The atmosphere is a gaseous envelope that surrounds the earth
- it is divided into several layers
     o the bottom layer (next to the ground) is the troposphere
          - this is the portion of the atmosphere that holds conditions that are favorable to life
          - this layer extends from the ground to 7 miles above the ground
     o the layer just above the troposphere is the stratosphere
          - this layer extends from 7 miles high to 31 miles above the ground
          - the stratosphere contains the ozone layer – this layer filters out harmful UV radiation

The atmosphere is responsible for the greenhouse effect.
- the greenhouse effect is what keeps the earth warm and suitable for life
      o basically, certain gasses in the atmosphere (called greenhouse gasses) absorb infrared
     (heat) radiation that is reflected of the surface of the earth
          - in so doing, these gasses prevent the heat from escaping, thus keeping the earth warm
     o the main greenhouse gasses are carbon dioxide and methane

Global warming refers to possible excessive heating of the earth surface from the addition of greenhouse gasses to the atmosphere from anthropogenic (human caused) sources
- the main sources of added greenhouse gasses comes from the combustion of fossil fuels
     o power plants (they burn coal), automobiles, factories

About 7 gigatons of carbon dioxide are added to the atmosphere from these sources each year
- of these 7 gigatons, about 3 gigatons remain in the atmosphere (the remainder is removed via natural processes – plants and diffusion into the ocean)
- at this current rate of accumulation, it is predicted that the earths average temperature will rise about 6 degrees over the next century
- this may cause sea levels to rise, some areas will experience droughts, excessive heat waves, and violent storms
- these changes will be extremely costly in economic terms
     o major crop growing regions will have to shift, thereby requiring major shifts in 
      infrastructure (transportation routes, settlement patterns, etc.)

Ozone Depletion refers to the loss of stratospheric ozone due to the presence of CFC’s (chlorofluorocarbons)
- this depletion of ozone occurs in the stratosphere and is not related to the “ozone action days” that are described on TV
- Stratospheric ozone is sometimes called the “good” ozone, because it filters out harmful UV radiation
     o Prevents this radiation from reaching the earth’s surface
     o Excessive exposure to UV radiation causes skin cancer

CFC’s were used for numerous applications
- Used in air conditioners as a coolant
- Used for cleaning electronic circuit boards
- Used as a solvent
- Once used as a propellant in aerosol cans (not any more)

When CFC’s reach the stratosphere, they break up ozone molecules
- one CFC molecule can destroy many ozone molecules and can last up to 50 years in the atmosphere
- as a result, small quantities of CFC’s lead to significant reduction in stratospheric ozone

Every year since the early 1980’s, a huge hole (the size of North America) in the ozone layer opens up over Antarctica
-  A similar thinning occurs over the north pole
-  These “holes” may be responsible for increasing rates of deadly skin cancer in recent years
Because of this, the international community has teamed up to eliminate CFC’s and other 
ozone depleting substances
- these measures seem to be helping – the ozone holes have stopped growing and there is evidence that stratospheric ozone may begin to be replenished in the future

Air Pollution
Air pollution refers to any substance that degrades the quality of air

There are many natural sources of air pollution
      E.g. Dust, volcanoes, forest fires, etc.
However, there are natural mechanisms to reduce these pollutants (i.e. rain, wind, etc)

Anthropogenic (human caused) air pollution is a problem for two reasons:

1.  Anthropogenic pollution results in overburden
     o substances are emitted into the air faster than the natural mechanisms can eliminate them
     o as a result these substances accumulate

2. Anthropogenic pollution contains many synthetic substances
     o synthetic substances are often very toxic because they interfere with the bodies 
     metabolic processes and because there are often no natural mechanisms to eliminate them
     from the body
     o there are often no natural mechanisms to remove them from the atmosphere

Primary Pollutants are substances emitted into the atmosphere that have a direct effect on air quality
      E.g.  Hydrocarbons (benzene, toluene, etc), carbon dioxide, etc.

