Unit 4: Natural cycle, Regional impact of global warming
Hydrological Cycle
Water cycle, also called hydrologic cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff. Although the total amount of water within the cycle remains essentially constant, its distribution among the various processes is continually changing.
hydrologic cycleIn the hydrologic cycle, water is transferred between the land surface, the ocean, and the atmosphere.Encyclopædia Britannica, Inc.
Evaporation, one of the major processes in the cycle, is the transfer of water from the surface of the Earth to the atmosphere. By evaporation, water in the liquid state is transferred to the gaseous, or vapour, state. This transfer occurs when some molecules in a water mass have attained sufficient kinetic energy to eject themselves from the
water surface. The main factors affecting evaporation are temperature, humidity, wind speed, and solar radiation. The direct measurement of evaporation, though desirable, is difficult and possible only at point locations. The principal source of water vapour is the oceans, but evaporation also occurs in soils, snow, and ice. Evaporation from snow and ice, the direct conversion from solid to vapour, is known as sublimation.
Transpiration is the evaporation of water through minute pores, or stomata, in the leaves of plants. For practical purposes, transpiration and the evaporation from all water, soils, snow, ice, vegetation, and other surfaces are lumped together and called evapotranspiration, or total evaporation.
Water vapour is the primary form of atmospheric moisture. Although its storage in the atmosphere is comparatively small, water vapour is extremely important in forming the moisture supply for dew, frost, fog, clouds, and precipitation. Practically all water vapour in the atmosphere is confined to the troposphere (the region below 6 to 8 miles [10 to 13 km] altitude).
The transition process from the vapour state to the liquid state is called condensation.
Condensation may take place as soon as the air contains more water vapour than it can receive from a free water surface through evaporation at the prevailing temperature. This condition occurs as the consequence of either cooling or the mixing of air masses of different temperatures. By condensation, water vapour in the atmosphere is released to form precipitation.
Precipitation that falls to the Earth is distributed in four main ways: some is returned to the atmosphere by evaporation, some may be intercepted by vegetation and then evaporated from the surface of leaves, some percolates into the soil by infiltration, and the remainder flows directly as surface runoff into the sea. Some of the infiltrated precipitation may later percolate into streams as groundwater runoff. Direct measurement of runoff is made by stream gauges and plotted against time on hydrographs.
Most groundwater is derived from precipitation that has percolated through the soil.
Groundwater flow rates, compared with those of surface water, are very slow and variable, ranging from a few millimetres to a few metres a day. Groundwater movement is studied by tracer techniques and remote sensing.
Ice also plays a role in the water cycle. Ice and snow on the Earth’s surface occur in various forms such as frost, sea ice, and glacier ice. When soil moisture freezes, ice also occurs beneath the Earth’s surface, forming permafrost in tundra climates. About 18,000 years ago glaciers and ice caps covered approximately one-third of the Earth’s land surface. Today about 12 percent of the land surface remains covered by ice masses.
Carbon Cycle
The carbon cycleis the biogeochemical cycle by whichcarbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.
Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. Along with the nitrogen cycle and the water cycle, the carbon cycle comprises a sequence of events that are key to make Earth capable of sustaining life. It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestrationto and release fromcarbon sinks.
Fig. Carbon cycle
Nitrogen Cycle
•Represents one of the most important nutrient cycles found in terrestrial ecosystems
•Used by living organisms to produce a number of complex organic molecules (amino acids, proteins)
•As a gas (N2) the store of nitrogen in the atmosphere plays an important role for life (about 1 million x larger than in living organisms)
•Also exists in organic matter in soil and oceans Nitrogen Cycle Atmosphere Hydrosphere Lithosp
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmosphere nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to ascarcityof usable nitrogen in many types ofecosystems.
The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle. Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health.
Nitrogen fixation
The conversion of nitrogen gas (N2) into nitrates and nitrites through atmospheric, industrial and biological processes is called nitrogen fixation. Atmospheric nitrogen must be processed, or "fixed", into a usable form to be taken up by plants. Between 5 and 10 billion kg per year are fixed bylightning strikes, but most fixation is done by
free-living or symbiotic bacteria known as diazotrophs. These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia, which is converted by the bacteria into otherorganic compounds.
Most biological nitrogen fixation occurs by the activity of Mo-nitrogenase, found in a wide variety of bacteria and some Archaea. Mo-nitrogenase is a complex two-component enzyme that has multiple metal-containing prosthetic groups. An example of free-living bacteria is Azotobacter. Symbiotic nitrogen-fixing bacteria such as Rhizobium usually live in the root nodules of legumes (such as peas, alfalfa, and locust trees). Here they form a mutualisticrelationship with the plant, producing ammonia in exchange for carbohydrates. Because of this relationship, legumes will often increase the nitrogen content of nitrogen-poor soils. A few non-legumes can also form such symbioses. Today, about 30% of the total fixed nitrogen is produced industrially using the Haber-Bosch process, which uses high temperatures and pressures to convert nitrogen gas and a hydrogen source (natural gas or petroleum) into ammonia.
Fig. Schematic representation of the flow of nitrogen through the ecosystem.
Photochemical Smog
Photochemical smog, often referred to as "summer smog", is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone. Photochemical smog depends on primary pollutants as well as the formation of secondary pollutants. These primary pollutants include nitrogen oxides, particularly nitric oxide (NO) and nitrogen dioxide (NO2), and volatile organic compounds. The relevant secondary pollutants include peroxylacyl nitrates(PAN), tropospheric ozone, and aldehydes. An important secondary pollutant for photochemical smog is ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight;
nitrogen dioxide (NO2), which is formed as nitric oxide (NO) combines with oxygen (O2) in the air. In addition, when SO2 and NOx are emitted they eventually are oxidized in the troposphere to nitric acid and sulfuric acid, which, when mixed with water, form the main components of acid rain. All of these harsh chemicals are usually highly reactive and oxidizing. Photochemical smog is therefore considered to be a problem of modern industrialization. It is present in all modern cities, but it is more common in cities with sunny, warm, dry climates and a large number of motor
vehicles. Because it travels with the wind, it can affect sparsely populated areas as well.
The composition and chemical reactions involved in photochemical smog were not understood until the 1950s. In 1948, flavor chemist Arie Haagen-Smit adapted some of his equipment to collect chemicals from polluted air, and identified ozone as a component of Los Angeles smog. Haagen-Smit went on to discover that nitrogen oxides from automotive exhausts and gaseous hydrocarbons from cars and oil refineries, exposed to sunlight, were key ingredients in the formation of ozone and photochemical smog.
Formation and Reactions
During the morning rush hour, a high concentration of nitric oxide and hydrocarbons are emitted to the atmosphere, mostly via on-road traffic but also from industrial sources. Some hydrocarbons are rapidly oxidized by OH· and form peroxy radicals, which convert nitric oxide (NO) to nitrogen dioxide (NO2).
