In addition to exposure to smoke from oil-well fires, military personnel might have had exposures to combustion products because they were close to military vehicles, aircraft, and heaters in poorly ventilated tents.

Physical and Chemical Properties

As discussed above, combustion products are complex mixtures of substances. The physical and chemical properties of the major components of combustion products are discussed below.

Hydrogen Sulfide

As described by the (ATSDR 1999a), H2S is a colorless, flammable gas under normal conditions. H2S—also known as hydrosulfuric acid, stink damp, and sewer gas—has an odor similar to that of rotten eggs. It is a naturally occurring compound found in crude petroleum, natural gas, volcanic gases, and hot springs. It can also be made by people, and it can be found in human and animal waste, sewage-treatment facilities, sediments of fish aquaculture, and livestock barns or manure areas. Petroleum refineries, natural-gas plants, petrochemical plants, coke-oven plants, kraft-paper mills, food-processing plants, and tanneries are other sources of H2S (ATSDR 1999a).

Sulfur Oxides

SOx easily dissolve in water. Sulfur is found in raw materials, including crude oil, coal, and ore that contains common metals, such as aluminum, copper, zinc, lead, and iron. When fuel that contains sulfur is burned, SOx is formed. SOx can also form when gasoline is extracted from oil, or metals are extracted from ore.

SO2 dissolves in water vapor to form sulfuric acid, and it interacts with other gases and particles in the air to form sulfates and other products. Sources of SO2 include electric utilities, petroleum refineries, cement manufacturing, and metal-processing facilities. Locomotives, large ships, and some nonroad diesel equipment burn high-sulfur fuel and release SO2 into the air (EPA 2003b).

Nitrogen Oxides

From the human-exposure perspective, NO2 is the most important and common nitrogen oxide. NO2 is a reddish brown, water-soluble, moderately oxidizing gas. The primary atmospheric reaction for NO2 production is the rapid oxidation of NO by oxidants, such as O3. Major sources of NO2 include the combustion of fossil fuels from stationary sources for heating and power generation and in motor-vehicle internal-combustion engines. As in the case of many other outdoor pollutants, concentrations of NO2 can vary with the time of day, the season, meteorologic conditions, and human activities (Gong 1992). Unvented combustion appliances, such as gas stoves and gas-fired water heaters, are major sources of indoor NO2.

Carbon Monoxide and Carbon Dioxide

The fourth-most abundant gas in the earth’s atmosphere, CO2 is a colorless, odorless, and faintly acid-tasting gas at room temperature. It is transformed into sugars and other forms of energy by plants during photosynthesis, and it is exhaled by animals as a waste product of

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