AIR POLLUTION AND GLOBAL ATMOSPHERIC CHANGE

 

Human beings breathe in and out about once every 4 seconds, 16 times a minute, 960 times an hour making up about 8.5 million times a year of air intake. This adds up to about 4 million liters (1 million gallons) of oxygen-containing air every year from the earth's surface.

 

NATURAL SOURCES OF AIR POLLUTION

 

a)  Carbon oxides, nitrogen oxides, ash and other particulate matter from lightning triggered

     forest fires  

b)  Massive eruption of volcanic dust, ash and particulate matter.

c)  Salt spray from the sea, 

d)  Methane and hydrogen sulfide from decaying plants

d)  Pollen (e.g. ragweed) from live plants, 

e)  Dust and other forms of suspended particulate matter from windstorms 

f)  The composition of natural air

 

A clean dry air is made up of the following elements:

     Nitrogen - - -      78%

     Oxygen - - - -      20.94%

     Argon  - - - -  0.9340%

     Carbon Dioxide 0.0310%

     Neon  - - - -   0.0018

     Helium  - - -  0.0005

     Methane - - - 0.0002

     Krypton - - - 0.0001

     Sulfur Dioxide 0.0001

Gases such as carbon dioxide, methane and sulfur dioxide are normal constituents of the clean air. However, they often reach much higher concentrations to make the air polluted and harmful to the environment and human life.

 

COMPOSITION AND STRUCTURE OF THE ATMOSPHERE

 

The atmosphere is divided into a number of layers based on temperature and gaseous content.

a)   The Homosphere:  or lower atmosphere extends between sea level and about 50 kms. It

      is a zone where gases are perfectly diffused so that they act as a single gas. 

 b)  There is also the Heterosphere - which extends from about 80 kms (50 miles) above the

      earth's surface.

 

The Homosphere:

 

The homosphere is further divided into a) the troposphere,  b) stratosphere and  c) mesosphere

1) Troposphere:  extends from sea-level to about 8-9 miles (13-14 kms). The zone inhabited by humans and hence one of most concern. Within the troposphere, temperature steadily decreases with altitude at an average rate of 3.5 degrees F per 1000 feet (6.4 degrees C / km). This is known as the Environmental lapse Rate. The opposite condition where temperature increases with height is termed Temperature Inversion. Calm winds prevail during temperature inversion. The greenhouse effect occurs in the Troposphere.

 

2) Stratosphere:  The next layer from the troposphere located between about 20 - 60 kms from the earth's surface. Air temperatures are essentially constant for most part until it begins to increase with increasing height at  about 50 kms from the earth's surface.  The ozone, a protective layer that shields the earth from the harmful ultraviolet radiation is located in this zone. Its depletion has been a concern for some time.

 

3) Mesosphere:  The third layer of the homosphere. Here temperature decreases with altitude

 

Effects of Air Pollution on the Climate:

 

a)  On Sunlight:  Air pollution can reduce the amount of sunlight that reaches the Earth because particles scatter and absorb solar radiation. Washington DC and Los Angeles for example receive 10%  less sunlight than they did at the beginning of this century when air was relatively unpolluted. 

 

b)  On Precipitation:  Particulates such as soot and dust in urban air serve as condensation nuclei that absorb tiny moisture droplets and can thus promote cloud formation and increase rainfall.

 

OUTDOOR AIR POLLUTION CAUSED BY HUMANS

 

Air pollution is considered the presence of one or more chemicals in the atmosphere in sufficient quantities and duration to cause harm to humans and their property. As a significant environmental problem, air pollution dates back to the Industrial revolution in Europe and the US. In 1909, 1,000 people died in Glasgow, Scotland as a result of polluted air. The word smog (a combination of smoke and fog) resulted from the Glasgow event. Today the emissions of traditional air pollutants, (sulfur dioxide and particulates) continue to rise particularly in developing countries.

     a)  In many of world' cities especially Shenyang and Xian in China where the estimated

          highest concentration of air sulfur dioxide and particulate matter occur, and Mexico

          City, the world's worst polluted city.

     b)  Eastern and Central Europe - particularly Romania, Poland, former Check republic and

          former states of the Soviet Union

 

SOURCES OF AIR POLLUTANTS

 

Stationary Sources:  Pollution sources that are stationary such as Smokestacks, Electric power generating plants and smelters. According to the World Bank and the UNO, burning coal to produce electricity is responsible for 67% SO₂ (sulfur oxides) 36% CO_2, 33% mercury, and 28% NOx emissions in the air.

