
Dr. Ian Marshall
Associate Director, Ricardo Energy & Environment, UK
Ian Marshall is Associate Director of the Ricardo Particle Measurement Centre. The Centre specialises in the calibration of particle counters and associated sampling and conditioning systems within an ISO 17025 accredited calibration facility. His background is chemistry and chemical engineering with 35 years’ experience in aerosol science. His areas of expertise are method standardisation and measurement system calibration.
Ian is a BSI nominated national expert on several CEN/ISO working groups covering size and concentration measurements of airborne particles.
Presentation:
Ultrafine Airborne Particle Measurement
The term “Ultrafine” is used to describe particles that are smaller than 100 nm in diameter (or smaller than 100 nm in at least one dimension). Such particles are present in the air, both indoor and outdoor, at typical concentrations of thousands of particles per cubic centimetre. They can be detrimental to human health and have an impact on the environment. It is typical for >90% of the number of particles in the air to be in the ultrafine particle size range; but the contribution of these particles to the total mass of particles in the air is almost insignificant. This is because such small particles individually have extraordinarily little mass; for example, one million particles of 10 nm diameter are equivalent in mass to only one particle of 1 μm (1000 nm) diameter of the same density. Consequently, measurement methods for ultrafine particles are based on particle number counting rather than particle mass determination.
Ultrafine particles originate both as a primary emission from sources such as fuel combustion and as a secondary source from chemical reactions in the atmosphere. Ultrafine particles undergo a variety of dynamic transformations in the atmosphere due to processes such as coagulation, growth by condensation, evaporation and deposition.
Measurement of ultrafine particles to a consistent standard are essential to:
- understand the concentrations close to suspected sources and to show how these concentrations vary with location and time
- quantify exposure for epidemiological studies
- assess the effectiveness of abatement techniques
- confirm that sources meet legislative limits where such limits exist.
A variety of measurement techniques are available to quantify airborne ultrafine particles in terms of both particle number concentration and particle size distribution. Each technique has its own advantages and limitations. A working knowledge of these characteristics is vital to ensure that suitable techniques are used for any given application. There are several sources of good practice guidance including European and International Standards covering topics such as design, validation, sampling and calibration.
The session will aim to review the most common measurement techniques: Condensation Particle Counters, Diffusion Chargers combined with Faraday Cup Aerosol Electrometers and Mobility Particle Size Spectrometers. It will cover their operating principles, offer best practice guidance, consider measurement traceability through proper calibration and highlight further sources of useful information.