Environmental Engineering Reference
In-Depth Information
the highest concentrations of fossil-fueled electricity-
generating plants, private vehicles, and trucks. The global
annual total of NO
x
was about 25 Mt N in 2005.
Part of this flux contributes, after oxidation to nitrates,
to the global aerosol load, but in many urban areas these
gases enter into complex photochemical reactions with
volatile organic compounds, released from incomplete
combustion of fuels and from the processing, distribu-
tion, marketing, and combustion of petroleum products,
and with CO from vehicle emissions, which culminate
in the formation of photochemical smog (Colbeck and
MacKenzie 1994; Mage et al. 1996; Heinsohn and
Kabel 1999). The brownish haze of smoggy regions
limits visibility (in extremes to just 10
1
m) and damages
materials. Its health impacts range from eye irritation to
increased frequency of asthmatic attacks and a higher
incidence of chronic emphysema. These effects are
due mostly to the formation of highly reactive O
3
and
peroxyacetyl nitrate. Photochemical smog has become a
recurrent seasonal presence in large cities as far as 50
N
and a semipermanent nuisance in many subtropical and
tropical megacities, including Ciudad Mexico, Bangkok,
Hong Kong, and Taipei.
High smog levels have affected increasingly larger
areas surrounding many major cities in North America,
Western Europe, and East Asia. By the 1990s these ex-
tensive metro-agro-plexes (combining cities, industries,
and intensive cropping) accounted for about 75% of
global fossil fuel use and for a third of worldwide cereal
production, yet their O
3
levels were above the threshold
where cumulative exposures during the growing season
lower crop yields (50-70 ppb). High levels of surface
O
3
are most worrisome in China. The country's size
makes it imperative that it remain largely self-sufficient
in food production, but high O
3
concentrations may
significantly reduce yields of spring wheat, soybean, and
corn (Aunan, Berntsen, and Seip 2000). Finally, it is
important to note that in many traditional societies it
is indoor air pollution—emissions from low-efficiency
combustion of biomass fuels in unventilated or poorly
ventilated rooms—that poses much higher health risks
than does the outdoor contamination of air (Smith
1993).
11.5 Interference in Grand Biospheric Cycles
In spite of its large demands for oxygen, fossil-fueled
civilization has a negligible effect on the planetary cycling
of the element indispensable for all heterotrophic life (see
section 11.4). The water needs of energy industries
(see section 11.3) diminish, delay, or accelerate local or
regional flows by altering surface and underground stor-
age, runoff, and evaporation, but these changes have a
minuscule impact on the ocean-dominated global water
volume. Most of the nutrients essential for photosynthe-
sis and heterotrophic metabolism do not really cycle. In-
soluble minerals stay put unless moved by water or wind
erosion, and soluble elements have just one-way flows,
piggybacking on a segment of the water cycle as they
move from continents to oceans, with temporary inter-
ruptions en route. Thus the focus must be on those
elements that are introduced into the environment by
fossil-fueled civilization in large quantities and that are
doubly mobile, that is, both water-soluble and airborne.
Only three elements are in this class: carbon, nitrogen,
and sulfur. All are needed to sustain life, and each one
has a unique role in the biota.
Carbon provides the basic matrix of life, accounting
for nearly half of the dry living mass; without nitrogen
there can be no amino acids (essential building blocks of
proteins), nucleic acids, enzymes, and chlorophyll; and
