Page 240 - Fundamentals of Air Pollution 3E

II. Analysis and Measurement of Participate Pollutants 203

lists individual hydrocarbons measured in ambient air by advanced GC
techniques.
Other types of detectors include the flame photometric detector (FPD)
and the electron capture detector (ECD). The FID is composed of an H 2
flarne through which the hydrocarbon gases are burned, forming charged
carbon atoms, and an electrometer grid which generates a signal current
proportional to the number of carbon atoms in the flame. The example of
1 ppmV methane, CH 4/ and 1 ppmV (but 2 ppmC) ethane, C 2H 6, is related
to this detection principle. One ppmV of CH 4 and 1 ppmV of C 2H 6 in air
have the same number of molecules of hydrocarbon in a given volume of
air, but if an aliquot of each mixture were run through an FID, the signal
for ethane would be nearly twice the methane signal: 2 ppmC ethane
compared to 1 ppmC methane.
The FPD is also used to measure sulfur-containing compounds and there-
fore is useful for measurement of sulfur-containing hydrocarbons such
as dimethylsulfide or furan. The FPD has an H 2 flame in which sulfur-
containing gases are burned. In the combustion process, electronically ex-
cited S 2* is formed. A photomultiplier tube detects light emitted from the
excited sulfur at —395 nm. The ECD is preferred for measuring nitrogen-
containing compounds such as PAN and other peroxyacyl nitrate com-
pounds. The ECD contains a radioactive source which establishes a stable
ion field. Nitrogen-containing compounds capture electrons in passing
through the field. Alterations in the electronic signal are related to the
concentration of the nitrogen species.

F. General
The methods that have been discussed require specially designed instru-
ments. Laboratories without such instruments can measure these gases
using general-purpose chemical analytical equipment. A compendium of
methods for these laboratories is the "Manual on Methods of Air Sampling
and Analysis"published by the American Public Health Association. (10).

II. ANALYSIS AND MEASUREMENT OF
PARTICULATE POLLUTANTS

The three major characteristics of particulate pollutants in the ambient
atmosphere are total mass concentration, size distribution, and chemical
composition. In the United States, the PM 10 concentration, particulate mat-
ter with an aerodynamic diameter <10 /xm, is the quantity measured for
an air quality standard to protect human health from effects caused by
inhalation of suspended particulate matter. As shown in Chapter 7, the
size distribution of particulate pollutants is very important in understanding