17
Atmospheric Science and Air Pollution
Chapter Objectives This chapter will help you:
Describe the composition, structure, and function of Earth’s atmosphere Relate weather and climate to atmospheric conditions Identify major pollutants, outline the scope of outdoor air pollution, and assess potential solutions
Explain stratospheric ozone depletion and identify steps taken to address it Define acidic deposition and illustrate its consequences Characterize the scope of indoor air pollution and assess potential solutions
Lecture Outline I. Central Case: L.A. and its Sister Cities Struggle for A Breath of Clean Air
A. Today, L.A. still suffers the nation’s worst smog, but its skies are clearer than in some of its “sister cities” elsewhere in the world.
B. One of L.A.’s sister cities is Tehran, the capital of Iran. Both cities have a lot of smog.
C. Health authorities blame several thousand premature deaths per year in Tehran on lung and respiratory diseases resulting from air pollution. In 2006, fully 3,600 people succumbed in just a month.
D. As in Los Angeles, traffic generates most of the pollution in Tehran.
E. As with Los Angeles, topography worsens the problem.
F. And as with Los Angeles in recent decades, people are streaming Tehran from elsewhere. As a result, the government’s efforts to rein in pollution are being overwhelmed by population growth.
G. Cities like Tehran are taking steps to improve their air quality, just as American cities like Los Angeles have done before them.
II. The Atmosphere
1. The atmosphere is a thin layer of gases that surrounds Earth.
2. Earth’s atmosphere consists of 78% nitrogen (N2) and 21% oxygen (O2). The remaining 1% is composed of argon (Ar) and minute concentrations of several other gases.
3. Over our planet’s long history, the atmosphere’s composition has changed.
A. The atmosphere is layered.
1. The bottommost layer is the troposphere, which blanket’s Earth surface and gives us the air we need to live.
2. The stratosphere extends from 11-50 km above sea level, its temperature rising gradually with altitude.
3. A portion of the stratosphere between 17 km and 30 km above sea level contains most of the atmosphere’s ozone and is called the ozone layer. This layer greatly reduces the amount of UV radiation that reaches Earth’s surface. The protection of the ozone layer is vital for life on Earth.
4. Above the stratosphere lies the mesosphere, which extends from 50-80 km above sea level.
5. From the outer mesosphere, the thermosphere extends upward to an altitude of 500 km.
B. Atmospheric properties include temperature, pressure, and humidity.
1. Atmospheric pressure measures the force per unit area produced by a column of air, and decreases with altitude.
2. Relative humidity is the ratio of water vapor a given volume of air contains to the maximum amount it could contain at a given temperature.
3. The temperature of air varies with location and time.
C. Solar energy heats the atmosphere, helps create seasons, and causes air to circulate.
1. Energy from the sun heats air in the atmosphere, drives air movement, helps create seasons, and influences weather and climate.
2. The spatial relationship between Earth and the sun determines how much solar radiation strikes each point on Earth’s surface.
3. Because Earth is tilted on its axis (an imaginary line connecting the poles, running perpendicular to the equator) by about 23.5°, the Northern and Southern Hemispheres each tilt toward the sun for half the year, resulting in the seasons.
4. Land and surface water absorb solar energy and then radiate heat, causing some water to evaporate.
5. The difference in air temperatures at different altitudes sets into motion convective circulation as warm air rises, cools, expands, and descends past other warm air that is rising.
D. The atmosphere drives weather and climate.
1. Weather specifies atmospheric conditions over short time periods, typically hours or days, and within relatively small geographic areas.
2. Climate, in contrast, describes the pattern of atmospheric conditions found across large geographic regions over long periods of time, typically seasons, years, or millennia.
E. Air masses interact to produce weather.
1. The boundary between air masses that differ in temperature and moisture (and therefore density) is called a front.
a. A mass of warmer, moister air replacing a mass of colder, drier air is a warm front.
b. A mass of colder, drier air displacing a warmer, moister air mass is a cold front.
