Most changes in our environment are not random. They are a result of basic physical and biological processes.

1. Persistent changes: take place in one direction over time increasing or decreasing.
Example: the rate of rotation of the Earth is slowing and the days are getting longer.

2. Rhythmic changes: also called periodic changes. A periodic phenomenon repeats itself at regular, predictable
intervals.
Example: the rotation of the Earth on its axis produces day and night and the primary tides.

3. Cyclical oscillations: an aperiodic or cyclical variable repeats itself, but at irregular intervals and varying intensity.
Example: a drought which recurs but difficult to predict the actual time of  occurrence.

Aside: Difference between weather and climate:
Weather: condition of the atmosphere at any given point in space and time. Weather changes constantly with time,
but the intervals are short (measured in hours, days, or weeks).
Climate: consists of the weather regime over a given place over a longer period. Includes frequently occurring
types of weather in addition to infrequent types. Weather changes rapidly with time whereas climate changes over
longer periods of time.

Cyclical oscillations can be also categorized into 3 groups:

a. Short-term oscillations: short swings toward extremes (1-10 years). Verified by actual measurements.
Example: El Nino

b. Intermediate length: range from 10 to 100 years. Difficult to verify by measurements.

c. Long-term oscillations: occur at intervals longer than 1000 years.

4. Short-lived events: occur in the environment spanning days or even seconds. They are sporadic in space
and time. Represent major deviations from normal conditions. Usually include violent events.

5. Anthropogenic change: some of the changes in the environment are a direct result of human activities:
a. increasing population
b. unequal distribution of population
 

II. THE CHANGING ATMOSPHERE: GLOBAL CLIMATIC CHANGE

1. GLOBAL CLIMATE

Modern technology and enhance scientific research are providing information and new insight on climate change. Many
factors are important in climatic change. Some examples include:

1. Composition and concentration of gases and aerosols
2. Amount of solar radiation reaching the Earth from the sun
3. Shape and location of continents and ocean
4. Atmosphere/ocean circulation patterns
5. Human involvement
6. The interaction of biogeochemical cycles in the ecosystem
7. Natural events such as volcanic explosions, etc.

2. DEFINITIONS

1. Climate Change: Change is unidirectional, meaning that it will not necessariy go back to its original state

2. Climate Variability: Change is about a mean state

3. Temporal Scale: Period of time that it takes for a process to occur (time scale)

4. Spatial Scale: Physical extent (space scale). Examples: local, regional, national, continental, and global.

5. Feedback Mechanisms: Processes that amplify or diminish a change in the system.  These processes make prediction and analysis rather difficult. There are two types of feedback mechanisms:  1. Positive feedback, amplifies,  2. Negative feedback, weakens. Please refer to the examples given in class for both negative and positive feedback mechanisms.
 

3. PALEOCLIMATIC INFORMATION

Actual observations do not go back far enough, but we can gather some information from other sources, i.e.,
1. ice cores
2. deep-sea sediment cores

1. Ice cores: Examination of ice cores gives us an idea of the composition and chemical changes in atmospheric
gases and also temperatures on the Earth. These ice cores are retrieved from Antarctica and the Greenland ice
caps. Some contain data going back to approximately 250,000 years.

2. Deep-sea sediment cores: contain fossils of microscopic plants, animals, and pollen which can also provide
 

POSSIBLE CAUSES OF CLIMATE CHANGE

Earth's climate has experienced changes of  different magnitudes and time scales over time.  Several possible causes
have been identified in order to explain these changes and possible future changes.  Some of these include variations
in the intensity of radiation emitted by the sun, changes in the Earth's orbit.  It is important to note that many of
these causes do not operate separately, but tend to operate simultaneously with others.

1. Variations in solar output

Earth's climate is sensitive to sun's output.  Radiometers aboard satellites suggest that the sun's energy output varies
considerably more than we had thought earlier. The sun's energy output tends to change with sunspot activity.  Sunspots
are huge magnetic storms which shows up as a dark region on the surface of the sun. They occur in cycles, with the number
and size reaching a maximum about every 11 years. There is also an approximate 22 year cycle which is known as the
double sunspot cycle. During periods of maximum sunspot activity, the sun emits more energy (about 0.1 percent more)
than during the minimum period. This happens since the greater number of bright areas around the sunspots radiate more
energy which offsets the effect of the dark spots.
Some evidence for connection between climate and solar output is given by studying the Maunder Minimum (the period of
minimal sunspot activity between 1645 and 1715. This period coincided with one of the coldest periods of the Little Ice
Age. But this has not always been the case.
Scientists have found that there is a relationship between the 11-year sunspot activity and weather patterns in the Northern
Hemisphere. It is possible that the warming in the winter might be related to the variations in sunspots and to the
reverse in the pattern of the winds in the troposphere over the tropics.
The changes in the solar output may be responsible for climatic changes over very long time scales (decades and centuries).
 

