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Earth's atmosphere:
mixture of gases that forms a layer about 250 miles thick around the earth
bottom 5 - 11 miles (7 - 16 km) contains most (75%) of the air
Composition of clean, dry air:
Air pollution
presence of chemicals in the atmosphere in quantities and duration that are
harmful to human health and the environment
Types of air pollutants:
o Primary pollutants - products of natural events (like fires and volcanic
eruptions) and human activities added directly to the air
o Secondary pollutants - formed by interaction of primary pollutants with
each other or with normal components of the air
Major Classes of Air Pollutants:
Carbon oxides (CO & CO2)
o sources = incomplete combustion of fossil fuels
 transportation, industry, & home heating
o CO2 is an important greenhouse gas
o CO (carbon monoxide)
 the most abundant pollutant know to affect human health
 combines with hemoglobin & may create problems for infants, the
elderly, & those with heart or respiratory diseases
Sulfur oxides (mainly SO2, or sulfur dioxide)
o source = combustion of coal & oil (esp. coal)
 SO2 released in the U.S. comes from:
 utilities 69.5%
 industrial manufacturing processes 12.7%
 industrial combustion 11.6%
 transportation 3.7%
 other sources 2.5%.
o can react with gases in atmosphere to form sulfuric acid ('acid rain')
o 20 million tons released in U.S. every year
o Exposure to SO2 can cause impairment of respiratory function,
aggravation of existing respiratory disease (especially bronchitis), and a
decrease in the ability of the lungs to clear foreign particles. It can also
lead to increased mortality, especially if elevated levels of particulate
matter (PM) are also present. Groups that appear most sensitive to the
effects of SO2 include asthmatics and other individuals with hyperactive
airways, and individuals with chronic obstructive lung or cardiovascular
disease. Elderly people and children are also likely to be more sensitive to
Nitrogen oxides - NO (nitric oxide) & NO2 (nitrogen dioxide)
o source = motor vehicles & industry (burning fossil fuels)
o can react with other gases in atmosphere to from nitric acid (HNO3) ('acid
Volatile organic compounds (hydrocarbons) - methane, benzene, propane, &
chlorofluorocarbons (CFC's)
o source = motor vehicles (evaporation from gas tanks), industry, & various
household products
o 18 million tons released each year in U.S.
o Concentrations of many VOCs are consistently higher indoors than
outdoors. A study by the EPA, covering six communities in various parts
of the United States, found indoor levels up to ten times higher than those
outdoors-even in locations with significant outdoor pollution sources, such
as petrochemical plants.
Eye and respiratory tract irritation, headaches, dizziness, visual disorders,
and memory impairment are among the immediate symptoms that some
people have experienced soon after exposure to some organics. At present,
not much is known about what health effects occur from the levels of
organics usually found in homes. Many organic compounds are known to
cause cancer in animals; some are suspected of causing, or are known to
cause, cancer in humans.
Suspended particulate matter
o solid particles (e.g., dust, soot, & asbestos) & liquid droplets (e.g.,
o sources = power plants, iron/steel mills, land clearing, highway
construction, mining, & other activities that disturb or disrupt the earth's
o act as respiratory irritants; some are known carcinogens (e.g., asbestos)
o can aggravate heart/respiratory diseases
Toxic compounds
o trace amounts of at least 600 toxic substances (such as lead and mercury)
produced by human activities
 Mercury is an element that occurs naturally in the earth’s crust.
Most people and wildlife can generally tolerate the extremely low
levels of this naturally occuring substance. When mercury enters
the body it becomes concentrated in tissue, an effect known as
bioaccumulation. Because this element is toxic at very low
concentrations, even slight increases in the minute concentrations
naturally present in the environment can have serious effects on
humans and wildlife. Once mercury enters the water it can be
converted to its most toxic form, methyl mercury, by bacteria or
chemical reactions. Methyl mercury is absorbed by tiny aquatic
organisms, which are then eaten by small fish. The chemical is
stored in the fish tissue and is passed on at increasing
concentrations to larger predator fish. People and wildlife at the
top of the food chain are consequently exposed to elevated
amounts of methyl mercury through the contaminated fish they
 sources of mercury = burning coal and waste (such as medical
Photochemical oxidants
o mainly ozone
 Because sunlight has a critical role in its formation, ozone
pollution is principally a daytime problem in the summer months.
