Question 5.17: In this example, the definition and classification of air po...

A. Organic compounds that have a vapor pressure of greater than 1 mm Hg at 25°C are defined to be volatile. As such, these compounds constitute the family of “volatile organic compounds” or VOCs. Commonly encountered VOCs are the following:

1. All monochlorinated solvents and several other chlorinated solvents such as trichloroethylene, trichloroethane, and tetrachloroethane.
2. The simple aromatic solvents such as benzene, xylene, toluene, ethyl benzene, and so forth.
3. Most of the alkane solvents up to decane (C_{10}).

B. Some inorganic compounds also meet the definition of volatility just defined (vapor pressure greater than 1 mm Hg at 25°C. As such, these are the “volatile inorganic compounds” or VICs. They include inorganic gases (e.g., hydrogen sulfide, chlorine, and sulfur dioxide).
C. When an organic compound has a vapor pressure of less than 1 but greater than 10^{−7} mm Hg, such a compound is classified as being in the “semivolatile organic compounds,” or SVOCs, family. Such organics commonly encountered are as follows:

1. Most polychlorinated biphenolics, dichlorobenzene, phthalates, nitrogen substituted aromatics such as nitroaniline, and so forth.
2. Most pesticides (e.g., dieldrin, toxaphene, parathion, etc.)
3. Most complex alkanes (e.g., dodecane, octadecane, etc).
4. Most of the polynuclear aromatics (naphthalene, phenanthrene, benz(a)anthracene, etc.)

D. Likewise, at the same vapor pressure as given in Part C, inorganic compounds are defined to be “semivolatile inorganic compounds” or SVICs. Elemental mercury is a semivolatile inorganic.

E. A compound or other substance is defined as being “nonvolatile” if it has a vapor pressure < 10^{−7} mm Hg at 25°C. This is also another way of defining a solid. Therefore, almost all particulate matter (PM) is nonvolatile. Examples of compounds that are found in PM, which result in such PM being considered HAP, are as follows:

1. The large polynuclear (also polycyclic) aromatics such as chrysene.
2. Heavy metals (e.g., lead, chromium, etc.).
3. Other inorganics (e.g., asbestos, arsenic, and cyanides).

F. It is now appropriate to classify hazardous, undesirable, or otherwise unwanted air pollutants:

1. Aromatic hydrocarbons: benzene, toluene, xylenes, ethylbenzene, and so forth.
2. Aliphatic hydrocarbons: hexane, heptane, and so forth.
3. Halogenated hydrocarbons: methylene chloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, trichloroethylene, 1,1,1- richloroethane, tetrachloroethylene, chlorobenzene, and so forth.
4. Ketones and aldehydes: acetone, formaldehyde, methyl ethyl ketone, and so forth.
5. Oxygenated hydrocarbons: methanol, phenols, ethylene glycol, and so forth.
6. Inorganic gases: hydrogen sulfide, hydrogen chloride, sulfur dioxide, nitrogen oxide, nitrogen dioxide, and so forth.
7. Metals: mercury, lead, cadmium, arsenic, zinc, and so forth.
8. Polynuclear aromatics: naphthalene, benzo(a)pyrene, anthracene, chrysene, polychlorinated biphenyls (PCBs), and so forth.
9. Pesticides, herbicides: chlordane, lindane, parathion, and so forth.
10. Other (miscellaneous): asbestos, cyanides, radionuclides, and so forth.

The appendix A lists compounds classified as hazardous by the US Environmental Protection Agency (US EPA) when present in an air emission stream (33). Original equipment suppliers (OEMs) of commercial absorber (scrubber) systems in North America are available refs. 31 and 34–36.