Carbon monoxide

Worldwide, the emission of carbon monoxide is 350 million tones a year. The chief source is the internal combustion engine. If the combustion of petrol is incomplete, the exhaust gases contain carbon monoxide and carbon as well as the harmless combustion products, carbon dioxide and water. Incomplete combustion occurs when there is insufficient oxygen for full oxidation of the hydrocarbons in petrol. Car designers find that maximum performance is obtained when fuel-rich mixtures are burned in the cylinders. This design leads to the discharge of carbon monoxide, carbon and unburned hydrocarbons.

What harm does carbon monoxide do? Carbon monoxide combines with hemoglobin. Hemoglobin is the red substance in blood which transports oxygen round the body. It combines with oxygen in the lungs, carries oxygen as oxyhemoglobin round the body and releases oxygen to the tissues.

In the lungs: hemoglobin + oxygen = oxyhemoglobin

In the tissues: oxyhemoglobin = oxygen + hemoglobin

The freed hemoglobin then circulates back to the lungs to pick up more oxygen. If carbon monoxide is present be in the lungs, it combines with hemoglobin: carbon monoxide + hemoglobin = carboxyhemoglobin

Carbon monoxide is 200 times better at combining with hemoglobin than oxygen is. It therefore ties up hemoglobin so that hemoglobin can no longer combine with oxygen. At a level of 1%, carbon monoxide will kill quickly; at lower levels, it causes headaches and dizziness and affects reaction times.

Being colourless and odourless, carbon monoxide gives no warning of its presence. Measurements have shown fairly high levels of carbon monoxide in crowded streets during rush hours. Since carbon monoxide is concentrated at street level, it is most likely to affect people when they are driving and need sound judgment and quick reflexes.

What can be done? Nature can deal with carbon monoxide. Soil organisms can convert it into carbon dioxide or methane. In city streets, where the concentration of carbon monoxide is high, there is little soil to remove it. People are working on a number of solutions to the problem.

· The tuning of vehicle can be altered to provide more air and produce only carbon dioxide and water. A snag is that this increases the formation of oxides of nitrogen.

· Many cars are now fitted with catalytic converters. The hot exhaust gases pass over a catalyst, which helps to oxidize carbon monoxide to carbon dioxide. Catalytic converters only work when the petrol contains no lead compounds.

· In the nearest future, vehicles may be powered by fuels which burn more cleanly than hydrocarbons.

SUMMARY NOTE

Carbon monoxide is produced when hydrocarbon fuels burn incompletely in an inadequate supply of air. It is a poison which combines with hemoglobin in the blood, thus starving the body from oxygen. Catalytic converters can be fitted in the exhaust pipes of cars to bring about the oxidation of carbon monoxide to the harmless product, carbon dioxide.

2. Answer the questions:

1. Which two gases are considered to be very important atmospheric contaminants?

2. What is the cause of air pollution with these gases?

3. What is the chief source ofcarbon monoxide?

4. What harm can carbon monoxide do to human health?

5. What are the ways to solve the problem?

3. Choose the proper ending of the sentences:

1. The chief source of carbon monoxide is …

2. If the combustion of petrol is incomplete, the exhaust gases contain …

3. Incomplete combustion occurs when there is …

4. In a human body carbon monoxide ties up …

5. Measurements have shown fairly high levels of carbon monoxide in …

Дата добавления: 2015-10-30