 

Mobile Sources:  These are sources of air pollution that move around from one place to another, such as Automobiles, Boats, Trains, Satellites and other Aircraft. Vehicle emissions account for 75% of CO₂ and 44% of No_x in the US urban air. In car-clogged cities such as Los Angeles, Mexico City, Bangkok etc vehicle emissions account for between 80-88% of the air pollution.

 

TYPES OF AIR POLLUTION:

 

Primary Pollutants: These pollutants are emitted directly into the air in a potentially harmful form. While in the atmosphere, these primary pollutants may react with one another or with basic components of air to form new pollutants called Secondary Pollutants.

 

CRITERIA POLLUTANTS

 

These are specific environmental air pollutants that adversely affect human health and welfare and for which the EPA has set air quality standards.

 

1.  Carbon Monoxide  (CO.

 

2.  Sulfur Dioxide:  (SO₂)

 

3.  Hydrocarbons:  Also called Volatile Organic Compounds.

 

4.   Particulate Matter:  

 

5.   Nitrogen Oxides (NOx):

 

6.  Ground-level Ozone: 

 

7.   Lead:   

 

LOCAL, REGIONAL AND GLOBAL PROBLEMS FROM AIR POLLUTION

 

1. Photochemical Smog:   

Formed as a result of the action of sunlight on hydrocarbon emissions from motor cars, factories and other sources in areas of low pollutant dispersion. Photochemical rwaction begin when the nitrogen and oxygen in the air react at the high temperatures found inside automobile engines and the boilers of coal-burning power plants to producr colorless nitric oxide (N2 + O2 à 2NO). Once in the troposphers the nitric oxide reacts with oxygen to form Nitrogen Dioxide – a yellowish-brown gas with a choking odor. Photochemical smog occurs in all cities but it is common in cities with sunny, warm, dry climates with lots of motor vehicles (Los Angeles, Salt Lake City, Mexico City, Sao Paulo, Brizil.

 

2. Industrial Smog.

Occurs in cities where large amounts of coal and heavy oil (containing sulfur) are burned in power plants and factories and for space heating. When burned, the sulfur in coal and oil react with oxygen to produce sulfur dioxide – a colorless suffocating gas. The production of smog ceases at nightfall when human activity ceases. Industrial smog is a big problem in many industrial cities. In one example in the US, a week from October 26, 1948, thermal inversion occurred at Donora, 30 miles south of Pittysburg, in Pennsylvania and caused industrial smog. In a town of 12,000 people, 43% became ill -5910 people, and 20 people died within only 5 days.

 

3.  Acid Rain:

Causes deposition of Acids on the earth's surface through the processes of precipitation (rain, snowfall etc).

Composition:  Sulfur dioxide (SO₂) combines with oxygen and water to form sulfuric acid (H2SO4); and Nitrogen oxides (NOx) combine with water to form Nitric acid (NHO3). This results in a pH value in the low 3's and 4's approximating vinegar. Of the two, sulfur dioxide causes more property damage.

Source:  Derived primarily from combustion of impure fossil fuels mainly in the US manufacturing belt. Coal burning power plants from Illinois to Pennsylvania are the greatest culprits. The largest single source in the world is a nickel smelter at Sudbury in Ontario, Canada.

Effects:  Because a drop in pH makes minerals more soluble, acid rain adversely impacts fish, plant communities like forest, drinking water, work of art, building stones and exposed metals.

Control:  Requires International cooperation, but the following might help:

     a)  Install sulfur scrubbers in smoke stacks at factories,

     b)  Reduce combustion temperature,

     c)  Effective legislation

 

4.  Greenhouse Effect and Global Warming

 

The greenhouse effect results because carbon dioxide in the atmosphere is transparent to the relatively short-wave solar radiation but opaque to the long wave terrestrial radiation. The concentration of carbon dioxide in the atmosphere therefore causes an atmospheric lid trapping heat on the earth's surface. Increase in carbon dioxide content result from the burning of fossil fuels, deforestation and soil deterioration (loss of soil carbon).

Global Impacts:  a) Causes more rapid plant growth,  b)  Average temperature of the atmosphere may rise or increase in cloud cover may serve to lower temperatures.

