Page 478 - Environment: The Science Behind the Stories

oxygen (O ) to form SO . Once in the atmosphere, SO may 200
2
2
2
react to form sulfur trioxide (SO ) and sulfuric acid (H SO ), 300
2
4
3
which may then settle back to Earth in acid deposition (p. 491). 150 Year (–99%) 250
1970
2012
Nitrogen oxides Nitrogen oxides are a family of compounds (–73%) (% change) 200
that include nitric oxide (NO) and nitrogen dioxide (NO ). Nitro- 100
2
gen oxides result when atmospheric nitrogen and oxygen react at Millions of tons emitted 150 Thousands of tons
high temperatures. Most U.S. NO emissions result from com- 100
X
bustion in vehicle engines. Electrical utility and industrial com- 50 (–62%)
bustion account for most of the rest. NO emissions contribute to (–58%) (–83%) 50
X
smog, acid deposition, and stratospheric ozone depletion. (–85%)
0 0
VOCs
Volatile organic compounds Volatile organic compounds CO NO x Air pollutant SO 2 PM 10 Pb
(VOCs) are carbon-containing chemicals used in and emitted by
vehicle engines and a wide variety of solvents, industrial pro- (a) Declines in six major pollutants
cesses, household chemicals, and consumer items. One group of
VOCs consists of hydrocarbons (p. 46) such as methane (CH , 250 +212%
4
the primary component of natural gas), propane (C H , used 200
3
8
as a portable fuel), butane (C H , found in cigarette lighters), +167%
4
10
and octane (C H , a component of gasoline). Human activities 150
18
8
account for about half the VOC emissions in the United States. 100
The remainder comes from natural sources; for example, plants Percent change (1970–2011) +52% +45%
produce isoprene and terpenes, compounds that generate a blu- 50
ish haze that has given the Blue Ridge Mountains their name. 0
VOCs can react to produce a number of secondary pollutants. –50
Particulate matter Particulate matter is composed –100 –68%
Vehicle
Energy
of solid or liquid particles small enough to be suspended in Emissions Population consumption miles GDP
the atmosphere and able to damage respiratory tissues when traveled
inhaled. Particulate matter includes primary pollutants such as (b) Trends in major indicators
dust and soot, as well as secondary pollutants such as sulfates
and nitrates. Scientists classify particulate matter by the size of Figure 17.14 U.S. emissions have declined sharply since
the particles. PM pollutants consist of particles less than 10 1970. We have achieved reductions (a) in the six major pollut-
10
microns in diameter (one-seventh the width of a human hair), ants tracked by the EPA, despite increases (b) in U.S. population,
whereas PM pollutants consist of still-finer particles less energy consumption, vehicle miles traveled, and gross domestic
2.5
than 2.5 microns in diameter. Most PM pollution is from road product. Data from U.S. EPA.
10
dust, whereas most PM pollution results from combustion.
2.5 By what percentage has population increased since 1970?
By what percentage have emissions decreased? Using
Lead Lead is a heavy metal that enters the atmosphere as a these two amounts, calculate the change in emissions per person.
particulate pollutant. The lead-containing compounds tetraethyl
lead and tetramethyl lead, when added to gasoline, improve in emissions have occurred despite significant increases in the CHAPTER 17 • AT m os PHER i C sC i E n CE , Ai R Qu A li T y, A nd Poll u T i on Con TR ol
engine performance. However, exhaust from the combustion of nation’s population, energy consumption, miles traveled by
leaded gasoline emits airborne lead, which can be inhaled or can vehicle, and gross domestic product (Figure 17.14b). Likewise,
be deposited on land and water. Lead can enter the food chain, most other industrialized nations have taken their own steps to
accumulate in body tissues, and cause central nervous system reduce emissions and have attained similar results.
malfunction and many other ailments (p. 385). Since the 1980s, We have achieved this success in controlling pollution
leaded gasoline has been phased out in most industrialized as a result of policy steps and technological developments,
nations (p. 26), and as a result lead pollution has plummeted. each motivated by grassroots social demand for cleaner
The United States led the way, Mexico City phased out leaded air. Cleaner-burning motor vehicle engines and automo-
gasoline in the 1990s, and today most developing nations are tive technologies such as catalytic converters (Figure 17.15)
following suit, although auto exhaust still creates significant lead have played a large part, reducing the emissions of carbon
pollution in many of them. In developed nations today, the main monoxide and other pollutants from motor vehicles. In fac-
source of atmospheric lead pollution is industrial metal smelting. tories, power plants, and refineries, technologies such as
baghouse filters, electrostatic precipitators, and scrubbers
We have reduced pollutant emissions (Figure 17.16) have been installed to chemically convert or
physically remove airborne pollutants before they are emit-
Since passage of the Clean Air Act of 1970, the United States ted from smokestacks. The sulfur-dioxide permit-trading
has reduced emissions of each of the six monitored pollut- program (p. 201) and clean coal technologies (p. 555) have
ants substantially (Figure 17.14a). These dramatic reductions reduced SO emissions. And phaseouts of leaded gasoline 477
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