This series of equations is referred to as the photostationary state (PSS). However, because of the presence of Reaction 2 and 3, NOx and ozone are not in a perfect steady state. By replacing Reaction 6 with Reaction 2 and Reaction 3, the O3molecule is no longer destroyed. Therefore, the concentration of ozone keeps increasing throughout the day. This mechanism can escalate the formation of ozone in smog.
Other reactions such as the photooxidation of formaldehyde (HCHO), a common secondary pollutant, can also contribute to the increased concentration of ozone and NO2. Photochemical smog is more prevalent during summer days since incident solar radiation fluxes are high, which favors the formation of ozone (reactions 4 and 5). The presence of a temperature inversion layer is another important factor. That is because it prevents the vertical convective mixing of the air and thus allows the pollutants, including ozone, to accumulate near the ground level, which again favors the formation of photochemical smog.
There are certain reactions that can limit the formation of O3 in smog. The main limiting reaction in polluted areas is:
This reaction removes NO2 which limits the amount of O3that can be produced from its photolysis (reaction 4). HNO3 is a sticky compound that can easily be removed onto surfaces (dry deposition) or dissolved in water and be rained out (wet deposition).
Both ways are common in the atmosphere and can efficiently remove the radicals and nitrogen dioxide.
Effect of photochemical smog
The effects of photochemical smog on human beings, plants and materials have been studied where it usually occurs. Additional information has also been obtained by stimulating photochemical smog in environmental chambers3 . Following are the important effects of photochemical smog –
(i) Eye irritation: Probably, the compounds responsible for eye irritation are formaldehyde, acrolein, PAN and peroxy benzoyl nitrate.
(ii) Vegetation damage: The effects observed are silvering and bronzing of underside of leaves followed by collapse of cells, and necrosis. Growth retardation has also been
reported. The three principal phytoxicants are ozone, nitrogen dioxide and PAN. This has resulted in economic loss.
(iii) Visibility reduction: This is perhaps the most commonly observed effect of photochemical smog. The aerosol particles causing the photochemical smog contain compounds of carbon, oxygen, hydrogen, nitrogen, sulphur, and halides.
(iv) Cracking of rubber: This is primarily due to the ozone constituents of photochemical smog. An important economic effect of smog is deterioration of the side walls of automobile tyres. To overcome this problem, an antiozonant is being used.
(v) Fading of dyes: This is another important economic effect of photochemical smog.
Photochemical smog is a complex mixture of several compounds. Among its various constituents, ozone and PAN (peroxy acetyl nitrate) are significant. Photochemical air pollution occurs predominantly in highly motorised areas and where inversion conditions prevail in the atmosphere. The size of the particles is about 0.3 µ.
Figure 2. Photochemical smog formation; sunlight reacts with NO2which then interacts with other molecules in the air to form smog.[5]
Alternative Fuels
Alternative fuel as defined is any material or substance, other than petroleum (oil), which is consumed to provide energy to power an engine. Some alternative fuels are biodiesel, ethanol, butanol, chemically stored electricity (batteries and fuel cells), hydrogen, methane, natural gas, wood, and vegetable oil. The need for the development of alternative fuel sources has been growing due to concerns that the production of oil will no longer supply the demand.
Necessities for the search of Alternative fuels
1. To ensure that when the short fall in crude oil occurs, there can be a smooth transition to other fuels.
2. To provide long-term security of supply because well over half of the world’s crude oil is in the Middle East.
3. To improve air quality because the alternative fuel may give cleaner exhaust gases as, for example, is claimed for methanol as a replacement for gasoline. However, the improvements in exhaust emissions resulting from the use of reformulated gasoline’s will delay the general introduction of alternative fuel such as methanol.
4. To overcome the absence of an indigenous crude oil supply together with an adverse balance of payments situation. An example has been the use of ethanol as an automotive fuel in braxil, where expensive crude oil had to be imported but ethanol could be manufactured relatively cheaply
Classification of Alternative Fuels
Some of these come into the category of renewable energy. Renewable energy includes electricity generation for the home, while the term "alternative fuels" tends to refer to mobile energy. Some alternative fuels and the cars they power are:
Gasoline type biofuels
Butanol as a direct replacement for gasoline
Ethanol or mixtures with gasoline E85,
Hydrogen internal-combustion car (see hydrogen car) Diesel type biofuels
Hempseed oil fuel or other Straight vegetable oils
Biodiesel
Others with internal combustion
Natural gas, compressed or liquified
Propane (LPG, LP gas)
Synfuel synthetic fuels
Oil shale,
Plug-in hybrid electric vehicle External combustion
Steam engine cars (like the Stanley Steamer)
Coal-oven steam cars
Organic waste fuel
Wood gas on board gasification No combustion
Electric vehicle
Solar cell powered or charged electric cars
Tesla's electric car (with antenna)
Hydrogen fuel cell liquefied or compressed hydrogen
MAGLEV with induction drive (a variety of electric mass transit)
Air car working on compressed air.
Introduction to Alternative Fuels:
Ethanol:
Essentially 100 percent pure grain alcohol made unfit to drink, ethanol is produced by fermenting plant sugars. It can be made from corn, potatoes, wood, waste paper, wheat, brewery waste, and many other agricultural products and food wastes.
Anything containing sugar, starch, or cellulose can be fermented and distilled into ethanol. More than 90 percent of U.S. ethanol production comes from corn. Pure ethanol is rarely used for transportation; usually it is mixed with gasoline. The most popular blend for light-duty vehicles is known as E85, which is 85 percent ethanol and 15 percent gasoline. Heavy-duty trucks typically use E95 (ethanol blended with five percent unleaded gasoline) and E93 (ethanol blended with five percent methanol and two percent kerosene). For many years, ethanol has also been used as a 10 percent mixture with gasoline in a blend called “gasohol” or E10 to reduce carbon monoxide
emissions during winter. Finally, ethanol is often blended in gasoline as an oxygenate to meet clean fuel requirements.
The technology to produce ethanol is well established, and all the resources needed to produce it can be supplied domestically.
Methanol:
Methanol is the simplest alcohol chemically, containing one carbon atom per molecule. Commonly known as “wood alcohol,” it is a toxic, colorless, tasteless liquid with a very faint odor. Because it is produced as a liquid, methanol is stored and handled like gasoline. Most methanol is currently made from natural gas, but it can also be made from a wide range of renewable sources, such as wood or waste paper.
Methanol also offers important emissions benefits compared with gasoline—it can reduce hydrocarbon emissions by 30 to 40 percent with M85 and up to 80 percent with M100 fuels. Emissions are considerably lower when methanol is used in a fuel cell vehicle— automobiles that convert the chemical energy of a fuel into electricity and heat without combustion.
Compressed Natural Gas:
CNG is odorless, colorless, and tasteless. It consists mostly of methane and is drawn from gas wells or in conjunction with crude oil production. CNG vehicles store natural gas in highpressure fuel cylinders at 3,000 to 3,600 pounds per square inch.
An odorant is normally added to CNG for safety reasons.
Two types of CNG fuel systems are on the market: dedicated vehicles, which operate exclusively on natural gas, and dual-fuel vehicles, which can use both natural gas and gasoline.
