Choosing the right air quality sensors is essential, but the way they are used and their data accuracy matter just as much. Here's how to get emissions monitoring right from start to finish.
Image Credit: Azariah Reese/Shutterstock.com
Monitoring emissions is essential to understanding how we are meeting environmental standards, protecting public health, and guiding industrial compliance. Effective monitoring depends on more than just putting a device in the air and logging the results. The challenge begins with choosing the right sensor and extends to how, where, and why it's used.
Understanding the Two Monitoring Types
In the United States, the Environmental Protection Agency (EPA) distinguishes between two core types of emissions monitoring: ambient air quality monitoring and stationary source monitoring. The former focuses on measuring pollutants in the surrounding atmosphere, helping to determine whether areas meet the National Ambient Air Quality Standards. These data are used to assess general air quality over time and across locations.
The latter targets emissions at the source, such as factories, refineries, and power plants, ensuring compliance with regulatory limits under the Clean Air Act and associated state plans. While they serve different functions, these systems are intertwined. Emissions from fixed facilities affect regional air quality, and both monitoring types contribute to a broader understanding of atmospheric pollution and its effects.1
Climate Now Debate: How are greenhouse gas emissions monitored?
Sensors: The Basics
Sensors are becoming increasingly important in air quality monitoring.
These devices, which detect either particulate matter or specific gases, now offer greater spatial and temporal resolution than traditional reference instruments.
Air quality sensors are generally categorized into particulate matter (PM) sensors and gaseous sensors, which detect pollutants like nitrogen dioxide and carbon monoxide. Both have multiple subcategories based on detection methods. Selecting an appropriate sensor depends on how they will be used, and the pollutants they are monitoring.2
There are additional factors to consider. Local environmental conditions such as temperature, humidity, and wind speed can influence sensor accuracy, sensitivity, and long-term stability. Integration and standardization of data across different sensors is also causing issues with environmental monitoring.
These variations make field testing and calibration essential. While manufacturers may publish performance metrics based on laboratory conditions, they rarely reflect real-world scenarios. Comparing sensor outputs to regulatory-grade monitors through collocation studies is a necessary step for validating performance across different settings.2
Selecting The Right Sensor
Choosing the appropriate sensor for a given task depends first on the pollutants involved and the reasons for monitoring. Costs tend to increase with the number and type of pollutants measured, so defining clear objectives upfront helps narrow the options. Additionally, the detection limit must align with the expected concentration range in the monitored area. Similarly, the sensor’s measurement range should accommodate both low background levels and potential pollution spikes, especially when placed near emission sources.3
Accuracy is often misunderstood. It isn’t just about matching a reference monitor on average; it involves both precision (how consistent the readings are under the same conditions) and bias, or systematic error, which might cause a sensor to consistently over- or underestimate pollutant levels. These factors can shift over time as sensors age or are exposed to changing environmental conditions.3
Additionally, raw data from sensors often contains noise resulting from electrical interference, atmospheric variability, or even how frequently the readings are averaged. Averaging data over longer time intervals can help reduce such noise, making long-term patterns more discernible.
Not all sensors respond to pollutants at the same rate. Fast-response sensors are well suited for applications where pollutant concentrations change rapidly, such as mobile monitoring near roads or during short-term industrial releases. Others, with slower response times, are more appropriate for stationary deployments aimed at tracking longer-term trends. Matching sensor responsiveness with the monitoring goal is essential.3
Download your PDF copy now!
Deployment of Sensors
There are several factors to consider when selecting sites for sensor deployment. For example, deploying sensors near major pollution sources like highways, industrial zones, or power plants captures the highest pollution levels and reflects the exposure faced by nearby populations. Wind and other weather conditions also influence how pollutants spread, so understanding local meteorological patterns improves placement decisions and enhances the data accuracy.2
To have the best overall picture of emissions, sensors must be distributed by factoring in land use, population density, and traffic flow. This identifies pollution variations across various neighborhoods and reveals potential emission hotspots.2
Engaging local communities in the decision-making process can further improve the sensor site selection process by focusing on the biggest concerns of residents. Overall, thoughtful sensor deployment guided by environmental, social, and technical considerations can help to create a more accurate understanding of emissions across regions.2
Logistical Considerations for Sensor Deployment
There is still more to consider when it comes to successful sensor deployment. Placement, security, connectivity, power, and site access all play a role too. Site access is essential for installation, inspection, and maintenance. If the site is not directly controlled by the monitoring organization, formal agreements are often required to clarify access terms, security responsibilities, and maintenance schedules.4
Physical placement matters for obtaining the best readings. Air should flow freely, so sensors need to be placed away from walls and obstructions. Installations must also avoid proximity to electronic interference sources like high-voltage power lines, which affect sensor performance.4
Power supply options vary by sensor model. Some require constant connection to mains electricity, while others can operate on solar power or support both. In urban settings, installing wired power can be costly and logistically difficult, especially when infrastructure is limited. Solar-powered sensors offer greater flexibility but depend on sufficient sunlight and require regular cleaning to maintain panel efficiency. They also provide security in areas prone to outages, helping to ensure uninterrupted monitoring.4
Sensors and their accompanying equipment, like solar panels, can be vulnerable to tampering and theft. Installing sensors behind locked barriers, in elevated/hidden locations, or within secure perimeters may be a necessary step to prevent unauthorized access.4
There is yet more to consider. Sensors transmit data using various technologies like cellular networks, Wi-Fi, or long-range (LoRa) communication protocols. Some sensors support only one communication method, while others offer multiple options. So, ensuring compatibility with local infrastructure, including bandwidth availability and signal coverage, is essential. In remote or bandwidth-limited areas, adjusting the sensor’s transmission frequency may help reduce data usage without sacrificing data quality.4
The System Is Important
Taken together, these factors highlight a central point: emissions monitoring is a systems challenge. It isn’t solved by hardware alone. Success depends on aligning the capabilities of the sensor with the goals of the monitoring campaign, integrating technical and logistical planning, and, most importantly, ensuring that data quality is maintained over time.
When set up properly, sensors can serve not just as compliance tools but as sources of valuable insight. They can guide emissions reductions, inform public health policy, and support efforts to make cleaner air a possibility.
References and Further Reading
- Basic Information about Air Emissions Monitoring [Online] Available at https://www.epa.gov/air-emissions-monitoring-knowledge-base/basic-information-about-air-emissions-monitoring (Accessed on 05 August)
- The Application of Air Quality Sensors For Monitoring Air Pollution in Communities [Online] Available at https://www.carteeh.org/wp-content/uploads/2024/03/05-36-TTI-THE-APPLICATION-OF-AIR-QUALITY-SENSORS-FOR-MONITORING-AIR-POLLUTION-IN-COMMUNITIES.pdf (Accessed on 05 August)
- Clements, A., Duvall, R. (2022) The Enhanced Air Sensor Guidebook [Online] Available at https://cfpub.epa.gov/si/si_public_file_download.cfm?p_download_id=545843&Lab=CEMM (Accessed on 05 August)
- A Guide to Siting and Installing Air Sensors [Online] Available at https://www.epa.gov/air-sensor-toolbox/guide-siting-and-installing-air-sensors (Accessed on 05 August)
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.