Measuring Pollutants: Techniques And Tools For Environmental Monitoring

Air pollution is a critical issue that threatens human health and contributes to climate change, biodiversity loss, and pollution. According to the World Health Organization, 99% of the global population breathes unclean air, leading to approximately 7 million premature deaths annually. To address this crisis, it is essential to measure air pollution accurately to implement effective solutions. Air pollution measurement involves collecting and analyzing air samples to determine the presence and concentration of various pollutants. This process can be performed through passive or active methods, utilizing devices such as diffusion tubes, deposit gauges, and automated sensors. These sensors can be handheld, wearable, or static, providing real-time data on specific pollutants like ozone, particulate matter, carbon monoxide, and nitrogen dioxide. By understanding the levels and impacts of different pollutants, governments and researchers can develop strategies to improve air quality and mitigate the adverse effects of pollution on human health and the environment.

Air Quality Index (AQI)

The Air Quality Index (AQI) is a tool developed by the Environmental Protection Agency (EPA) to communicate information about outdoor air quality and health. The AQI includes six colour-coded categories, each corresponding to a range of index values. The higher the AQI value, the greater the level of air pollution and the greater the health concern.

An AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. AQI values at or below 100 are generally considered satisfactory. When AQI values are above 100, the air quality is unhealthy, initially for certain sensitive groups of people, and then for everyone as AQI values increase.

The AQI is calculated based on the 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 a variety of methods, including passive and active devices. Passive devices are relatively simple and low-cost, absorbing or collecting air samples that are then analysed in a laboratory. Active devices are more complex and automated or semi-automated, using physical or chemical methods to analyse air samples.

The AQI is an important tool for understanding the health effects of air pollution and taking action to improve air quality. For example, the American Lung Association (ALA) uses AQI data to highlight the number of high-ozone days in Los Angeles, which average around 114 per year. This information can help raise awareness about the health risks associated with poor air quality and inform decisions to reduce air pollution.

Satellite imaging

Satellite data of atmospheric pollutants are being used more widely in decision-making and environmental management activities by public, private sector, and non-profit organizations. They are used for estimating emissions, tracking pollutant plumes, supporting air quality forecasting, providing evidence for “exceptional event” declarations, monitoring regional long-term trends, and evaluating air quality model output.

The Copernicus Sentinel-5P satellite, operational since early 2018, is starting to return high-resolution maps of air-polluting gases that are invisible to the human eye. It is the first Copernicus satellite dedicated to monitoring atmospheric chemistry. Sentinel-5P can measure pollution emitted by individual cities or parts of a city. It measures global levels of key trace gases such as ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), methane (CH4), and formaldehyde (HCHO), as well as aerosols in the Earth’s atmosphere.

NASA's Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite mission measures air pollutants in the atmosphere, including ozone, nitrogen dioxide, and formaldehyde, every hour across greater North America down to a neighborhood scale.

Ground-level monitoring

One common approach is the use of ambient air quality monitoring, which collects and measures samples of ambient air pollutants to evaluate the status of the atmosphere compared to clean air standards and historical data. These devices, often placed in public places like busy railway stations, continuously sample and measure the levels of pollutants such as nitrogen dioxide and particulate matter. The data collected helps identify areas with high pollutant concentrations, allowing for targeted actions to improve air quality.

Another technique is stationary source emissions monitoring, which focuses on individual stationary sources of emissions, such as manufacturing plants and industrial facilities. These measurements are combined with ambient air quality data to understand how these sources contribute to overall air pollution levels. Stationary sources may employ Continuous Emission Monitoring Systems (CEMS) to directly measure pollutants like nitrogen oxides (NOx) and carbon monoxide (CO), which are indicators of incomplete combustion.

Low-cost, portable, and wearable sensors have also gained popularity in ground-level monitoring. These sensors empower individuals and communities to understand their exposure to air pollution. They can be carried or worn, providing real-time measurements of local air quality. Additionally, drive-by sensing systems, utilising sensors mounted on vehicles like taxis and buses, offer a promising approach for mobile air quality monitoring.