Liquefied Natural Gas:
LNG is odorless, colorless, noncorrosive, and nontoxic. When extracted from underground reserves, natural gas is composed of approximately 90 percent methane.
During the liquefaction process, oxygen, carbon dioxide, sulfur compounds, and water are removed, purifying the fuel and increasing its methane content to almost 100 percent. As a result, LNG-fueled vehicles can offer significant emissions benefits compared with older diesel-powered vehicles, and can significantly reduce carbon monoxide and particulate emissions as well as nitrogen oxide emissions.
Liquefied Petroleum Gas or LPG
Propane (otherwise known as Liquefied Petroleum Gas or LPG) is a byproduct of natural gas processing and petroleum refining. In its natural state, propane is a colorless, nontoxic gas—at least 90 percent propane, 2.5 percent butane and higher hydrocarbons, and the balance ethane and propylene. An odorant is added to the gas so it can be detected for safety reasons. Under moderate pressure, propane gas turns into a liquid mixture, making it easier to transport and store in vehicle fuel tanks.
Compared with gasoline, propane can lower carbon dioxide, carbon monoxide, and other toxic emissions.
Bio-diesel:
Today, the diesel engine is still capable of running on “biodiesel” fuel, which can be produced from a variety of renewable sources, including soybean oil, canola oil, sunflower oil, cottonseed oil, and animal fats. These sources can be obtained from agricultural feedstocks or by recycling used oil such as cooking grease. Most biodiesel produced in the United States is made from soybean oil due to this feedstock’s abundance. Biodiesel is usable in its pure form, known as “neat biodiesel”
or B100. In addition, it is available in various blends with petrodiesel, the most common of which is known as B20 (20 percent biodiesel and 80 percent petrodiesel).
It is also used in smaller percentages as a lubricating fuel additive.
Biogas Plants
Biogas is a clean and efficient fuel. It is a mixture of methane (CH4), carbon dioxide (CO2), hydrogen (H2) and hydrogen sulphide (H2S).The chief constituent of biogas is methane (65%).
Advantages of biogas as a fuel
High calorific value
Clean fuel
No residue produced
No smoke produced
Non polluting
Economical
Can be supplied through pipe lines
Burns readily - has a convenient ignition temperature Uses of biogas
Domestic fuel
For street lighting
Generation of electricity Advantages of biogas plants
Reduces burden on forests and fossil fuels
Produces a clean fuel - helps in controlling air pollution
Provides nutrient rich (N & P) manure for plants
Controls water pollution by decomposing sewage, animal dung and human excreta.
Limitations of biogas plants
Initial cost of installation of the plant is high.
Number of cattle owned by an average family of farmers is inadequate to feed a biogas plant.
Hydrogen as an Alternatie Fuel
Hydrogen or H2 gas is highly flammable and will burn at concentrations as low as 4% H2 in air. For automotive applications, hydrogen is generally used in two forms:
internal combustion or fuel cell conversion.
In combustion, it is essentially burned as conventional gaseous fuels are, whereas a fuel cell uses the hydrogen to generate electricity that in turn is used to power electric motors on the vehicle.
Hydrogen gas must be produced and is therefore is an energy storage medium, not an energy source. The energy used to produce it usually comes from a more conventional source. Hydrogen holds the promise of very low vehicle emissions and flexible energy storage; however, many believe the technical challenges required to realize these benefits may delay hydrogen’s widespread implementation for several decades.
Hydrogen can be obtained through various thermochemical methods utilizing methane (natural gas), coal, liquified petroleum gas, or biomass (biomass gasification), from electrolysis of water, or by a process called thermolysis. Each of these methods poses its own challenges
Electric Vehicles
Electric vehicles (EVs) use electric motors powered by electricity stored in batteries.
EVs produce a little noise and zero emissions.
An EV averages between 80 and 112 km before recharging. Temperature, vehicle load, speed affect this range
Nickel-metal hydride or lead-acid batteries and permanent magnet motors have extended the operating range.
Regenerative braking and highly efficient accessories (such as a heat pump for passenger heating and cooling) is used to increase battery life.
Although an EV is a zero emission vehicles, there are emissions associated with electricity generation.
Hybrid Electric Vehicles
Hybrid electric vehicles (HEVs) are or will soon be available from all of the major
automobile manufacturers.
Any vehicle that combines 2 or more sources of power is called a hybrid.
Current HEVs have an internal combustion engine and an electric motor.
Series hybrid
Some HEV designs are close to being an electric vehicle in that the engine is used to drive a generator that charges the battery or powers the electric motor.
The electric motor powers the vehicle.
The engine is there only to extend the vehicle’s driving range.
A gasoline or diesel engine can be used
Toyota Hybrid Layout Parallel hybrid
– The most common design of hybrid vehicle relies on power from the electric motor or engine, and in some cases power from both.
– When the vehicle moves from a stop and has a light load, the motor moves the vehicle.
– Power for the electric motor comes from stored electricity in the battery pack.
Fuel cell vehicles
Fuel cell vehicles (FCVs) are electric vehicles that use fuel cells to convert chemical
energy into electrical energy.
Fuel cells do not store electricity; rather, electricity is converted, as it is needed, to spin the electric motors that move the vehicle.
Fuel cells release energy derived from the reaction between hydrogen and oxygen.
The basic operation of a fuel cell
They have high efficiency and, depending on the fuel used, produce little or no
emissions.
Fuel cells operating on hydrogen emit nothing but pure water.
There are various options for storing hydrogen and feeding it into a fuel cell, the most common of which is reforming it from other fuels
Solar Car
A solar vehicle is an electric vehicle powered by a type of renewable energy, by solar energy obtained from solar panels on the surface (generally, the roof) of the vehicle.
Asolar car is a solar vehicle used for land transport. Solar cars only run on solar power from the sun. They are very stable and can come in different sizes. To keep the car running smoothly, the driver must keep an eye on these gauges to spot possible problems. Cars without gauges almost always feature wireless telemetry, which allows the driver's team to monitor the car's energy consumption, solar energy capture and other parameters and thereby freeing the driver to concentrate on driving
Solar Car consists of
Solar Array
Power Trackers
Electric Motor
Speed Controller
Chassis
Battery
Wheel
Advantages of Solar Powered Cars
Unlike regular cars, solar energy powered cars are able to utilize their full power at any speed.
Solar powered cars do not require any expense for running.
Solar cars are quite.
Solar cars require very low maintenance.
Solar cars produce no harmful emissions.
Disadvantages
Solar cars don’t have speed or power that regular cars have.
Solar powered cars can operate only for limited distances is there is no sun.
If it is dark out for many days, the car battery will not charge and you this can seem as a problem to many problem. This is the main reason why people don’t rely on solar cars.
A good solar powered car is expensive. It will cost $200,000 or more.
What is Indoor Air Pollution?
