Page 33 - Air Pollution Control Engineering

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Air Quality and Pollution Control 13

ber (causing it to stress crack), paper, clothes, and other material, reacts with stone and
masonry, and just plain “dirties” surfaces.
One indirect effect of air pollution on the environment is the “greenhouse effect”
phenomenon. Here, the presence of pollution in the atmosphere helps produce a stable
atmospheric layer. Incoming solar radiation passes through the layer and warms the
earth. The layer retards convection and radiation processes, resulting in heat buildup.
Conversely, the pollution layer could prevent incoming radiation from reaching the
surface and produce cooling.
Acid rain pollution has not been adequately investigated, but the acidity of rain
downwind from fossil fuel power stations has been measured at values of pH 3 and less,
which is 300 times the acidity of normal rain. Normal rain in the United States is acid,
with an average pH of about 5.5. This could result from sulfur, nitrogen, and/or carbon
oxides. Particulates in the atmosphere can react to form secondary pollutants such as
sulfites/sulfates and nitrites/nitrates. It has already been pointed out that these materials
dominate the submicron group of bimodally distributed atmospheric aerosols, and it is
these small particulates (about 0.2 µm) that are most detrimental when inhaled by
humans. Atmospheric particulates act as nucleation sites that cause abnormalities in
rainfall. They also cause haze and reduced visibility.
A final example of a possible adverse effect of atmospheric pollutants on the envi-
ronment has already been mentioned: the fluorocarbon–ozone problem, which may
result in ozone destruction and consequent increased radiation levels that could cause
an increase in skin cancer. As is true with many of the other effects discussed, more
study is needed to fully evaluate this potential hazard.

6. MEASUREMENTS

Measurements of air pollution generally fall into two broad categories: ambient
and source. Well-designed procedural, setup, and analytical techniques are minimum
requirements to obtain meaningful data for both types. Unfortunately, too many insignif-
icant data are reported, and the problem often becomes one of sorting out the good from
the bad.
Several points apply to measurements made in both categories. As previously noted,
gaseous air pollutants and air are treated as ideal gases, and the ideal gas law can be used:

PV = nRT (6)
where P is absolute pressure, V is volume, n is number of moles, R is the gas constant,
and T is absolute temperature.
Dalton’s law of partial pressure is also used:

P = y P (7)
A A T
where P is the partial pressure of component A, y is the mole fraction of component
A A
A, and P is the total pressure. The sum of all the individual partial pressures equals the
T
total pressure:
P = P + P + P +.... (8)
T A B C