This article provides guidance on adopting specific and most relevant portions of the US Environmental Protection Agency regulations on continuous emissions monitoring systems for industrial facilities in the Middle East.

To demonstrate compliance, industrial facilities in the Middle East that are subject to regulatory emissions limits and air quality permit conditions must frequently implement sophisticated continuous emissions monitoring systems (CEMS).

The monitoring equipment is used to demonstrate compliance with applicable emissions limits and standards. These limits and standards are either concentration based – parts per million (ppm) and parts per billion (ppb) – or mass based; for example, pounds per hour or day.

Pollutants monitored include sulphur dioxide (SO2), nitrogen oxide (NOx), carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbons (THC or VOC – O3), lead (Pb), and particulate matter (PM) – including PM10.

As shown in Figure 1, essentially a sample system continuously extracts a representative sample of stack gas from a process unit to the monitoring equipment, which includes various analysers. Once the gas sample has been analysed, the associated results are fed into a data acquisition and handling system (DAHS) that processes the voluminous data and outputs this to the facility’s reporting system.

The regulated industries in the Middle East often refer to the monitoring, recordkeeping, and reporting requirements developed by the United States Environmental Protection Agency (US EPA). There is a lack of guidance and clarity, however, when it comes to implementing the specifics of the US EPA’s regulations on the specialised types of industries located in the Middle East. Accordingly, there is confusion among the regulated industries in the Middle East on this matter.

Prior to equipment specification, installation and implementation of CEMS in Middle East industries, a solid understanding of the applicable US EPA regulatory requirements is first required.

Furthermore, the ongoing operation of an effective CEMS programme that consistently meets compliance requirements would entail significant effort in terms of quality control, maintenance, training, auditing, and reporting. The level of effort associated with these tasks requires specialised expertise and an organised, well defined approach.

Types of CEMS

The table below details the four major types of CEMS.

While a qualified CEMS supplier can assist with selection, installation and certification of equipment, as well as other elements such as the development of an adequate quality assurance and quality control (QA/QC) and maintenance plan, ongoing training, reporting, and auditing remain largely the responsibility of the facility.

Assuring and controlling quality

Environmental permits in the Middle East that require the CEMS to demonstrate compliance include provisions for ensuring data quality. In fact, QA/QC programmes are the backbone for CEMS compliance with regulatory requirements.

As shown in Figure 2, quality assurance pertains to ensuring the accuracy and reliability of the emissions data via proper planning and frequent audits. Quality control, on the other hand, includes the activities involved in maintaining or improving the accuracy and reliability of the emissions data, via routine calibrations and preventative maintenance.

Setting up appropriate QA/QC procedures, establishing missing data substitution provisions and specifying DAHS calculation procedures are just a few key elements of an effective QA/QC programme.

The quality assurance section of the QA/QC programme comprises the quality assurance plan together with routine audits. Quality control for the CEMS is ensured through the maintenance plan and calibrations.

Regulatory requirements for CEMS QA/QC vary, but all include tasks such as daily calibration, linearity tests, calibration gas audits (CGAs), and relative accuracy test audits (RATAs). Furthermore, data must be accurate, representative, reliable, complete and precise.

Maintenance programming

An effective CEMS maintenance programme that prevents breakdowns is essential to provide accurate and reliable data for compliance with applicable air quality regulations. The preventive maintenance programme should be organised, scheduled and efficient. Tasks are scheduled by frequency, such as daily or weekly, and they should log the person responsible, as well as the status of tasks, such as completed or not completed.

In the case of daily calibrations, the operator should ensure a quick response to failed calibrations, monitor and record calibration trends, and for facilities with multiple systems, scheduled daily calibration times should be staggered. Other maintenance tasks should be scheduled to avoid conflict with auto calibrations, to maximise data collection and minimise downtime.

Prior to initiating any preventative or maintenance activity, it is important to place the system into maintenance mode. This will mark the associated data with a maintenance flag, thus preventing the data from being used in hourly averages. Likewise, the system must be taken out of maintenance mode immediately following any maintenance activity.

Daily maintenance activities

As part of the preventative maintenance activities the system’s operator must visit each shelter daily and record in the log book the following parameters:

• Outlet pump pressure • Sample system vacuum • Sample flow to analysers • Temperature • Presence of alarms or faults • Cooler temperature • Peristaltic pump status – on or off

Frequently, the permit to operate requires that the log book be kept with the system. The log book provides a performance history of the system, information on previous issues and how those issues were resolved. The log book also provides a record of trends in flow, vacuum, pressure and temperature.

Another way some facilities maintain performance history of CEMS is through the use of maintenance forms. These are often more detailed than traditional log books, can be enabled on mobile devices and stored digitally.

Weekly maintenance activities

In addition to the daily activities, the system’s operator is responsible for weekly activities:

• Recording analyser test function readings, such as slope and offset • Recording calibration gas bottle pressures • Replacing calibration gas bottles if pressure is less than 150-200 psi • Monitoring for trends in daily calibrations, adjusting zero and span if needed

With respect to the analyser test functions, a downward trending slope could indicate a problem with the calibration response, such as a dirty lens or UV filter. This can be easily addressed, the system recalibrated and availability preserved.

