Sunday, December 20, 2009

Air Pollution

The quality of human life is directly related to the quality of the environment. Air pollution is a major environmental health problem affecting everyone. Air pollution is defined as the unwanted introduction of particulates, gases and aerosols into the lower atmosphere. Air pollution is generally most widespread and some air pollutants are poisonous. Air pollution increases the risk of respiratory and heart disease in the population.

Sources of air pollution

Natural sources - volcanoes, fumaroles and hot springs, decay from marshes, bogs
Stationary sources - those that are fixed in location.
Point sources -e.g. smoke stacks, 14% air pollution from plants generating electricity;
Fugitive sources -e.g. construction sites, exposed areas;
Area sources- e.g. dense urban community or agricultural area
Mobile sources - those that move while polluting, e.g. trucks, cars, buses etc. 60% of air pollution from motor vehicles. 80-88% in major cities.

Kinds of air pollutants

Primary pollutants  - Pollutants that are emitted directly from identifiable sources –produced by both natural events or human activities e.g. sulfur dioxide (SO2), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2)
Secondary Pollutants: those that form as a result of a chemical reaction of the primary pollutant with a natural component of the environment.; e.g. some ozone, sulfuric and nitric acids.
Air pollution reduces visual range and atmospheric clarity, less contrast, less visibility. Air pollutants  damage  vegetation, including leaves, needles, fruit, growth rate, reproduction, hardiness. Air pollution  is responsible for decline in net primary productivity NPP. There is degradation of human health, from mild problems e.g. eye irritation, to severe e.g. respiratory disease asthma, bronchitis, emphysema, cancer. CO, carbon monoxide combines with hemoglobin and reduces bloods ability to carry oxygen. 150,000-350,000 deaths/yr.  Air pollution degrades  animal health with impacts on respiration, bones, teeth, reproduction; increase lake acidity, decline in NPP. When air pollutants settle, they cause  degradation of soil and water. Air pollution cause deterioration of man-made structures, break down car paint, roofing; acid rain chemically dissolves marble statues and other building materials

Human –induced greenhouse effect and global warming

Greenhouse gases  (GHGs)
Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occuring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Carbon dioxide is a product of burning fossil fuels and wood. Nitrous oxide (NO2), produced by fertilizer use and released from decomposition of animal wastes. Methane (CH4) is produced by bacteria from sediments, swamps, and in flooded rice paddies.Chlorofluorocarbons (CFCs), Freon (a refrigerant) deplete the ozone layer in the upper atmosphere. Halons, such as halocarbons), are released from fire extinguishers. Water vapor in clouds reradiate heat back to Earth.
Carbon dioxide and other gases allow light to pass, but trap heat in the atmosphere much like glass in a greenhouse traps heat. This greenhouse effect is thought to be responsible for global warming. Carbon dioxide contributes to only 56% of greenhouse heating. The average surface temperature of Earth is about 15°C (59°F). Global Warming is increase in the average temperature of the atmosphere, oceans, and landmasses of Earth. Global temperatures may increase by 3oC-4oC by the end of the next century .

Impact of Global warming

n  Temperature extremes 
n  Rise in sea level, and change in precipitation
n  Injuries from storms, coastal flooding 
n  Interruption of power supply, contamination of drinking water 
n  Drought 
n  Food shortages due to shift in agricultural food production 
n  Air pollution ( made worse by warming) 
n  Asthma, bronchitis, emphysema complications 
n  Strain on public health systems 
n  Increased need due to population migrations 
n  Unable to contain spread of infectious diseases 

The Ozone Layer

Earth's atmosphere consists of a number of different layers. The troposphere is the lower atmospheric layer. The stratosphere is often referred to as the upper atmosphere. The stratosphere contains the ozone shield, a layer of ozone (O3) in the stratosphere, 50 km above the ground. Ozone (Greek ozein, “to smell”), pale blue, highly poisonous gas with a strong odor. Ozone is considered a pollutant at ground level. Breathing O3 affects both the respiratory and nervous systems, resulting in respiratory distress, headache, and exhaustion. Ozone is damaging to plants, resulting in leaf mottling and reduced growth.
Health effects of Ozone depletion
Each 1% drop in ozone is thought to increase human skin cancer rates by 4-6%. The United Nations Environment Program predicts a 26 percent rise in cataracts and non-melanoma skin cancers for every 10% drop in ozone. This translates to 1.75 million cases of cataracts and 300,000 more cases of skin cancer every year.
Ozone Hole  above Antarctica
During the 1980s scientists discovered a "hole" in the ozone over Antarctica. The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33% of their pre-1975 values. By the 1990s atmospheric scientists had detected an annual loss of 40-50% of the ozone above Antarctica, which produced an ozone hole every spring. One CFC molecule can destroy 100,000 ozone molecules.
Acid precipitation  (acid rain)
The term "acid rain" is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. The more accurate term is "acid precipitation.“ "Clean" or unpolluted rain is slightly acidic, its pH being about 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid.
H2O  + CO2  → H2CO3 (aq)
The extra acidity in rain comes from the reaction of primary air pollutants, primarily sulfur oxides and nitrogen oxides, with water in the air to form strong acids (like sulfuric and nitric acid). The main sources of these pollutants are vehicles and industrial and power-generating plants. Nitric oxide & sulfur dioxide released primarily from electric power plants & motor vehicles
SO2 + water vapor + ozone ---> H2SO4
NO + sunlight + O2 ---> NO2 + various atmospheric gases ---> HNO3
Environmental Impact of Acid deposition
n  Sterilization of lakes and forests.
n  Reducing the populations of small invertebrates and decomposers.
n  Reducing agricultural yields.
n  Causing extensive structural damage by corroding marble, metal, and stonework.
n  Degrading water supplies by leaching heavy metals from the soil into drinking-water supplies.
n  Increases in lung cancer and colon cancer.

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