Chemistry

Free online chemistry lesson for elementary school, middle school and high school.

 

Air and atmosphere

Threats to the Earth's atmosphere

The atmosphere is polluted by gases that humans produce (cars, industries etc).

- The fumes produced during combustions consist of microparticles that are dispersed into the air. These fumes are responsible for the blackening of the facades of buildings and their degradation.

- Acid rains form after releases to air of nitrogen oxides and sulfur oxides. These rains are harmful to vegetation and can destroy entire forests. They can also damage some building materials (marble, iron, aluminum, zinc). The limitation of emissions of sulfur oxides and nitrogen oxides has helped reduce this phenomenon.

- Destruction of the ozone layer is caused by chlorinated compounds released into the air. The ozone layer has regularly regressed: its thickness decreases and even tends to disappear completely at the poles.

- The amplification of greenhouse effect leads to a general increase in temperatures.
The greenhouse effect is a natural phenomenon necessary to maintain temperatures favorable for life on Earth but the rejection of some gases (mainly carbon dioxide and methane) amplifies it.
 If this rise of temperatures continues it will be responsible for dramatic changes. This change may:
- favors the expansion of arid areas
- multiplies extreme weather events such as cyclones
- changes vegetation
- causes a rise in sea level making disappear many coastal areas and islands,
- rises acidity of oceans and make disappear many marine species.

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