Many people, when they think of air pollution, they think about smog and car emissions. This is what is called outdoor air pollution but it is more dangerous when it becomes indoor air pollution. Indoor air pollution occurs when certain air pollutants from particles and gases contaminate the air of indoor areas. These air pollutants can cause respiratory diseases or even cancer. Removing the air pollutants can improve the quality of your indoor air.
Millions of people around the world prepare their meals using traditional methods (i.e. wood, charcoal, coal, dung, crop wastes) on open fires. Such inefficient practices can increase the amount of air pollutants inside the home and can also cause serious
health problems. According to WHO, 4.3 million people a year die from the exposure to household air pollution.
This type of pollution is significantly more dangerous due to how concentrated the air is in indoor environments. According to recent findings, over 2 million deaths occur every single year due to indoor air pollution. So what can we do about it? That is the question that many ask themselves every single day. Before you can fully comprehend the effects of indoor air pollution you must first be able to understand the causes of it as well as what we can do to improve our quality of air both indoors and outdoors.
Causes of Indoor Air Pollution
Toxic products, inadequate ventilation, high temperature and humidity are few of the primary causes of indoor air pollution in our homes.
1. Asbestos is the leading cause of indoor air pollution. Asbestos can be found in various materials used commonly in the automotive industry as well as home construction. They are most commonly found in coatings, paints, building materials, and ceiling and floor tiles.
You won’t find asbestos as often as you used because newer products do not contain asbestos. However, if you have an old home that was constructed a long time ago, the risks for asbestos are much greater than that of a newer home. Asbestos has been banned in the US and is no longer being used.
2. Formaldehyde is another leading cause of indoor air pollution. It is no longer produced in the United States due to its ban in 1970 but can still be found in paints, sealants, and wood floors.
3.Radonwhich can be found underneath your home in various types of bedrock and other building materials, can also be a cause of indoor air pollution. Radon can get into the walls of your home and put both you and your family at risk.
4.Tobacco smokethat comes from outdoor and indoor areas can also be an indoor air pollutant.
5. Many contaminants that grow in damp environments can be brought in from outdoor areas. These contaminants such as mildew, mold, bacteria, dust mites, as well as animal dander, can come into the home and make you sick.
6. There are many objects that you have in your home that also cause indoor air pollution. Objects such as wood stoves, space heaters, and fireplaces, all put out carbon monoxide as well as nitrogen dioxide. There are still billions of people who use these types of fuels to heat their homes on a daily basis.
7. Other household products such as varnishes, paints, and certain cleaning products can also emit pollution into the air that you breathe inside your home.
Serious Effects of Indoor Air Pollution
Effects of indoor air pollution can be life threatening. Kids and old age people are more prone to the after-effects of indoor air pollution.
1. If Asbestos is found in your home it can cause you very serious health problems such aslung cancer, asbestosis, mesothelioma, and various other types of cancers.
2. If contaminants such as animal dander, dust mites or other bacteria get into the home there will also be some serious effects from them. You will start to experience asthma symptoms, throat irritation, flu, and other types of infectious diseases.
3. If lead is found in the home it can also be severely life threatening. It can cause brain and nerve damage, kidney failure, anemia, and a defective cardiovascular system.
4. Formaldehyde, one of the most common indoor air pollutants, can also cause health problems. You may experience irritation of the throat, eyes, and nose, as well as allergic reactions. There have been a number of cases where it has also caused cancer.
5. Tobacco smoke causes individuals to experience severe respiratory irritation, pneumonia, bronchitis, emphysema, heart disease, as well as lung cancer.
6. Chemicals such as those that are used in certain cleaning agents and paints can cause you to experience aloss of coordination, liver, brain, and kidney damage, as well as a number of types of cancer.
7. If you use gas stoves in your home it can cause respiratory infections and damage and irritation to the lungs.
Ways to Improve Indoor Air Quality
1. Smoking is one of the most common types of indoor air pollution. The best thing to do is toquit smoking and make your home anti-smoking zone. The less smoke that is emitted into the air the less chance of one of the listed effects happening to someone that you love. Smoking is a leading cause of cancer. Lung cancer is the most common form of cancer caused by smoking.
2. Make sure you check the ingredients on any of your cleaning supplies to make sure they are environmentally friendly. Do your homework on what is considered to be a dangerous ingredient. You can also find an environmentally friendly cleaning list online so you know exactly what to buy.
3. Have your home checked for asbestos. This is typically done before you move into the home. If you have a home that was built prior to the ban of asbestos, it is important to make sure there is none still lingering within the home.
4.Stop using gas stovesin your home as well as certain types of space heaters. They release harmful chemicals that could be dangerous to human health.
5. Have your home inspected for any mold, radon, or any other harmful chemical or bacteria that may be in your home. These types of inspections are traditionally done before you move in so keep that in mind as well.
6. Use a good vacuum cleaner that has strong brushesto keep out chemicals and allergens that can accumulate in your home. Areas in your home which are most commonly visited must be cleaned thoroughly by using the vacuum several times.
7. Most of the dirt comes in the home from the shoes.Keep a large mat out of every room that will reduce the amount of dirt, and other pollutants from getting into your home.
Regional Impact of Global warming
Human basic needs, such as food, water, health, and shelter, are affected by climate.
Changes in climate may threaten these needs with increased temperatures, sea level rise, changes in precipitation, and more frequent or intense extreme events.
Climate change will affect individuals and groups differently. Certain groups of people are particularly sensitive to climate change impacts, such as the elderly, the infirm, children and pregnant women, native and tribal groups, and low-income populations.
Climate change may also threaten key natural resources, affecting water and food security. Conflicts, mass migrations, health impacts, or environmental stresses in other parts of the world could raise economic, health, and national security issues for the United States.
Although climate change is an inherently global issue, the impacts will not be felt equally across the planet. Impacts are likely to differ in both magnitude and rate of change in different continents, countries, and regions. Some nations will likely experience more adverse effects than others. Other nations may benefit from climate changes. The capacity to adapt to climate change can influence how climate change affects individuals, communities, countries, and the global population.
Impacts on Basic Needs
Impacts on Agriculture and Food
Changes in climate could have significant impacts on food production around the world. Heat stress, droughts, and flooding events may lead to reductions in crop yields and livestock productivity. Areas that are already affected by drought, such as Australia and the Sahel in Africa, will likely experience reductions in water available for irrigation.
At middle to high latitudes, cereal crop yields are projected to increase slightly, depending on local rates of warming and crop type. At lower latitudes, cereal crop
yields are projected to decrease. The greatest decreases in crop yields will likely occur in dry and tropical regions. In some African countries, for example, wheat yields could decline by as much as 35% by 2050.
Climate change is affecting many fisheries around the world. Increasing ocean temperatures have shifted some marine species to cooler waters outside of their normal range. Fisheries are important for the food supply and economy of many countries. For example, more than 40 million people rely on the fish caught in the Lower Mekong delta in Asia, which is the largest freshwater fishery in the world.
Projected reductions in water flows and increases in sea level may negatively affect water quality and fish species in regions like these, affecting the food supply for communities that depend on these resources.
