Environmental Chemistry
The Chemistry of Earth, Water and Air in Balance
An introduction to the study of the chemistry of the environment: earth's crust, atmosphere and hydrosphere.
The environment is one of the buzz topics of the twenty-first century. You can't go far without being reminded about pollution, global warming and the ozone layer. Chemistry plays an intrinsic part in issues surrounding the environment, some would even blame “chemistry” for most of what's going wrong. So how is chemistry related to the environment? What is the chemistry of the environment?
The Environment
The environment is an over-used term that does not have a strictly defined meaning. People have a vague notion of what they are talking about; “the air around us”, “nature” or “rivers and streams”; but the environment is far more comprehensive than that.
Earth-Air-Water
The environment encompasses three main zones or “spheres”: the earth's crust or simply “earth”, the hydrosphere or the water on the surface of the earth like oceans, lakes, rivers and groundwater, and the atmosphere or the air around us. These three zones and their interactions with one another are collectively “the environment”. So the chemistry of the environment is the chemistry of what goes on in the three areas and their interfaces.
Crust
Geochemists study the chemistry of the earth's crust. This is a thin layer of rock, some 40km thick, that covers the whole surface of the planet. In terms of elements, the crust is 46% oxygen, 28% silicon, 8% aluminium, and 5% iron with smaller amounts of other elements. These elements are combined into mainly silicon dioxide (silica) based rocks.
Water
The hydrosphere encompasses the water gathered in different places on the surface of the earth. The huge majority of this water is found in the oceans and trapped beneath them in sediments. Only about 0.5% of water is found on the continents in rivers, lakes, glaciers and groundwaters. The oceans play an important part in absorbing a transporting solar energy which controls climate. They also are involved in the evaporation-precipitation cycles which so affect life on the planet. The chemistry of water is a huge subject and its ability as a solvent is the basis of all life on earth.
Atmosphere
Finally atmospheric chemists study the chemistry of the air around us. The air is 78% nitrogen and 21% oxygen with the remaining 1% made up of argon and carbon dioxide. Several important chemical reactions go on in the atmosphere and affect the planet greatly. Photosynthesis, in which plants convert carbon dioxide from the air into new organic matter, releasing oxygen, is absolutely foundational to life on this planet. The photodissociation reactions in the upper atmosphere control the thickness of the ozone layer, which protects us from harmful wavelengths in sunlight. The quantity of carbon dioxide in the atmosphere has been increasing due to the explosion in fossil fuel combustion since the industrial revolution, becoming a key element of the dreaded “Climate Change”.
The chemistry of the environment is as broad and deep as the environment itself. Understanding this chemistry will help in our attempts to preserve this planet for future generations.
Reference:
Environmental Chemistry by Raiswell, Brimblecombe, Dent & Liss, Edward Arnold, London 1980
