Environmental Engineering Reference
In-Depth Information
trometry has been used to identify volatile and semivolatile compounds in
solid sources.
Solvent extraction and subsequent analytical quantification was widely
used in the 1980s in attempts to characterize the potential potency of HCHO-
emitting sources. Except for the perforator method (extraction with toluene),
such techniques were not standardized nor were attempts made to relate
extractable free HCHO concentrations to source emission potentials.
Wet products such as paints, varnishes, and other coatings can be sam-
pled and analyzed directly to determine their composition as well as con-
centrations of potentially volatile or semivolatile substances. Concentrations
are usually expressed on a weight-to-volume basis (with reference to the
contents of either solids or liquids present or both). A standard method for
the determination of VOCs from liquid or semiliquid compounds has been
published by the American Society for Testing and Materials.
1. Static headspace analysis
Emissions from indoor sources can be better determined by using headspace
analysis techniques, wherein samples of source materials are placed in a small
airtight chamber made of or lined with inert materials (commonly glass).
After a period of equilibration at room or elevated temperature (to increase
emissions), samples are drawn from the chamber with a gas syringe and
injected into a gas chromatograph linked to a mass spectrometer for analysis.
In some cases, the chamber is purged with an inert gas, and contaminants
are collected on a sorbent prior to analysis (purge and trap method). Head-
space analyses continue to be widely used as a screening tool to identify
potential contaminants of concern and their relative emission potential.
2. Static equilibrium chambers
Wood-product manufacturers use static equilibrium chambers and testing
techniques on a day-to-day basis to evaluate emissions of HCHO from prod-
uct batches. Samples of UF-bonded wood products are placed in a glass
desiccator where, upon reaching equilibrium, the concentration of HCHO
in an absorbing solution in a standard collecting vessel (usually a glass petri
dish) is measured after a period of sample collection of 2 or 24 hours.
Equilibrium chamber concentrations have been shown to be directly related
to those obtained in large chambers. A simple linear regression equation is
used to convert equilibrium chamber values to large chamber values.
3. Dynamic chamber testing
a. Small chambers.
Emission rate data from source materials are
determined using dynamic flow-through chamber testing. Usually, such
determinations are made using small chambers, with volumes ranging from
<1 L to 1.5 m
3
. Less commonly, large (15 to 30 m
3
) chambers are used. In
either case, testing is conducted under carefully controlled conditions (tem-
perature, humidity, airflow rate) so that emission rate data can be applied
