Meghan Hodges
Air pollution is a pressing issue that has gained global attention due to its detrimental effects on human health, the natural environment, and economies. To address this challenge, it is crucial to measure air pollution accurately and comprehensively. The measurement of air pollution involves assessing the concentration of various pollutants in the air, including gases and particulate matter. This process can be conducted through passive or active methods, utilizing ground-level monitoring, satellite technology, or a combination of both. While passive devices, such as diffusion tubes and deposit gauges, collect samples for subsequent laboratory analysis, active devices employ automated or semi-automated mechanisms to analyze pollutants in real-time or store them for later examination. Modern technology, such as the tapered element oscillating microbalance (TEOM), optical photodetectors, and condensation particle counters, enhances the accuracy and efficiency of air pollution measurements. These measurements are crucial for developing strategies to mitigate pollution and safeguard public health.
| Characteristics | Values |
|---|---|
| Air Quality Index | AQI tracks five major air pollutants: ground-level ozone, airborne particles, nitrogen dioxide, carbon monoxide, and methane. |
| Air Quality Index Values | 0-50 (Good), 51-100 (Moderate), 100+ (Unhealthy) |
| Air Quality Index Categories | Green, Yellow, Red |
| Air Pollution Measurement Tools | Passive (e.g., diffusion tubes, deposit gauges) and Active (e.g., automated or semi-automated devices with fans and filters) |
| Modern Air Pollution Measurement Devices | Absorbent test tubes (diffusion tubes), chemical and physical sensors, tapered element oscillating microbalance (TEOM), optical photodetectors, gravimetric analysis, aethalometer-type instruments, condensation particle counters |
| Satellite-Based Measurements | NOAA's GOES-R and JPSS satellites, used by the World Bank |
| Ground-Based Measurements | Monitoring stations, such as the London Air Quality Network and the Automatic Urban and Rural Network (AURN) |
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What You'll Learn
Air Quality Index (AQI)
Air pollution is a complex issue, and air quality is typically measured using the Air Quality Index (AQI). The AQI is a numerical system that measures the level of air pollution in a given region. It is a useful tool for communicating about outdoor air quality and health. The higher the AQI value, the worse the air quality and the greater the health concern.
The AQI is split into six colour-coded categories, each with a different numerical value and level of concern. The categories are:
- Green (0-50) – Good: Air pollution is of little to no risk.
- Yellow (51-100) – Moderate: Air quality is acceptable, but some may be at risk, particularly those sensitive to air pollution.
- Red (101-150) – Unhealthy for sensitive groups: Members of sensitive groups may experience health effects, but the general public is unlikely to be affected.
- Purple (151-200) – Unhealthy: Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
- Dark Purple (201-300) – Very Unhealthy: Health warnings of emergency conditions, everyone may experience more serious health effects.
- Maroon (300+) – Hazardous: Health alert, everyone may experience more serious health effects.
The AQI tracks five major air pollutants, including ground-level ozone and airborne particles, which are the two pollutants that pose the greatest risk to human health. Ground-level ozone is created when sunlight reacts with certain chemical emissions, such as nitrogen dioxide, carbon monoxide, and methane. These chemicals can come from industrial facilities, car exhaust, gasoline vapours, and other sources.
To measure air quality, instruments on the ground and satellites orbiting the Earth collect information about the particles in our air. Satellites, such as those in the NOAA’s GOES-R series, monitor particle pollution, providing measurements approximately every five minutes during the day. The Joint Polar Satellite System (JPSS) also collects information about particles in our air, including smoke particles from wildfires, airborne dust during dust and sandstorms, urban and industrial pollution, and ash from erupting volcanoes.
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Satellite observations
The Geostationary Environmental Monitoring Spectrometer (GEMS) launched by South Korea in 2020, provides a view of the daily rhythms of nitrogen dioxide pollution across much of Asia. It has also tracked dust storms from northern China and climate-cooling sulfur dioxide from volcanic eruptions. NASA's NEO provides easy access to global satellite images for teachers, students, museums, and citizen scientists. It generates images based on data from various satellite instruments and assigns a color to a range of aerosol optical depth values.
The Joint Polar Satellite System (JPSS) collects information about particles in the air, including smoke particles from wildfires, airborne dust during dust and sandstorms, urban and industrial pollution, and ash from erupting volcanoes. It can also measure ground-level ozone. The GOES-R Series of satellites can provide particle pollution measurements approximately every five minutes during the day.
While satellites provide a powerful tool for observing pollution, they also have limitations. For instance, they can only measure daytime data and are limited to relatively cloud-free days. In addition, satellite images may not provide information about pollution levels on the ground, as the pollutants observed could be kilometers above the ground. Ground measurements are, therefore, necessary to "ground truth" or calibrate satellite-based estimates.