Please consult the Web material used in class for further information:  www.SunspotCycle.com
 

2.  Plate tectonics

Theory of Plate Tectonics: Slow shifting of continents and ocean floor.  In 1965 the ideas of Wegner and sea floor spreading were combined into a unified theory called Plate Tectonics by J. Tuzo Wilson. In this theory, the Earth's lithosphere is made of several plates, each between 70 and 100 km thick floating on the Asthenosphere. Plate movement is slow, about 5 cm per year. The lithospheric plates move driven by mantle convection and interact with one another. The interaction of these plates cause earthquakes, mountain building, volcanic activity, create ocean basins, and destroy ocean basins.

Fossiliferous Evidence for Plate Tectonics:  Plants that exist in swampy areas near glacier margins are found in South America, Southern Africa, India, Australia, and Antarctica.
Also aquatic reptiles half a meter long , found only in Eastern South America and Southwestern Africa.

Benefit of the theory: 1.  Insight into geological processes, 2. Explains past climates. For example, finding different glacial features near sea level in Africa today might be a result of the  area having undergone glaciation or ice sheets formed when this land mass was at a higher altitude.

Climate changes as a result of Plate Tectonics:
1. Large high latitude bodies of water may be pinched off such as the arctic.
2. Different arrangement of land masses affects the path of ocean currents, this in turn alters the heat transport, and changes the global wind system and change the climate in middle and high latitudes.
3. Mountain Building may cause a change in circulation patterns.
4. Subduction causes outgasing of greenhouse gases.
5. Formation of an oceanic ridge which may lead to volcanic eruptions.
 

3. Changes in radiation balance

The Earth-Atmosphere system is in a balance between incoming and outgoing energy. Energy entering the Earth-Atmosphere
system must equal the energy that leaves the system. Hence the net input of solar radiation must balance the output of infrared
radiation. If this balance is upset, global climate can experience a change.
Global radiation balance is affected by changes in:
1. solar constant
2. planetary albedo
3. gas and aerosol composition

Radiative equilibrium:

Radiative equilibrium can be shown by a mathematical expression:

Energy in:
..If we show the radiation incident on the E-A system given by the solar constant., S  (solar constant is the rate at which the solar
radiation falls on an area. ~1372 Watts/m2).

..We show the the amount of energy reflected or scattered back into space as alpha (planetary albedo= reflected radiation/incident radiation).

..Now we can show the energy available to drive the atmosphere as S(1-alpha)

.. Earth intercepts this energy (Earth has an area of  (3.14*R2) where R=radius of the Earth), so the net energy input can be shown as:
(3.14 R2)S(1-alpha)

Energy out:
Energy emitted by the E-A system is in the form of infrared radiation (longwave). Energy output can shown as:
E= e sigma T4
This is called the Stefan-Boltzmann Law. This law states that the total radiational output of an object is proportional to its temperature. This law
works for a blackbody (a perfect absorber and emitter). Since the E-A system is not quite a blackbody, a correction factor (e) is introduced. So
energy emitted from the entire surface area (4*3.14 R2) is:
(4*3.14 R2) e sigma T 4
where sigma is a constant and T is the temperature.

Now we can go back and write the expression for the radiative equilibrium:
what comes in = what goes out

(3.14 R2)S (1-alpha) = (4*3.14 R2) e sigma T4

A change in any one or any combination of these variables will change T and will have an affect on the climate.

In-class example.
 

4. Climate change and variations in the Earth's orbit

Milankovitch theory: proposed in the 1930s, links the changes in the Earth's orbit to changes in climate. Based on 3 cyclic movements:

1. Changes in the shape of the Earth's orbit (goes from elliptical to circular). Cycle is about 100,000 years. Right now, we have low
eccentricity. Earth is closer to the sun in January and farther in July.  A change can have an affect on the length of seasons.

2. Earth rotates on its axis. Cycle takes about 23,000 years. Right now, the Earth is closer to the sun in January and farther in July.
In about 11,000 years, reverse will be true (seasonal variations will be greater in NH than now).

3. Changes in the tilt of the Earth. Currently at 23.5 degrees. Cycle takes about 41,000 years. A smaller tilt leads to less seasonal
variations.
 

Some evidence suggests that the Milankovitch cycles may be related to climate variations. Based on the evidence found in:
. deep-ocean sediments
. during the past 800,000 years, ice sheets have peaked every 100,000 years
. smaller ice advances at intervals of about 41,000 and 23,000 years.

Based on other evidence, it is difficult to conclude that the orbital changes are solely responsible for the changes.
 

5. Aerosols and climatic variability

Definition of an aerosol: Small, suspended liquid or solid particles in the atmosphere. Aerosols can enter the atmosphere directly (as solid or liquid particles), or indirectly (through reactions with solar radiation and photochemical processes).  Aerosols can exist both in the troposphere and in the stratosphere. Some natural sources of aerosols are volcanoes, wild fires, wind blown dust, emissions of biologically produced gases, and sea salt spray.
Aerosols absorb solar (visible), and infrared radiation (from the surface of the Earth). They also reflect and scatter the incoming
solar radiation back to space. This reduces the amount of shortwave radiation reaching the surface which results in cooling.
Aerosol content of the atmosphere is called turbidity. These aerosols are called sulfurous or sulfate. About 90% of these
aerosols are a result of burning of fossil fuels. Sulfur pollution enters the atmosphere as sulfur dioxide gas and transforms into
small sulfate particles.  These tend to stay mainly in the troposphere, stay for a few days and so generally do not have enough time to
spread globally. They are removed by removal processes (precipiation and wind).
They can also act as cloud condensation nuclei and so will change the composition of clouds. Furthermore, when they act as condensation nuclei, it may lead to an increased number of condensation nuclei, fighting for the same amount of moisture, and as a result the cloud nuclei may remain small and reduce precipitation.