 

5.  Depletion of Stratographic Ozone

 

A group of synthetic substances that are compounds of chlorine, fluorine and carbon form a potent compound called Chlorofluorcarbons (CFC’s). These chemical compounds are widely used in refrigeration, aerosols and in many industrial processes. They are chemically inert, and remain stable and intact in the atmosphere and do not break down for a period of over 100 years. They reduce ozone in the atmosphere and allow cancer-causing UV radiation to reach the earth’s surface.

 

FACTORS THAT INTENSIFY AIR POLLUTION

 

Winds, Rain and Snow can help clean up urban air pollution as against other conditions that promote the concentration of air pollutants:

 

a) The excessive emission of pollutants within a confined area

b) Insufficient Atmospheric Dispersal of pollutants

c) A dense population

d) A very dense concentration of Industries

e) The presence of temperature Inversion

f)   Urban buildings that can slow down wind speed

g) Hills and Mountains that tend to reduce the flow of air in valleys below them.  

h) High summer temperatures that promote chemical reactions and produce ground ozone

      and photochemical smogs.

i)   The type of fuel for generating power and used in factories and automobiles

j)   Temperature Inversions

 

1.   Temperature Inversion:

The build up of atmospheric contaminants on the earth's surface is facilitated by a meteorological condition known as Temperature inversion. It is a condition in the atmosphere during which warm air overlies cooler air. This prevents the vertical rising of warm air and hence little or no winds may blow. Inversions restrict air circulation and thus may serve as atmospheric lids that trap pollutants in urban areas. There are three main types:

 

Radiation inversion:  Develops in clear, relatively calm weather. On clear nights, the ground radiates heat upward and without clouds, it escapes into space. As a result, both the ground and the air layer close to it cool off rapidly- more quickly than the air above them forming and inversion.  

 

Subsidence Inversion:  Less common than radiation inversions but lasts longer and may be more extensive. Subsidence develops when an air mass sinks slowly over a large area towards the ground (as in high pressure cells). As the air mass sinks, the atmosphere is compressed and hence the air warms up more than the ground layer of air.

 

Advection inversion: Occurs on the west coast when warm sea breezes pass over cold currents prior to reaching land. The air over the cold surface of the ground thus becomes cooler than the intruding warm air that overlies the cool air.

 

INDOOR AIR POLLUTION

 

Sources: 

 

a)          Gas stoves, faulty furnaces, unvented gas stoves and kerosene heaters, wood stoves, burning of    candles etc., release carbon monoxide and nitrogen dioxide into the air

 

b)         Paints and other materials in the home may contain lead

 

c)           Formaldehyde fumes from furniture stuffing foams, insulation in carpets and plywood releases cancer risk fumes.

 

d)         Tobacco Smoking releases carbon monoxide, sulfur dioxide, oxides of nitrogen in addition to quantities of cancer-causing pollutants like cadmium, nickel and radioactive polonium.

 

e)           Radon-222, radioactive soil and rock surrounding building foundation and water supply

 

f)             Pipe Insulations, Vinyl ceiling and floor tiles may release asbestos into the air.

 

g)          Chroline-treated water in hot showers may release chroloform

 

Controlling indoor Pollution:

 

1.  Installation of air-to-heat exchanger to expel heated air and replace it with fresh air.

2.  The use of vegetation as living air purifiers.

3.  The use of a sub-basement vent system

4.  Controlling smoking indoors.

 

AIR POLLUTION CONTROL

 

1.  Clean Air Act:

Ÿ         Passed originally in 1963, and amended in 1967, 1970, 1977 and expired in 1982 but renewed in 1990. It established standards for air quality for five major pollutants and provides time tables for their achievements.  Some of the mandates are the following:

     a)  All 1994 cars were required to cut emissions of hydrocarbons by 40% and nitrogen

                 oxides by 60%.

     b)  Power plants must cut their sulfur dioxide emissions in half by year 2000

     c)  Carbon Monoxide emissions must be substantially reduced.

     d)  Emissions of 189 cancer-causing chemicals must be reduced by 90% by 2003 

 

2.   Pollution Standards Index

Ÿ         A uniform air quality index adopted by the EPA in 1978. It makes it possible to compare the air quality of different cities. It utilizes a scale as follows:

     0 - 99            Air is good

     100 - 200 Unhealthy, Air quality alert

     200 - 300 Air pollution warning

     > 300       Air pollution Emergency.

Ÿ         Based on PSI ratings, the most badly polluted cities include; Los Angeles, Houston, Washington, Philadelphia and New York.