The presence of hydrocarbons and nitrogen oxide in sunlight with
little air movement leads to the generation of ozone. These two
compounds are produced by cars, trucks, factories, and powergenerating plants or wherever gasoline, diesel fuel, kerosene, oil,
or natural gas are combusted. These gases combine together with
sunlight, producing ozone. Urban areas with heavy traffic and
large industrialized communities are primary areas for ozone
The greatest concern about ozone pollution is the potential damage
it may inflict on human health. High concentrations of ozone are
especially hazardous to children, the elderly, and people with
respiratory problems. Each year many food crops are damaged by
ozone. Ozone also damages rubber, nylon, plastics, dyes, and
EPA provides maps showing levels of ozone pollution:
Source: Environmental Protection Agency
Map shows where pollutants exceeded EPA standards in September, 1996.
forms from mixture of primarily nitrogen oxides (from vehicles), volatile organic
compounds, & sunlight
complex mixture of gases but primarily ozone
more common in cities with sunny, dry, warm climates, such as Los Angeles,
Denver, Salt Lake City, Sydney, & Mexico City
Effects of Air Pollution on Human Health
Much evidence links air pollutants to respiratory & other diseases in humans
Examples of air pollution-related diseases:
Pulmonary irritation & impaired lung function:
 chronic bronchitis
 emphysema
Systemic toxicity:
 Lead
 Mercury
Increased susceptibility to disease
Effects of Air Pollution on other animals & plants:
Wild & domestic animals probably affected in the same ways as humans
Plants damaged by ozone, sulfur dioxide, & acids:
o ozone - weakens pine needles & makes them more susceptible to insects &
o sulfur dioxide - suppresses growth
o acid - damages leaves & needles & also removes nutrients
Acid Precipitation
Where do acids come from?
Nitric oxide & sulfur dioxide released primarily from electric power plants &
motor vehicles
SO2 + water vapor + ozone ---> H2SO4
NO + sunlight + O2 ---> NO2 + various atmospheric gases ---> HNO3
Acid Transport
Prevailing winds transport the compounds, sometimes hundreds of miles, across
state and national borders.
Source: EPA
Average annual pH of rainfall:
The pH scale and acid rain:
Acid rain is measured using a scale called "pH." The lower a substance's pH, the
more acidic it is. Pure water has a pH of 7.0. Normal rain is slightly acidic
because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the
year 2000, the most acidic rain falling in the US has a pH of about 4.3.
Effects of Acid Deposition
acidification of lakes and streams
o Acid rain causes a cascade of effects that harm or kill individual fish,
reduce fish population numbers, completely eliminate fish species from a
waterbody, and decrease biodiversity. As acid rain flows through soils in a
watershed, aluminum is released from soils into the lakes and streams
located in that watershed. So, as pH in a lake or stream decreases,
aluminum levels increase. Both low pH and increased aluminum levels are
directly toxic to fish. In addition, low pH and increased aluminum levels
cause chronic stress that may not kill individual fish, but leads to lower
body weight and smaller size and makes fish less able to compete for food
and habitat. Generally, the young of most species are more sensitive to
environmental conditions than adults. At pH 5, most fish eggs cannot
hatch. At lower pH levels, some adult fish die. Some acid lakes have no
contributes to damage of trees
o Acid rain does not usually kill trees directly. Instead, it is more likely to
weaken trees by damaging their leaves, limiting the nutrients available to
them, or exposing them to toxic substances slowly released from the soil.
