Greta Jimenez
Air pollution is a pressing issue that requires constant monitoring to ensure the health and safety of communities. To address this, various instruments and technologies are employed to measure pollution levels in the lower atmosphere, including ground-based and remote sensing methods. Ground-based instruments range from static monitors in public places to portable, low-cost sensors that individuals can use to assess their immediate surroundings. Remote sensing systems, on the other hand, utilize satellites, aircraft, or ground-based platforms to detect pollutants and provide coverage over wide areas. These systems employ techniques such as spectroscopy, gas chromatography, and mass spectrometry to identify and quantify pollutants in the atmosphere. NASA's TEMPO mission, for example, uses an advanced spectrometer to detect pollution within reflected sunlight, providing valuable data on air quality over North America.
| Characteristics | Values |
|---|---|
| Instrument Name | TEMPO (Tropospheric Emissions: Monitoring of Pollution) |
| Type | Space-based instrument |
| Orbit | 22,000 miles above the equator |
| Coverage | North America, from the Atlantic Ocean to the Pacific coast and from roughly Mexico City to central Canada |
| Scanning Frequency | Hourly daytime scans |
| Primary Instrument | Advanced spectrometer |
| Pollutants Measured | Ozone, nitrogen dioxide, formaldehyde, aerosols, water vapour, and several trace gases |
| Data Application | Regulatory monitoring network expansion, providing general air quality information to the public, air toxics monitoring |
| Monitoring Technologies | Remote sensing, mobile platforms, satellite-based platforms, ground-based platforms, direct-reading instruments, gas chromatography, mass spectrometry, spectrometry, spectroscopy, spectrophotometry, flame photometry, optical photodetectors, gravimetric analysis, condensation particle counters, multi-gas monitors |
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What You'll Learn
Remote monitoring of pollution
One example of remote pollution monitoring is the Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument, a satellite-based platform that will monitor air quality in the troposphere during daylight hours. TEMPO is part of NASA's Earth Venture Instrument program and will join other satellites such as South Korea's Geostationary Environment Monitoring Spectrometer (GEMS) and the European Space Agency's Sentinel-4 to create a global air-quality satellite constellation. These satellites will provide coordinated observations of air pollution across the Northern Hemisphere, with TEMPO focusing on North America.
TEMPO's sensors can detect tiny differences in the light reflected when sunlight strikes molecules in the atmosphere, allowing it to track pollutants such as ozone, nitrogen dioxide, sulfur dioxide, bromine, formaldehyde, and aerosols. However, it will not directly measure fine soot (PM2.5). Scientists are working on converting TEMPO's measurements of aerosols into PM2.5 estimates using models and data from ground-based monitors.
In addition to satellite-based remote sensing, aircraft remote sensing covers a larger area than ground-based monitoring but has limited sampling duration. Ground-based platforms, on the other hand, can provide more accurate and timely air quality information, utilizing technologies such as air sensors, laboratory-grade instrumentation, and regulatory-grade instrumentation. Static monitors, for example, can continuously sample and measure air quality in a specific urban location, providing immediate feedback on local air quality.
The development of low-cost sensing technologies has also revolutionized air pollution monitoring by enabling broader participation and utilization of information by communities and individuals. These sensors can be worn by individuals or placed in public places to monitor local air quality levels and empower people to understand their exposure to air pollution risks. However, the interpretation of data from low-cost sensors requires in-depth expertise in atmospheric science to identify appropriate technologies and address potential measurement artifacts.
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Portable gas chromatographs
Several instruments are used to measure pollution levels in the lower atmosphere. One such instrument is a portable gas chromatograph, which is used to chemically analyse substances.
Gas chromatography is an analytical technique used to separate a mixture of chemical substances into its individual components. Portable gas chromatographs are used to detect and identify chemicals in the field within minutes. They are often used by emergency responders to analyse substances suspected to be toxic industrial chemicals, narcotics, or chemical warfare agents.
The FROG 5000™ is an example of a portable gas chromatograph that weighs less than 5 lbs. It incorporates separate sensors for oxygen, combustible atmosphere, and up to three toxic gases in the same handheld monitor. The sample concentration is displayed in ppm, percent oxygen, or percent LEL (Lower Explosive Limit).
