Environmental Engineering Reference
In-Depth Information
Figure 9.5
Direct-read passive CO
sampler.
2
measurements can also be made using gas sampling tubes. The
principal advantage of using gas sampling tubes is their relatively low cost.
Cost, as well as time required to collect samples, increases significantly when
there is a need to collect many samples in different locations.
CO
2
2.
Carbon monoxide
Carbon monoxide levels are often measured in problem building investi-
gations and residential environments when there is reason to suspect that
a potential CO exposure problem exists. Carbon monoxide levels are usually
measured by real-time, direct-read electronic instruments or by gas sam-
pling tubes.
A variety of electronic direct-read CO measuring devices are available.
These instruments measure CO concentrations in ranges from a few ppmv
to several thousand ppmv. They determine CO levels by chemically oxidiz-
ing CO to CO
. As oxidation takes place, an electrical signal is produced
which is proportional to the CO concentration in the sampled air stream.
Both pump-driven and passive, hand-held sampling devices are available.
The former produces instantaneous real-time values, whereas the latter is
somewhat slower, requiring a minute or more to respond.
Real-time or quasi-real-time CO monitors have advantages similar to
those used for CO
2
. Pump-driven devices can be easily calibrated with stan-
dard gas mixtures, providing relatively good accuracy. Electrochemical cells
have a limited lifetime and must be periodically replaced.
Gas sampling tubes are commonly used in investigations where signif-
icant CO exposures may have occurred. Their accuracy is relatively good.
They are available in several concentration ranges, with ranges of 1 to
50 ppmv and 5 to 500 ppmv used in IAQ/IE investigations.
2
3.
Formaldehyde
Formaldehyde measurements were widely made in mobile homes,
urea-formaldehyde foam-insulated (UFFI) houses, and a variety of stick-built
