Kiera Jefferson
There are various systems in place to monitor air pollution, including satellite technology, low-cost sensors, regulatory and non-regulatory air quality networks, and computational air quality modelling. Low-cost sensors, for example, can be used to assess indoor air pollutants and other environmental factors. They can provide users with a simple and quick way to determine levels of some air pollutants. However, there is limited information on the accuracy of these monitors, and their performance can vary depending on factors such as placement, time in use, temperature, and humidity. On the other hand, satellite technology can provide a bird's-eye view of air pollution over a wider geographic area, but its spatial and temporal resolution are currently low. Regulatory monitoring systems include continuous emission monitoring systems (CEMS), which directly measure actual emissions levels from stationary sources, and continuous opacity monitoring systems (COMS), which measure the opacity of emissions as an indicator of particulate matter.
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What You'll Learn
Low-cost air pollution monitors
There is limited information on the accuracy and precision of low-cost air pollution monitors, and their accuracy can be impacted by factors such as placement, time in use, data processing methods, temperature, humidity, and the presence of multiple contaminants in the air. The accuracy and precision of pollutant-detecting monitors can also vary across manufacturers and within product lines.
Despite these limitations, low-cost air pollution monitors have several advantages. Their lower investment costs and setup times make them more accessible for community groups and citizen scientists to track air quality conditions in communities without monitoring or to supplement existing monitoring. They are also useful for improving the spatial characterization of highly variable pollution exposures within a city and can be deployed in a greater number of locations worldwide. Additionally, when used as part of mobile monitoring platforms, they can provide monitoring with greater temporal and spatial resolution, capturing transient or short-term peaks in concentrations at the street level.
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Continuous emissions monitoring systems (CEMS)
The standard CEM system consists of a sample probe, filter, sample line (umbilical), gas conditioning system, calibration gas system, and a series of gas analyzers that reflect the parameters being monitored. Typical monitored emissions include sulfur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, hydrogen chloride, airborne particulate matter, mercury, volatile organic compounds, and oxygen. CEM systems can also measure airflow, flue gas opacity, and moisture.
CEMS are required under some EPA regulations for either continual compliance determinations or the determination of exceedances of the standards. The accuracy of the system is demonstrated in several ways. An internal quality assurance check is achieved by introducing a certified concentration of gas to the sample probe daily. The CEMS measurement is then compared against the known concentration to arrive at a Calibration Error percentage. A zero gas reading is also taken and compared. If the calibration error % exceeds 2x the performance specification for 5 consecutive days or 4x the performance specification in 24 hours, the CEMS is considered out of control, meaning the data cannot be relied upon as accurate until it is brought back into control.
CEMS are also used to measure the concentration of air pollutants (such as SO2, NOx, CO, CO2, THC, and O2) and other parameters in accordance with the applicable regulations for the emission source. Required parameters depend on the type of stationary source.
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Satellite technology
Satellite remote sensing offers several advantages over traditional ground-based monitoring. It provides a more comprehensive view of air pollution by covering larger areas and delivering data with high spatial resolution. This enables the identification of air pollution hotspots and the tracking of airborne contaminants such as smog, helping to understand their origins and behaviour. Additionally, satellite data can be used to monitor criteria air pollutants like PM2.5 and NO2, and greenhouse gases such as CH4 and CO2.
One example of a satellite-based air pollution monitoring initiative is the Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument, supported by NASA. TEMPO will monitor air pollution over North America in near real-time, providing data on nitrogen dioxide, a key ingredient in ground-level ozone, which is linked to respiratory health issues. TEMPO will join other satellite missions such as South Korea's Geostationary Environmental Monitoring Spectrometer (GEMS), which has been tracking nitrogen dioxide pollution and air-fouling dust storms across Asia since 2020.
While satellite technology offers significant benefits, it also has limitations. Ground measurements are still necessary to calibrate satellite-based estimates, particularly for certain exposures like pollen, where remote observations might be insufficient. Additionally, challenges remain in the algorithms used to derive surface conditions from atmospheric column measurements. However, advancements in satellite technology are rapidly improving our ability to monitor air pollution and associated health risks on a global scale.
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Regulatory and non-regulatory air quality networks
Regulatory air quality networks refer to the official monitoring systems and standards set by government agencies, such as the US Environmental Protection Agency (EPA). The EPA, for instance, has established the National Ambient Air Quality Standards (NAAQS) under the Clean Air Act (CAA). The NAAQS sets standards for six common air pollutants, and states are required to develop plans to attain and maintain these standards. The EPA also regulates emissions from specific industrial sources and sets protective limits. To ensure compliance, the EPA employs various measurement techniques, including continuous emission monitoring systems (CEMS), continuous opacity monitoring systems (COMS), and continuous parametric monitoring systems (CPMS). These systems directly measure pollutant concentrations and parameters affecting emissions levels.
Non-regulatory air quality networks, on the other hand, refer to monitoring efforts that are not mandated by government regulations. These often include low-cost sensor systems, which can be stationary or portable, and are typically employed by communities, governments, and industries. For example, the US EPA's Environmental Justice Thriving Communities Grantmaking program provides funding for underserved and marginalized communities to access resources for air quality monitoring. Non-regulatory monitors are advantageous due to their lower costs and setup times, allowing for improved spatial characterization of pollution exposures within cities and increased deployment worldwide. However, one challenge with non-regulatory monitors is the variability in performance between units and over time.
Both regulatory and non-regulatory air quality networks play a crucial role in monitoring and managing air pollution. By utilizing a combination of technologies and approaches, these networks help to ensure that air quality standards are met and that the public is informed about potential health risks associated with air pollution.
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Manual inspections
During a manual inspection, inspectors physically examine the process equipment and emission control devices, evaluating their condition and proper functioning. This includes a thorough inspection of the current operating conditions, which is facilitated by monitoring gauges that indicate emission levels and the presence of visible emissions or unusual odours. Inspectors also assess the usage and techniques employed to maximise the efficiency of air quality control equipment, ensuring that facilities are utilising the best practices to minimise air pollution.
One of the key focuses of manual inspections is record-keeping. Inspectors scrutinise the thoroughness and accuracy of records related to air emissions control and facility operations. This includes examining historical data, process conditions, and work practices to identify any discrepancies or violations of air pollution regulations. Facilities are expected to maintain detailed logs of their emissions, operating conditions, and any corrective actions taken in response to previous inspections.
The frequency of manual inspections can vary depending on several factors. Facilities with a history of non-compliance or those that emit a large quantity of emissions are typically inspected more frequently. Additionally, inspections may be triggered by the implementation of new regulations or when a facility makes significant operational changes that could potentially impact their emissions.
In cases where violations or problems are identified during a manual inspection, inspectors work closely with the facility to resolve these issues as promptly as possible. This collaborative approach ensures that facilities understand the necessary corrective actions and are provided with guidance to improve their compliance with air pollution regulations.
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