Basic Calculations for Occupational Safety and Environmental Health Professionals - Mathematics and Statistics for the Environment - page 397

Two major environmental problems have developed in highly industrialized regions of the world
where the atmospheric sulfur dioxide concentration has been relatively high: sulfurous smog and
acid rain. Sulfurous smog is the haze that develops in the atmosphere when molecules of sulfuric
acid serve as light screeners. The second problem, acid rain, is precipitation contaminated with
dissolved acids such as sulfuric acid. Acid rain has posed a threat to the environment by causing
certain lakes to become devoid of aquatic life. Sulfur dioxide produces blotches that are white to
straw-colored on broad-leafed plants.

15.5.1.5 Carbon Monoxide (CO)
Carbon monoxide (CO) is a colorless, odorless, tasteless gas that is by far the most abundant of the
primary pollutants; it is formed when carbon in fuel is not burned completely. It is a component of
motor vehicle exhaust, which contributes about 56% of all CO emissions nationwide. Other non-
road engines and vehicles (such as construction equipment and boats) contribute about 22% of all
CO emissions nationwide. Higher levels of CO generally occur in areas with heavy traffic conges-
tion. In cities, 85 to 95% of all CO emissions come from motor vehicle exhaust. Other sources of
CO emissions include industrial processes (such as metals processing and chemical manufactur-
ing), residential wood burning, and natural sources such as forest fires. Woodstoves, gas stoves,
cigarette smoke, and unvented gas and kerosene space heaters are sources of CO indoors. The
highest levels of CO in the outside air typically occur during the colder months of the year when
inversion conditions are more frequent. The air pollution becomes trapped near the ground beneath
a layer of warm air.

15.5.1.6 Lead
Lead is a metal found naturally in the environment as well as in manufactured products. The major
sources of lead emissions have historically been motor vehicles (such as cars and trucks) and indus-
trial sources. At present, because of the phase out of leaded gasoline, metals processing is the major
source of lead emissions to the air. The highest levels of lead in air are generally found near lead
smelters. Other stationary sources are waste incinerators, utilities, and lead-acid battery manu-
facturers. In high concentrations, lead can damage human health and the environment. Once lead
enters the ecosystem, it remains there permanently. The good news is that, since the 1970s, stricter
emission standards have caused a dramatic reduction in lead output.

15.5.2 g ases
Gases are important not only from the standpoint that a gas can be a pollutant, but also because
gases convey the particulate and gaseous pollutants. For most air pollution work, expressing pollut-
ant concentrations in volumetric terms is customary. For example, the concentration of a gaseous
pollutant in parts per million (ppm), is the volume of pollutant per million parts of the air mixture.
That is,

Partsofcontamination
Million partsof

ppm = (15.1)

air

Note that calculations for gas concentrations are based on the gas laws:

• The volume of gas under constant temperature is inversely proportional to the pressure.
• The volume of a gas under constant pressure is directly proportional to the Kelvin tempera-
ture. The Kelvin temperature scale is based on absolute zero (0°C = 273 K).
• The pressure of a gas of a constant volume is directly proportional to the Kelvin temperature.