Volcanic eruptions and aerosols in the stratosphere

During an eruption, particles of ash and dust (also gases) can be sent into the stratosphere. Greatest effect is usually detected after
eruptions with a lof of sulfur gases. Sulfur gases combine with water vapor and from small sulfuric acid particles. If the particles
get larger haze forms. A haze layer may stay for years in the stratosphere which would reflect and absorb  solar radiation. This will
in turn cause warming of the stratosphere and cooling of the global surface temperature.

 Note: Difference between stratospheric and tropospheric aerosols: stratospheric aerosols are generally smaller and tend to stay longer in the layer, and have global effects, whereas tropospheric aerosols are larger, only last for a few days, and are removed by atmospheric removal processes.

Global scale ocean circulations (Thermohaline circulation)

It is part of the total ocean circulation that is driven by fluxes of heat and freshwater through the sea surface. It is produced by temperature and salinity differences. It is simply a large flow of warm water northward in the Atlantic supplying tropical heat to the North Atlantic.  For more details and a simulation please see www.cru.uea.ac.uk/cru/info/thc .
Ocean sediments and ice cores show that the this circulation (also referred to as the conveyor belt) has been on and off during the last glacial period, and may be related to periods of rapid climate change. Causes of variablity are due to the changes in deep water circulation as a result of changes in the salinity of the North Atlantic ocean. This may be a result of changes in precipiation, changes in the flux of fresh North Pacific water into the northern North Atlantic, and massive iceberg discharge among others. The sensitivity of the thermohaline circulation to changes in salinity is still being studied.
Please review the articles discussed in class and the possible role of the increased greenhouse gas concentrations on the thermohaline circulation.

Other possible factors in climate change:

1. Nuclear winter- climate change induced by nuclear war
A nuclear war would give rise to a thick smoke (soot) as a result of large fires which would burn for long periods of
time. This smoke would eventually make its way to the upper level of the atmosphere and become a part of the
upper level winds (westerlies) and circle the NH especially in the midlatitudes.
These particles tend to absorb solar radiation and not reflect much of the incoming radiation. The absorption of solar
radiation by these particles would induce cooling at the surface. Temperatures might go below freezing even in the
summer. This phenomenon is called nuclear winter.
Also as the lower troposphere cools, upper layers warm due to absorption which results in a stable layer. Stability
limits convection and in turn would have an affect on precipitation.

2. Chaos
Theory proposed by MIT meteorologist Edward Lorenz in 1963. It is also called the butterfly effect. This theory states
that certain systems are very sensitive to initial conditions.  Internal instabilities  cause complex  behavior in a
system.
The Earth-Atmosphere system  is a dynamical chaotic
system meaning that the system's evolution can be explained by a number of mathematical equations and in chaotic
since its initial conditions are basically unknown. The term chaotic does not indicate random behavior. Certain physical
laws  explain the system and so chaos takes place within boundaries. So chaos has an underlying order or structure.
Chaos theory raises the question of whether there are internal  limitations on the way that we can predict weather
and climate. Also this theory brings up the idea that climate change might simply be a result  of the natural
variability  of the system.
 
 

GREENHOUSE EFFECT

Absorption characteristics of greenhouse gases are compared to a greenhouse. Accumulation of heat-absorbing
greenhouse gases could result in an enhanced greenhouse effect (and possible global warming). Greenhouse
gases are strong absorbers of longwave (infrared) radiation and poor absorbers of shortwave (visible) radiation.
Major greenhouse gases are: water vapor, carbon dioxide, methane, tropospheric ozone, nitrus oxide, CFCs. These
gases comprise less than 1% of gases in the air.

1. Carbon dioxide
In 1957, accurate measurements of carbon dioxide concentration of air began in Hawaii at 3400 m above sea level
in the Pacific Ocean. This location was far from the major pollution sources and so a good representative of the
actual number. The concentration is now measured at the south pole in addition to other locations. All sites show
an increase in concentration. In 1957, the concentration was measured to be 280 parts per million per volume of air.
In  1992, it was measured to be 356 ppmv. Most of this increase is due to fossil fuel burning and deforestation.
Rate of increase slowed in 1991 following the eruption of Mt. Pinatubo (~ 0.4 ppm/year). It is now at 1.5 ppm/year.
It is difficult to explain the balance of the carbon system. In the 1980s, 7.1 billion tons of carbon were released
into the atmosphere. 3.3 billion tons remained in the atmosphere and 3.8 billion cannot be accounted for. Oceans
are thought to be a strong sink of anthropogenic carbon dioxide.

