by Wilberforce » Sun Oct 26, 2008 2:35 pm
I agree, Ernest, about the European and Australian practice of using particle counts
as opposed to particle mass to define air pollution levels. I surmise that the original
usage of particle mass data was to measure the direct effluent exiting a smokestack
(or vehicle exhaust pipe) since the gross amounts of particles present could not be
accurately counted, due to their sheer numbers. Besides, the technology to do accurate
particle counts did not exist in the 1960s, (laser counting was only recently invented)
when these measurements became necessary to perform, due to imposed regulations.
Hence, mass-value parameters were used (and still are used) for this purpose.
A problem arises, however, when this system of mass count is employed to measure
ambient air particles. The problem is that the total mass involved is very small. While
the larger particles (10 µm) might be measured this way, a problem arises when the
ultra-fine (nanoparticles of 0.10 µm) must be measured. These are really just large
clumps of individual molecules which have so little mass that the measurement itself
may come into question due to the limits of the instrumentation in use.
Perhaps it may be all right to measure direct chimney effluent with a mass-type system,
but I feel as though particle counting is by far the better means of defining nanoparticle
pollution levels in the atmosphere as a whole. As such, we need not rely on necessarily
expensive instrumentation to measure vanishingly small masses, along with the potential
for inaccuracy. Even under laboratory conditions, mass-data must be collected and
interpreted carefully.
In summary, I feel that counting is the superior method to use. Can we petition the EPA
to abandon the particle mass method, and begin adopting a particle count method?