Environmental Engineering Reference
In-Depth Information
Figure 9.3
Palmes diffusion tube. (From Palmes, E.P. et al.,
AIHAJ
, 37, 570, 1976.
With permission.)
include small badges that provide relatively high sampling rates over a
period of 8 hours (
Figure 9.4
)
, and charcoal canisters used for radon mea-
surements over a period of 2 to 7 days. Track-etch detectors are passive
samplers that record alpha particle tracks on plastic film over a period of
months. Unlike most passive samplers, track-etch detectors do not use the
principle of diffusion directly.
Passive samplers have the advantage of low cost, simplicity of use, and
reliability. They are designed to have an acceptable accuracy/precision (e.g.,
±25%). Their accuracy/precision is diminished by changes in face velocity
(due to changes in room airflow), which may occur during sampling. Passive
samplers are not particularly useful in conducting problem building inves-
tigations because of the long sampling times required (generally 8 hours or
more). They have, however, been widely used in screening measurements
of HCHO, NO
, and radon in indoor environments.
2
Figure 9.4
Badge-type passive samplers.