2. Nitrus oxide
It is a naturally occurring gas produced by activity in soils and the ocean. It is vented to the atmosphere due to
combustion of fossil fuels, industrial, and agricultural activity. It is increasing at a rate of 0.8 ppb/year. It is
now at about 310 ppb. It is chemically inert in the troposphere and eventually makes it into the stratosphere
(involved in the destruction of ozone).

3. Methane
It is produced largely by agricultural activities (live stock, rice paddies). Methane's concentration is less tha
carbon dioxide, but it is much more effective in trapping infrared radiation. Methane's concentration has
increased (doubled) since pre-industrial era. Rate of increase is about 8 ppbv/year.

4. CFCs
Compounds that contain carbon, chlorine, and fluorine. Include CFC-11, CFC-12. They are responsible for
stratospheric depletion. Its concentration than carbon dioxide, but more powerful and very long-lived. CFC-11
remains in the atmosphere for 50 years. CFC-12 remains for about 102 years. Since the Montreal protocol (1987),
rate of increase has declined. CFC-11 peaked in 1994 (~276pptv). CFC-12  and there was a peak in 1999 (555 pptv).

STRATOSPHERIC OZONE DEPLETION

Measurements were first taken in 1931 by Dobson. Measurements are done through satellites (total ozone
mapping spectrometer). Data shows a decrease in the ozone content of the upper atmosphere. A possible
cause are the CFCs.
Most dramatic change in ozone is found over the antarctica. This loss of stratospheric ozone has happened
every september and october since the late 70s. During the antarctic spring, a decrease in ozone from the
pole to ~ 45 degrees S takes place (this is when the sun first reaches this area). The cause is understood to
be man-made CFCs. CFCs go under photodissociation and release chlorine atoms. Loss of ozone due to
CL atoms is complicated by special meteorological conditions of the antarctic.
Meteorological conditions:  1. clouds- winter over antarctica characterized by a large mass of very cold, dry
air. There are very cold temperatures in the stratosphere (as cold as -90C). Due to these cold temperatures,
very little water vapor exists and so the clouds are mainly composed of ice crystals. These high, thin clouds
are called polar stratospheric clouds (PSCs). Chemical reactions on the surface of ice crystals (within these
clouds) convert CL from less-reactive to unstable (reacts to sunlight to destroy ozone).
2. circumpolar circulation- strong circulation in the antarctic stratosphere isolates the air at the center from the
warmer, ozone rich air outside the vortex. This vortex breaks up in the late spring. Areas of air with little
ozone go from the pole to other areas.
The ozone hole over the north pole is not as large. Some decrease (~10%) has been observed. The smaller
decrease is a result of the weaker vortex and the higher startrospheric temperatures are higher over the north pole.
 

Global Climates

a. Past global Climates

. Earth has generally been a warm planet, much warmer than today.
. Records show warmer times and shorter colder times
. The cold periods called Ice Houses (low levels of CO2) last a long time before the Earth returns to its
   Hot House (greenhouse) state.
. Four Ice Houses are known to have occurred (2.5 billion, 700 million, 300 million, and 35 million years ago). Most
  of the human existence has been spent in the most recent ice age.
. The last century: There have been 2 episodes of warming during this century .
. How do we explain the rising temperatures of the last few decades?
        Recall that changes in global climate occur on a wide variety of time scales. So is this recent rise in
        temperature just a a part of natural variability in climate or caused by human-induced warming (a result of
        an increase in greenhouse gases)?
. Important note: Climatic changes are not restricted to mean values. There can also be changes in the frequency of
  rare events

b. Climate classification system

There are many different climate types for various regions on the planet.. The factors that produce climate in any
given place are:
1. intensity of solar radiation and its variation with latitude
2. distribution of land and water
3. ocean currents
4. winds
5. intensity, and positions of high and low pressure areas
6. terrain variability
7. altitude

Major classification system (Koppen system:

1. Tropical Moist Climates (group A)
General Characteristics:
Year-round warm temperatures. Mean temperature of above 64 F. Mean annual precipitation >60 inches.
Major types based on seasonal distribution of rainfall:
1. tropical wet (AF)
2. tropical monsoon (AM)
3. tropical wet and dry (AW)

Example: AF Peru near the equator
                 AM- India
                 AW- Western Central America

2. Dry Climates ( group B)
General Characteristics:
Minimal precipitation (evaporation.precipitation)
Major types:
1. arid (BW)
2. true desert (BS)
3. semiarid (BS)

Dry regions occupy more land area than any other major climatic type.

Example: BW- west coast of South America, most of interior Australia
                 BS- Great Plains region in U.S.

3. Moist Subtropical Mid-Latitude Climates (group C)
General Characteristics:
Humid with mild winters. Temperatures of coldest months normally between 27-64 F.
Major types:
1. humid subtropical (Cfa)
2. marine (Cfb)
3. dry-summer subtropical (Cs)
4. mediterranean (Cs)

Group C climates of midlatitudes have distinct summer and  winter seasons.