The Griffin G510 GC/MS (gas chromatograph mass spectrometer) is another portable device that can identify thousands of organic species by combining mass spectrometry with gas chromatography. It can detect trace levels of narcotics, opioids, explosives, environmental pollutants, and other chemicals of interest. The integrated GC separates complex sample mixtures into individual components, while the MS detects and identifies trace-level components by matching them against an on-board library of over 270,000 chemicals.
In addition to these specialised devices, there are also portable multi-gas monitors that can detect oxygen, combustible atmospheres, and toxic gases. These monitors may operate in passive or active modes, and they often feature alarms that warn of hazardous conditions or malfunctions.
Other Methods of Measuring Pollution
Other methods of measuring pollution include the use of remote sensing systems, such as lidar, drones, and satellites, as well as in-person sampling with direct-reading instruments. Direct-reading instruments provide real-time data and are useful for identifying point-source contamination, such as gas leaks. Personal sensors can also be used to monitor local air quality levels and identify "urban valleys" where pollution is trapped by buildings.
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Multi-gas monitors
The monitoring process is simplified by using a multi-gas monitor with sensors for oxygen, lower explosive limits (LELs), and toxic gases. LELs indicate the lowest concentration of a gas or vapour that can combust with an ignition source, and understanding these levels is crucial for worker safety. Multi-gas monitors may also be used to detect irritant gases like ammonia or chlorine, which can cause respiratory issues when inhaled.
In addition to handheld devices, there are static monitors that continuously sample and measure air quality in specific urban locations. These static monitors can provide immediate feedback on local air quality, including levels of nitrogen dioxide and other pollutants.
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Direct-reading air quality instruments
There are many types of direct-reading instruments available, each designed for a specific monitoring purpose. For example, the FROG 5000™ is a portable gas chromatograph that provides speed and accuracy in the field. Multi-gas monitors, such as those used in the FROG 5000™, incorporate separate sensors for oxygen, combustible atmosphere, and up to three toxic gases in the same handheld monitor. These monitors can operate in passive (diffusive) mode or active mode, where a pump module draws air across the sensors.
Another example of a direct-reading instrument is the Mercury Vapour Indicator (MVI), a hand-held device that can quickly and accurately locate and measure mercury vapour. The MVI provides continuous readings and is used to keep workers and responders safe and ensure companies comply with government regulations.
Direct-reading instruments are also used to monitor particulates, or particulate matter (PM), which is a mix of solid particles and liquid droplets suspended in the air. Examples of direct-reading instruments for particulates include the HazDust - EPAM 5000 and the tapered element oscillating microbalance (TEOM). The TEOM is based on a glass tube that vibrates more or less as particles accumulate on it.
In addition to these instruments, remote sensing systems can also be used for direct reading of pollution levels in the lower atmosphere. These systems can be passive, detecting incoming radiation from the sun or planet, or active, emitting radiation and detecting the backscattered signal. Remote sensing can be useful for detecting particulate matter, gaseous pollutants, and volatile organic compounds.
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Air Quality Index (AQI)
Air pollution can be measured using various instruments and sensors. These include lidar, drones, satellites, and laboratory-grade or regulatory-grade instrumentation. Remote sensing systems, for instance, can detect radiation to indirectly estimate the composition of the atmosphere.
The Air Quality Index (AQI) is a tool used by the EPA to communicate information about outdoor air quality and health. It provides a quantitative understanding of air quality by detecting the presence and amount of pollutants in the environment. The AQI includes six color-coded categories, each corresponding to a range of index values. An AQI value of 50 or below represents good air quality, while a value over 300 represents hazardous air quality. Values above 100 indicate that the air quality is unhealthy, initially for sensitive groups of people and then for everyone as values increase.
The AQI is calculated for five major air pollutants regulated by the Clean Air Act: ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. These pollutants are measured using various instruments, including particulate matter samplers, optical photodetectors, gravimetric analysis, and condensation particle counters.
AirNow.gov is a website that provides air quality data at the local, state, national, and global levels. It offers interactive maps, calculators, and other resources to help individuals understand and monitor air quality. Personal sensors and static monitors are also available to empower individuals and communities to better understand their exposure to air pollution and take appropriate actions to improve the air around them.
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