Quite often, injury or death of trees is a result of these effects of acid rain
in combination with one or more additional threats. Acidic water dissolves
the nutrients and helpful minerals in the soil and then washes them away
before trees and other plants can use them to grow. At the same time, acid
rain causes the release of substances that are toxic to trees and plants, such
as aluminum, into the soil.
o Forests in high mountain regions often are exposed to greater amounts of
acid than other forests because they tend to be surrounded by acidic clouds
and fog that are more acidic than rainfall. Scientists believe that when
leaves are frequently bathed in this acid fog, essential nutrients in their
leaves and needles are stripped away. This loss of nutrients in their foliage
makes trees more susceptible to damage by other environmental factors,
particularly cold winter weather.
accelerates the decay of building materials and paints, including irreplaceable
buildings, statues,and sculptures that are part of our nation's cultural heritage.
Controlling Acid Deposition
Clean up smokestacks and exhaust pipes
o Almost all electricity comes from burning fossil fuels like coal, natural
gas, and oil. Acid deposition is caused by two pollutants that are released
into the atmosphere, or emitted, when these fuels are burned: sulfur
dioxide (SO2) and nitrogen oxides (NOx). Coal accounts for most U.S.
sulfur dioxide (SO2) emissions and a large portion of NOx emissions.
Sulfur is present in coal as an impurity, and it reacts with air when the coal
is burned to form SO2. In contrast, NOx is formed when any fossil fuel is
o Options for reducing SO2 & NOx emissions
using coal containing less sulfur, washing the coal, and using
devices called scrubbers to chemically remove the SO2 from the
gases leaving the smokestack.
 Power plants can also switch fuels; for example burning natural
gas creates much less SO2 than burning coal. Certain approaches
will also have additional benefits of reducing other pollutants such
as mercury and carbon dioxide.
 catalytic converters reduce NOx emissions from cars. These
devices have been required for over twenty years in the U.S., and it
is important to keep them working properly.
Use alternative energy sources
o There are other sources of electricity besides fossil fuels. They include:
hydropower, wind energy, geothermal energy, and solar energy. There are
also alternative energies available to power automobiles, including natural
gas powered vehicles, battery-powered cars, fuel cells, and combinations
of alternative and gasoline powered vehicles.
Take action as individuals
o Individuals can contribute directly by conserving energy, since energy
production causes the largest portion of the acid deposition problem. For
example, you can:
 Turn off lights, computers, and other appliances when you're not
using them
 Use energy efficient appliances: lighting, air conditioners, heaters,
refrigerators, washing machines, etc.
 Keep your thermostat at 68 F in the winter and 72 F in the summer.
 Carpool, use public transportation, or better yet, walk or bicycle
whenever possible
Global Warming
Some greenhouse gases occur naturally in the atmosphere, while others result
from human activities. Naturally occuring greenhouse gases include water vapor,
carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities,
however, add to the levels of most of these naturally occurring gases:
o CO2
o methane
 emitted during the production and transport of coal, natural gas,
and oil. Methane emissions also result from the decomposition of
organic wastes in municipal solid waste landfills, and the raising of
o nitrous oxide
o Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), & sulfur
hexafluoride (SF6)
 These compounds are potent greenhouse gases. In addition to
having high global warming potentials, SF6 and many HFCs and
PFCs have extremely long atmospheric lifetimes, resulting in their
essentially irreversible accumulation in the atmosphere. Sulfur
hexafluoride, itself, is the most potent greenhouse gas the IPCC
has evaluated.
 generated in a variety of industrial processes
Source: EPA
CO2 levels in the atmosphere have risen substantially
What do we know?
Since 1860, the mean global temperature has risen 0.7 - 1.3 degrees Fahrenheit
10 of the 15 years from 1980 - 1994 were among the hottest in the 113-year
recorded history of temperature measurement
1998 was the warmest year of the last century based on thermometer data and the
warmest of the last millenium based on proxy temperature data. The 2003 average
global temperature ranked as second warmest on record, tied with 2002 (but
cooler than the record warm year of 1998). The 10 warmest years on record have
all occurred since 1990.