Secondary Pollutants are substances that are the product of primary pollutants reacting together in the atmosphere
      E.g.  Nitric Oxides and Sulfur Oxides react with water to form nitric acid and sulfuric acid 
     (form acid rain).  In this case nitric acid and sulfuric acid are secondary pollutants

The six most important primary pollutants are:

1. Carbon Dioxide
2. Carbon Monoxide
3. Sulfur Oxides
4. Nitric Oxides
5. Hydrocarbons
6. Particulates

Carbon dioxide is responsible for global warming (already described)

Major source of carbon dioxide, carbon monoxide, sulfur oxides, nitric oxides, and 
particulates is combustion of fossil fuels

Hydrocarbons are also produced form combustion of fossil fuels, but their main source is the petrochemical industry
- oil refineries, metal smelters, rolling mills, plastic factories, chemical manufacturers

Sulfur oxides and nitric oxides react in the atmosphere to produce sulfuric acid and nitric 
acid
- these substances form acid precipitation (acid rain, acid snow, acid fogs, etc)
- The main source of both is from automobiles, refineries, coal power plants

Acid precipitation refers to any precipitation whose pH is below 5.5
- pH is a measure of acidity – low numbers indicate high acidity
     o e.g.  Car battery acid has a pH of about 1.0, vinegar has a pH of about 3

Every year, the U.S. is responsible for dumping 60 million tons of sulfur and nitric oxides into
the atmosphere
- most of this is sulfur oxides

Most of these emission occur in Southern California and the Industrial Heartland
      I.e. the U.S. Midwest – Ohio, Indiana, Illinois, Kentucky
      In Los Angeles – acid fogs of pH 1.7 have been recorded

Acid precipitation causes extensive damage to both terrestrial and aquatic ecosystems
- acidified streams and lakes undergo marked changes in vegetation, invertebrate populations, and fish populations.
- For example, in the Adirondacks of NY, many lakes have become so acidified that they can no longer support populations of fish. (about 200 lakes affected)
- In Vermont, 50% of the red spruce tree population had died from exposure to chronic acid rain (pH ranging from 3.1 to 4.1)

Hydrocarbons (Volatile Organic Compounds)
In chemistry, any carbon containing compound is referred to as organic.
However, these substances are often anything but natural
- can be extremely toxic – e.g. PCB’s, dioxins, benzene, acetone, formaldehyde, etc.
- can be carcinogens – cause cancer
- can be mutagens – cause mutations in DNA
- can be teratogens – cause birth defects

There are literally thousands of toxic organic compounds produced by various industries
- many of these are not regulated

People living in areas near chemical plants often have much higher risk of cancer and birth defects (so-called "cancer clusters")
- e.g. Port Neches Texas is home to the Texaco Neches West Chemical Plant
     o they dump 1 million pounds of butadiene into the air each year
     o people living in Port Neches have 10 times the nation average cancer rate

Particulates are small particles emitted into the air
- anthropogenic particulates often contain heavy metals (e.g. Lead, mercury, cadmium, arsenic, selenium)
- these substances accumulate in tissues
     o for example, lead has been shown to accumulate in brain tissues
          - it is linked to learning disabilities and mental retardation
- in addition, many particulates are respiratory irritants
     o can cause or increase the effects of bronchitis and asthma
- particulates are particularly prevalent in urban areas and in industrial areas

Ozone is a secondary pollutant when it occurs near the ground (tropospheric ozone)
- it is a severe respiratory irritant – therefore tropospheric ozone is often referred to as the 
“bad” ozone.
- Tropospheric ozone is a product of the mixing of nitric oxides, hydrocarbons, and oxygen 
in the presence of heat and sunlight.
     o Conditions that favor ozone production are hot, sunny days, when there is little or 
       no wind.
          - These are the “ozone action days” that you hear about on the news
- tropospheric ozone is particularly dangerous to the elderly and to children
     o e.g. In Los Angeles, 50% of urban children show evidence of lung damage caused by 
       exposure to excessive levels of ozone

