Kathy Poon 6s 28

6.Explain the cause and effects of ozone depletion, global warming and acid rain. State the role of individual in overcoming these problems.


        The distribution of ozone in the stratosphere is a function of altitude, latitude and season. It is determined by photochemical and transport processes. The ozone layer is located between 10 and 50 km above the Earth's surface and contains 90% of all stratospheric ozone. Under normal conditions, stratospheric ozone is formed by a photochemical reaction between oxygen molecules, oxygen atoms and solar radiation.

The ozone layer is essential to life on earth, as it absorbs harmful ultraviolet-B radiation from the sun. In recent years the thickness of this layer has been decreasing, leading in extreme cases to holes in the layer. Measurements carried out in the Antarctic have shown that at certain times, more than 95% of the ozone concentrations found at altitudes of between 15 and 20 km and more than 50% of total ozone are destroyed, with reductions being most pronounced during winter and in early spring. Natural phenomena, such as sun-spots and stratospheric winds, also decrease stratospheric ozone levels, but typically not by more than 1-2%.

The main cause of ozone layer depletion is the increased stratospheric concentration of chlorine from industrially produced CFCs , halons and selected solvents. Once in the stratosphere, every chlorine atom can destroy up to 100 000 ozone molecules. The amount of damage that an agent can do to the ozone layer is expressed relative to that of CFC-11 and is called the Ozone Depletion Potential (ODP), where the ODP of CFC-11 is 1.

The lifetime of some of these ozone depleting substances is very long, and they may continue to deplete the ozone layer long after their use has been phased out. In this publication the ODP values for 100-year timespan are used. Nevertheless some shorter-lived substances may have a very high chlorine loading potential and thus their effect in the short term is much larger than reflected by their ODP value.

Aircraft emissions of nitrogen oxides and water vapour add to this depletion effect by creating ice crystals that serve as a base for ozone destroying reactions.

The main potential consequences of this ozone depletion are to increase in UV-B radiation at ground level: a one percent loss of ozone leads to a two percent increase in UV radiation. Continuous exposure to UV radiation affects humans, animals and plants, and can lead to skin problems (ageing, cancer), depression of the immune system, and corneal cataracts (an eye disease that often leads to blindness). Increased UV radiation may also lead to a massive die-off of photoplancton (a CO 2 "sink") and therefore to increased global warming. Disturb the thermal structure of the atmosphere, probably resulting in changes in atmospheric circulation; Reduce the ozone greenhouse effect: ozone is considered to be a greenhouse gas. A depleted ozone layer may partially dampen the greenhouse effect. Therefore efforts to tackle ozone depletion may result in increased global warming. Changing the tropospheric ozone and in the oxidising capacity of the troposphere.

International targets for the reduction of ozone depleting substances have resulted in the almost complete phasing out of CFCs, halons and carbon tetrachloride in the EU. Methyl chloroform and methyl bromide will be phased out by 2005 and HCFC by 2040.


Global warming refers to the gradual increase in the average temperature in the atmosphere as a result of the accumulation of greenhouse gases. The increase in concentration of greenhouse gases in the atmosphere slows down the heat loss from the earth to the space. As a result, the atmosphere is warming up. This leads to changes in climate and other subsequent effects on the earth.

Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases:
Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned.
Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock.
Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.
Very powerful greenhouse gases that are not naturally occurring include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF
6), which are generated in a variety of industrial processes.
Each greenhouse gas differs in its ability to absorb heat in the atmosphere. HFCs and PFCs are the most heat-absorbent. Methane traps over 21 times more heat per molecule than carbon dioxide, and nitrous oxide absorbs 270 times more heat per molecule than carbon dioxide. Often, estimates of greenhouse gas emissions are presented in units of millions of metric tons of carbon equivalents (MMTCE), which weights each gas by its GWP value, or Global Warming Potential.

        Greenhouse gases are generated by various human activities. Tremendous amounts of carbon dioxide are released into the atmosphere through burning of fossil fuels in motor vehicles, power stations and factories. The consumption of fossil fuels has been increasing since the industrial revolution. Today, the growth in human population, improvement of living standards and rapid industrial development are further increasing the demands for energy. A subsequent increase in release of carbon dioxide to the atmosphere is resulted. Deforestation also accounts for the increase in atmospheric carbon dioxide content. This decrease in the quantity of trees reduces the rate of removal of carbon dioxide in the air by photosynthesis. Timber may be used as fuel wood and burnt, or may be used to produce paper, furniture, etc. which are eventually incinerated or decomposed naturally. As a result, the large quantity of carbon stored in the trees will combine with oxygen and enter the atmosphere as carbon dioxide. The extensive use of cooling agents, blowing agents, insulating and packaging materials, aerosol sprays and solvents leads to the release of a large amount of chlorofluorocarbon compounds into the atmosphere. Extensive rearing of livestock is also a cause of global warming. A significant quantity of methane is released into the atmosphere from the manure of livestock in some countries.

