Friday, November 25, 2005

Particle Size

The Dodger encountered this new journal while trolling medline. The author, Jim Vincent, is a solid citizen in the particle field.

The abstract is a model of conveying no information. The Dodger wonders, in addition, what's the difference between a "critical" review, a "systematic" review, and a just plain review. Is there a heirarchy? Below just plain reviews are there uncritical and unsystematic reviews?

Lurking behind the abstract in the full text is actually long and informative discussion of discussion of particle sizing advances since the Dodger went to industrial hygiene school.

There are at least two new things.

First is inhalable fraction, which includes particles larger than 10 microns [up to maybe 50]. In certain circumstances, like the WTC collapse, the large majority of the airborne mass is in this fraction which is excluded by the IH standard total particulate as measured by a closed face filter in a 37 mm cassette. Parallel with being aware that these particles exist, is recognition that reaction of the nasal surfaces can have systematic effects, such as observed among WTC recovery workers. Also, where the material may be absorbed, like lead, this near field divergence of actual mass from "total" mass may account for lack of correlation with body burden, and must be taken into account for quantitative risk assessment.

Second, we have the sub micron fraction, variously fine, ultrafine and nanoparticles. Most of the particle count in the fine [respirable, PM 2.5] is in the 1 micron range, arising from agglomeration of condensation processes. When you get below the 1 micron size, these particles are now known to penetrate the lung surfaces into systemic circulation.


Critical Review

Journal of Environmental Monitoring, 2005, 7(11), 1037 - 1053
DOI: 10.1039/b509617k

Health-related aerosol measurement: a review of existing sampling criteria and proposals for new ones

James H. Vincent

Interest in particle size-selective sampling for aerosols in working and ambient living environments began in the early 1900s when it became apparent that the penetration into—and deposition in—the respiratory tract of aerosol-exposed humans of inhaled particles was dependent on particle size. Coarse particles tended to be filtered out during inhalation and in the upper parts of the respiratory tract, so only progressively smaller particles penetrated down to the deep regions of the lung. Over time, following experimental studies with breathing mannequins in wind tunnels and with human volunteer subjects in the laboratory, a clear picture has emerged of the physical, physiological and anatomical factors that control the extent to which particles may or may not reach certain parts of the respiratory tract. Such understanding has increasingly been the subject of discussions about aerosol standards, in particular the criteria by which exposure might be defined in relation to given classes of aerosol-related health effect—and in to turn aerosol monitoring. The ultimate goal has been to develop a set of criteria by which exposure standards are scientifically relevant to the health effects in question. This paper reviews the scientific basis for such criteria. It discusses the criteria that have already been widely discussed and so are either being applied or are on the threshold of practical application in standards. It also discusses how new advanced knowledge may allow us to extend the list of particle size-selective criteria to fractions that have not yet been widely discussed but which may be of importance in the future.

Graphical abstract image for this article  (ID: b509617k)

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