ATMOSPHERIC COMPOSITION, TEMPERATURE & FUNCTION

 

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.

 

Protective functions of the Atmosphere

 

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 Atmosphere and Air Pressure

 

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:

Symbol % by Volume Parts per Million

N2 78.084 780,840

O2 20.946 209,460

Ar 0.934 9,340

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.

 

NATURAL SOURCES OF AIR POLLUTANTS

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

 

Natural factors that affect Air Pollution

 

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.

 

Photochemical Smog 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.

 

Anthropogenic Sources of Air Pollution

 

 

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