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14 Lawrence K. Wang et al.

It is important that consistent units be used in these equations. A convenient constant
to remember is the volume of ideal gas at standard temperature and pressure (STP):
3
22.4 L/g mol (359 ft /lb mol). Conditions of STP are 1 atm pressure and 0ºC (273 K).
Using this constant and Eq. (6) enables one to derive values of the gas constant (R) in
any convenient units. For example,
/
3
R = 82.05 atm cm g mol ºK
or
4
2
m /
R = 4.968 × 10 lb ft lb-mol ºR
(where lb means pounds of mass). R also equals 1.987 cal/g mol K.
m
Both ambient and source particulates occur in a distribution of size; that is, they are
polydisperse. These size distributions are usually log-normal and can be plotted on log
probability coordinates, as shown in Fig. 1. A probability plot of any sample containing
several types of material or material that has been treated by different techniques will
most likely be two or more straight intersecting lines. For example, a probability plot of
a pure crystalline substance should be a single line; if some of the crystals were thermal-
ly shocked by rapid cooling at the walls of the crystallizer or if some were mechanically
ground by the agitator, the plot may show as two or more intersecting lines.

6.1. Ambient Sampling

The US EPA announced ambient air-monitoring methods in 1971 (9), in 1973 (10), and
in 2004 (www.epa.gov). These announcements provide information on sampling proce-
dures, rates, times, quantities, operating instructions, and calibration methods. The basic
reference methods for gases are often wet chemistry analytical procedures, which include
the use of 24-h bubbler systems and very precise laboratory analyses. Accepted equivalent
methods include instrumental techniques, which are to be used under specific conditions
and must be calibrated. Briefly, the reference methods for gases are as follows:

1. SO , pararosaniline method
2
2. CO, nondispersive infrared methods
3. Photochemical oxidants, neutral-buffered potassium iodide photochemical method
4. Hydrocarbon, flame ionization methods
5. NO , Saltzman method
2
The reference method for suspended particulates in the atmosphere is the “high values
sampler,” which is discussed in a government publication (9).
Numerous instrumental methods are available for measuring atmosphere gaseous pol-
lutants, several of which are noted in Table 3. The systems are grouped into categories
according to the detection principle used, and some suppliers of the systems are noted.
The proper placement of ambient-air-monitoring systems can be as important as
the analytical method selected for obtaining good samples. The site location will
influence what is sampled. To obtain “typical” ambient air data, locations not directly
adjacent to roadways and other concentrated sources should be used and there should
be nonrestricted airflow around the site.
Many devices are located outside in the ambient air and, as such, minimize losses
resulting from sample lines. High-volume samplers are always taken outdoors, and
many bubblers are enclosed in protective, heated cases and kept outside. Some devices