The main sources of air pollution are the industries, agriculture, vehicle emission, and energy generation. Air pollutants are emitted in combustion and other production processes. Some of these substances are not directly harmful to the atmosphere, but they form harmful chemicals when they react with other substances present in air.
Sulphur dioxide
One air pollutant is sulphur dioxide, SO2. Sulphur dioxide is produced by volcanoes and also mainly given out during the combustion of sulphur-containing fossil fuels, such as crude oil and coal. Sulfur dioxide is the product of the burning of sulphur: S8 + 8 O2 → 8 SO2
Sulphur dioxide is a major air pollutant and has great impacts on human health. It is a stinging gas and it irritates strongly the eyes and the respiratory tract. Inhalation of the gas may cause lung oedema. Rapid evaporation of the liquid may cause frostbite. The substance may cause effects on the respiratory tract , resulting in asthma-like reactions, reflex spasm of the larynx and respiratory arrest. Exposure may result in death.
Further oxidation of sulphur dioxide, usually in the presence of a catalyst such as nitrogen dioxide, forms sulphuric acid, and thus acid rain, which then causes problems like corrosion of buildings, acidification of rivers and lakes, and winter smog. Acid rain attacks metals including aluminium, iron, steel, brass, copper and nickel in presence of water. High concentration of sulfur dioxide in the atmosphere can also adversely affect plant and animal life.
Oxides of nitrogen, NOx
Oxides of nitrogen is a group of different gases made up of different amount of oxygen and nitrogen. The two most common ones are nitrogen dioxide and nitric oxide. Oxides of nitrogen are formed when certain fuels (oil, gas and coal) are combusted at a high temperature in motor vehicles, power plants, and other industries. Nitrogen oxides are also released from farmland in the agricultural sector. Using catalyzers in car exhausts can prevent emissions of nitrogen oxides.
In the troposphere, during daylight, NO reacts with partly oxidized organic species to form NO2, which is then photolyzed by sunlight to reform NO:
NO + CH3O2 → NO2 + CH3O
NO2 + sunlight → NO + O
Nitrogen oxides play an important role in the formation of ozone in the lower atmosphere, and in acidification and eutrophication. Eutrophicaton is when the environment becomes enriched with nutrients and lead to excessive plant growth. Nitrogen oxides are involved in the formation of acid rain. They contribute to global warming, hamper the growth of plants, and can react with other pollutants to form toxic chemicals. Ozone is a harmful gas to humans at the lower atmosphere.
Nitrogen oxides can also deeply penetrate the lungs and damage human lung functions. Small levels of nitrogen oxides can cause nausea, irritated eyes and nose, fluid forming in lungs and shortness of breath. Breathing in high levels of nitrogen oxides can lead to problems like spasms, swelling of throat, reduced oxygen intake, and even death. They can also react with aerosols from aerosols cans and cause respiratory problems.
To reduce the level of nitrogen oxide pollution, we can do the following:
- Reduce the usage of motor vehicles
- Support efforts to use renewable and non-polluting power sources
- Don’t smoke cigarettes
- Don’t use aerosol cans
Carbon monoxide
Carbon monoxide consists of one carbon atom and one oxygen atom, connected by a triple bond. It is a colorless, odorless, and tasteless gas. Carbon monoxide is produced from the partial oxidation of carbon-containing compounds. It forms when there is not enough oxygen to produce carbon dioxide.
An incomplete combustion equation is:
100CH4 + 190 O2 à 100H20 + 80CO2 + 20CO.
Carbon monoxide contributes to the greenhouse effect, smog and acidification. The gas can bind to haemoglobin in blood, preventing oxygen transport through the body. This results in oxygen depletion of the heart, brains and blood vessels, eventually causing death.
Energy generation and air pollution
The industries are responsible for emissions of many air pollutants like carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen oxides, small dust particles, methane, ammonia and radioactive radiation. During energy generation, chemicals such as methane are released into the air as a result of oil and natural gas extraction. The combustion of coal and natural gas for electricity production causes the release of sulphur dioxide, nitrogen oxides and carbon dioxide into the air.
Greenhouse gases and global warming
Greenhouse gases allow sunlight to enter the atmosphere freely by absorbing this infrared radiation and trap the heat in the atmosphere. Rising concentrations of greenhouse gases leads to an increase in the average temperature of the Earth, this causing global warming. This in turn causes climate change. Greenhouse gas emissions come mostly from energy use.