2. Adjacent air masses may also differ in atmospheric pressure.
a. A high-pressure system contains air that descends because it is cool and then spreads outward as it nears the ground. High-pressure systems typically bring fair weather.
b. In a low-pressure system, warmer air rises, drawing air inward toward the center of low atmospheric pressure. The rising air expands and cools, and clouds and precipitation often result.
3. One type of weather event has implications for environmental health.
a. If a layer of cool air occurs beneath a layer of warmer air, this is known as a temperature inversion, or thermal inversion.
b. The band of air in which temperature rises with altitude is called an inversion layer.
F. Large-scale circulation systems produce global climate patterns.
1. Near the equator, solar radiation sets in motion a pair of convective cells known as Hadley cells.
2. Two pairs of similar but less intense convective cells, called Ferrel cells and polar cells, lift air and create precipitation around 60° latitude north and south and cause air to descend at around 30° latitude and in the polar regions.
3. These three pairs of cells account for the latitudinal distribution of moisture across Earth’s surface.
4. As Earth rotates on its axis, north–south air currents of convective cells appear to be deflected from a straight path; this is called the Coriolis effect.
G. Storms pose hazards.
1. Hurricanes form when winds rush into areas of low pressure where warm moisture-laden air over tropical oceans is rising.
2. Tornadoes form when a mass of warm air meets a mass of cold air and the warm air rises quickly, setting a powerful convective current in motion.
III. Outdoor Air Pollution
1. Whether from primitive wood fires or modern coal-burning power plants, people have generated air pollutants, gases and particulate material added to the atmosphere that can affect climate or harm people or other organisms.
2. Air pollution refers to the release of air pollutants.
3. In recent decades, government policy and improved technologies have helped us reduce most types of outdoor air pollution (often called ambient air pollution) in industrialized nations.
A. Natural sources can pollute.
1. Natural processes produce a great deal of air pollution. Some of these natural impacts are made worse by human activity and land-use policies.
2. Volcanic eruptions release large quantities of particulate matter, as well as sulfur dioxide and other gases, into the troposphere.
3. Sulfur dioxide reacts with water and oxygen and condenses into fine particles called aerosols.
4. Fires from burning vegetation also pollute the atmosphere with soot and gases.
5. Winds sweeping over arid terrain can send huge amounts of dust aloft.
B. We create outdoor air pollution.
1. Since the onset of industrialization, human activity has introduced a variety of sources of air pollution. Air pollution can emanate from mobile or stationary sources, and from point sources or non-point sources.
2. Once in the air, a pollutant may do harm directly or may induce chemical reactions that produce harmful compounds.
a. Primary pollutants, such as soot and carbon monoxide, are pollutants emitted into the troposphere in a form that can be directly harmful or that can react to form harmful substances.
b. Secondary pollutants are harmful substances produced when primary pollutants interact or react with constituents of the atmosphere.
3. Pollutants differ in the amount of time they spend in the atmosphere— called their residence time—because substances differ in how readily they react in air and in how quickly they settle to the ground.
C. Clean Air Act legislation addresses pollution in the United States.
1. Congress has passed a number of laws dealing with pollution.
a. The Clean Air Act of 1970 set strict standards for air quality, imposed limits on emissions, provided funds for research, and allowed citizens to sue parties violating the standards.
b. The Clean Air Act of 1990 sought to strengthen regulations pertaining to air quality standards, auto emissions, toxic air pollution, acidic deposition, and ozone depletion, while introducing an emissions trading program.
c. In 1995, businesses and industry were allocated permits to release sulfur dioxide that they could buy, sell, or trade among one another. This market-based incentive program reduced sulfur dioxide levels.
