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# Question: Pharmaceutical class 100000 particulate as compared to pm2.5

by Ag8n |

In the pharmaceutical industry, we frequently had to certify clean rooms as class 100,000 (or better). This took laser particle counters that counted and sized each individual particle. We had them both for air and liquids. So the question is- how do you convert class 100,000 to pm2.5 or pm10?

Hello!

So, pm2.5 and pm10 are typically measured in the unit microgram per cubic meter, μg/m3. From what I've read about clean room standards, the clean room classifications are measured as # of particles per cubic meter. However, some clean room standards are measured as # of particles per cubic foot. So first, figure out if the particle counts you have are per m3 or per ft3.

To convert from a particle count into a mass concentration, you have to make several assumptions about the particle:

• All particles are spherical
• All particles have a density of 1.65E12 μg/m3 [1]
• The radius of a particle in the PM2.5 channel is 0.44 μm [2]
• The radius of a particle in the PM10 channel is 2.60 μm [2]

caution: convert the aforementioned radius values into m3 before doing this calculation

With those assumptions, solve for the volume of each particle in m3:

then solve for the mass of each particle in micrograms, μg:

= density*volume

and then solve for the concentration in μg/m3 by multiplying:

= (# of particles per cubic meter) * mass

If you're particle count is actually per ft3 then you'll need an extra conversion factor:

(# of particles per cubic meter) = 0.0283168*(# of particles per cubic feet)

Citations: [1] Tittarelli, T. et al., “Estimation of particle mass concentration in ambient air using a particle counter,” Atmospheric Environment, vol. 42, pp. 8543-8548, 2008.

[2] Lee, J. et al., “Seasonal variations of particle size distributions of PAHs at Seoul, South Korea,” Air Quality Atmospheric Health, vol. 1, pp. 57-68, 2008.