One greenhouse gas is carbon dioxide, which is emitted from combustion of petroleum and natural gas for energy generation. Another greenhouse gas, methane, comes from landfills, coalmines, oil and gas operations, and agriculture. The third greenhouse gas is nitrous oxide, which is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste. Last but not least are fluorinated gases like hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride, which are greenhouse gases emitted from a variety of industrial processes.
Usage of motor vehicles is responsible for one-third of the greenhouse gas emissions. Emissions caused by motor vehicles are mainly those of carbon dioxide, carbon monoxide, nitrogen oxides, and small dust particles.
Environmental impacts
When emissions of sulphur dioxide and nitrogen oxides come in contact with water, they will become sulphuric acid and nitric acid. When acidifying agents, such as sulphur dioxide, nitrogen oxides and ammonia, end up in plants, surface water and soils, it can cause the following:
- When acidity is high more metals will dissolve in water. This can cause surface water to become polluted, which has serious health effects on aquatic plants and animals. For example, a poisonous metal, mercury can be dispersed through surface water, causing it to accumulate in fish. Mercury can magnify up the food chain, and then taken up by humans eventually.
- Buildings and monuments may be damaged through erosion. Sulphur dioxide breaks down limestone by reacting with calcium carbonate, causing limestone to absorb water during rainfall. Limestone will then disintegrate.
- Eutrophication is caused by an increase in plant nutrients in water. The higher availability of nutrients causes certain water plants, such as algae to grow excessively. This blocks sunlight from going into water. The plants also use up the oxygen supplies, which cannot be produced by underwater plants because heterotrophic plants and bacteria need light to photosynthesize. Hence, eutrophication disrupts the ecosystem.
Smog is a combination of the words smoke and fog. Photochemical smog, or summer smog, mainly consists of ozone. It is a brown, oxidising fog. The causes of photochemical smog are nitrogen oxides which come from motor vehicles and industries. Ozone is formed according to the following chemical reactions:
NO2 + UV --> NO + O
O + O2 --> O3
The reverse reaction is:
NO + O3 --> NO2 + O2
Ozone is created in the atmosphere through chemical reactions under the influence of UV-light and is decomposed under the influence of visible light and UV-A light. During ozone decomposition an oxygen-poor molecule is released, which aids the breakdown of ozone. There are a number of compounds that catalyze ozone decomposition, like hydroxide, nitrogen oxides, chlorine and bromine.
Chlorine mainly aids the decomposition of ozone when it is a part of CFC-bonds. These compounds are not lost during the chemical reaction, causing them to decompose ozone many times. Human activities have caused large concentrations of ozone-decomposing chemicals to enter the atmosphere, causing the loss of large amounts of ozone.
Ozone is very important for all life on earth, because it absorbs harmful UV-B radiation from the sun. The highest concentrations of ozone are located in the atmospheric layer between twenty and forty kilometres above the earth. When the ozone concentrations in this layer decrease, UV-B radiation may reach the earth. This radiation damages DNA, causes skin cancer, and damages the human immune system. The radiation can decrease growth and photosynthesis activity in a number of plants and trees.
Ways to reduce impact of pollution
- Plant trees and plants because they help take carbon out of the environment and the air we breathe. Planting more trees and landscaping helps with preventing pollution and keeps the environment cleaner
- Minimize Vehicle Use. One way to reduce pollution is to drive electric vehicles or a hybrid which is more environmentally-friendly and will help in preventing pollution.
- Replace fossil fuel use with renewable energy. Fossil fuels cause a lot of damage to the environment through pollution. Even to get them out of the earth is very polluting, because mining of any kind damages the earth and harms the environment. So we should switch to using energy generated by clean, renewable sources such as wind and solar.
- Conserve energy when possible. Decreasing demand for energy helps conserve resources that would be utilized otherwise. Some examples of ways to save energy include: switching off the lights in rooms not in use, replace incandescent bulbs with fluorescent ones, use fans instead of air-condition units, and using thermostats in air-conditions.
Educate people about global warming
- Organize a competition where students draw out their ideas on how they plan to help reduce global warming
- Hold a no-motor vehicles day where everyone is encouraged to travel around on foot or by bicycles instead of by cars
- Set aside a day where no electricity is used by holding lessons outdoors
Sources
http://www.gasheating.co.uk/CarbonMonoxide.html
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