Furthermore, regulatory bodies like the Environmental Protection Agency (EPA) in the United States oversee the development of various instruments and methods for detecting ambient air pollutants. They employ mobile air measurement systems, which are vehicles fitted with real-time pollution tracking instruments, to identify emission sources and levels near industrial facilities, refineries, and other large source areas.

Personal monitors

Personal air pollution monitors are an increasingly popular way to measure pollutants. These monitors are usually small, portable devices that can be worn by individuals or placed in a specific location, such as a home or office. They are equipped with sensors designed to detect and measure specific pollutants, such as particulate matter (PM), carbon dioxide (CO2), volatile organic compounds (VOCs), radon, and carbon monoxide. Some monitors can also measure environmental factors such as temperature, humidity, and even noise levels.

One example of a personal air pollution monitor is the AirBeam2©, which has been used in reproductive epidemiology studies. This monitor is small and portable, and can be clipped onto a belt or bag, or placed on a table or desk. It offers several advantages, including low cost, the ability to collect multiple size fractions of PM data every second, GPS tracking, and a long battery life. However, one disadvantage is that it may have frequent connection issues with iOS-based smartphones.

Another example of a personal monitor is the emmET, which is a lunchbox-sized device that measures PM2.5, NO2, CO2, temperature, relative humidity, and noise. This monitor is designed for extended time periods and can be shipped directly to participants, eliminating the need for in-person setup by trained technicians. The emmET offers high accuracy and the ability to collect data over a long period without burdening the participant. However, it is important to note that it only measures the indoor home environment.

When choosing a personal air pollution monitor, it is essential to consider the specific pollutants and environmental factors you want to detect. For example, if you are primarily concerned with particulate pollution, you should look for a monitor that provides PM1, PM2.5, and PM10 readings. On the other hand, if you want to monitor indoor air quality, a VOC sensor is crucial as VOCs tend to pose a more significant threat indoors. Additionally, some individuals may consider a CO2 sensor essential for understanding their indoor air quality.

It is worth noting that low-cost air pollution monitors have certain limitations. They may not provide a complete representation of indoor air quality, as they can only detect the contaminants or environmental factors for which they are designed. Additionally, the accuracy and precision of these monitors can be impacted by factors such as placement, time in use, data processing methods, temperature, humidity, and the presence of multiple contaminants. Currently, there are no widely accepted performance criteria or standardisation for measurements and alert thresholds, and the cost of a monitor does not always reflect its performance.

In conclusion, personal air pollution monitors offer a convenient and accessible way to measure pollutants. They can provide valuable data on specific pollutants and environmental factors, helping individuals understand their exposure to air pollution. However, it is important to be aware of the limitations of these devices and to consider factors such as sensor type, accuracy, and standardisation when interpreting the data.

Remote sensing balloons

In terms of atmospheric pollution, balloons can be used to measure the distribution of trace gases, aerosols, and greenhouse gases. For example, NASA/JPL's California Laboratory for Atmospheric Remote Sensing (CLARS) uses remote sensing instruments to measure trace gases, aerosols, and greenhouse gases in the LA Basin.

Balloons are also useful for monitoring air pollution in urban areas, such as in street canyons. In addition, Doppler techniques can be employed to measure wind profiles and the height of the cloud base, as well as to track pollutant plumes.

For water pollution monitoring, MixZon, Inc. has developed a system that uses lightweight infrared (IR) and video cameras mounted on a tethered helium balloon to remotely sense water quality. This system can measure the spatial distribution of surface water temperature within the mixing zone, which is the area where the initial dilution of a point-source discharge occurs. This technology is particularly useful for regulatory management and simulation model development in the context of the National Pollutant Discharge Elimination System (NPDES).

Overall, remote sensing balloons offer a low-cost, flexible, and quick response solution for monitoring pollutants in both the atmosphere and water, especially in areas that are difficult to access or are spread over a large geographical area.

Frequently asked questions