Examples:  Cfa- Southeastern U.S.
                    Cfb- Northwest coast of North America
                    Cs- Portland, Oregon

4. Moist Continental Climates (group D)
General Characteristics:
Warm to cool summers and cold winters. Average temperature of warmest month > 50 F. Average temperature
of coldest month < 27 F. Severe winters with snowstorms.
Major types:
1. humid continental with hot summers (Dfa)
2. humid continental with cool summers (Dfb)
3. subpolar (Dfc)

D climates controlled by large land masses are found only in the Northern Hemisphere.

Examples: Dfa- Des Moines, Iowa
                   Dfb- Winnipeg, Canada
                   Dfc- Norway

5. Polar Climates (group E)
General Characteristics:
Year-round low temperatures. Average temperature of the warmest month <50 F.
Major types:
1. polar tundra (ET)
2.  polar ice caps (EF)

Example: ET- North of Fairbanks Alaska (Fairbanks is Dfc (subpolar)
                 EF- Interior ice sheets of Greenland and Antarctica
 

2. DEFINING CLIMATE CHANGE

a. Climatic norm
Definition: average of a climatic element such as temperature or snowfall  Normal does not indicate static. Climate
is variable with time.  Climatic norm contains the total variation in the climate record:
a. averages
b. extremes
Climatic norm is computed over a 30-year period.  30 year averages are computed for temperature, precipitation,
and pressure. There is obviously a problem with this practice since a 30-year period does not provide a long
enough record for some climatic events. It tends to be a reasonable assumption for temperature. For temperature
we can assume that we have a normal distribution (mean=median=mode).
Example:
Can assume that about half of Januarys are warmer than the 30-year mean and half of Januarys are colder than
the 30-year mean.

Precipitation is mainly different since the distribution of precipitation is not  Gaussian (mean is not equal to median).
Example: A dry climate (not much rain in the summer) might have only a small number of Julys with more rain
than the mean and more than half of Julys would be drier than the mean. For precipitation the value of the
median might be a better value.

b. Climatic anomalies
Definition: deviations from long-term climatic averages are anomalies. They usually do not happen with the
same magnitude everywhere.
Above long-term averages are called a positive anomaly and below long-term averages are called a negative
anomaly.
Geographic variability of anomalies is related to:
1. Westerly wave pattern (controls air masses and storm tracks). A number of westerly waves circle the atmosphere.
Hence a single weather extreme would not happen over a large area.
Example: severe weather would not happen over the entire United States at the same time.
Precipitation displays a more complex anomaly pattern than the temperature. This is a result of the greater spatial
differences in rainfall due to storm tracks and random distribution of convective storms.
Example: In spring, in the midlatitudes neighboring countries  can have opposite rainfall anomalies. One could be
above average while the other is below average.
 

c. Climate controls
1. latitude- seasonal changes of solar radiation and length of day change with latitude.
2. elevation- elevation influences temperature and affects precipitation (rain vs. snow).
3. topography- can affect distribution of cloud and precipitin patterns.
4. proximity to large bodies of water- large bodies of water moderate seasons.
5. atmospheric circulations- is not regular and tends to be a function of weather systems.

First four are fixed and tend to have a regular and predictable influence on climate.

Global patterns of temperature:
. Highest mean annual temperature at about 10 degrees north latitude.
. Temperature decreases toward the poles
. Northern Hemisphere is warmer than the Southern Hemisphere:
  1. Polar regions have different radiational characteristics
  ...Antarctic is covered by a glacial ice sheet (high albedo-----intense cooling)
  ...NH polar region is mostly covered by ice, but some water areas show up in the summer.
2. Greater land area in tropical latitudes
...land warms up more than water (tropical regains in NH warmer than SH).
3. Ocean circulation
... more warm water is transported to NH.
...annual range of temperature is greater over land than water.

Global patterns of precipitation:
.Great spatial variability:
1. topography
2. distribution of land and sea
3. circulations
 
 

III.  THE CHANGING ATMOSPHERE

1. CHEMISTRY OF THE ATMOSPHERE

Atmosphere is a mixture of gases. Some gases have constant concentrations and some have variable concentrations.
Nitrogen is the most abundant.  Nitrogen is not very important in affecting the weather. It does serve as a precursor
molecule for formation of nitrate nitrogen required for plants to make amino acids chlorophyll. Molecular oxygen
is the most important for life on the planet. Water vapor has the most degree of variability.. (see handout for
other gases). Water vapor concentration varies depending on time and place. It is a source of clouds and precipitation.
It is also important in absorbing IR radiation from the Earth. As water vapor changes from one state to another, it
absorbs or releases heat which is an important source of energy for driving storms.

Atmospheric pollutants: The mixture of gases in the atmosphere becomes polluted when it is changed by addition
of particles and gases. This altered atmosphere may pose harm due to its impact on weather, climate, human health,
animals, or vegetation.

Definition of air pollution: Presence of foreign substances that interfere with the well being of living things.

