Atmosphere Chemistry Essay, Research Paper

Topic: Atmosphere Chemistry

Pollution has always been an emotive irrespective of whether it occurs in the air, on land or at sea. In the latter half of this century much attention has been drawn to air pollution caused by modern methods of communication, although some cradles of the Industrial Revolution must have experienced local levels of high pollution quite unimaginable by present standards. Campaigns against the more widespread effects of atmospheric pollution are constantly mounted by the media, of which the printed word is only a part; meanwhile scientific knowledge still advances on all fronts. This greater appreciation allows a more fundamental understanding of the consequences of pollution upon the whole environment and all those who live in it.

Atmosphere chemistry involves understanding the chemical composition of the natural atmosphere, the way gasses, liquids, and solids interact with each other and how human activities may be changing the chemical and physical characteristics of the atmosphere. The difficulty is making out what it all means and what the consequences are to all of us and to the world in which we live.

The enhancing of the Green House Effect, air pollution and the depletion of the Earth s Ozone Layer are the major hazards/consequences that the human race has put on itself over the last one hundred years for revolutionizing into a much more sophisticated society. Fossil fuels such as crude oil or petroleum, coal, natural gas are burnt to provide society with the adequate energies, communication, and transport we need to keep extending and functioning. By burning these fossil fuels, a variety of pollutants are emitted (Carbon dioxide, oxides of Nitrogen, Hydrocarbons, Chlorofluorocarbons (CFC s), and Sulfur dioxide) into the Earth s Troposphere/Stratosphere. These pollutants are altering the characteristics of the Earth s atmosphere, thus having an effect on all life forms upon the Earth. The problems associated with the changes in our atmosphere include acid rain, photochemical smog, changes in the carbon and nitrogen cycles, and the Greenhouse effect.

Acid rain

When coal is burnt, for example in a smelting plant, it releases sulfur in to the atmosphere and combines with the oxygen molecules in the atmosphere to produce sulfur dioxide and sulfur trioxide.

S (in coal) + 02 SO2 (sulfur dioxide)

2SO2 + O2 2SO3 (sulfur trioxide)

When sulfur dioxide and trioxide gasses are in the atmosphere they combine with water to form sulfurous and sulfuric acid. Oxidation also occurs in the clouds and in heavily polluted air where other compounds such as ammonia and ozone help to catalyze the reaction, converting more sulfur gasses into acids.

The carbon cycle

The carbon in the atmosphere is continually recycled. The movement of carbon to carbon dioxide in the air through living things and back into the air is called the carbon cycle. Other gasses, including methane, carbon monoxide, and chlorofluorocarbons, are also found in the atmosphere.

The CO 2 is removed from the atmosphere and stored by plants (as starch and cellulose), by the ocean (which is able to dissolve some CO2), by carbonate rocks (most often shelled marine animals) by other animals (which eat plants) and by fossil fuels. CO2 is returned to the atmosphere by combustion of carbon compounds and by respiration.

These sources of carbon are called sinks or reservoirs, and represent a long-term store for carbon. By burning fossil fuels humans are releasing enormous quantities of carbon dioxide into the atmosphere in a very short time span. Such action alters the balance between the carbon reservoirs and may ultimately impact on global climate patterns.

The nitrogen cycle

The movement of nitrogen from the air and nitrogen compounds from the soil, through living things, and then back into the air and the soil is called the nitrogen cycle. The nitrogen cycle is dominated by reaction involving biological material by the following series of changes. Oxides of nitrogen: Firstly natural inorganic reaction mechanisms do not produce ammonia from nitrogen. However, high temperatures (caused by lighting, bush fires, and by car engines and industrial furnaces) can cause nitrogen and oxygen to combine to form oxides of nitrogen.

Humans have altered the balance of the nitrogen cycle through the wide spread planting of leguminous plants and the large-scale fixation of nitrogen in the manufacture of inorganic fertilizers such as ammonia (NH3), and ammonium nitrate (NH4NO3). The consequences are that these nitrates react with water vapor in the atmosphere causing an acidic solution, thus producing acid rain.

Unburnt hydrocarbons and photochemical smog

Evaporation of solvents and fuels, as well as incomplete combustion of fossil fuels, cause a different wide range of hydrocarbons to be released into the atmosphere. By far the greatest global problem with unsaturated hydrocarbons is their ability to promote the formation of photochemical smog in the presence of oxides of nitrogen, strong sunlight and stable meteorological conditions. The reaction chains involved in photochemical formation may be long and complicated because one reaction involving a free radical often generates another, which in turn reacts to generate a third, and so on. Ozone may also attack unsaturated hydrocarbons to produce similar free radicals as well as aldehydes to permit reaction.

Many of these free radicals generated in strong sunlight are thought to be responsible for the eye irritation experienced by individuals exposed to photochemical smog.

The ozone layer and chloroflurocarbons

Ozone gas (O3) is poisonous to humans, even in small concentrations. It is produced by electric discharges, naturally by lighting, and has a characteristic odour. Ozone is located 25 km above the Earth in the stratosphere and protects the Earth from ultra violet radiation produced by the sun. The ozone layer exists because oxygen from the troposphere seeps up into the stratosphere and reacts with sunlight to form tri-atomic molecules of ozone.

High energy ultra violet radiation (UV-C) is absorbed by oxygen molecules in the upper levels of the stratosphere.

Warming of the ozone layer produces a steep temperature inversion between 15 and 50 km. The effect of a warm stratosphere is to act as a lid to the vertical motion of the troposphere. Any weakening of the stratospheric inversion would affect atmospheric circulation thereby affecting weather and climate. A reduction of ozone would also cause more ultraviolet and visible radiation to reach the ground, so leading to the warming of the lower atmosphere and impacting on plants and humans.

One of the major factors contributing to the depletion of the ozone layer is chloroflurocarbons. Chloroflurocarbons are widely used aerosol propellants, refrigerants etc and were once thought to be inert and harmless. The problems start when these chloroflurocarbons entered the stratosphere, and by complicated reactions they are broken down and react with ozone to form a oxide and diatomic oxygen atom.

The green house effect

Gasses in the air act like the glass roof in a green house, trapping heat and warming the temperature. Carbon dioxide acts as like the glass in the green house.

Since the Industrial Revolution increasing amounts of carbon dioxide and other green house gasses have been pouring into the atmosphere. These extra gasses are leading to a human induced increase in temperature. In recent years the term greenhouse effect has become the standard phrase to describe the global warming expected as a result from human induced changes to atmospheric gasses. More than 5 billion tones of carbon dioxide are being exposed to the atmosphere every year, although oceans and plants are able to store about 50% of the extra carbon dioxide.

As the condition of the atmosphere becomes more critical towards human survival, the warming of the world and its atmosphere may cause changes to weather patterns and plant growth characteristics. There may be changes in sea levels, cycles will harder to predict and maybe damage done is already to late.

Throughout Earth s history, there have been numerous examples of both plant and animal species going through a cycle of emergence, stabilization, rapid expansion in numbers, then extinction or decline. Has homo sapiens reached the zenith of evolutionary radiation? Is extinction or decline the next step.