Introduction
Ozone is made up of 3 oxygen molecules and because of this chemical formulation, a single atom of oxygen is unstable as it wants to return to the diatomic state by giving up an oxygen atom. Ozone still has the same chemical formula whether it is found in the stratosphere or the troposphere.
Secondary pollutants are synthesized in the environment by chemical reactions involving primary, or emitted chemicals. These secondary compounds, especially ozone, are the harmful ingredients of oxidizing or photochemical smogs that cause damages to people and vegetation exposed to this type of pollution. Low-level ozone also acts as a greenhouse gas, restricting the escape of heat from the earth’s surface and thus contributing to the global warming process.
Low concentrations of ground-level ozone can irritate the eyes, nose and throat. Ozone can also irritate the lung airways, and make them red and swollen (inflammation). People with lung problems are most at risk, but even healthy people who are active outdoors can be affected when ozone levels are high.
Ozone in the Stratosphere
In the stratosphere, we find the “good” ozone that protects life on earth from the harmful effects of the sun’s ultraviolet rays.
Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the sun, providing a shield that prevents this radiation from passing to the earth’s surface. Only ozone effectively absorbs UV-C and UV-B, which causes biological damage. The protective role of the ozone layer in the upper atmosphere is so vital that scientists believe life on land probably would not have evolved – and could not exist today – without it.
Ozone continuously breaks apart into its oxygen atoms and reforms as ozone molecules, so a particular ozone molecule doesn’t last very long. The “shield” changes constantly, but the atmospheric chemical processes maintain a dynamic equilibrium that keeps the overall amount of ozone constant – that is, it would if humans did not contribute to the chemical processes.
Ozone in the Troposphere
In the troposphere, the ground-level or “bad” ozone is an air pollutant that damages human health, vegetation, and many common materials.
In the troposphere, ozone is not wanted. Ozone is even more scarce in the troposphere than the stratosphere with concentrations of about 0.02 to 0.3 parts per million. But even in such small doses, this molecule can do a lot of damage.
Ozone in the troposphere is one of the greenhouse gases. The naturally occurring greenhouse gases (including ozone) are what make earth habitable for life as we know it. In the troposphere, accelerated ozone levels deal us with a key ingredient in smog and as a powerful greenhouse gas.
UV-B effects on terrestrial plants (from the 1991 Report Summary, Teramura et al.)
- The potential importance of current solar UV-B levels, even in the absence of further ozone reduction, has been demonstrated experimentally. There is concern for agriculture, forestry, and natural ecosystems as the ozone layer is depleted.
- Increased UV-B has also been shown to alter the biotic relationships of higher plants as demonstrated by the changes in plant disease susceptibility and the balance of competition between plant species.
- Both long-term UV-B irradiation of whole plants and short-term irradiation of chloroplasts may induce the synthesis of certain polypeptides in photosynthetic membranes that could play a role in mitigating UV-B damage.
- The influence of UV-B on growth appears to be mediated by phytohormones, either through photodestruction or enzymatic reactions. Preliminary greenhouse studies indicate that growth, photosynthesis, and yield decreased in some rice cultivars.
- Several of the world’s major crop species are particularly vulnerable to increased UV, resulting in reduced growth, photosynthesis and flowering. These species include wheat, rice, barley, oats, corn, soybeans, peas, tomatoes, cucumbers, cauliflower, broccoli and carrots. Only a few commercially important trees have been tested for UV (UV-B) sensitivity, but early results suggest that plant growth, especially in seedlings, is harmed by more intense UV radiation.Wood, plastic, rubber, fabrics and many construction materials are degraded by UV radiation. The economic impact of replacing and/or protecting materials could be significant.
UV-B effects on aquatic ecosystems (from the 1991 Report Summary, D.-P. Däder et al.)
