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There are a wide variety of environmental regulations related to air emissions monitoring and reporting for U.S. facilities. Generally speaking, continuous emission monitoring systems (CEMS) are used to monitor emissions and demonstrate compliance with applicable emission limits or standards. The U.S.  Environmental Protection Agency (EPA) specifically outlines the performance specifications and quality assurance requirements for most CEMS in 40 CFR Part 60 Appendix B and Appendix F, respectively. The performance specifications in Appendix B detail the design, installation, and performance requirements for a wide variety of pollutant and diluent CEMS. Appendix F Procedure 1 details the quality assurance and quality control requirements for CEMS to ensure the data produced are of a high enough quality to demonstrate compliance with Part 60 emission standards on a continuous basis. Although other regulations may require the use of CEMS to demonstrate compliance with an applicable standard (Cement Maximum Achievable Control Technology [MACT], Boiler MACT, Refinery MACT, Prevention of Significant Deterioration limits), the performance specifications and quality assurance requirements that are detailed in Appendix B and Appendix F are referenced in most standards that require CEMS. 

Developing and implementing a robust, compliant CEMS program can strain limited plant resources. A major component to maintaining a compliant, cost-effective CEMS program is ensuring the monitoring equipment is receiving the appropriate level of preventive maintenance. CEMS-specific and regulatory training can assist CEMS technicians and environmental managers in understanding the specific applicable requirements to ensure compliance. A comprehensive Quality Assurance (QA) Plan defines the equipment being monitored, the monitoring equipment itself, and step-by-step procedures for adequately maintaining the monitoring equipment, and also assigns responsibility for specific aspects of the CEMS program.

CEMS Maintenance Programs

Three types of CEMS maintenance are generally practiced: reactive, predictive, and preventive. Reactive maintenance is performed after a component has malfunctioned or stopped working. Predictive maintenance is performed when a facility attempts to anticipate or predict when a component will malfunction and replace the component just before the anticipated breakdown or failure. Preventive maintenance is performed when maintenance activities are scheduled to be performed on a pre-determined basis based upon the facility's experience with each CEMS and manufacturers' recommendations. The most successful CEMS programs rely upon preventive maintenance to assist in ensuring that CEMS perform reliably and produce representative, accurate data. A successful CEMS preventive maintenance program will result in the facility having a higher level of CEMS data availability than the level achieved if following only reactive or predictive maintenance practices.

An effective CEMS preventive maintenance program is organized, scheduled, and efficient. Preventive maintenance schedules are classified by frequency (daily, weekly, monthly, quarterly, semi-annually, and annually). Good preventive maintenance schedules identify the tasks to be performed on specific CEMS units, the frequency of the tasks, the status of the tasks (completed/not completed), and the person completing the tasks and the date completed. The specific tasks included in the preventive maintenance program will be determined by the type of CEMS in operation. A dry extractive CEMS preventive maintenance program, for instance, will likely include tasks such as sample pump rebuild or replacement, sample probe filter replacement, peristaltic pump head or tubing replacement, and a system leak check. A dilution extractive CEMS preventive maintenance program will involve different tasks since the major components of the sample system are completely different. Customizing the preventive maintenance program for each CEMS is essential to optimizing its effectiveness.  

Quality Assurance

One component of any preventive maintenance program that won't change EQ Winter CEMS 1regardless of the type of CEMS being utilized is the quality assurance (QA) requirements of the applicable regulation. Consider 40 CFR Part 60, for instance: regardless of whether the facility has a dry extractive, dilution extractive, hot wet extractive, or a Fourier-Transform Infrared Spectroscopy (FTIR) CEMS, the QA requirements are identical. 40 CFR Part 60 requires a relative accuracy test audit (RATA) once per four calendar quarters and a cylinder gas audit (CGA) in three out of four quarters (excluding the quarter the RATA is performed). Although some may argue that the required QA activities are not part of the preventive maintenance program, the preparation for and results of these QA checks are useful in determining the effectiveness of the preventive maintenance program; therefore, these QA checks form an integral part of the preventive maintenance program. For example, consider a facility that performed the required quarterly CGA and passed the CGA with a relative accuracy of 13.5%. Although the facility completed the required quarterly QA audit and passed, a relative accuracy of 13.5% indicates a CEMS performance issue. As a responsible CEMS program manager, the next step would be to investigate the cause of the elevated relative accuracy level to ensure the CEMS is producing reliable, accurate data moving forward. The primary goal of performing the required QA audits is to pass, but the results of the QA audits should also be used to improve CEMS performance.

