Atmospheric Pollutants

1.Gases in The Air

Sources of Sulfur Dioxide

There a diverse range of natural sources of sulfur dioxide in the atmosphere such as from volcanic gases: S(s) + O2(g) ( SO2 (g), geysers and combustion of organic matter in bushfires. Also, anaerobic bacteria in poor aerated soil oxidize H2S to SO2: . Emissions of sulfur dioxide have accelerated since the Industrial revolution. Industrial emissions of sulfur dioxide have accelerated since the Industrial revolution. Industrially sulfur is produced by the combustion of brown coal, containing impurities like FeS2, in power stations: . In smelting plats metals like copper and zinc are extracted from sulfide ores. E.g. when extracting copper from chalcopyrite (CuFeS2): and extracting zinc: , sulfur dioxide is released. Also in the Contact Process, where sulfuric acid is prepared from sulfur: S(s) + O2(g) ( SO2 (g), sulfur dioxide is released. Furthermore, the incineration of garbage, petroleum refineries, food preservation industries, paper industry (to bleach paper) and sewage all release sulfur dioxide.

Sources of Oxides of Nitrogen:

During thunderstorms, atmospheric nitrogen and oxygen react: . Nitrogen monoxide and dinitrogen monoxide are produced by soil bacteria that oxidise nitrogen in the soil. Nitrogen dioxide is also produced naturally by the action of sunlight on NO and O2.

The oxides of nitrogen are also acidic oxide pollutants in the atmosphere. Dinitrogen monoxide, specifically manufactured as a fuel for combustion in racing cars and also used as a sedative/analgesic (named laughing gas) contributes to oxides of nitrogen in the air. Nitrogen oxides are formed in high temperature combustion environments such as in car engines by the following reactions: 1. 2. 3. .

2.How Much, How Harmful

Evidence:

Effects:

Industrial SO2 mainly comes from burning fossil fuels and smelting sulfide ores. When oxides of sulfur dissolve in water acid rain forms: . Industrial nitrogen oxide mainly come form car engines and other high temperature combustion environments when the following reaction occurs: . This gas is neutral but when it reacts with oxygen acidic nitrogen dioxide is formed: . Acid rain is formed when this NO2 reacts with water: . Evidence for the increasing concentrations of these oxides are evident form the increasing occurrences of acid rain, that is creating more damage to the biosphere than in the past. Damage from acid rain to forests and crops, composition of soil, ecosystems in acidified lakes and streams and damage to marble, stone and metal buildings is becoming more prominent due to increased emissions of these gases. Further evidence is the increased occurrences of photochemical smog that occurs from NO2, a brown gas, that forms a haze over many major cities. These increasing amounts of nitrogen dioxide absorb UV to form pollutants like ozone that has a corrosive effect on plant and animal tissue: .

Current Debate:

Global Concern:

Major companies like Xcel Energy in the US are changing their operations to become environmental leaders rather than contributors to global problems. This graph shows their planned reductions in sulfur and nitrogen oxide emissions for the future. Companies like Xcel are setting an example for other international companies.

These graphs show futher interesting global trends in emission levels for nitrous oxides and sulfur dioxide.

3. The Problem of Acid rain

Formation of Acid Rain

All rain is slightly acidic due to dissolved carbon dioxide: . Rain with a pH lower than 5 is acidic and is formed from the dissolved SO2 and SO3 and NO2. When sulfur and nitrogen oxides dissolve in rain acid rain is formed. Carbon dioxide is an acidic oxide and greenhouse gas that forms acid rain when dissolved in water: .

Effects of Acid Rain

Acid rain cause four main problems:

Developments

This has became a serous global issue as rain of up to pH 2 has occurred in some densely populated and highly industrialized regions with Australia having occurrences of pH 3.6 in the Hunter Valley in Sydney. Consequently much research and new laws have been enforced to immediately reduce the emission of these pollutants. Recent research development have been made to reduce sulfur content of coal before combustion and inventions like the catalytic converter and the scrubber have been developed.

4. What About Ozone?

Origins

Chlorofluorocarbons are halogenated alkanes that have all hydrogens substituted with chlorine and fluorine atoms e.g. dichlorodifluoromethane. While halons are halogenated hydrocarbons with every hydrogen substituted by either a bromine or fluorine atom. E.g. Bromotrifluromethane. Although sometimes produced by micro organisms, most CFCs and halons are synthetically created. Chlorofluorocarbons were manufactured from the 1930's where they replaced ammonia as a refrigerant due to properties of being non-toxic, inert and able to be easily liquefied and returned to gaseous state. As more uses were found, they were produced in greater quantity as a result of the demand for refrigeration and air conditioners grew. Before 1996 chlorofluorocarbons mostly originated from refrigeration, air conditioning, foam plastics and electronics cleaning. Halons were also extensively used in fire extinguishers as they had the property of not supporting combustion.

Problems