        Carbon dioxide is present in small amounts in the lower atmosphere. It allows the incoming solar radiation to pass through. However, it absorbs the infrared radiation which is emitted from the earth to the space. In other words, part of the energy is trapped in the atmosphere by carbon dioxide. This phenomenon is known as greenhouse effect.

        The effects of global warming are that the rising global temperatures are expected to raise sea level, and change precipitation and other local climate conditions. Changing regional climate could alter forests, crop yields, and water supplies. It could also affect human health, animals, and many types of ecosystems. Deserts may expand into existing rangelands, and features of some of our National Parks may be permanently altered.
Most of the United States is expected to warm, although sulfates may limit warming in some areas. Scientists currently are unable to determine which parts of the United States will become wetter or drier, but there is likely to be an overall trend toward increased precipitation and evaporation, more intense rainstorms, and drier soils.
Unfortunately, many of the potentially most important impacts depend upon whether rainfall increases or decreases, which can not be reliably projected for specific areas.

        individuals should recognize that collectively they can make a difference. Think back to the days before recycling became popular – when everyone threw everything out in the trash. In less than 20 years, most households have gone from recycling little to nothing to recycling newspapers, plastics, glass and metal. Many businesses recycle paper and buy recycled products and many industries practice source reduction in their packaging efforts. An entire mindset has changed in one generation!
Taking action on global warming (or climate change) is similar. In some cases, it only takes a little change in lifestyle and behavior to make some big changes in greenhouse gas reductions. For other types of actions, the changes are more significant. When that action is multiplied by the 270 million people in the U.S. or the 6 billion people worldwide, the savings are significant.
"Individuals Can Make A Difference" identifies actions that many households can take that reduce greenhouse gas emissions in addition to other benefits, including saving you money! The actions range from changes in the house, in the yard, in the car, and in the store.


        Acid rain is a serious environmental problem that affects large parts of the US and Canada. This section of the Web site provides information about acid rain's causes and effects, how we measure acid rain, and what is being done to solve the problem. "Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry. Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved, and the types of fish, trees, and other living things that rely on the water.

Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone. Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles. Scientists discovered, and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. In the US, About 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal. Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid.

 Acid rain is usually regarded as a regional problem rather than a global problem. It is because the acidic components remain in the atmosphere only for a short period. However, acid rain is a serious problem in many places. The harmful effects are acid rain causes damage to buildings, statues and monuments. Marble and various metals are corroded by acid rain. Acid rain causes human respiratory disease such as bronchitis and asthma. Acid rain can damage tree foliage directly and weaken the trees so that they become more susceptible to diseases, insects and drought. Acid rain increases the acidity of soil. Soil has a natural capacity to neutralize some inputs of acids. This normal soil-buffering capacity will be depleted in the presence of acid rain. When the soil pH is below4.5, most valuable nutrients are rapidly lost and bacterial activities will be greatly reduced. This affects the soil fertility and in turn, affects the growth of forest trees and crops. Acid rain can induce the release of aluminium ions from soil particles. Once released, the water-soluble aluminium ions may reach a concentration that is poisonous to plants. This can damage the roots of trees. Once the aluminium ions are washed into the water bodies, they can also kill aquatic organism. Acid rain can acidify lakes. With increased acidity, moderately toxic inorganic mercury compounds in lake-bottom sediment are converted into methyl mercury, which is highly toxic and can accumulate in the fatty tissues of animals. The compound can reach high concentrations in food chains and food webs.

        Since energy production creates large amounts of the pollutants that cause acid rain, one important step you can take is to conserve energy. Individuals can do this in a number of ways:

Turn off lights, computers, televisions, video games, and other electrical equipment when you're not using them.

Encourage your parents to buy equipment that uses less electricity, including lights, air conditioners, heaters, refrigerators, and washing machines. Such equipment might have the Energy Star label.

Try to limit the use of air conditioning.

Ask your parents to adjust the thermostat (the device used to control the temperature in your home) when you go on vacation.

Driving cars and trucks also produces large amounts of nitrogen oxides, which cause acid rain. To help cut down on air pollution from cars, you can carpool or take public transportation, such as buses and trains. Also, ask your parents to walk or bike with you to a nearby store or friend’s house instead of driving.