Water pollution is caused by any substance that degrades the quality of water
- many of these pollutants are similar to the ones found in air pollution

However, water pollution is much complicated
o This is because we have so many different uses for water and, therefore, there are many ways that water pollution can affect us.
o Water is used for drinking, cooking, bathing, raising crops, watering livestock, etc.
o Also, there are many different kinds of water
     - Surface water – lakes, rivers, creeks, oceans, marshes, etc
     - Ground water – soil water, subsurface (perched) water, aquifers
     - Rain, snow, hail, etc

Effects of water pollution can depend on residence time
- residence time is the length of time that a pollutant will stay in a system
- e.g. lakes tend to have longer residence times than do rivers
- in a fast stream, residence time may be only a few minutes
- in a large aquifer, residence time can be thousands of years

Dead Organic Matter
- comes from sewage, urban garbage, agriculture
- consists of carcasses, plant and animal wastes, raw sewage
- leads to high biological oxygen demand (BOD)
     o biological oxygen demand is caused by decomposition.  Bacteria consume oxygen, 
thereby depleting the oxygen in the water.  This disrupts aquatic ecosystems, eliminates 
oxygen dependant species (like fish).

Pathogens
- come from raw sewage and human wastes (also medical wastes)
- pathogens are the microorganisms or their byproducts which cause human diseases
     o e.g. cholera, typhoid, dysentery, giardiasis, etc.
- pathogens are usually detected by coliform testing.
     o Involves taking a sample of water and culturing it for coliform bacteria
     o Since coliform bacteria can only live in the lower intestinal tracts of warm-blooded 
       organisms, the presence of coliform bacteria is an indicator that the water has been 
       contaminated with sewage

Organic Chemicals
- come mainly from agricultural sources and industries
- these are carbon containing molecules – most dangerous ones are pesticides, PCB’s, dioxins, solvents, etc.
- these substances are directly toxic to humans and wildlife, thus causing ecosystem disruption
- also, many of these substances are carcinogens, teratogens, or lower fertility

Nutrients
- come mostly from agricultural sources
- especially nitrogen and phosphorous – used to fertilize crops
- nutrients cause “algal blooms” in aquatic systems
     o an algal bloom occurs in stages
          - first nutrients are added to the water
          - algae then proliferates and covers the pond
          - this block light from the bottom, killing the bottom dwelling plants
          - the algae begins to die and the dead algae sink to the bottom
          - the build-up of dead algae on the bottom begins to decay
          - this cause the oxygen to be depleted from the water
          -? the end result is the loss of all oxygen dependant species (e.g. fish)

Heavy Metals
- come from agriculture, industries, and urban run-off
- heavy metals like mercury, selenium, cadmium, lead, and chromium have direct toxic effects
- therefore, lead to ecosystem damage and human health problems

Acids
- mostly from industrial and domestic sources
- acid rain is a problem already described under air pollution
- some industries dump strong acids directly into aquatic systems
o these acids are directly toxic to many organisms – this leads to ecosystem failure

Sediments
- come from construction sites, agriculture, forestry, and urban run-off
- sediments alter energy flow through the water and alter bottom environments
     o many aquatic organisms can only live in clear waters with rocky or gravelly bottoms 
          - sediments eliminate these species
     o sediments lead to high turbidity in the water.
          - Turbidity prevents sunlight from reaching the bottom, eliminating bottom-dwelling 
            plants
          - This eliminates all species dependant on these bottom-dwelling plants

Heat
- comes from industries and power plants
- excessive heat from industrial cooling water causes water to lose oxygen and eliminates any cold-water species that are present in the system

e.g.  In the northern U.S. cooling waters are linked to the loss of trout, walleye, and other game fishes, these artificially warmed waters are often invaded by “trash fish” like carp, suckers, and catfish.