Climate change is very likely to affect global, regional, and local food security by disrupting food availability, decreasing access to food, and making utilization more difficult. Climate risks to food security are greatest for poor populations and in tropical regions. The potential of climate change to affect global food security is important for food producers and consumers in the United States.
Impacts on Water Supply and Quality
Semi-arid and arid areas (such as the Mediterranean, southern Africa, and northeastern Brazil) are particularly vulnerable to the impacts of climate change on water supply. Over the next century, these areas will likely experience decreases in water resources, especially in areas that are already water-stressed due to droughts, population pressures, and water resource extraction.
As climate changes, water is very likely to become scarce at least part of the time in many areas, but more plentiful part of the time in some areas as well. The availability of water is strongly related to the amount and timing of runoff and precipitation. With a 2.7°F rise in global mean temperature, annual average streamflow is projected to increase by 10-50% at high latitudes and in some wet tropical areas, but decrease by 10-50% in some dry regions at mid-latitudes and in the subtropics. As temperatures rise, snowpack is declining in many regions and glaciers are melting at unprecedented rates, making water less available in areas that depend on it from melting snow and glaciers during spring and summer. Droughts are likely to become more widespread.
When it does rain, more precipitation is expected to fall in extreme heavy precipitation events. Increases in heavy precipitation events would not increase water supply, but instead result in increased flooding, except in river basins with large dams able to hold excess water until it is needed.
Indus River in Southern Pakistan (Left: August 2009; Right: August 2010). In August 2010, record monsoon rains flooded significant portions of Pakistan. Twenty percent of the country was underwater as a result of the floods, affecting about 20 million Pakistanis and rendering six million homeless. In the image from 2009, the Indus is about 0.6 miles wide. In the 2010 image, the river is 14 miles wide or more in parts.
Water quality is important for ecosystems, human health and sanitation, agriculture, and other purposes. Increases in temperature, changes in precipitation, sea level rise, and extreme events could diminish water quality in many regions. Large rainstorms may cause large amounts of pollutants to enter rivers and estuaries, as excess water may overwhelm wastewater systems and natural buffers. Increased pollution as well as increasing water temperatures can cause algal blooms and potentially increase bacteria in water bodies. In coastal areas and small islands, saltwater from rising sea level and storm surges threaten water supplies. These impacts may require communities to begin treating their water in order to provide safe water resources for human uses.
Impacts on Human Health
The risks of climate-sensitive diseases and health impacts can be high in countries that have little capacity to prevent and treat illness. There are many examples of health impacts related to climate change.
Increases in temperatures are linked to more frequent and severe heat stress.
Worsened air quality that often accompanies heat waves or wildfires can lead to breathing problems and exacerbate respiratory and cardiovascular diseases.
Impacts of climate change on agriculture and other food systems can increase rates of malnutrition and foodborne illnesses.
Climate changes can influence infectious diseases. The spread of meningococcal (epidemic) meningitis is often linked to climate changes,
especially drought. Areas of sub-Saharan and West Africa are sensitive to the spread of meningitis, and will be particularly at-risk if droughts become more frequent and severe.
The spread of mosquito-borne diseases such as malaria, dengue, and West Nile virus may increase in areas projected to receive more precipitation and flooding.
Increases in rainfall and temperature can cause spreading of dengue fever.
Changes in precipitation patters and extreme weather events can lead to cascading health impacts, particularly when power, water, or transportation systems are disrupted. Diarrheal diseases from contaminated water and food sources are a major concern, particularly for children.
The effects of global climate change on mental health and well-being are integral parts of the overall climate-related human health impacts. Mental health consequences of climate change range from minimal stress and distress symptoms to clinical disorders, such as anxiety, depression, post-traumatic stress, and suicidal thoughts.
Certain groups of people in low-income countries are especially at risk for adverse health effects from climate change. These at-risk groups include urban people living in poverty, older adults, young children, traditional societies, subsistence farmers, and coastal populations. Many regions, such as Europe, South Asia, Australia, and North America, have experienced heat-related health impacts. Rural populations, older adults, outdoor workers, and those without access to air conditioning are often the most vulnerable to heat-related illness and death.
Impacts on Shelter
Climate change affects the migration of people within and between countries around the world. A variety of reasons may force people to migrate into other areas. These reasons include conflicts, such as ethnic or resource conflicts, degraded ecosystem services, such as lack of viable agricultural land or fresh water, and extreme events, such as flooding, drought, and hurricanes. Extreme events displace many people, especially in areas that do not have the ability or resources to quickly respond or rebuild after disasters. Many types of extreme events are becoming more frequent or severe because of climate change, which exacerbates existing conflicts. This will likely increase the numbers of people migrating during and after these types of events.
Coastal settlements and low-lying areas are particularly vulnerable to climate change impacts, such as sea level rise, erosion, and extreme storms. Rising ocean temperatures and acidity may also threaten coastal ecosystems. As coastal habitats (such as barrier islands, wetlands, deltas, and estuaries) are destroyed, coastal settlements can become more vulnerable to flooding from storm surges and erosion.
Both developing and developed countries are vulnerable to the impacts of sea level rise. For example, Bangladesh, the Netherlands, and Guyana are particularly at-risk.
Impacts on Vulnerable Populations
Three women reach their water source, a low water level lake in India. Indigenous groups in various regions--such as the United States, Latin and South America, Europe, and Africa--are already experiencing threats to their traditional livelihoods.
Rising sea levels and extreme events threaten native groups that inhabit low-lying island nations. Higher temperatures and reduced snow, ice, and permafrost threaten groups that live in mountainous and polar areas. Climate effects in these areas can affect hunting, fishing, transport, and other activities.
Approximately 1.4 billion people, close to one fifth of the world’s population, live below the World Bank's measure of extreme poverty, earning less than US $1.25 a day Many lower-income groups depend on publicly provided resources and services such as water, energy, and transportation. Extreme events can affect and disrupt these resources and services, sometimes beyond replacement or repair. Many people in lower-income countries cannot afford or gain access to adaptation mechanisms such as air conditioning, heating, or disaster insurance. This lack of adaptive capacity makes the world’s poor especially vulnerable to the impacts of climate extremes, exacerbating existing conditions of poverty and inequality, and ultimately leading to more poverty.
Older and younger people are also especially sensitive to climate change impacts.
Children's developing immune, respiratory, and neurological systems make them more sensitive to some climate change impacts, including more frequent or severe extreme events, increased heat, and worsened air quality. Elderly populations are also at risk due to frail health and limited mobility. Extreme heat and storm events can disproportionately affect older people.
Climate change impacts can differ according to gender. Worldwide, women have a higher rate of mortality than men from severe storms or other extreme events,
although there is regional variation. In some regions, working-age men who work outdoors are more vulnerable to heat-related deaths. Women developing countries women may be particularly vulnerable to extreme events due to differences in poverty and physical vulnerability due to undernutrition or pregnancy. As climate change causes extreme events to become more frequent or severe, women may be disproportionately affected.
