Page 66 - Fundamentals of Air Pollution

42 4. Air Quality

Fig. 4-1. The same atmosphere measured by (a) a rapid-response instrument and by
sampling and analytical procedures that integrate the concentration arriving at the receptor
over a time period of (b) 15 min, (c) 1 hr, and (d) 6 hr.

nor Fig. 4-l(a) from Fig. 4-l(b). In these examples the time intervals involved
in Figs. 4-l(b), (c), and (d)—15 minutes, 1 hour, and 6 hours, respec-
tively—are the averaging times of the measurement of pollutant exposure
at the receptor.
The averaging time of the rapid-response record [Fig. 4-l(a)] is an inherent
characteristic of the instrument and the data acquisition system. It can
become almost an instantaneous record of concentration at the receptor.
However, in most cases this is not desirable, because such an instantaneous
record cannot be put to any practical air pollution control use. What such
a record reveals is something of the turbulent structure of the atmosphere,
and thus it has some utility in meteorological research. In communications