially reduce their health risks from air pollution. Initiatives like the MIT Senseable City Lab's "City Scanner" project aim to empower community groups and citizens to measure local air pollution, identify sources, and collaborate with officials for cleaner environments. This grassroots approach to air quality monitoring has the potential to create a network of informed communities actively working towards improving air quality.
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Frequently asked questions
The Air Quality Index 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 ranges from 0 to 500 and has six color-coded categories to indicate the level of health concern.
Air pollution is measured by collecting and measuring the components of air pollution, notably gases and particulates. Modern air pollution measurement is largely automated and carried out using many different devices and techniques. These range from simple absorbent test tubes known as diffusion tubes to highly sophisticated chemical and physical sensors that give almost real-time pollution measurements.
Air pollution is measured in two different ways: passively or actively. Passive devices are relatively simple and low-cost. They work by soaking up or otherwise passively collecting a sample of the ambient air, which then has to be analyzed in a laboratory. Active measurement devices are automated or semi-automated and tend to be more complex and sophisticated than passive devices. They use fans to suck in the air, filter it, and either analyze it automatically or collect and store it for later analysis in a laboratory.
One of the most common forms of passive measurement is the diffusion tube, which is fastened to something like a lamp post to absorb one or more specific pollutant gases. After a period of time, the tube is taken down and sent to a laboratory for analysis. Deposit gauges, one of the oldest forms of pollution measurement, are another type of passive device that collects soot or other particulates and drains them into sampling bottles for analysis. Active measurement devices include large, expensive, static street-side monitoring stations that constantly sample the various different pollutants commonly found in urban air for local authorities.