- In particular, plankton (tiny organisms in the surface layer of oceans) are threatened by increased UV radiation. Plankton are the first vital step in aquatic food chains. Decreases in plankton could disrupt the fresh and saltwater food chains, and lead to a species shift in Canadian waters. Loss of biodiversity in our oceans, rivers and lakes could reduce fish yields for commercial and sport fisheries.
- An increased understanding of Antarctic trophic dynamics suggests that the likelihood of direct UV-B radiation effects on consumers is small. Rather, it is the possibility of indirect effects that may significantly affect the Antarctic trophic structure, such as different species sensitivities to UV-B radiation, or decreases in total available primary production.
- Because more than 30% of the world’s animal protein for human consumption comes from the sea, the human populations may also be affected by the direct and indirect consequences of increased solar UV-B radiation on aquatic food webs.
UV effects on the human immune system
- Enhanced UV radiation reduced the body’s ability to fight off infection. In humans, the skin is the principal barrier to the outside world, and thus the first line of defense against foreign agents that may threaten health. In order to fulfill this role, the skin hosts a number of cells from the immune system that can mount or modify immune responses against such ‘foreign invaders’ or against skin cells that have become ‘strange’, e.g., by virus infection or transformation into a cancer cell.
- However, to function optimally, the immune system needs to be able to discriminate between ‘self’ and ‘strange’ or ‘non-self’, and eliminate only the latter, especially if it is (potentially) harmful.
- The skin contains a wide range of molecules, including both proteins and DNA, which undergo photochemical reactions upon absorbing UVR. The cell-surface proteins which are used to determine ‘self’ are evidently modified in such photochemical reactions so that, at certain UV doses, the skin becomes swamped with ‘non-self’ cells.
UV effects on skin diseases
- Small amounts of UV are beneficial for people and essential in the production of vitamin D. UV radiation is also used to treat several diseases, including rickets, psoriasis, eczema and jaundice. This takes place under medical supervision and the benefits of treatment tend to outweigh the risks of UV radiation exposure.
- The risk of UV-related health effects on the eye and immune system is independent of skin type. Overexposure to solar radiation may result in acute and chronic health effects on the skin, eye and immune system. Many believe that only fair-skinned people need to be concerned about overexposure to the sun. Darker skin has more protective melanin pigment, and the incidence of skin cancer is lower in dark-skinned people. Nevertheless skin cancers do occur with this group and unfortunately they are often detected at a later, more dangerous stage.
Adverse impacts on agriculture, forestry and natural ecosystems:
- Several of the world’s major crop species are particularly vulnerable to increased UV, resulting in reduced growth, photosynthesis and flowering. These species include wheat, rice, barley, oats, corn, soybeans, peas, tomatoes, cucumbers, cauliflower, broccoli and carrots.
- The effect of ozone depletion on the Canadian agricultural sector could be significant.
- Only a few commercially important trees have been tested for UV (UV-B) sensitivity, but early results suggest that plant growth, especially in seedlings, is harmed by more intense UV radiation.
Damage to marine life:
- In particular, plankton (tiny organisms in the surface layer of oceans) are threatened by increased UV radiation. Plankton are the first vital step in aquatic food chains.
- Decreases in plankton could disrupt the fresh and saltwater food chains, and lead to a species shift in Canadian waters.
- Loss of biodiversity in our oceans, rivers and lakes could reduce fish yields for commercial and sport fisheries.
Animals:
- In domestic animals, UV overexposure may cause eye and skin cancers. Species of marine animals in their developmental stage (e.g. young fish, shrimp larvae and crab larvae) have been threatened in recent years by the increased UV radiation under the Antarctic ozone hole.
Materials:
- Wood, plastic, rubber, fabrics and many construction materials are degraded by UV radiation.
- The economic impact of replacing and/or protecting materials could be significant.
References
http://www.bcairquality.ca/101/ozone-depletion-impacts.html
http://science.jrank.org/pages/6028/Secondary-Pollutants.html#ixzz4cMZNJKOI