Chapter 17
Air and Air Pollution
The Atmosphere
• Each layer
characterized by
abrupt changes in
temperature, the
result of differences
in the absorption of
incoming solar
energy.
• Troposphere:
Weather Breeder
• Stratosphere:
Earth’s Global
Sunscreen
Outdoor Air Pollutants
• Air pollution: presence of one or more
chemicals in the atmosphere in sufficient
quantities and duration that 1) cause harm to
us and 2) alter the weather
– Come from both natural and human activities
– Natural pollutants are spread out and rarely reach
harmful levels
• In urban areas pollutants enter through
stationary sources (power plants, factories) and
mobile sources (vehicles)
Types of Outdoor Pollutants
• Primary Pollutants: emitted directly into the
troposphere in a potentially harmful form.
– Soot or particulate matter (PM10); lead, asbestos
– Hydrocarbons, CO, CO2, SO2,NO,NO2
– Volatile Organic Compounds (VOCs); paints, aerosols,
dry cleaners
• Secondary Pollutants: caused by reaction of
primary pollutants with the atmosphere
– SO3, HNO3, H2SO4, H2O2
Fig. 17-4 p. 421
Measurement Units
• Most common is parts per million (ppm)
• Example: concentration of 400 ppm of carbon
monoxide would be equal to 0.04%
• Other common measurements: parts per
billion (ppb or nano) and parts per trillion (ppt
or pico)
Smog
• Photochemical smog (brown air smog): air
pollution that is a mixture of primary and
secondary pollutants catalyzed by sunlight
– Nitrogen-based
– NO2 is responsible for the brown haze that hangs over
cities during sunny afternoons
– Hydrocarbons, oxygen and NO2 react to produce
peroxyacyl nitrates (PANs)
– NO2, O3, and PANs are called photochemical oxidants
– Net Result:
• NO + VOCs + O2 + UV = O3 + PANS
Photochemical Smog
Smog cont…
• Industrial Smog( gray air smog): consists of
sulfur dioxide, sulfuric acid and aerosols
– Suspended particles of ammonium sulfate salts
and carbon soot give the air a gray color.
– Urban industrial smog big problem in China, India,
Ukraine where there are inadequate pollution
control
Fig. 17-6 p. 424
Temperature Inversions
• Air temp. increases with height above the ground
(normally decreases temp. with height)
• A layer of warm air lies atop a layer of cool air near
the ground
• Because cooler air is denser than the warm air
above it, the air near the ground cannot rise
• Pollutants can concentrate in this layer of cold air
near the ground.
• 2 types:
– Subsidence temperature inversion (Los Angeles)
– Radiation temperature inversion
Acid Deposition
• Sometimes called acid rain
• Consists of rain, snow, dust, or gas with a pH
lower than 5.6
• In U.S. acid deposition regional problem in
eastern states because coal burning power
plants in Ohio Valley emit largest quantities of
sulfur dioxide.
• Eastern precipitation has average pH 4.2-4.7
and can get as low as 2.3 in some areas.
• Basic compounds CaCO3 (limestone) can buffer
some inputs of acids.
Indoor Air Pollution
• Come from 1) infiltration of polluted outside air
and 2) chemicals used or produced inside
buildings
• Health risks are magnified because people
spend 70-98% if their time inside
– EPA linked pollutants inside buildings to “sickbuilding syndrome”
• 3 most dangerous pollutants
– Cigarette smoke, formaldehyde, radon-222 gas
– Radon very common in homes, seeps into through
the soil into foundations and drain openings
Solutions: Preventing and Reducing Air
Pollution
• Clean Air Acts
– 1963** (set emission standards for stationary
sources—power plants, etc)
– 1970** (included mobile sources; established
• Primary standard: protects human health
• Secondary standard: prevents environmental and
property damage
– Directed EPA to establish national ambient air
quality standards (NAAQS)
Improving the Clean Air Act
• To help reduce SO2 emissions, CAA 1990
allows emissions trading policy
– Enables 110 most polluting power and industrial
plants to buy and sell SO2 pollution rights.
– Each year given certain # of credits that allow it to
emit SO2
• Environmentalists point to deficiencies:
– Continuing to rely on pollution clean-up than
prevention
– Failing to increase fuel efficiency for cars
– Not adequately regulating emissions