The IPCC (Intergovernmental Panel on Climate Change) concluded in 1995 that
human activities were influencing global climate
In 2001, the IPCC issued its Third Assessment Report stating that "most of the
observed warming over the last 50 years is likely to have been due to the increase
in greenhouse gas concentrations". IPCC points out a number of features of the
climate system, like intensity of rainstorms, that have already changed and
estimates that warming of the coming century will reach 1.4°C-5.8°C (2.5°F10.4°F) if emissions are not limited. IPCC finds that warming of between 1°C2°C (1.8°F-3.8°F) is likely to pose high risks to unique and threatened
ecosystems, and to lead to increases in the risk of extreme climate events.
Possible Effects of a Warmer World
Changes in food production
Reductions in biodiversity
o Plants and animals generally react to consistently warmer tempartures by
moving to higher latitudes and elevations. Recent studies reveal that some
species have already started to shift their ranges, consistent with warming
trends. Many populations and species may become more vulnerable to
declining numbers or extinction if warming occurs faster than they can
respond or if human development presents barriers to their migration.
Rise in sea level
o Warmer temperatures increase melting of mountain glaciers and cause
ocean water to expand. Largely as a result of these effects, global sea level
has risen 4 to 10 inches over the past 100 years. With additional warming,
sea level is projected to rise from half a foot to 3 feet more during the next
100 years. On average, 50 to 100 feet of beach are lost for every foot of
sea-level rise.
More extreme weather
o climate change will lead to more hurricanes, floods, and droughts
Threats to human health
o Intergovernmental Panel on Climate Change (IPCC), is a United Nationssponsored organization made up of 2,500 scientists from around the world.
The IPCC projects that more frequent and more severe heat waves will be
an early effect of global warming. Events such as the deadly stretch of hot
days that killed 669 people in the Midwest during the summer of 1995 and
250 in the Eastern United States in July 1999 are likely to become more
o As temperatures rise, disease-carrying mosquitoes and rodents move into
new areas, infecting people in their wake. Global warming will likely put
as much as 65% of the world's population at risk of infection—an increase
of 20%. Scientists at the Harvard Medical School have linked recent U.S.
outbreaks of dengue ("breakbone") fever, malaria, hantavirus and other
diseases to climate change.
Slowing Global Warming
Cut fossil fuel use
o Car makers could dramatically increase the fuel economy of their cars and
o Most electric utilities still use coal to produce electricity, spewing millions
of tons of carbon dioxide and other pollution into the atmosphere every
year. Part of the problem could be solved by converting these plants to
burn cleaner natural gas.
Improve energy efficiency
o Our cars and light trucks, home appliances and power plants could be
made much more efficient by simply installing the best current
technology. Energy efficiency is the cleanest, safest, most economical way
to begin to curb global warming.
We could do much more to save energy in our homes and office buildings.
More energy efficient lighting, heating and air-conditioning could keep
millions of tons of carbon dioxide out of our air each year.
Reduce deforestation & plant trees
o Because global vegetation and soils contain about three times as much
carbon as the planet's atmosphere, terrestrial ecosystems offer an
opportunity to absorb and store (sequester) a significant amount of carbon
dioxide from the atmosphere. By planting trees, preserving forests, and
changing cultivation practices to increase soil carbon, for example, it is
possible to increase the size of carbon sinks.
Slow human population growth
Any progress in meeting these objectives?
Only 4 MDCs (Great Britain, Denmark, Germany, & Norway) have produced
plans to substantially reduce CO2 emissions
CO2 emissions by LDCs are increasing about 5%/year
Overall, global CO2 emissions are still increasing 2-3%/year
Greenhouse Gas Emissions in the U.S.
Source: EPA
Governments should be leading the way to a fundamentally new energy direction
based on clean renewable energy, like wind or solar power. But at present many
governments, including the U.S. government, instead use taxpayers money to
support the agenda of the companies which continue to spend billions of dollars
on development of coal, oil or gas - the climate-damaging fossil fuels.