Impacts on National Security e
Water scarcity led to tensions in southern Kazakhstan. Climate change impacts are expected to exacerbate national security issues and increase the number of international conflicts. The Department of Defense reports that climate change is likely cause instability in other countries-- impairing access to food and water, damaging infrastructure, spreading disease, uprooting and displacing large numbers of people—which also affects the United States. They report: “Climate change will affect the Department of Defense's ability to defend the Nation and poses immediate risks to U.S. National security.”
Many concerns revolve around the use of natural resources, such as water. In many parts of the world, water issues cross local and national borders. Access to consistent and reliable sources of water in these regions is greatly valued. Changes in the timing and intensity of rainfall would threaten already limited water sources and potentially cause future conflicts. Evidence suggests most conflict is likely to occur between local communities, socioeconomic groups, and states, while bilateral and multilateral interactions have shown evidence of formal cooperation over resources.
Threatened food security in parts of Asia and sub-Saharan Africa could also lead to conflict. Rapid population growth and changes in precipitation and temperature, among other factors, are already affecting crop yields. Resulting food shortages could increase the risk of humanitarian crises and trigger population migration across national borders, ultimately sparking political instability.
The ongoing loss of the ice cover in the Arctic Ocean is very likely to have with national security implications. The Arctic Ocean has a long history of modest, though growing, shipping activity, including trans-Arctic shipping routes. Declining sea ice coverage will allow more access to these waters. However, a number of other international issues will influence the potential growth in shipping. In the case of the Arctic Ocean, increasing access to these waters means that issues of sovereignty
(priority in control over an area), security (responsibility for policing the passageways), environmental protection (control of ship-based air and water pollution, noise, or ship strikes of whales), and safety (responsibility for rescue and response) will become more important.
Regional Impacts
Highlights of recent and projected regional impacts are shown below.
Impacts on Africa
Africa may be the most vulnerable continent to climate variability and change because of multiple existing stresses and low adaptive capacity. Existing stresses include poverty, food insecurity, political conflicts, and ecosystem degradation.
By 2050, between 350 million and 600 million people are projected to experience increased water stress due to climate change. Urban population is also projected to triple, increasing by 800 million people, complicating urban poverty and access to basic services.
Climate variability and change is projected to severely compromise agricultural production, including access to food, in many African countries and regions.
Toward the end of the 21st century, projected sea level rise will likely affect low-lying coastal areas with large populations, including Senegal, Liberia, and Mozambique.
Climate variability and change can negatively impact human health. In many African countries, existing health threats – such as malnutrition, malaria and other vector-borne diseases -- can be exacerbated by climate change.
Impacts on Asia
Glaciers in Asia are retreating at faster rates than ever documented in historical records. Some glaciers currently cover 20% of the land that they covered a century ago. Melting glaciers increase the risks of flooding and rock avalanches from destabilized slopes.
Climate change is projected to decrease freshwater availability, especially in central and southeast Asia, particularly in large river basins. With population growth and increasing demand from higher standards of living, this decrease could adversely affect more than a billion people by 2050.
Increased flooding from the sea and, in some cases, from rivers threatens coastal areas, especially heavily populated delta regions in south and southeast Asia.
The impacts of climate change on crop yields are likely to vary drastically depending on region, crop type, and regional changes in temperature and precipitation. For example, by the mid-21st century, climate change could increase crop yield up to 20% in east and southeast Asia, while decreasing yield up to 30% in central and south Asia.
Sickness and death due to diarrheal disease will likely increase in east, south, and southeast Asia due to projected changes in the hydrological cycle associated with climate change.
Impacts on Australia and New Zealand
Water security problems are projected to intensify with a 1°C global average warming in southwestern and southeastern Australia, and in the northern and some eastern parts of New Zealand.
Biodiversity within some ecologically rich sites, including the Great Barrier Reef and Queensland Wet Tropics, will be at significant risk by 2050.
Sea level rise and more severe storms and coastal flooding will continue to affect coastal areas. Coastal development and population growth in areas such as Cairns and Southeast Queensland (Australia) and Northland to Bay of Plenty (New Zealand), would place more people and infrastructure at risk.
Increased drought and fire are projected to cause declines in agricultural and forestry production over much of southern Australia and the northern and eastern parts of New Zealand.
Cascading and interacting economic, social, and daily life circumstances have accompanied prolonged drought in rural regions. Drought-related worry and psychological distress increased in drought-declared Australian regions, particularly for those experiencing loss of livelihood and industry. Long-term
drought has been linked to increased incidence of suicide among male farmers in Australia.
Extreme storm events are likely to increase the failure of dikes, levees, drainage, and sewerage systems. They are also likely to increase the damage from storms and fires.
More heat waves are likely to cause more deaths and more electrical blackouts.
Indigenous populations are more exposed the risks of climate change than most other Australians and New Zealanders.
Impacts on Europe
Wide-ranging impacts of climate change are already being documented in Europe, including retreating glaciers, sea level rise, longer growing seasons, species range shifts, and heat wave-related health impacts.
Future impacts of climate change will likely negatively affect nearly all European regions, with adverse social, health, and infrastructure effects. Many economic sectors, such as agriculture and energy, could face challenges.
In southern Europe, higher temperatures and drought may reduce water availability, hydropower potential, summer tourism, and crop productivity, hampering economic activity more than other European regions.
In central and eastern Europe, summer precipitation is projected to decrease, causing higher water stress. Forest productivity is projected to decline. The frequency of peatland fires is projected to increase.
In northern Europe, climate change is initially projected to bring mixed effects, including some benefits such as reduced demand for heating, increased crop yields, and increased forest growth. However, as climate change continues, negative impacts are likely to outweigh benefits. These include more frequent winter floods, endangered ecosystems, and increasing ground instability from thawing permafrost.
Impacts on Central and South America
By mid-century, increases in temperature and decreases in soil moisture are projected to cause savanna to gradually replace tropical forest in eastern Amazonia.
In drier areas, climate change will likely worsen drought, leading to salinization (increased salt content) and desertification (land degradation) of agricultural land.
The productivity of livestock and some important crops such as maize and coffee is projected to decrease in some areas, with adverse consequences for food security. In temperate zones, soybean yields are projected to increase.
Sea level rise is projected to increase risk of flooding, displacement of people, salinization of drinking water resources, and coastal erosion in low-lying areas.
These risks threaten fish stocks, recreation, and tourism.
Changes in precipitation patterns and the melting of glaciers are projected to significantly affect water availability for human consumption, agriculture, and energy generation.
Climate change and land use changes are expected to increase the rates of species extinction.
Warmer weather, milder winters, and changes in precipitation may increase incidence of some vector-borne diseases, such as the chikungunya virus, which is transmitted by mosquitoes.
Impacts on North America
Warming in western mountains will decrease snowpack, increase winter flooding, and reduce summer flows, exacerbating competition for over-allocated water resources.
Disturbances from pests, diseases, and fire are projected to increasingly affect forests, with extended periods of high fire risk and large increases in area burned.
