Gas analysis - a matter of quality

Speciality gases have long been used to test emissions to air from sources in a wide range of industries. Now, new European legislation is aiming to standardise this important area of testing, to ensure that specified emission limit values are met and reliable measurements are made

In order to standardise emissions testing systems across Europe, the European Community is taking a two-pronged approach. On the one hand, a raft of new emissions control directives is establishing new or revised emission limit values on an industry-by-industry basis and on the other hand, a new European quality standard is specifying exactly how emissions testing should be carried out.

So far, the legislative change has been far-reaching and multi-layered, including directives such as the Integrated Pollution Prevention and Control (IPPC) Directive (96/61/EC) and other industry specific legislation like the Waste Incineration Directive (2000/76/EC) and the Large Combustion Plant Directive (2001/80/EC). In each case, the affected installations have a direct responsibility to ensure that the emissions limit values set are being achieved.

A matter of quality

As well as identifying new emission limit values, this environmental legislation requires that emissions testing and monitoring is carried out according to certain quality standards. In most cases the directives state that, where possible, the appropriate European Committee for Standardisation (CEN) standard should be used.

Clearly, introducing a standardised approach to emissions monitoring will bring a number of benefits. For industry, guidance on emissions testing will be welcomed as it introduces clarity in an area which previously lacked a uniform approach. At a European level, this quality-led approach will also allow EU member states to accurately compare emissions inventories, in the knowledge that identical monitoring and testing techniques have been employed.

Now in force across the EU, the new quality standard for stationary source emissions – Quality Assurance of Automated Measuring Systems (AMS) or Continuous Emissions Monitoring Systems (CEMs) as they are known in the UK -  is EN 14181. The standard was approved by CEN on 3 November 2003 and was adopted by the UK in July 2004.

In the past, most industrial operators in Europe installed, operated and maintained their emissions monitoring systems in a fairly informal and unregulated way. With the introduction of this quality standard, systems for the monitoring of stationary source emissions must now follow detailed criteria set by EN 14181 and the operator is directly responsible for ensuring that these procedures are followed.

About EN 14181

The new standard defines three different Quality Assurance Levels (QAL 1, QAL 2 and QAL 3) and explains how they should be applied as part of a plant’s ongoing emissions control and monitoring system. They cover everything from demonstrating the suitability of an AMS for its measuring task (QAL 1) to the validation and commissioning of the AMS (QAL 2) and the on-going operation and maintenance of the AMS insitu (QAL 3).  An Annual Surveillance Test (AST) is also defined.
                                              Emissions control is now standardised

In the UK, QAL 1 procedures are covered by certification under the MCERTS scheme for Continuous Emissions Monitoring Systems. Adding further endorsement to this scheme, the Source Testing Association has recently established the MCERTS competency standard and advocates that all operators responsible for emissions control and monitoring systems have achieved a minimum Level 2 MCERTS competency. From April 2006, this will be a condition of the plant’s or testing laboratory’s UKAS accreditation.

The new quality assurance requirements specified by EN 14181 can be summarised as follows:

QAL 1 (selecting an AMS)
• All emissions monitoring systems require some form of performance approval, such as MCERTS in the UK and must be shown to be suitable for the measurement task.
• To demonstrate QAL 1 compliance, the uncertainty of the measurement must be compared with uncertainty values set out in relevant EU or national legislation, which are given as percentages of the emission limit values.

QAL 2 (commissioning and validation of an AMS)
• All emissions monitoring equipment must be shown to be suitable for its application, prior to installation.
• Once commissioned, formal validation of the AMS is required. This starts with an assessment of the location of the sample point to ensure suitability.
• A comprehensive commissioning programme should be adopted.
• After installation, a full-scale validation programme should be followed. This involves the use of equipment provided from ISO 17025 test laboratories and a series of inspections, functional tests and comparisons against Standard Reference Methods (SRMs), to demonstrate relative accuracy.
• QAL 2 will determine calibration functions for each component; test compliance against uncertainty requirements and establish a valid calibration range for the AMS. It is this range that ultimately determines the operating limit for the plant.
• Where appropriate, for waste incineration plants or large combustion plants, further validation procedures must be followed at the required intervals.

QAL 3(ongoing operation and maintenance)
• A quality assurance system is needed to prove ongoing compliance.
• Maintenance activities must be properly monitored and controlled as part of an overall quality assurance programme.

For the Annual Surveillance Test (AST), a series of comparisons against a standard reference method are made to ensure that uncertainty requirements are still being met. In addition, an installation inspection and functional tests are completed and the maintenance regime is audited.

Technology ensures quality

Providers of gas handling equipment and speciality gases have been quick to respond to the demands of the emissions monitoring industry. In recent years, there have been a number of technological developments designed to address the need for enhanced quality and the reliability of analytical results. Emissions testing systems are now capable of providing accurate analytical measurements for all emissions regardless of their reactivity or their concentrations. In particular, it is now possible to achieve accurate analyses for reactive gases such as HCl and HF emissions, against average daily values set to 10 mg/m3 and 2mg/m3 respectively in Annex V of the Waste Emissions Directive.

New filling techniques and cylinder treatments have helped to ensure the reliability of results by ensuring that even complex calibration gases are of a consistently high quality. Many providers’ of gases and handling equipment, such as Air Products, have developed these techniques based on years of experience in the production and supply of ultra high purity gases and gas mixtures and draw on detailed knowledge about how individual gas components behave, at varying pressures and in different gas mixtures. By applying the right cylinder treatment and by using appropriate filling techniques, for example by adapting the way the compounds are weighed and added to the cylinder, the stability of a gas mixture can be significantly improved. These filling techniques are especially useful for ppb calibrations or with reactive compounds where long term stability is critical.

For zero and carrier gases, recent technological advances now mean that external purification is no longer necessary to guarantee high purity consistency. For example, Air Products’ patented BIP technology is providing gases with less than 10 ppb oxygen and less than 20 ppb moisture from the first to the last molecule. This is obviously a major step forward and removes a significant hassle factor for the operator by eliminating the need for external purification equipment and ruling out so-called rogue cylinders.

As a supplier of speciality gases and gas handling equipment for emissions testing, Air Products’ Experis range of gas products includes calibration gas mixtures specifying uncertainties for each gas component and allowing traceability to national standards. They also supply a wide range of certified gas mixtures, produced at our European laboratory, which is accredited to ISO 17025 standard.

With EN 14181 in place and amid increasing demand for accurate and reliable gas analysis, all those involved in emissions monitoring will need to work even more closely together to find ways of meeting the requirements of European legislation as efficiently as possible. For technological providers and operators alike, ensuring quality is now a priority issue and will continue to drive future developments.

For more information about the quality and legislative framework for the emissions testing and monitoring industry visit:

Source Testing Association - www.s-t-a.org
Environment Agency’s MCERTS – a certification scheme for instruments and monitoring and analytical services – www.mcerts.net
Air Products – www.airproducts.com/experis

By Anne-Catherine Gridelet, Air Products’ marketing specialist for Analytical and Laboratories Europe