Types of air pollutants:
1. Primary pollutants- these enter the atmosphere directly (from smoke stacks, tail pipes)
2. Secondary pollutants- form when a chemical reaction occurs between a primary pollutant and another component
in the air (water vapor)

Sources of air pollution (primary pollutants)

1. Natural processes- Volcanic activity, forest fires, soil erosion, plant and animal decomposition processes, hydrocarbons
emitted by vegetation, pollen, ozone and nitrogen oxides from electrical storms. Natural air pollution is not a major
concern even though nature does pollute more than man. It is not a major problem for human health and welfare since:
1. levels are typically low
2. Usually large distances separate sources of natural pollution and human populations
3. Major sources of natural pollution are episodic and transient

2. Anthropogenic processes- serious since high levels of pollutants are produced in environment harmful to human
health. Sources include:
1. Industrial (paper mills, refineries)
2. Personal (cars, fireplaces)

Characteristics of major pollutants

1. Particulate matter- It is any matter dispersed in the air. It could be solid or liquid (known as aerosols). Individual
particles are larger than small molecules but smaller than 500 microns. Particles smaller than 1 micron (in diameter)
originate in atmosphere through condensation. Larger particles originate through erosion. Solid particles may irritate
people but usually are not poisonous. Some examples include dust, smoke, and pollen. Some of the more dangerous
variety include asbestos fibers and arsenic. These pollutants normally reduce visibility in urban areas. Particulate
matter collected in cities include iron, copper, nickel, lead. This type can hurt human respiratory system. Lead particles
are the most dangerous. They can accumulate in bone and soft tissues. High concentrations can lead to brain
damage. Industrial processes account for 40% of the total particulate matter in U.S.
The main problem with particulate problem is that it may stay in the atmosphere for a while. This depends on
size and amount of precipitation. Heavier particles pose no problem since they usually settle to the ground
in about a day. Lighter particles can remain suspended for several weeks.

2. Carbon monoxide
It is a product of incomplete combustion of fuels. It is colorless and odorless. It is absorbed through lungs and reacts
with hemoglobin in red blood cells and decreases the oxygen carrying capacity of the blood.  It is normally quickly
removed from the atmosphere by microorganisms in the soil.  It is a problem in poorly ventilated areas. It cannot
be seen or smelled, so can kill without warning. Symptoms include headaches, fatigue, and drowsiness.

3. Hydrocarbons
Individual organic compounds composed of hydrogen and carbon. It is primarily associated with the processing,
marketing, and use of petroleum products. They make up the major portion of volatile organic compounds (VOCs).
The can be solid, liquid, or gas at room temperature. Methane which occurs naturally in the atmosphere is the most
abundant. Other VOCs include benzene, formaldehyde, and CFCs. Certain VOCs are carcinogens (cancer-causing
agent).
Nitrogen oxides- form when nitrogen in the air reacts with oxygen during high-temperature combustion of fuel.
2 primary nitrogen pollutants are nitrogen oxide and nitric oxide. They are both produced by natural bacterial
processes. Concentrations are great in urban environments. Nitrogen dioxide reacts with water vapor to form
nitric acid adding problems to acid rain. Primary sources of nitrogen oxides include cars and power plants. VOCs
can become dangerous when they react with nitrogen oxides to produce secondary pollutants.

4. Sulfur dioxide
It is colorless and comes from burning of sulfur-containing fossil fuels. Primary source includes power plants
and refineries. The y can also get into the atmosphere naturally through volcanoes. It oxidizes to form secondary
pollutants sulfur trioxide and sulfuric acid. High concentrations aggravate respiratory problems. It can also damage
plants. Sulfur emissions have decreased since the 1980s.

5. Ozone in the troposphere
Tropospheric ozone is the main component of photochemical smog. Photochemical smog forms in large cities when chemical reactions take place with sunlight. Examples are Los Angeles and Mexico City.

Ozone production in polluted air: Ozone forms as a result of reactions of hydrocarbons and nitrogen oxides. These reactions are faster on hot sunny days. Sunlight dissociates nitrogen oxide into nitric oxide and atomic oxygen. Oxygen then combines with the molecular oxygen and a third molecule. Ozone is destroyed by combining with nitric oxide. If there is sunlight, nitrogen dioxide will break into nitric oxide and atomic oxygen. Atomic oxygen then combines with molecular oxygen to form ozone. Large concentrations of ozone can form if some of the nitric oxide reacts with other gases without removing ozone. Hydrocarbons emitted from cars and industry and hydroxyl radicals contribute to this process. These reactions can lead to
formation of nitric oxide which can react with hydrocarbons to form nitrogen dioxide without removing ozone.
 

Meteorology of air pollution

1. Factors affecting air pollution

a. Wind, wind is important in diluting the pollutants. Wind speed determines how fast the pollutants mix with air and how fast they move away from their source. Strong winds lower the concentration of pollutants by spreading them apart.  The stronger winds create more turbulence in the atmosphere which creates eddies (swirls). These eddies dilute the pollutants by mixing them with the cleaner surrounding air.

b. Role of stability and inversions, stability of the atmosphere determines how much air will rise.  A stable atmosphere resists vertical motion. Atmospheric stability is determined by how temperature changes with height (lapse rate). When the temperature decreases with height, then the atmosphere is unstable, and when the temperature increases with height, the atmosphere is mainly stable (inversion: temperature increasing with height).

