Page 130 - Fundamentals of Air Pollution

100 7. Effects on Human Health and Welfare

reactions and removal rates of CO 2, its concentration has been increasing
steadily since the beginning of the Industrial Revolution (Fig. 2-4).
In its natural cycle, CO 2 enters the global atmosphere from vegetative
decay and atmospheric oxidation of methane and is removed from the
atmosphere by photosynthesis and solution by water bodies. These natural
sources and sinks of CO 2 have balanced over thousands of years to result
in an atmospheric CO 2 concentration of about 200-250 ppm by volume.
Over the past 200 years, however, the burning of fossil fuels has caused
a steady increase in the atmospheric CO 2 concentration to its current value
of —360 ppm by volume, with projected concentrations over the next 50
years ranging up to 400-600 ppm by volume worldwide (2). In raising the
concentration of CO 2, humans are clearly interacting with nature on a global
scale, producing a potential for atmospheric warming and subsequent
changes in ocean depths and agricultural zones. This topic is currently
subject to considerable research. Current research topics include further
development of radiative-convective models, determination of global tem-
perature trends, measurement of changes in polar ice packs, and refinement
of the global carbon cycle.

B. The Sulfur Cycle: Regional Scale
Human production of sulfur from fossil fuel and ore smelting has caused
an observable impact on the regional scale (hundreds of kilometers). Con-
siderable evidence suggests that long-range transport of SO 2 occurs in the
troposphere. In transit, quantities of SO 2 are converted to sulfate, with
eventual deposition by dry or wet processes on the surface far from the
original source of SO 2. Sulfate deposition plays the principal role in acid
deposition which results in lowering the pH of freshwater lakes and alters
the composition of some soils. These changes affect the viability of some
plant and aquatic species. The long-range transport of SO 2 and the presence
of sulfates as fine particulate matter play a significant role in reduction of
visibility in the atmosphere.

C. The Fluoride Cycle: Local Scale

The movement of fluoride through the atmosphere and into a food chain
illustrates an air-water interaction at the local scale (<100 km) (3). Industrial
sources of fluoride include phosphate fertilizer, aluminum, and glass manu-
facturing plants. Domestic livestock in the vicinity of substantial fluoride
sources are exposed to fluoride by ingestion of forage crops. Fluoride re-
leased into the air by industry is deposited and accumulated in vegetation.
Its concentration is sufficient to cause damage to the teeth and bone struc-
ture of the animals that consume the crops.