NPL service provides high-tech air quality measurement

Melanie Williams, Environmental Measurements Group Leader at the National Physical Laboratory, outlines the NPL's sophisticated services in the measurement of a range of gases

Monitoring the air we breathe is becoming ever more important as the UK implements new EU legislation. Local authorities are tasked with the job of improving air quality in areas where pollution levels are too high, but putting an appropriate measurement campaign into action is not always straightforward.

As local authorities put plans into place for their Air Quality Management Areas (AQMAs), the National Physical Laboratory (NPL) is there to offer advice and consultancy. We routinely measure, nitrogen oxides, sulphur dioxide, acid gases, carbon monoxide, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons, metals and particulates. We will ensure that the measurement campaign will accurately assess the improvements achieved by specific measures in the action plan.

National standards

NPL is the United Kingdom's national standards laboratory, an internationally respected and independent centre of excellence in research and development in measurement and materials science. For more than a century we have developed and maintained the nation's primary measurement standards - the heart of an infrastructure designed to ensure accuracy, consistency and innovation in physical measurement.

In the area of air quality, our field monitoring services are underpinned by extensive scientific research and method validation to ensure the best measurement techniques are applied. An ambient air quality survey from NPL is UKAS accredited for sampling and analysis and can be used to:

  • Monitor boundary fences and community locations
  • Identify air quality zones and areas of exceedence
  • Monitor roadside and urban air quality
  • Validate pollution abatement measures
  • Characterise odour problems

    Concerned employers are now also becoming aware of the importance of the quality of indoor air to the well being of their employees. An indoor air survey from NPL can highlight the impact of a nearby industrial facility.

    NPL also plays a fundamental role supplying traceability to the air quality network measurements carried out throughout the UK, on behalf of both DEFRA and local authorities throughout the UK. These networks exist to provide public health information; to ensure compliance with UK and EU regulation; and to further air quality modelling and research aims.

    Traceability & data quality

    Traceability and data quality are provided by NPL in two ways:

  • Traceability and instrument performance audits to the monitoring sites
  • Quality assurance of monitoring data based on the audit results. This includes data-processing and statistical and other checks of the datasets themselves.

    These processes, the first of which is UKAS accredited as a calibration service (No 0478), work in conjunction to provide a final, readily defensible, dataset of the highest possible quality.

    Measurement technology is advancing not only to meet the public's demands for cleaner air, but also to anticipate changes in industrial processes. We are at the forefront of research to find the best way of measuring particulates of different size ranges. Quantifying smaller and smaller particulates will become more important as nanotechnology is introduced into industrial processes.

    NPL has also anticipated future measurement needs by developing a laser based instrument, DIAL, to provide rapid, accurate measurements of airborne emissions up to 3km away from industrial plant. The DIAL technology is particularly useful for remote asurements into inaccessible areas, measurement of total industrial site emissions, quantification of leaks and plume tracking from complex industrial plant. As attention shifts to assessing the overall impact of industrial sites then this technique will be ready to provide the necessary measurements.

    NPL has developed a Controlled Flow Air Sampler to meet EU benzene monitoring requirements and it has been in service in this role since 2001. The system pumps controlled air samples alternately through two standard sampler tubes. The use of two samplers allows measurement repeatability to be checked. The sample is taken through a 1/8 inch, electro-polished stainless steel tube at a flow rate of approximately 2 litres per minute. This avoids sample losses to the walls of the pipe. The system performs a number of diagnostic tests. Circuits continuously monitor the power supplies, reference voltages, and the internal clock, and also compare the measured flow with the set point of the mass flow controller. In the event of a failure in any of these an indicator LED ceases to flash. NPL offers a high quality calibration service for ambient pollution analysers both at NPL and at field sites. Species covered, at ambient concentrations, are nitrogen oxides, PM10, sulphur dioxide, carbon monoxide and ozone. NPL maintains measurement standards for these species, which undergo regular national and international comparison with standards held by other national measurement institutes. As well as calibrations of pollution analysers, NPL can supply certified transfer gas standards for the gaseous pollutants named above. Utilisation of a traceable calibration standard is the first step in ensuring accurate monitoring data. Our standards are shipped with ISO 17025 compliant certificates with uncertainties (at 95% confidence limits) of ±3%.

    NPL and the RSC (Royal Society of Chemistry) are holding an event for all those who wish to keep up to date with air quality monitoring advances and discuss issues informally. Monitoring Ambient Air: Implications and Implementation of the New Directives and Standard will take place in London on 15-16 December 2004. See www.npl.co.uk/agac for more details.


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