Types of stable atmosphere

1. Radiation inversion, usually exists during the night and early morning under clear skies and light winds. Only lasts for a few hours, and the inversion weakens as the sun warms up the surface. By afternoon, the atmosphere becomes more unstable, winds become stronger and the pollutants can be dispersed.

2. Subsidence inversion, forms as a deep high pressure system (anticyclone) sinks and warms. May last for several days or more. It is usually associated with major air pollution episodes. The unstable air under the inversion layer allows the pollutants to be mixed, this layer is called the mixing layer. The stable layer within the inversion layer acts as a lid on the pollution.

Mixing Depth (mixing height). Movement of the air in the vertical is influenced by the vertical temperature differences. The  larger the temperature gradient (difference), the more mixing takes place in the atmosphere due to more convective and turbulent activity. The region of the relatively unstable air extends from the surface to the base of the inversion layer, this is called the mixing layer. The extent of the mixing layer is called the mixing depth. If the inversion rises, the mixing depth  increases and the pollutants would be dispersed in a larger volume of the air. If the inversion lowers, the mixing depth decreases, pollutants become more concentrated. Normally, the atmosphere is most unstable in the afternoon and most stable in early morning. The greatest mixing depth is in the afternoon.

c. Location of high pressure systems

d. Topography, topography can affect air motions near point and area sources. Most urban areas are near a body of water (New York City, Los Angeles, Chicago) Local flow patterns have an impact on pollution dispersion.

1. Lake, sea, and land breezes- Land/water circulation is a result of differences in heating/cooling of land and water. During the summer and with clear skies, land warms up faster than water. Warm air rises and moves toward the water. Due to the differences of temperature and pressure, air flows in from the water, this is called sea or lake breeze. At night, a land breeze is formed. A land breeze is usually weaker than a sea breeze. Circulations of land/sea breezes may cause pollutants to be recirculated.

2. Valleys, chosen for industry because of water (in river valleys) for transportation of raw materials. Valleys normally suffer sever air pollution problems since air flows downhill into the valley floor. As air reaches the valley floor, it flows along the valley, cool air sinks and accumulates, intensifying the surface inversion. Surface inversions are usually destroyed by morning, and the layer of pollutants comes to the ground level.

3. Hill and mountains

Mountains can affect local air flow by increasing the surface roughness and as a result the wind speed decreases, they can also act as a barrier to the air movement.
 

Characteristics of air pollution episodes

1. stagnating anticyclonic weather systems

2. temperature inversion

3. low wind speeds

4. increased concentrations of smoke, sulfur dioxide, etc.

5. usually lasts 2-7 days

6. rapid effects
 

Dispersion from a point source

A plume is created when the pollutants are being emitted from a smokestack.  Factors controlling the plume are:
1. physical and chemical nature of the pollutants
2. meteorological conditions
3. location of the source
4. downwind topography/ physical obstructions
Point source plumes are usually a mixture of gas and particulate phase substances. Particles with diameters of greater than 20 micrometers deposit closer to their source whereas the ones with diamteres less than 1 micrometer disperse more (by diffusion). Diffusion causes the plumes to spread horizontally and vertically. Normally maximum ground level concentrations will be from the area close to the smokestack to a few km downwind. Most plumes are a mixture of gases and particulate matter. Large particles settle near the source, and smaller ones stay suspended for a longer period of time.

Plume Rise, height of the plume tells us about the pollutant concentrations near the ground. The larger is the rise, the greater distance downwind (carried for a greater distance before reaching the ground).

Effective Stack Height, the height of the stack plus the plume rise is called the effective stack height. The higher is the effective stack height, the greater the dispersion will be. Effective stack height can be increased by 1. building taller stacks
2. emitting pollutants at higher temperatures. Approximate stack heights of about 250-300 meters are commonly used. Some might be about 400 meters.

Plume transport, horizontal wind speeds will affect plume rise. The higher is the wind speed, the quicker the plume is transported. High winds enhance dispersion. Plume rise is also affected by stability. When the atmosphere is stable, the plume rise is reduced, dispersion is decreased, and so there will be higher concentrations at the ground level.

Plume Characteristics
As a result of differences in atmospheric stability, plumes have different shapes:

1. looping, happens under stable conditions, clear sunny days with light winds
2. coning, happens on cloudy days or windy days when the atmosphere is slightly unstable
3. fanning, happens under stable conditions, smoke spreads horizontally rather than vertically. happens on clear nights with light winds.
4. lofting, maybe produced at sunset or on a clear evening
5. fumigating, produced when a fanning plume and surface inversion break up due to surface heating. usually formed on clear sunny days with light winds.
6. trapping, occurs if there is an inversion above and below the plume. produced on clear sunny days and clear nights (stagnating high pressure)

Large-scale transport and dispersion
Urban Plume: large polluted air masses that affect air quality for hundreds of kilometers downwind.  Usually the airflow is controlled by high and low pressure systems.
Planetary Transport: atmospheric pheonomena at the equator retard the airflows from one hemisphere to another. Cross-equatorial mixing time is about 1 year so significant differences in concentration exist between Southern Hemisphere and Northern Hemisphere.
Exchange between the troposphere and stratosphere.:  This makes the mixing of the tropospheric and stratospheric air possible.
Stratospheric Circulation: Movement of ozone poleward is strong in the winter and affects the concentration in different areas.

