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