Moderate climate change in the early decades of the century is projected to increase aggregate yields of rain-fed agriculture in northern areas, but temperature increases will reduce corn, soy, and cotton yields in the Midwest and South by 2020. Crops that are near the warm end of their suitable range or that depend on highly utilized water resources will likely face major challenges. High emissions scenarios project reductions in yields by as much as 80% by the end of the century.
Increases in the number, intensity, and duration of heat waves during the course of the century are projected to further challenge cities that currently experience
heat waves, with potential for adverse health impacts and increased stress on energy systems. Older populations are most at risk.
Climate change will likely increasingly stress coastal communities and habitats, worsening the existing stresses of population, development, and pollution on infrastructure, human health, and the ecosystem.
Impacts on Polar Regions
Climate changes will likely reduce the thickness and extent of glaciers and ice sheets.
Changes in natural ecosystems will likely have detrimental effects on many organisms including migratory birds, mammals, and higher predators as marine species shift their ranges.
In the Arctic, climate changes will likely reduce the extent of sea ice and permafrost, which can have mixed effects on human settlements. Negative impacts could include damage to infrastructure and changes to winter activities such as ice fishing and ice road transportation. Positive impacts could include more navigable northern sea routes.
The reduction and thawing of permafrost, sea level rise, and stronger storms may worsen coastal erosion and disrupt both natural and social systems.
Climate change effects uch as increases in coastal erosion, changes in the ranges of some fish, increased weather unpredictability—are already disrupting traditional hunting and subsistence practices of indigenous Arctic communities, and may force relocation of villages.
Terrestrial and marine ecosystems and habitats are projected to be at risk to invasive species, as climatic barriers are lowered in both polar regions.
Impacts on Small Islands
Small islands, whether located in the tropics or higher latitudes, are highly vulnerable to extreme weather events, changes in sea level, increases in air and surface temperatures, and changing rainfall patterns.
Deterioration in coastal conditions, such as beach erosion and coral bleaching, will likely affect local resources such as fisheries, as well as the value of tourism destinations.
Sea level rise is projected to worsen inundation, storm surge, erosion, and other coastal hazards. These impacts would threaten vital infrastructure, settlements, and facilities that support the livelihood of island communities.
By mid-century, on many small islands (such as the Caribbean and Pacific), climate change is projected to reduce already limited water resources to the point that they become insufficient to meet demand during low-rainfall periods.
Invasion by non-native species is projected to increase with higher temperatures, particularly in mid- and high-latitude islands.
Health and Environmental Effects of prolonged exposure of Ultraviolet Radiation
The sun is the principal source of exposure for most people. Solar UV undergoes significant absorption by the atmosphere. With depletion of the stratospheric ozone people and the environment will be exposed to higher intensities of UV. The consequences of this added UV exposure are considered so serious that it was a major topic for discussion at the World Environment Conference, held in Rio de Janeiro in 1992. In Agenda 21, adopted by the Conference, it was specifically recommended to
"undertake, as a matter of urgency, research on the effects on human health of the increasing ultraviolet radiation reaching the earth's surface as the consequence of depletion of the stratospheric ozone layer." It is this issue that underscores the current need to better understand the potential health and environmental risks of UV exposure.
INTERSUN, global UV project, is WHO's response to the need to disseminate information about the health and environmental hazards of excessive UV exposure.
INTERSUN has developed a document entitled "UV Protective Measures" in response to the need to educate the public and workers on measures they can take to reduce their UV exposure, and has been involved in the development of a Solar UV Index, an index related to daily UV exposure, reported with the news and weather,
that facilitates a continuing educational process about possible health effects and measures to reduce UV exposure.
Summary of the major health concerns
Skin cancer and cataracts are important public health concerns. The social cost of these diseases, such as death, disfigurement and blindness, can be overwhelming both in terms of human suffering and the financial burden. Solar UV exposure is known to be associated with various skin cancers, accelerated skin aging, cataract of the lens of the eye and other eye diseases, and possibly has an adverse effect a person's ability to resist infectious diseases. Most of these health concerns could be avoided by reducing exposure to solar UV. The United Nations Environment Programme has estimated that over 2 million non-melanoma skin cancers and 200,000 malignant melanomas occur globally each year. In the event of a 10% decrease in stratospheric ozone, with current trends and behaviour, an additional 300,000 non-melanoma and 4,500 melanoma skin cancers could be expected world-wide. Some 12 to 15 million people in the world are blind because they have cataracts. WHO has estimated that up to 20%
of cataracts or 3 million per year could be due to UV exposure to the eye. It has been estimated that for each 1% sustained decrease in stratospheric ozone there would be an increase of 0.5% in the number of cataracts caused by solar UV (van der Leun et al 1989). In the United States alone, it costs the US Government $US 3.4 billion for 1.2 million cataract operations per year. Substantial savings in cost to health care can be made by prevention or delay in the onset of cataracts.
Ultraviolet radiation
UV is one of the non-ionizing radiations in the electromagnetic spectrum and lies within the range of wavelengths 100 nm to 400 nm (see figure 1). The short wavelength limit of the UV region is often taken as the boundary between the ionizing radiation spectrum (wavelengths < 100 nm) and the non-ionizing radiation spectrum.
UV can be classified into UVA (315 - 400 nm), UVB (280 - 315 nm) and UVC (100 - 280 nm) regions, although other conventions for UVA, UVB and UVC wavelength bands are in use. Most artificial sources of UV, except for lasers, emit a spectral continuum of UV containing characteristic peaks, troughs and lines. These sources include various lamps used in medicine, industry, commerce, research and the home.
Figure 1: Solar optical emissions before and after absorption by the atmosphere.
Since UV is normally absorbed over a surface it can be measured as a radiant exposure, the incident UV energy divided by the receptor surface area in joules per square metre (J m-2). UV can also be measured as an irradiance, the incident power divided by the receptor surface area in watts per square metre (W m-2).
Biological effectiveness of UV
UV-induced biological effects depend on the wavelengths of the radiation emitted by the source. Thus, for a proper determination of hazard it is necessary to have information on the spectral (range of wavelength) emissions. These consist of spectral irradiance (W m-2 nm-1) measurements from the source. The total irradiance (W m-2) is obtained by summing over all wavelengths emitted. The biological or hazard weighted irradiance (W m-2 effective), commonly called the effective UV irradiance or dose rate (exposure), is determined by multiplying the spectral irradiance at each wavelength by the biological or hazard weighting factor (which quantifies the relative efficacy at each wavelength for causing the effect) and summing over all wavelengths.
Such factors or weighting functions are obtained from action spectra.
Animal Studies Skin cancer
Solar UV exposure has been shown to produce cancers in domestic and food animals.
In experimental animals UV causes predominantly squamous cell carcinomas (SCCs).
UVB is most effective at producing SCCs, although they are produced by UVA but at much higher intensities, similar to the levels needed for erythema and tanning. The effectiveness of UVC is unknown except at one wavelength (254 nm). At this wavelength the effectiveness is less than UVB. Melanomas are much less common and only two animal models have been found for induction of melanoma by UV alone.
