Page 243 - Fundamentals of Air Pollution

206 14. Ambient Air Pollutant Analysis and Measurement

Pretreatment of the collected participate matter may be required for chem-
ical analysis. Pretreatment generally involves extraction of the particulate
matter into a liquid. The solution may be further treated to transform the
material into a form suitable for analysis. Trace metals may be determined
by atomic absorption spectroscopy (AA), emission spectroscopy, polarogra-
phy, and anodic stripping voltammetry. Analysis of anions is possible by
2
colorimetric techniques and ion chromatography. Sulfate (S0 4 "~), sulfite
2
(SO 3 ~), nitrate (NO 3~), chloride Cl~), and fluoride (F~) maybe determined
by ion chromatography (15).
Analytical methods available to laboratories with only general-purpose
analytical equipment may be found in the "Methods of Air Sampling and
Analysis" cited at the end of the previous section.

III. ANALYSIS AND MEASUREMENT OF ODORS

Odorants are chemical compounds such as H 2S, which smells like rotten
eggs, and may be measured by chemical or organoleptic methods. Organo-
leptic methods are those which rely on the response to odor of the human
nose. Although chemical methods may be useful in identifying and quanti-
fying specific odorants, human response is the only way to assess the
degree of acceptability of odorants in the atmosphere. This is due to several
factors: the nonlinear relationship between odorant concentration and hu-
man response, the variability of individual responses to a given odorant
concentration, and the sensory attributes of odor.
Four characteristics of odor are subject to measurement by sensory tech-
niques: intensity, detectability, character (quality), and hedonic tone (pleas-
antness-unpleasantness) (16). Odor intensity is the magnitude of the per-
ceived sensation and is classified by a descriptive scale, e.g.,
faint-moderate-strong, or a 1-10 numerical scale. The detectability of an
odor or threshold limit is not an absolute level but depends on how the
odorant is present, e.g., alone or in a mixture. Odor character or quality
is the characteristic which permits its description or classification by compar-
ison to other odors, i.e., sweet or sour, or like that of a skunk. The last
characteristic is the hedonic type, which refers to the acceptability of an
odorant. For the infrequent visitor, the smell of a large commercial bread
bakery may be of high intensity but pleasant. For the nearby resident, the
smell may be less acceptable.
The sensory technique used for assessing human perception of odors is
called olfactometry. The basic technique is to present odorants at different
concentrations to a panel of subjects and assess their response. The process
favored by the U.S. National Academy of Sciences is dynamic olfactometry
(16). This technique involves a sample dilution method in which a flow of
clean, nonodorous air is mixed with the odorant under dynamic or constant