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Passive and active measurement
Active measurement devices, on the other hand, are automated or semi-automated and tend to be more complex and sophisticated than passive devices. They use fans or pumps to suck in the air, filter it, and either analyze it automatically or collect and store it for later analysis. Active devices can be small, handheld, and wearable, or large-scale static monitoring stations in urban areas. They are more expensive and complex, requiring power sources, regular maintenance, and calibration. They offer more precise and immediate data on air pollutant concentrations.
Both passive and active measurements play crucial roles in environmental monitoring and are suited to different applications. Passive samplers are ideal for long-term environmental assessment, while active samplers are preferred for real-time monitoring or when high temporal resolution is needed. Active samplers are also more suitable for detecting very low pollutant concentrations.
An example of passive measurement is the diffusion tube, which is used to measure nitrogen dioxide (NO2). This method takes time to collect samples, analyze them, and produce results. Active measurement methods for nitrogen dioxide include the Griess-Saltzman method and the Jacobs-Hocheiser method, which can be performed manually or automatically. Another active method is the use of a chemiluminescence analyzer, which determines nitrogen oxide levels from the light emitted.
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Air pollution calculators
Air pollution is a complex issue that has a significant impact on public health and the environment. It is essential to measure and understand air pollution to address its adverse effects effectively. Air pollution calculators are valuable tools that enable public health officials and researchers to quantify air pollution levels, assess risks, and develop strategies to improve air quality. These calculators employ various methods, equations, and data sources to provide insights into specific pollutants and their impacts.
One commonly used metric in air pollution calculations is the Air Quality Index (AQI). The AQI is a numerical system that indicates the level of air pollution in a given region. It is designed by the U.S. Environmental Protection Agency (EPA) and provides a comprehensive assessment of air quality. The AQI considers five major air pollutants: ground-level ozone, airborne particles, carbon monoxide, nitrogen dioxide, and methane. These pollutants primarily originate from industrial facilities, car exhaust, gasoline vapors, and similar sources. The AQI values range from 0 to 500, with higher numbers indicating poorer air quality. The index is further categorised into six colour-coded categories, each representing a different level of concern.
Online AQI calculators, such as those provided by AirNow.gov, allow users to input a specific pollutant and its AQI value. The calculator then responds with the concentration level and corresponding AQI category, along with information relevant to sensitive groups and health impact statements. These calculators are valuable tools for public health officials and individuals seeking to understand the implications of specific pollutants on human health and well-being. Additionally, AQI calculators can aid in decision-making processes, helping determine if current emissions processes require adjustments to mitigate potential risks.
While AQI calculators are useful, it is important to recognise the limitations of certain methodologies and data sources. For instance, satellite data, such as that used by NOAA's GOES-R series and the Joint Polar Satellite System (JPSS), can provide valuable particle pollution measurements. However, they are limited to daytime data and cloud-free observations, which can impact the accuracy of annual averages, particularly in regions with high seasonal and spatial variability in pollution levels. Ground-level monitoring is considered essential by scientists, but it requires sophisticated equipment, sustained funding, technical expertise, and regulatory support, which may not be readily available in all regions.
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Particulate matter samplers
Manual samplers, as the name suggests, require manual operation. They draw a known volume of air through a filter, which is then weighed on an analytical balance. By calculating the difference in weight before and after sampling and dividing it by the volume of air pulled through, the mass concentration of the particulate can be determined.
Automated samplers, on the other hand, perform the weighing process directly in the field. There are two common types of automated samplers: those that use a beta gauge for mass measurement and those that employ a tapered element oscillating microbalance (TEOM). Beta gauge samplers resemble reel-to-reel tape recorders in appearance.
The choice between manual and automated samplers depends on various factors, including the specific application, durability, maintenance requirements, the capability to operate in wet or humid environments, and ease of transportation.
Additionally, different types of samplers are available to suit specific needs. For example, solar-powered and battery-powered samplers are designed to prevent disruptions from power outages and enable long-term monitoring. Furthermore, high-volume samplers are necessary for certain applications, such as collecting particulate matter from burns, to obtain sufficient samples during the short duration of the event.
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Frequently asked questions
Air pollution is measured in Air Quality Index (AQI) values. The higher the AQI value, the greater the level of air pollution and the greater the health concern.
The AQI is measured using satellites orbiting the Earth, as well as instruments on the ground. The satellites in NOAA’s GOES-R series and the Joint Polar Satellite System (JPSS) are examples of tools used to monitor particle pollution in the atmosphere.
Passive devices work by collecting samples of ambient air, which are then analyzed in a laboratory. One of the most common forms of passive measurement is the diffusion tube, which absorbs specific pollutant gases. Active devices are automated or semi-automated and use fans to suck in and filter the air. An example of an active device is the tapered element oscillating microbalance (TEOM), which measures coarse and fine particulates.
