There are many types of particle counters dependent upon the depth of particle analysis required:
Some manufacturers of light scattering optical particle counters (OPC) calibrate their instruments for well-defined particle material, to convert optical equivalent size both into aerodynamic and volume equivalent diameters. For specific test dusts, the calibrated OPC provides a direct read-out dust mass vs. aerodynamic diameter (assuming a standard density for the particle) and data is then provided as continuous particle mass measurements such as PM2.5 mass concentration.
A helpful analysis is studying particles generated by resuspension or cleaning efforts in a room. Much of the dust that becomes airborne is resuspended dust which is typically not submicron but more in the range of 2 microns and above. Thus for this work the use of standard optical particle light scattering equipment, with size discrimination may be well suited for the work. It would be best to look at real time instrumentation that can provide several bin size range outputs beginning around 0.1 to 0.5 microns.
When and where to measure
This is very much a function of what the study objectives will be. If researchers will be attempting to capture temporal variation in airborne particle concentrations as a function of some activity, then clearly they will need to establish a baseline/background concentration of the concentration to be able to gauge changes as a function of the activity of interest. Depending on occupant activity, there must be careful attention applied to identifying sites that have consistent occupancy and use for the duration of the work. If comparing sites such as one with vacuuming twice per week as compared to once per month, there is a need to ensure sites are similar in nature during the study. In addition, extended real time measurements may be necessary to gauge differences under these circumstances. Settled dust measurements may be another good indicator to measure over prescribed periods during tests to gauge impact of cleaning regimes on the environment.
It is important to conduct a power analysis of a number of measurement sites/tests necessary to achieve a given degree of statistical significance to ensure the data generated will be representative commensurate to the goals of the project.
Will any of this work be conducted within a chamber environment with set parameters or will it all come from field data of occupied settings? These are key questions that also need answering.
It is important to formulate a study plan that will produce sound and defensible results.
How to Select and Use a Particle Counter: Created on August 7th, 2009. Last Modified on August 7th, 2009
Dr. Richard J. Shaughnessy has served as Program Director of IAQ Research at the University of Tulsa since 1987. He has published extensively with respect to indoor air particulates, air cleaner evaluation, indoor air chemistry, school environment studies, flooring studies, asthma/housing research, ozone-initiated indoor reactions, and resolution and remediation of bioaerosol-related problems. He is currently researching the association between IAQ and student performance. He received his Ph.D. in Chemical Engineering from the University of Tulsa.
Dr. Shaughnessy was recently inducted by the Academy of Indoor Air Sciences of the International Society of Indoor Air and Climate, an award of recognition for his contributions both in the US and internationally in the field of Indoor Air.
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