D. The EPA sets standards for “criteria pollutants.”
1. The EPA and the states focus on six criteria pollutants, pollutants judged to pose especially great threats to human health.
a. Carbon monoxide is a colorless, odorless gas produced primarily by the incomplete combustion of fuels.
b. Sulfur dioxide is a colorless gas with a pungent odor that is released when coal is burned. It contributes to acid deposition.
c. Nitrogen dioxide is a highly reactive, foul-smelling reddish gas that contributes to smog and acid deposition.
d. Tropospheric ozone results from the interaction of sunlight, heat, nitrogen oxides, and volatile organic compounds.
e. Particulate matter is any solid or liquid particle small enough to be carried aloft; it may cause damage to respiratory tissues when inhaled.
f. Lead is a metal that enters the atmosphere as a particulate pollutant, released by industrial processes and fuel combustion.
E. Agencies monitor emissions.
1. Volatile organic compounds (VOCs) are carbon-containing chemicals used in and emitted by vehicle engines and a wide variety of solvents and industrial processes, as well as by many household chemicals and consumer items.
2. In the United States in 2008, human activity polluted the air with 123 million tons of the six monitored pollutants.
F. We have reduced U.S. air pollution.
1. Reduction in air pollutants have occurred despite population increases.
2. New technologies such as catalytic converters, electrostatic precipitators, and scrubbers helped to reduce pollutants.
G. Toxic pollutants pose health risks.
1. Toxic air pollutants are substances known to cause cancer, reproductive defects, or neurological, developmental, immune system, and respiratory problems in people and other organisms.
H. Industrializing nations are suffering increasing air pollution.
1. Chinese cities suffer the worst air pollution as they industrialize rapidly.
I. Air quality is a rural issue, too.
J. Smog is our most common air quality problem.
1. Since the onset of the industrial revolution, cities have suffered a type of smog we call industrial smog, or gray-air smog.
K. Photochemical smog results from a series of reactions.
1. Photochemical smog, or brown-air smog, is formed when sunlight drives chemical reactions between primary pollutants and normal atmospheric compounds, producing a mix of over 100 different chemicals, tropospheric ozone often being the most abundant.
L. We can take steps to reduce smog.
M. Synthetic chemicals deplete stratospheric ozone.
1. Ozone molecules are considered a pollutant at low altitudes, but at altitudes of 25 km (15 mi) they are highly effective at absorbing incoming ultraviolet radiation from the sun, thus protecting life on Earth’s surface.
2. Years of dynamic research by hundreds of scientists revealed that certain airborne chemicals can destroy ozone by splitting its molecules apart, and that most of these ozone-depleting substances are human-made.
3. In particular, researchers pinpointed halocarbons—human-made compounds derived from simple hydrocarbons such as ethane and methane in which hydrogen atoms are replaced by halogen atoms such as chlorine, bromine, or fluorine.
a. Industry was mass-producing one class of halocarbon, chlorofluorocarbons (CFCs), at a rate of a million tons per year in the early 1970s, and this rate was growing by 20% a year.
4. CFCs reach the stratosphere unchanged and can linger there for a century or more.
N. The Antarctic ozone hole appears each spring.
1. In 1985, researchers shocked the world by announcing that stratospheric ozone levels over Antarctica in springtime had declined by half in just the previous decade, leaving a thinned ozone concentration that was soon dubbed the ozone hole.
2. In the Antarctic spring (starting in September), sunshine returns and UV radiation dissipates the clouds, releasing chlorine atoms, which begin destroying ozone.
3. The ozone hole vanishes until the following spring, and the globe as a whole loses a bit more of its ozone layer.
O. The Montreal Protocol addressed ozone depletion.
1. The world community came together in 1987 to design the Montreal Protocol, which has been signed by 196 nations.
2. As a result, we have evidently stopped the Antarctic ozone hole from growing worse. However, the ozone layer is not expected to recover completely until 2060–2075.
