The earth’s atmosphere is a reservoir of gases. Air
is a mixture of gases that is naturally odorless, colorless, tasteless
and formless. The atmosphere is bound to the Earth by gravity.
a) Air is
the medium of life on Earth’s surface
b) A major
industrial and chemical raw material
c) Absorbs and interacts with harmful
electromagnetic radiation and stream of charged particles in the solar wind.
d) Protects the earth from natural and
human-caused space debris.
The 300 miles (480 km) long column of air (making up the atmosphere) exerts its weight pressing downward under the force of gravity.
The weight of the atmosphere exerted on a surface produces AIR PRESSURE.
This force (air pressure) is approximately 14.7 lb per square inch at
sea level, equivalent to 1013.12 mb/m2 or 29.92 inches of
mercury (in a barometer).
Air molecules create pressure on all surfaces
through their motion, size and number.
STRUCTURE
AND COMPOSITION OF THE ATMOSPHERE
The atmosphere is conveniently classified using 3
criteria:
a) Composition
b) Temperature
c) Function.
CHEMICAL COMPOSITION CRITERION:
Based on chemical composition, the atmosphere is divided
into 2 broad regions:
a)
The
Heterosphere and…
b) The
Homosphere.
a)
HETEROSPHERE:
The
outer atmosphere beginning from about 50 miles from the earth’s surface and
extending to space Gases are not evenly mixed but assorted by gravity according
to their atomic weight and reaction of the gases with solar radiation. Less
than 0.001% of the mass of the earth’s atmosphere is in the
heterosphere.
b)
HOMOSPHERE:
Extends from earth’s surface to about 50 miles (80 kms).
Density of air changes with altitude but the proportion of gases is nearly
uniform. Exceptions are: Ozone O3, Water vapor, Pollutants & Some trace
chemicals.
Mixture of gases in the
Homosphere:
O2 20.946 209,460
CO2 0.037 368
Nitrogen: an inert gas principally
originating from volcanic sources. Oxygen: a by-product of
photosynthesis. Argon, an inert gas that is a residue from the
radioactive decay of a form of potassium. Carbon dioxide is a natural
by-product of life processes.
ATMOSPHERIC TEMPERATURE criterion
Using temperature, the atmosphere can be divided
into 4 distinct zones.
a)
The
Thermosphere
b)
Mesosphere
c) Stratosphere
and…
d) Troposphere
a) Thermosphere: Between 50–300miles (80 –
480kms into outer space. Temperature rises to 22000F (12000C)
and higher.
b) Mesosphere:
From 30–50 miles (50–80kms) above the earth’s surface.
The
Mesopause (outer layer of Mesosphere) is the coldest region in the atmosphere
about –1300F (-900C)
c) Stratosphere: 11–31 miles (18–50kms) from
the Earth’s surface. Temperature increases with altitude
d) Troposphere: the atmospheric layer that supports life. Home of the biosphere.
Holds 90% of total mass of atmosphere and all water vapor, clouds, weather and
air pollution.
Normal Lapse Rate: the phenomena by which temperature
decreases rapidly with altitude. Temperature Inversion: a phenomenon by
which temperature increases with altitude.
ATMOSPHERIC FUNCTION criterion
Based on function, the atmosphere has 2 zones that
remove harmful solar radiation and charged particles:
a)
The
Ionosphere and…
b) The
ozonosphere (ozone layer).
a)
Ionosphere:
extends throughout the thermosphere into the mesosphere. I absorbs Cosmic rays,
gamma rays, X-rays and Ultraviolet radiation.
b) Ozonosphere: a
layer of ozone gas (O3). Absorbs UV light and re-radiates it as long wave
infrared radiation.
POLLUTANTS IN THE TROPOSPHERE
The
troposphere contains variable quantities of both natural and human-caused gases
and chemicals that cause air pollution.
a)
Volcanoes – particulates, sulfur oxides.
b) Forest fires - carbon monoxide (CO) and
dioxide (CO2), nitrogen oxides, particulates
c) Plants
– pollens, hydrocarbons
d) Decaying Plants - methane, hydrogen sulfides
e) Soil
- dust, viruses
f)
Ocean
– salt spray and particulate matter
1. Winds: move pollutants from one place to another reducing
concentrating at one point while increasing it in another region.
2. Mountains and Hills (local landscape) can form
barriers to air movement or direct pollutants from one area to another.
3. Temperature Inversion: Temperature inversion prevents
the rise of cooler (hence denser) air to rise beneath thereby halting vertical
mixing of pollutants and preventing winds from blowing.
HUMAN-INDUCED
AIR POLLUTION
Human-induced
pollutants are found in Urban areas. About 2% of all annual deaths (50,000
people) in the United States are attributable to Air Pollution.
Developed with the advent of the automobile. It
results from interaction of Sunlight with combustion products in automobile
exhausts (nitrogen oxides, VOC’s).
Industrial Smog and Sulfur Oxides:
Industrial smog is associated with coal-burning
industries. A London physician coined the term SMOG to describe the combination
of smoke and fog. Once in the atmosphere, Sulfur dioxide (SO2) reacts with
oxygen (O) to form Sulfur trioxide (SO3) and in the presence of water forms
(sulfate aerosols) Sulfuric Acid (H2SO4). The water could become acidic leading
to ACID RAIN.
|
NAME |
SYMBOL |
SOURCE |
EFFECTS |
|
Carbon monoxide |
CO |
Incomplete combustion of fuels |
Displaces O2 in bloodstream |
|
Carbon Dioxide |
CO2 |
Complete combustion mainly from fossil fuels |
Principal greenhouse gas, |
|
Nitrogen oxides
|
NO, NO2 |
High
temperature and pressure combustion.
|
Destroys lung tissue, harms plants |
|
Volatile Organic Compounds |
VOC |
Incomplete combustion of fossil fuels |
Forms lower level ozone, harms respiratory system. |
|
Peroxycateyl |
PAN |
Photochemical reactions |
|
|
Ozone |
O3 |
Photochemical reactions |
Damages plants |
|
Sulfur Oxides |
SO2, SO3 |
Combusting of sulfur-containing fuels – e.g. coal |
Impairs breathing, asthma and bronchitis |
|
Particulate Matter |
PM |
Dust, dirt, & salt from construction,
agriculture, roads |
Affects visibility, respiratory system |
|
Methane |
CH4 |
Organic Processes |
Secondary greenhouse gas |
|
Water Vapor |
H2O |
Combustion processes, Evaporation |
|