where:
W1 = tare weight of filter before sampling (mg)
W2 = post-sampling weight of sample-containing filter (mg)
B1 = mean tare weight of blank filters (mg).
B2 = mean post-sampling weight of blank filters (mg)
V = volume as sampled at the nominal flowrate (i.e., 1.7 L/min or 2.2 L/min)