A Particle Sizer for Real-time Measurement of rapidly changing aerosols - Mark Crooks

TSI® Incorporated recently launched the Fast Mobility Particle Sizer™ (FMPS™) Model 3091 (figure 1). The FMPS measures airborne particle size distributions in the nanometre size range with high time and size resolution. This technique allows simple and comprehensive measurement of rapidly changing aerosols such as are found in stacks, chimneys, ducts and even in ambient urban air.

TSI has been a specialist manufacturer of aerosol instrumentation for over 40 years. Our first commercial aerosol instrument, The Whitby Aerosol Analyser was introduced in the mid 1960’s. Since then the strategy of TSI has remained the same; to push forward the development of analytical technology, not simply because we can, but because there is a real, demonstrated need and application. During the past 40 years plus, aerosol science and instrumentation has taken many significant leaps forward, many of them due to TSI’s progressive Research and Development programs. Obviously improvements in micro processing and IT have had a big impact, not only on the instruments themselves but also on the process involved in the designing of those instruments, speeding up the time from inception to production and so reducing development costs and adding to the efficiency of TSI and therefore our reaction to our customers’ demands. In recent times TSI have made progress in a number of areas from being world leaders in Particle Image Velocimetry and Hand held Test and Measurement instruments to the area that we will concentrate on in this article, that of measuring ultrafine aerosol size distributions in “real time”.

The Scanning Mobility Particle Sizer™ (SMPS™) which has become one of the mainstays of the aerosol researcher around the world, is used to study everything from ambient aerosols to manmade products and has developed step by step as our understanding of the physical processes involved has also increased. However the SMPS is still, as the name suggests a “scanning” system, with a high resolution particle size distribution taking maybe 30-60 seconds to complete. For the vast majority of applications this system has become the defacto standard with a huge bibliography from across the world. It also has the added flexibility of being able to be modified by the selection of various components, such as interchangeable Condensation Particle Counters (CPCs), Differential Mobility Analyzers (DMAs), and impactors which allows the user to optimise instrument configuration to best meet their needs. Scan time was always a major concern for some applications where the physical nature of the aerosol is rapidly changing, has an active nucleation phase or may contain volatile materials, in addition there are situations where the aerosol is still in the process of reacting with the atmosphere or has to be “stored” prior to the measurement. The demand to study and measure in environments such as that produced from an internal combustion engine running a variable drive cycle has increased enormously. This has been partially driven by the promulgation of legislation and control related to the health effects of nano-materials, in the atmosphere, in industry and other environments. The development of such control limits requires the study and monitoring of such environments to a much greater degree than ever before. It is not only the mass of the particles that holds importance to the researcher but number concentration may also be important. Indeed the every decreasing size of these particles suggests that the number concentration of these atmospheres may well be an even more appropriate parameter than mass. This, added to the requirements of scientists around the world to look at ever smaller particles in ever more challenging environments has lead to a growing demand for “real time” measurement techniques.