Training for Success

One factor that contributes in a positive fashion to all CEMS programs is training: training from the analyzer manufacturers, training from the CEMS provider, and training regarding the requirements of applicable CEMS regulations. Effective  training can increase the level of knowledge related to the CEMS, thus helping to streamline  the jobs for all those involved, lessen the likelihood of non-compliance with applicable CEMS regulations, and ease the burden related to CEMS on already overstretched facility resources. All CEMS analyzer manufacturers and CEMS providers offer training on their products. Generally speaking, this training is not free (although it is sometimes included with the purchase of new analyzers or a new CEMS), but the knowledge gained by the technicians who work on the analyzers is invaluable and will assist the technicians in assessing and repairing an issue with a malfunctioning analyzer or CEMS much more quickly than without the training. This quicker resolution of a CEMS performance issue typically results in higher CEMS data availability, which in many cases can lower excess emissions and associated fines (if applicable). Training regarding the CEMS requirements of applicable regulations is very helpful in educating technicians on why they are required to perform certain tasks and how to prioritize tasks.  


CEMS Responsibility Structure

Having a well-established and defined CEMS responsibility structure is an important component to a successful CEMS program. Identifying who is responsible for specific requirements provides accountability and ownership of those specific CEMS-related tasks. Also, having a well-defined CEMS responsibility structure allows each team member to know where to direct questions on specific topics. The CEMS responsibility structure should be included in the facility's CEMS QA Plan.

QA Plan Requirements

40 CFR Part 60 Appendix F requires a facility to have a CEMS QA Plan if it uses a EQ Winter CEMS 2

CEMS to demonstrate compliance with an applicable emission standard. The QA Plan must include written step-by-step procedures for the following:


  • Calibration of the CEMS;
  • Calibration drift determination and adjustment;
  • Preventive maintenance tasks;
  • Spare parts inventory;
  • Data recording and calculations;
  • Accuracy audit procedures; and
  • Corrective actions for malfunctioning CEMS.

The QA Plan is a very important tool in building a successful CEMS program. The QA Plan can provide the initial structure and framework for developing and implementing detailed preventive maintenance and quality assurance activities. Often, facilities rely upon the CEMS knowledge of one or two individuals to maintain the system and to ensure the data being produced are reliable and accurate. Unfortunately, that leaves a knowledge void when those individuals retire or leave their positions. Having a specific, well-organized, structured QA Plan with step-by-step procedures for preventive maintenance, repairs, and QA activities can help ease the transition when highly experienced CEMS technicians leave. The QA Plan is a required part of the quality assurance/quality control program, but it also serves as a valuable tool for training and knowledge sharing, if the QA Plan is updated regularly to reflect what is actually being performed to maintain the CEMS at each facility.

The spare parts list, which is required as part of the QA Plan, is also an integral part of the CEMS program. If the necessary spare parts are not readily available, preventive maintenance and repairs cannot be completed. The spare parts list is intended to represent the spare parts that are on-site or easily accessible, not just to restate the manufacturer-recommended spare parts. Often, facilities refer to the manufacturer-recommended spare parts in the CEMS QA Plan, but in actuality that list does not reflect spare parts that are available on the shelf.


While there are numerous applicable CEMS-related regulatory requirements, most of the QA requirements refer back to 40 CFR Part 60, Appendix B and Appendix F. Regardless of the applicable regulations, utilizing a preventive maintenance program, receiving CEMS-specific training, and developing a robust QA Plan will certainly assist in easing the burden of complying with applicable CEMS regulations. If a facility develops and implements a well-defined CEMS program that includes step-by-step procedures for CEMS maintenance, QA activities, and repair of malfunctioning CEMS, and identifies the staff responsible for each aspect of the program, the foundation for ensuring compliance with applicable CEMS requirements will be in place, thus minimizing the likelihood of fines for non-compliance.