Radioactivity
- main sources are from industries, hospitals, and medical research facilities
- radioactive substances are extremely toxic in even very small quantities.
- Cause cancer and death to both humans and other organisms
 
 

Every year it is estimated that 1000 to 2000 species go extinct (3-5 species per day)
- at the current rate of extinction, close to ¼ of all terrestrial plants will be extinct in 50 years

There is debate over these numbers, though all scientists agree that the loss of biodiversity is an extremely serious problem

Part of the problem is we don’t really know how many species there are.
- since the 1700’s scientists have been describing species – there are currently 1.7 million described species:
     o Plants = 440,000
     o Vertebrates = 47,000
     o Insects = 751,000
     o Others = 462,000

It is estimated that only about 10% of the world’s species have been described
- implies that there are about 17 million species
- however, many scientists think this number may be way too small

Our knowledge of species is also very biased:
- we know much more about vertebrates than other groups
     o because they are large, visible, and easy to describe
- we know very little about more obscure groups like insects, bacteria, protozoans, etc.
- we know much more about species living in temperate areas of the world like Europe and North America
     o because these areas are easily accessible
- we know very little about species living in remote areas like tropical rainforests and the 
bottom of the oceans
- there are also problems in the identification of species – not all scientists can agree on exactly how many described species there are.
     o Because many species resemble each other very closely
     o Sometimes individuals that look dissimilar are actually members of the same species

Bottom Line:  We really have only a vague idea of how many species there are
- as a result, it is likely that extinction rates are much higher than estimates lead us to believe

How do we know when a species is extinct?
- The World Conservation Union (www.iucn.org) is the agency responsible for monitoring endangered species.
     o Their criterion is that a species is considered extinct if it has not been observed for more 
       than 30 years, in spite of extensive searching
     o This estimate may be inaccurate in remote areas, because a species could easily be 
       overlooked or missed.

E.g.  the American Ivory-billed Woodpecker – now considered extinct, last seen in the 1950’s

Some extinct North American Birds: (date and last location known to exist)
For pictures of these birds click  here.

Great Auk (1884 – Iceland)
Passenger Pigeon (1914 – Cincinnati Zoo)
Heath Hen (1925 – Martha’s Vineyard, Mass)
Carolina Parakeet (1914 – Cincinnati Zoo)
Labrador Duck (1875 – Long Island, NY)
Dusky Seaside Sparrow (1985 – Florida)
Ivory-billed Woodpecker (1955 – South Carolina)

The World Conservation Union (and the USEPA) uses two designations to identify species 
that are in trouble
- an Endangered Species is a species whose populations are so low that they are in immediate danger of extinction
- a Threatened Species is a species that has shown rapid population declines in recent years 
and is in immediate danger of becoming endangered.

Among the world’s species, the percentage that are Threatened are:
- 11% of birds
- 25% of mammals (45% of all primates)
- 20% of reptiles
- 25% or amphibians
- 34% of fishes

About ½ of all U.S. species of mussels and clams are either threatened or endangered

Threatened and endangered species are found on all continents and in all oceans
- however the most endangered and threatened species occur in SE Asia, Central Africa, 
Islands, Tropical Americas

There are several causes for endangerment
- over-harvest
- competition from introduced species
- habitat loss

The single most important cause of endangerment is habitat loss
 E.g. deforestation, damming of rivers, clearing for agriculture, etc.

The number of endangered species here in the U.S.:
- Mammals = 29 species
- Birds = 14 species
- Reptiles = 26 species
- Amphibians = 18 species
- Fish = 174 species
- Invertebrates = 701 species

Some Texas endangered species:  (for pictures click here)
- Eskimo Curlew
- Whooping Crane 
- Piping Plover
- Golden-cheeked Warbler
- Red-cockaded Woodpecker
- Aplomado Falcon
- Black-capped Vireo
-  Interior Least Tern
-  Attwater’s Prairie Chicken