An initial action spectrum determined for a type of hybrid fish indicates a peak in the UVB range but also shows a high level of effectiveness in the UVA. Basal cell carcinomas are rare in animals.
Immune response
Exposure to suberythemal doses of UV have been shown to exacerbate a variety of infections in rodent models. UV affects infections both at the site of exposure and at distant sites. Recent work indicates that systemic infections without skin involvement may be affected. Enhanced susceptibility appears to result from T-helper cell activity.
The mechanisms associated with this suppression appear to be the same as those identified with suppression to contact and delayed type hypersensitivity responses.
Suppression of these immune responses appears to be mediated by release of soluble mediators from UVB exposed skin which alters the antigen presentation by Langerhans and other cells so that they fail to activate TH1 cells. The resulting immune suppression is antigen specific, can occur regardless of whether or not antigen is applied at the site of exposure, and is relatively long lasting. UV exposure also prevents the development of protection immunity to a variety of infections in mice and rats.
Effects on the eye
Many studies in experimental animals have demonstrated that UV exposure can cause both acute and delayed effects such as cataract, photokeratitis, damage to the corneal epithelium and various retinal effects. Studies of photochemical retinal injury in aphakic monkeys have shown that the retina is six times more vulnerable to photochemical damage from UV than the visible wavelengths.
Health Effects on Humans Skin
The degree of damage that UV produces in skin will depend on the incident intensity and wavelength content (UVA or UVB), and on the depth of penetration of these wavelengths into the skin (see figure 4). Acute effects on the skin consist of solar erythema, "sunburn", which, if severe enough, may result in blistering and destruction of the surface of the skin with secondary infection and systemic effects, similar to those resulting from a first or second degree heat burn. Although UVC is very efficiently absorbed by nucleic acids, the overlying dead layers of skin absorb the radiation to such a degree that there is only mild erythema and, usually, no late sequelae, even after repeated exposures. Much less is known about the biological effects of UVA. However, doses of UVA, which alone may not show any biological effect, can, in the presence of certain environmental, consumer and medicinal chemical agents,
Figure 3: Depth of penetration of UV into the skin.
Chronic skin changes due to UV consist of skin cancer (both melanoma and non-melanocytic), benign abnormalities of melanocytes (freckles, melanocytic naevi and solar or senile lentigines), and a range of other chronic injuries resulting from UV
exposure to keratinocytes, blood vessels and fibrous tissue, often described as
"photoaging" (solar elastosis). The much increased rates of skin cancer in patients with xeroderma pigmentosum, who have a deficiency in the capacity to repair UV-induced DNA damage, suggest that direct UV damage of the DNA may be a step in the cause of these cancers. This suggestion has also been supported by the observation of UV specific mutations of the p53 tumour suppressor gene in a proportion of patients with non-melanocytic skin cancer. Oxidative and immune suppressant effects may also contribute to the capacity of UV to cause skin cancers.
Cancer of the lip is much more common in fair than dark skin populations and is associated with outdoor work. However possible confounding with tobacco and alcohol use has not been adequately controlled in any study, and so it is not possible at present to associate directly solar UV exposure in the cause of this cancer. Strong epidemiological evidence exists that sun exposure causes cutaneous melanoma and non-melanocytic skin cancer. Their incidence is less in darker than light skin groups living in the same geographical area. Risk of skin cancer decreases with increasing pigmentation. The anatomical site most seen for squamous cell carcinoma (SCC) is the head and neck, areas most exposed to the sun. Incidence of both melanoma and non-melanocytic skin cancer are increased in areas of high ambient solar UV radiation.
The worldwide incidence of malignant melanoma has continued to increase.
Cutaneous melanoma is the result of neoplastic transformation of melanocytes, the pigment producing cells in the epidermis. Four basic categories of melanoma have been identified in humans: superficial spreading melanoma, nodular melanoma, lentigo malignant melanoma (also known as Hutchinson's melanotic freckle), and unclassified melanoma. Melanoma is strongly related to frequency of recreational exposure to the sun and to history of sunburns. The evidence that risk of melanoma is related to intermittent exposure to UV, especially in childhood, is inferred from the locations of the melanomas over the body (larger numbers on irregularly exposed sites), higher occurrence in indoor than outdoor workers, and higher levels of exposure during childhood (prior to 15-20 years of age). There is suggestive evidence that exposure to sunlamps may increase the risk of melanoma, but the studies conducted so far have not consistently controlled confounding factors.
Immune system
A number of studies suggest that UV exposures at environmental levels suppress immune responses in both rodents and man. In rodents this immune suppression results in enhanced susceptibility to certain infectious diseases with skin involvement and some systemic infections. Mechanisms associated with UV-induced immunosuppression and host defence mechanisms which provide for protection against infectious agents, are similar in rodents and man. It is therefore reasonable to assume that exposure to UV may enhance the risk of infection and decrease the effectiveness of vaccines in humans. However additional research is necessary to substantiate this.
Eye
UV exposure of the eye depends on many factors: ground reflection, degree of brightness in the sky leading to activation of the squint reflex, the amount of atmospheric reflection and the use of eyewear. In addition, the target for UV-induced
damage will depend on the wavelength of the incident radiation as shown in figure 4.
The acute effects of UV on the eyes consist of the development of photokeratitis and photoconjunctivitis, which are unpleasant but usually reversible and easily prevented by appropriate eyewear. Chronic effects on the eye consist of the development of pterygium and squamous cell cancer of the conjunctiva and cataracts. A review of the studies suggests that there is sufficient evidence to link acute ocular exposure to photokeratitis but our knowledge of the effects of chronic exposure is less certain.
While there is sufficient evidence that cortical and posterior subcapsular cataracts (PSC) can be caused by UVB in laboratory animals, there is limited evidence to link cortical and PSC cataracts in humans to chronic ocular exposure to UVB. Figure 4:
Depth of penetration of UV into the eye. Insufficient information is available to separate out the other factors contributing to cataract formation, or to state the proportion of cataracts which can be attributed to UVB exposure. There is also limited evidence to link the development of climatic droplet keratopathy and pterygium, but insufficient evidence to link uveal melanoma with UV exposure.
Environment
Increased levels of UV due to ozone layer depletion may have serious consequences for living organisms. A 10% reduction in ozone could lead to as much as a 15-20%
increase in UV exposure depending on the biological process being considered. While the impact on human health, crop production, fisheries etc. is largely unknown, adverse effects of increased exposure to UVB have been reported on plant growth, photosynthesis and disease resistance. Further, the impact of increased UV levels on aquatic ecosystems (the major contributor to the earth's biomass) may be substantial (see figure 6). Figure 5: Biological food web in a marine ecosystem.
Phytoplankton, at the base of the aquatic food chain, serves as food for larvae of fish and shrimp. These in turn are consumed by fish, which subsequently provide an essential food source for many human beings and other animals. A significant reduction in phytoplankton from increased UVB exposure will directly affect the human and animal marine food source.
