Environmental Engineering Reference
In-Depth Information
size. Particles less than 10 micrometers (four ten-thousandths of an inch)
in diameter are designated as PM
10
; those less than 2.5 micrometers are
PM
2.5
(one ten-thousandth of an inch). Three-quarters of the particles less
than 2.5 micrometers in diameter have diameters less than 0.1 microme-
ter (1/250,000 of an inch). Such tiny sizes are diffi cult to envision. In
comparison, a strand of human hair is 100 micrometers in diameter and
is about the smallest thing a human eye can distinguish; a coarse PM
10
particle of 7 micrometers is the size of a red blood cell. When we discuss
particulate matter in the air, we are talking about extremely small parti-
cles—particles that are invisible without using an optical microscope or
an electron microscope.
Particulate matter is released from motor vehicles, power plants, and
industrial processes in nearly equal amounts. We see it as the smoky
exhaust from the tailpipes of cars, the dark material in the smokestacks
of industry, the exhaust from coal-fi red power plants, and the haze in
city air that scatters sunlight.
In chapters 6 and 9, we considered the contribution of fossil fuels to
climate change. They are thought by most climatologists to be public
enemy number one in this regard, and their effect is growing as affl uence
and resulting car ownership increase in countries around the world. They
are also high on the list of enemies when air pollution is considered (table
10.1). Cars emit about a third of America's air pollutants. Driving a car
is probably a typical citizen's most polluting daily activity, in part because
of the nature of hydrocarbons and in part because of the amount of
driving Americans do. Americans drive 3 trillion miles each year. Assum-
ing an average 20 miles per gallon, we burn 150 billion gallons of gaso-
line in a year. The love of Americans for their vehicles is evidenced by
the fact that we devote 15 to 22 percent of our household expenditures
to them, about twice as much as we spend for food.
More than 600 million cars are on the world's roads. The UN predicts
that car ownership worldwide will increase to 1 billion to 1.5 billion by
2030 as populous developing nations such as China and India become
more affl uent. Auto sales in China are growing very fast, and the country
has started to manufacture its own vehicles.
Another important source of soot in ports along American coastlines
is international shipping, which has increased enormously during the
past twenty years.
4
Shipping capacity has increased by 50 percent, and
cargo ships have become one of the nation's leading sources of air pol-
lution. Oceangoing ships burn the dirtiest grades of fuel. These low-grade
hydrocarbons have sulfur levels 3,000 times that of gasoline. A single
