Environmental Issues: The Ozone Layer The Greenhouse Effect Acid Rain
Heading into the 21st Century, the world faces a multitude of environmental problems. The resourcefulness of mankind as a whole will be challenged if we are to thrive and flourish on our native planet. In today's lecture, we will discuss 3 of the more publicized environmental issues, each of whose implications are only beginning to be understood.
The Ozone Layer
As we learned in the beginning of the semester, high up in the stratosphere, there is a high concentration of ozone. This layer makes up what is known as the ozone layer. The sun emits radiation over a vast portion of the electromagnetic spectrum, including the ultraviolet light portion. This radiation, often referred to as UV for short, is harmful and dangerous to terrestrial creatures.
UV light damages molecules in our cells that help to make up DNA and RNA which are essential for protein synthesis. UV light in high amounts can promote cancerous growths. Ozone in the stratosphere is important because it helps screen out harmful UV radiation before it can strike the Earth.
Ozone is actually composed of 3 oxygen atoms bonded together. The strength of the bonds in ozone is such that when ultraviolet radiation strikes it, it breaks apart into an oxygen molecule, O2, and a free oxygen atom. This free oxygen atom, called an oxygen radical, is extremely reactive. In normal circumstances, this oxygen radical will get back together with an oxygen molecule, to form another ozone molecule. So ozone in the stratosphere exists as the result of a continuous destruction-regeneration process.
A group of man-made chemicals called chloroflourocarbons often referred to as CFCs, is destroying stratospheric ozone. CFCs have extremely long residence times, meaning once released, they remain in the atmosphere for a very long time before reacting with anything. Therefore, they often infiltrate the stratosphere. Once in the stratosphere, they react with the oxygen radicals that have been dissociated.
CFCs are prevelant in a number of industrial processes, however, their usage is declining dramatically. Many products once widely used worldwide are outlawed now. An example of some substances that contain CFCs include refrigerants such as freon and styrofoam.
Interestingly, while ozone in the stratosphere is vital, ozone at the surface creates a pollution problem. Ozone is often produced during combustion in automobile engines. At high concentrations and in certain meteorological conditions, ozone causes respiratory distress and other symptoms in a lot of people particularly in urban areas.
Scientists first discovered the ozone depletion problem while researching the atmosphere over the continent of Antarctica. The now infamous Ozone Hole that was discovered at that time appears to be growing. In southern Australia for instance, there is an incidence of melanoma cancer that is about 13 times greater than the rest of the world.
The Greenhouse Effect - The Global Warming Issue
As we learned earlier in the semester, different substances absorb heat at different rates. It is easy to think of physical examples of this. Consider a white sheet versus blacktop. Which will become hotter faster? The blacktop of course. Just as different solids and liquids have different specific heats, depending on their physical properties, different gases have different specific heats as well, depending on their specific chemical properties.
Nitrogen and oxygen, the two primary constituents of our atmosphere, are very poor absorbers of heat. Therefore, they do not readily retain solar radiation. However, a variety of gases, often referred to as the Greenhouse Gases retain solar radiation much better than do oxygen and nitrogen. So, if the concentrations of these Greenhouse Gases in the atmosphere were to increase, the amount of radiation from the sun that was absorbed would be expected to increase and the average temperature of the atmosphere would be expected to increase as well. This is exactly what many scientists believe is occurring as we speak.
Greenhouse Gases come from a multitude of different sources. A few examples of Greenhouse Gases include carbon dioxide (which is probably the most infamous one), methane, nitrogen dioxide, and even water vapor. Carbon dioxide is released in combustion (the type of reaction that occurs when fossil fuel is burnt). Carbon dioxide also comes from natural sources as well. Animals breathe in oxygen and exhale carbon dioxide in a process called respiration. Plantlife however, breathes in carbon dioxide and exhales oxygen in a process called photosynthesis. The relationship between animals and plants is such that the concentrations of carbon dioxide and oxygen in the atmosphere had been balancing each other pretty closely.
With the invention of industrial machines that burn fossil fuels however, the concentration of carbon dioxide in the atmosphere has increased dramatically. Since carbon dioxide absorbs heat better than oxygen and nitrogen, more radiation is being absorbed by the atmosphere and the atmosphere is warming.
But just how much do Greenhouse Gases have to do with global warming? Perhaps the Earth is going through a natural climate variation. Variations in Earth's climate over long periods of time certainly exist. Most of them have to do with subtle variations in Earth's orbit, where sometimes, Earth's axis of rotation is tilted more than others, altering the global energy balance and causing glaciers in some time periods and tropical floods in others.
This is the subject of a heated debate that exists in much of the scientific community: just how much of global warming is real and if it does indeed exist, how much is due to Greenhouse Gases? There is no doubt that since meteorological records have come into existence, the average global temperature is on its way up. It is more difficult however to draw concrete conclusions as to the specific causes of this.
Scientists around the world are encouraging the mass planting of trees and plants. Since trees and plants breathe in carbon dioxide, it is thought that with more trees and plants in existence, more carbon dioxide will be filtered out of the atmosphere.
The Amazon River Valley in Brazil is the site of some of the world's thickest vegetation and most abundant and diverse plantlife. Much of the world's total oxygen is believed to originate in the Amazon River Valley through photosynthesis processes that take place there. However, there is mass deforestation occurring in the Amazon which will only serve to compound the fact that carbon dioxide concentrations are on their way up.
By the time the full implications of fossil fuel burning and increases Greenhouse Gases in the atmosphere is known, it may be too late to take action and our world may be on its way to severe climatological problems that cause mass agricultural shifts (leading to starvation) and much more.
Acid rain
Because so many different nitrogen and sulfur containing chemicals that are produced in fossil fuel combustion work their way up into the clouds, acid rain exists. Nitric Acid (HNO3) and Sulfuric Acid (H2SO4) are two of the more infamous acid rain producing acids.
When gases such as nitrogen dioxide (NO2) and sulfur dioxide (SO2) find their way into a cloud, they will react with the liquid water as well as water vapor to produce acid rain. Acid rain is polluting the rivers and lakes in many parts of the world. Some of the hardest hit areas are in the northeastern United States which is downwind of the many industrial centers and factories of the midwest and Ohio River Valley.