Less frequent maintenance activities

Monthly preventative maintenance includes all of the daily and weekly tasks, as well as preparing for any upcoming audits such as RATAs, CGAs and linearity tests. It is also a good interval to check the status of air conditioning filters and plant air filters and to make sure the air conditioning unit is in good working order, especially in warmer areas or times of the year.

Quarterly requirements for CEMS include the completion of linearity tests, CGAs and NO2 converter tests. The results of these tests can be used to improve accuracy and reliability, thus improving availability.

Annually, many CEMS consumables reach the end of their service life and must be replaced, as dictated by manufacturers’ recommendations. Activities include probe maintenance; for example, replacing O rings and bushings, and replacing peristaltic pump tubing as well as the pump diaphragm and gaskets.

System maintenance programmes should be reviewed on a frequent basis to ensure that they are comprised of the appropriate tasks. An audit of the programme can assist in improving effectiveness and efficiency, as well as highlighting areas of positive achievement. Annual or biannual auditing is needed to identify deficiencies in compliance or provide assurance of continuing compliance.

Audits should be performed by an outside resource that is experienced with CEMS programme audits. The focus during the audit should be DAHS data emissions calculations and data replacement procedures. The audit should also include an evaluation of the entire system, including equipment inspection.

Accuracy and system bias

Primary performance testing for CEMS is conducted via the RATA on a schedule agreed with the regulatory agency. The RATA is a comparative evaluation of the system’s performance against an independent reference method. A reference method can be an instrumental method, in which gas is extracted from the stack and analysed directly by suitably calibrated analysers. The reference methods typically used in the Middle East, again, as referenced to US EPA regulations (under 40 CFR 60, Appendix A) are as follows:

• Method 2 – Reference method for determination of stack gas velocity and volumetric flow • Method 6C – Instrumental reference method for SO2 • Method 7E – Instrumental method for NOx

In a RATA, a minimum of nine sets of paired monitoring systems and reference method test data are obtained. A tester may perform more than nine sets of reference method tests and may reject up to three data sets, as long as the total number of runs used in calculating test results are equal to or greater than nine. Data from the RATA is used to determine both the relative accuracy and bias, if any, of a CEMS.

Systematic and random errors can occur in all of the subsystems and components of a CEMS. It is left to the skill and experience of the system’s manufacturer, integrator and operator to minimise any bias and obtain the best possible accuracy and precision. It is then the responsibility of the system’s owner and operator to maintain the system to specified levels of accuracy and precision.

Specifically, bias problems can be associated with the following:

• Sampling location and stratification • Dilution extractive system biases • Source level extractive biases • In situ gas and flow monitor biases • Pollutant and diluent analyser biases • Data acquisition and handling system problems

Technically, the accuracy of a measurement refers to the degree of agreement between the measured value and a true value. In source measurements, as in physical science in general, the true value of a physical parameter is rarely known. Instead, an accepted true value is generally used for comparison against the CEMS measured values. In source testing, the ‘true’ value is assumed to be the value determined by the EPA reference method. A typical RATA using a monitoring van with automated test equipment is shown in Figure 3.

In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree to which measurements of a quantity truly express that quantity’s actual value.

In contrast to accuracy, the precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. The distinction between accuracy and precision is explained in the table below, and illustrated in Figure 4.

Reporting emissions to regulatory agencies

The DAHS is the brains of the operation. It receives emissions data from the programmable logic controller (PLC) or data logger and arranges it according to programme demands. It also performs data substitution, calculates emissions and creates quarterly reports. This is also the portion of the CEMS in which most non compliance issues are discovered. Data acquisition and handling is not a task to undertake yourself; rather, the facility should purchase a system with proven reliability. Annual DAHS audits are critical for ensuring reported emissions are accurate, assessing data availability calculations, and affirming data substitution procedures.

Additionally, while reporting to the regulatory agency, the results from the bias test conducted as part of the RATA must be considered. The bias test determines whether a monitoring system has a low bias with respect to the reference method, based on the RATA results. This test is required only for SO2, NOx and flow monitoring systems.

If a low bias is found, a bias adjustment factor (BAF) must be calculated and applied to the subsequent hourly emissions data. As examples in the following table show, while both plants had the same raw CEMS reading, by applying the BAF one plant passes while the other fails to meet the permit limit.

Essential training

A final element necessary for proper operation of CEMS is training. Both environmental managers and facility operators should understand applicable air quality requirements, including how to effectively and appropriately operate the units. Nearly all analyser manufacturers offer training for their equipment. Analyser manufacturer training provides insight and knowledge and will assist in increasing the system’s data availability. If a facility is having a new CEMS installed, it is important to ensure that the system’s manufacturer provides training in proper operation of the CEMS to all personnel who will have a role in the system’s operation, maintenance and reporting.


Regulatory requirements in the Middle East are driving the use of CEMS to demonstrate compliance. Creating and maintaining a successful CEMS programme can be a daunting task for any environmental professional. Ensuring the correct type of CEMS is used is essential to demonstrate regulatory compliance. Creating a structured and well defined programme of quality assurance and control is also important for complying with the applicable regulations. A well organised and executed preventative maintenance programme will assist in maximising the performance and reliability of the CEMS and provide the highest data availability achievable.

Understanding the results of RATA tests and the implications of using bias adjustment factors while reporting emissions to regulatory agencies is a must. Finally, having a well trained and knowledgeable team also contributes to the accuracy and reliability of the CEMS data.

Published: 27th Feb 2014 in AWE International