376 ENVIRONMENTAL ENGINEERING
Figure 19-1. High-volume sampler.Air flow through the filter is measured with a flow meter, usually calibrated in cubic
feet of air per minute. Because the filter collects dirt during its hours of operation, less
air passes through it during the latter part of the test than in the beginning, and the air
flow must therefore be measured at both the start and end of the test period and the
values averaged.
EXAMPLE 19.1. A clean filter is found to weigh 10.00 g. After 24 h in a hi-vol sampler,
the filter plus dust weighs 10.1Og. The air flow at start and end of the test was 60 and
40 fi3/min, respectively. What is the concentration of particulate matter?
Weight of the particulates (dust) = (10.10 - 10.00) g x lo6 pg/g = 0.1 x lo6 pg.
Average air flow = (60 + 40)/2 = 50 ft3/min.
Total air through the filter = 50 ft3/min x 60 mi& x 24 Wday x 1 day
= 72,000 ft3 x 0.0283 m3/ft3 = 2038 m3.Total suspended particulate matter = (0.1 x lo6 pg)/2038 m3 = 49 pg/m3.
The high-volume sampler operated in this way measures TSP. Hi-vol samplers
can be fitted with a variety of filters and used to measure smaller particles and particles
of a particular size. Measurement of 10-pm particles requires about 10 times the air
flow in a hi-vol sampler: 16.7 Wmin as compared to 1.4L/min for TSP. The ambient
standard is more stringent than it is for TSP (see Chap. 21).