Atmospheric effects of pollution

1. visibility
2. urban climates
3. frequency of rainfall
4. precipitation chemistry

1. visibility, greatly reduced as a result of increased pollution

2. urban climates, cities are generally warmer than the surrounding areas. This region of warmth is called urban heat island (a result of industry and other urban developments). Factors in the development of the heat island are:
a. heat entering the environment from industry (energy utilizing processes)
b. solar energy absorption of urban surfaces
c. decreases urban ventilation

Development of heat island: at night solar energy  stored in buildings and roads is released into the air. More heat is given off at night by cars and factories, and there is not a lot of ventilation. Also tall city structures do not allow the infrared radiation to easily leave the surface which leads to higher nighttime city temperatures. Heat islands are strongest at night, during the winter (longer nights), and high pressure areas (light winds, clear skies).  Effects of urban heat island are that it can have an effect on the climatological temperature records (artificial climatic warmth in cities). So we do need to consider this warming in interpreting climate change.

3. frequency of rainfall, precipitation may be more in cities as a result of increased surface roughness, since flow near the surface slows down and converges and rises. Also city heat warms the surface air and makes it unstable. Precipitation may be decreased downwind and if not enough moisture is available , then too many nuclei are competing for the moisture. In general, more cloudiness, more frequent thunderstorms, and more precipitation in urban areas compared to their surrounding areas.

4. precipitation chemistry, pollution emitted from industrial areas can be carried several kms. Some particles settle to the ground (dry deposition) and some are removed when clouds form and eventually fall as precipitation (wet deposition). Acid rain and acid precipitation explain wet deposition. Emissions of sulfur dioxide and nitrogen oxides settle over an area, and transform into acids when they interact with water. Some of the particles turn into sulfuric acid and nitric acid. These acid particles fall to the ground or attach to cloud or fog droplets and form acid fog.

Natural precipitation is slightly acidic, because carbon dioxide and trace quantities of other gases in the atmosphere dissolve in rain water and form a weak acid dominated by carbonic acid, with small amounts of sulfuric acid,
nitric acid, and organic acids (e.g., formic acid). Unpolluted rain normally shows up in the range of 5.2 to 5.6 on the pH scale. Acid rain is
precipitation with a pH of less than about 5 on an annual basis. Rain in many industrial areas may be up to 1000 times more acidic than
natural precipitation.  Acid rain falls worldwide, but eastern North America, central Europe and Scandinavia are most affected. High
concentrations can damage plants and water resources. Acid deposition can ruin foundations of structures. It can affect forests when the acid
deposition on the forest floor affects the nutrients necessary for trees.Acid Rain Program Overview: The Acid Rain Program has been
instrumental in controlling emissions of sulfur dioxide and nitrogen oxides into the atmosphere and as a result reducing the occurrence of acid
rain.
Acid Rain Program
Goal:  To achieve significant environmental and public health benefits through reductions in emissions of sulfur dioxide and nitrous oxides.  There were two phases associated with this program. Phase I began in 1995, which affected 263 units at 110 mostly coal burning electric utility plans located in 21 eastern and midwestern states. An additional 182 units joined later. These units reduced their sulfur dioxide emissions by almost 40% below their required levels. Phase II began in 2000 which tightened the annual emissions limits. the number of involved untils went to 2000. This phase called for a 2 million ton reduction in NOx. Acid rain program is viewed around the world as a prototype for tackling emerging environmental issues. The Acid Rain Program will result in a 10 million ton reduction of sulfur dioxide emissions from 1980 levels by the year 2010.
For further information on the Acid Rain Program please consult the EPA's information on the Acid Rain Program:
www.epa.gov/airmarkets/arp/overview.html

Federal Legislative History

At the end of the 19th century and first half of the 20th century, air pollution was seen as a local problem.  Changes  started in the 1950s as states started regulations led by California.  The federal role began at around the same time. 1955 marked the first clean air legislation. The first clean air act was in 1963 and was set to award grants for development and improvement of state and local air pollution control agencies, more research, training and technical assistance, federal research responsibility for cars, and sulfur oxides pollution, air quality criteria development. There were amendments to the clean air act of 1963 which included motor vehicle air pollution control act. The air quality act of 1967 developed a regional approach to air pollution control and the development of air quality standards. The 1970 clean air amendments: the national air pollution control administration was dissolved. Air pollution control functions were transfered to the US Environmental Protection Agency (EPA). The 1977 clean air act provided a correction to the primary initiatives, postponed and modified some of the federal car emissions standards. It also gave the EPA authority to regulate stratospheric ozone depleting chemicals. The 1990 clean air act was the first after 13 years and included the control of acid rain, and toxic air pollutants and the regulation of emissions from cars. There were also some changes in the timetables for achieving air quality standards. There were some changes to the clean air act in 1997 which inlcuded standards for ground level ozone and particulate matter and the development of a new program to control regional haze.
Please look at the clean air act information on www.epa.gov/oar/caa/contents.html