Ensuring the Accuracy of Air Emissions Monitoring

Responding to regulations that are progressively becoming more stringent means that plant operators have an increasing responsibility to make sure that all air emissions are correctly monitored, measured and kept within prescribed limits.

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This article evaluates how air emission guidelines are changing and how process operators can guarantee the accuracy of air emissions monitoring equipment.

Despite the extensive improvement in air quality over recent years, air pollution continues to have a harmful impact on the environment while presenting a global public health risk: the result is an increasing number of governments tightening air emission standards.1

Consequently, industries are now under increased regulatory pressure in order to minimize emissions. Evaluation of UK air emissions shows that levels of PM2.5, NOx, SO2, and NMVOCs have significantly decreased over the last thirty years.

However, the UK government has committed to additional action deeming it necessary meet emission reduction targets. As a result, the dedication to ‘continuous improvement’ means an exploration of more opportunities for further emissions reductions.

Numerous large emitters, including chemical process operators and power plants, carry the greatest responsibility. They must effectively manage and continue to reduce their air emissions. This means that accurate and reliable monitoring of emissions is vital if they are to stay within range of ever-tightening legal limits.

Installing Continuous Emissions Monitoring Systems (CEMS) allows plants to monitor, track, and report emissions over extended periods with excellent accuracy, although intermittent monitoring with portable emissions measuring systems (PEMS) is still a popular choice for certain applications, especially where there is comparatively low variability in emissions.2

Enhancing measurement technology in this sector would facilitate an improvement in monitoring accuracy. The best CEMS have the capacity to simultaneously measure over 50 different gas components and can generally detect a few ppm of gas to within ± 2% accuracy.

The Importance of Emissions Monitoring Equipment Calibration

Irrespective of the resolving power of any emissions monitoring system, every single measurement carried out depends on the initial calibration. It is therefore paramount that this calibration is conducted as accurately as possible for both CEMS and PEMS. 

A precise calibration can be accomplished through the use of good calibration gas mixtures. Traceability of calibration gases is also key. There should be an unbroken chain of comparisons between any calibration gas within an international or national standard. 

For each of the gas species to be measured, monitoring equipment must be calibrated precisely, necessitating the use of several gas cylinders.

This can create certain issues when sensors are positioned in hard-to-reach places, such as at the top of an industrial stack, as transporting multiple cylinders of calibration gases to the sensor makes performing the necessary calibration can become time-consuming, expensive and at times far from ideal from a safety perspective. 

Thankfully, the advancement of multi-component calibration gas mixtures in a single-cylinder has eradicated this problem.

Through a combination of several gas components at known concentrations within a single gas mix, the number of cylinders needed to conduct calibration can be significantly reduced, thereby accelerating the calibration procedure and making it easier to complete. 

Air Products manufactures a wide-range of portable calibration gas products and mixtures (specifically for the air emissions monitoring market), developed to make calibration in hard-to-reach places as easy and accurate as possible. 

Cylinders containing calibration mixtures with up to four gas components, and certified within ISO 17025 accreditation scope, are manufactured to the highest standards, affording power plants and process operators the confidence when calibrating emissions monitoring equipment and evaluating the data and measurements subsequently recorded.


  1.  DEFRA Clean Air Strategy 2019. Available at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/770715/clean-air-strategy-2019.pdf. (Accessed: 3rd February 2020)
  2. What’s the Difference Between Continuous Emissions Monitoring and Periodic Measurement? Available at: https://www.auburnsys.com/blog/whats-the-difference-between-continuous-emissions-monitoring-and-periodic-measurement. (Accessed: 18th December 2019)

This information has been sourced, reviewed and adapted from materials provided by Air Products PLC.

For more information on this source, please visit Air Products PLC.


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