In gravimetric PM measurement, the PM mass is determined by which of the following?

• A. The difference between pre- and post-sampling filter weights.
• B. The post-sampling filter weight alone.
• C. The pre-sampling filter weight alone.
• D. The ambient PM mass.

Answer: (A)

Gravimetric PM measurement determines the mass of particulate matter by weighing a filter before and after sampling and calculating the difference. The initial (pre-sampling) weight gives the clean filter’s mass, and after sampling the filter has gathered PM along with the filter itself held at controlled conditions. The post-sampling weight minus the pre-sampling weight yields the PM mass collected during the sampling period. For example, if the pre-weight is 1.0000 g and the post-weight is 1.0123 g, the PM mass is 0.0123 g (12.3 mg). The ambient PM mass isn’t read directly; it’s the mass increase on the filter that’s used, typically converted to a concentration by dividing by the sampled air volume.