3. Environmental scientists have attributed the success of the Montreal Protocol to several factors.
a. Informative scientific research developed rapidly, facilitated by new and evolving technologies. b. Policymakers engaged industry in helping to solve the problem. Industry became willing to develop replacement chemicals in part because patents on CFCs were running out and firms wanted to position themselves to profit from next-generation chemicals. c. Implementation of the Montreal Protocol after 1987 followed an adaptive management approach, adjusting strategies midstream in response to new scientific data, technological advances, or economic figures.
P. Acidic deposition is another transboundary pollution problem.
1. Acidic deposition refers to the deposition of acidic or acid-forming pollutants from the atmosphere onto Earth’s surface.
2. Acidic deposition is one type of atmospheric deposition, which is the wet or dry deposition on land of a wide variety of pollutants.
Q. Acidic deposition has many impacts.
1. Acid deposition can also mobilize toxic metal ions from the soil and convert them from insoluble to soluble molecules where they hinder nutrient uptake by plants.
2. Acid water running off the land is toxic to many aquatic and terrestrial life forms and has led to the death of ecosystems.
3. Other than altering natural ecosystems, acid precipitation also damages crops.
4. Because the pollutants leading to acid rain may travel long distances, their effects can be felt far from their points of origin.
R. We have begun to address acid deposition.
IV. Indoor Air Pollution
1. Indoor air generally contains higher concentrations of pollutants than does outdoor air. As a result, the health effects from indoor air pollution in workplaces, schools, and homes outweigh those from outdoor air pollution.
A. Indoor air pollution in the developing world arises from burning wood.
B. Tobacco smoke and radon are the most dangerous indoor pollutants in developed nations.
1. Secondhand smoke has been found to cause many of the same problems as directly inhaled cigarette smoke.
2. After cigarette smoke, radon gas is the second-leading cause of lung cancer for Americans.
C. Many VOCs pollute indoor air.
1. Products that emit VOCs surround us; VOCs are emitted in very small amounts.
2. The implications for human health of chronic exposure to VOCs are far from clear. There are so many, at such low levels, that it is difficult to study their effects.
D. Living organisms can pollute.
1. Dust mites, animal dander, fungi, mold, mildew, and bacteria can all cause health problems.
2. Microbes that induce allergic responses are thought to be one frequent cause of building-related illness.
3. When the cause of such an illness is a mystery, and when symptoms are general and nonspecific, the illness is often called sick-building syndrome.
E. We can reduce indoor air pollution.
1. Using low-toxicity materials, monitoring air quality, keeping rooms clean, and providing adequate ventilation are the keys to alleviating indoor air pollution in most situations.
2. In the developed world, we can try to limit our use of plastics and treated wood when possible and to limit our exposure to pesticides, cleaning fluids, and other known toxicants by keeping them in a garage or outdoor shed.
V. Conclusion
A. Indoor air pollution is a potentially serious health threat but one that we can do a great deal to minimize for ourselves and our families.
B. Outdoor air pollution has been addressed more effectively by government legislation and regulation.
C. Much room for improvement remains, particularly in reducing acidic deposition and photochemical smog.
Key Terms for Chapter 17 acidic deposition ozone hole acid rain ozone layer aerosols particulate matter air pollutant photochemical smog air pollution polar cell ambient air pollution primary pollutant atmosphere relative humidity atmospheric deposition residence time atmospheric pressure scrubbers carbon monoxide secondary pollutant chlorofluorocarbons (CFCs) sick-building syndrome Clean Air Act of 1970 stratosphere Clean Air Act of 1990 sulfur dioxide climate temperature inversion cold front thermal inversion convective circulation tornadoes Coriolis effect toxic air pollutant criteria pollutant troposphere Ferrel cell tropospheric ozone front volatile organic compounds (VOCs) ground-level ozone warm front Hadley cell weather halocarbons high-pressure system hurricanes indoor air pollution industrial smog inversion layer lead low-pressure system Montreal Protocol nitrogen dioxide nitrogen oxides outdoor air pollution ozone-depleting substances