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Question:How does the EPA measure things, especially the size of dust particles?

kgradow1 asked on October 01, 2017 12:11
116 | 1 answers | shortlink

I've spent a lot of the last day and half trying to catching up on PM monitoring techniques for the microscope project. In this article - https://publiclab.org/wiki/silica-monitoring - there are a number of references to EPA monitoring techniques for different particles sizes. Beyond writing up an explanation of scanning electron microscopy and X-ray diffraction (which seems useful on its own), it might be useful to do a methodology review for how the EPA measures differently sized particles.

A brief overview of measurement techniques might be useful for providing context for what people will and won't be able to see. SEM pictures are detailed and very beautiful, and I think they give people a misleading view of what you can see with at the 5-10 um level. I've found that to be confusing when working with the Open Flexure microscope

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kgradow1 16 days ago

Potential resource: A Guidebook for Particle Size Analysis (industry) https://www.horiba.com/fileadmin/uploads/Scientific/eMag/PSA/Guidebook/pdf/PSA_Guidebook.pdf

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1 Answers

For regulatory purposes, the EPA doesn't actually measure the size of individual particles. Rather, they use a pump with an impactor. This pumps in particles of a range of sizes, and as the particles travel around the impactor, they crash out due to inertia based on their size. The particles that make it through the system (with a 50% cut point for particles of 10 um diameter or 2.5 um diameter for "PM10" and "PM2.5," respectively) are collected on a filter, and that filter is weighed. By weighing the filter and dividing it by the volume of air pumped into the system, you obtain a weight per volume concentration of particles of an operationally defined size category. A drawing of this method is included here: https://publiclab.org/wiki/pm#Regulation.

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