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Atmospheric Pollution
Pollutants in the atmosphere behave differently than they do in water or in the ground.
Pollutants are influenced by the media and element in which they are found. The Atmosphere (Air) influences chemical, physical and biological reactions and characteristics, as well as behaviour patterns of pollutants.
Pollutants in the atmosphere are more mobile, and move rapidly, as well as cover large areas when transported by winds. Pollutants in the Atmosphere will interact Electromagnetic Radiation from the Sun. This will be lead to photochemical reactions. Pollutants in the atmosphere also interact with Infra Red energy radiating from Earth.
Acid Rain
Rain is naturally slightly acidic. To be more specific, the "natural" average part per Hydrogen (pH) of rain is of 5.6 pH.
Naturally Carbon Dioxide (CO2) dissolves, as result a dilute called Carbonic Acid is produced. Carbonic Acid is a weak acid, however this Oxidation process may be taken on by other gases resulting in stronger (higher pH) acid, and causing Acid Rain.
If rain has a pH higher than 5.6 it is called Acid Rain.
The main gases responsible for Acid Rain, are; Sulphur Dioxide (SO2), Sulphur Trioxide (SO3), Oxides of Nitrogen, and Ozone. In all the chemical reactions which cause or create acid rain, atoms of Oxygen are involved, the processes are generally Oxidation processes, which can be increasingly retroactive or active mechanism.
Examples of these processes are:
Sulphur Dioxide (SO2) dilutes and results in Sulphuric Acid (weak acid). Sources of Sulphur Dioxide: Burning Coal and Burning Oil.
Sulphur Trioxide (SO3) dilutes and results in Sulphuric Acid (strong acid). Sources of Sulphur Trioxide: Burning Coal and Burning Oil.
Oxides of Nitrogen (N)+(O) dilute and results in Nitric Acid (strong acid). Sources: Vehicle Exhaust, power stations emissions.
Tropospheric Ozone (O3) dilutes to Oxides Sulphur dioxide resulting in SO3 (strong acid). Source: Photochemical reactions involving oxides of Nitrogen and Oxygen.
Acid Rain: The Effects
On the Non-living (abiotic)
Acid deposition can corrode metals causing damage to infrastructure, and buildings. Examples of damages are: Railways, water pipes, overhead power lines, Limestone in Buildings which can be damages by acid when surface layers are exposed to it they may dissolve.
Effects of Acid Rain on Living organisms
The effects can be Direct, or Indirect. When the effects are Direct the toxic present in acid cause damage (change or alterations with negative consequences) on living organisms.
When the effects of Acid Rain are indirect they cause harmful environmental changes.
In the Direct Effects of Acid Rain the toxins affect the living organisms. They will denature the proteins in cell membranes and can inhibit enzyme action.
Tissues and organisms which are particularly sensible to acid damage are:
Cells inside leaf stomata
Plant root hairs
Germinating Seeds
Fish eggs and fish gills
Invertebrates with exoskeletons may die as the acids dissolve the calcium compound that form the exoskeletons.
Lichens are also very sensible to acid rain. They serve as Biotic Index as their size, state of health, abundance and diversity will be an accurate indicator to estimate acid rain and pollution.
Some of the living organisms affected by acid rains are keystone species, essential for the survival and overall health of the entire habitat. If a keystone specie is threatened the entire food web and processes of the elements of life that depend on it will be endangered.
Examples are: Insects, corals and certain plants.
Biotic Index is a measure of pollution based on the presence, abundance, state of health and diversity of a selected organisms. Pollution Biotic Index will give an indication of the amount of pollution in a system.
Indirect Effects of Acid Rain
When the acidity changes the solubility of many ions -including metals- become more soluble. Loss of ions from soils and mobilisations of toxic ions as a consequences are the dangers.
In Plant Nutrients the Calcium (CA 2+) and Magnesium (MG 2+) are lost first.
Once these are gone other ions are mobilised. Examples of newly mobilised ions as a result of the indirect effect of Acid Rain are: Aluminium (Al 3+) and Lead (Pb +).
Toxic ions inhibit enzyme actions affecting the health of roots, soil, aquatic organisms, rivers and lakes, as well as human health.
For example: Aluminium is associated with Alzheimer’s Disease.
Tropospheric Ozone
Ozone (O3) is toxic to plants and reduces the rate of trees and crops.
In Humans levels of Ozone may cause difficulty in breathing and increase rates of asthma. The normal concentration of Ozone is of 20-60 ppbv. At 120 ppbv breathing become difficult. Polluted cities may sometimes reach these levels- Ozone can be fatal if present in 1,0000 ppbv (1 ppbv).
Sources of Tropospheric Ozone
Tropospheric Ozone is a secondary pollutant produced by the chemical reactions which involve primary pollutants.
They are directly linked to human activity.
The most common reaction is:
NO2 ---------UV-A--------------- NO + O + O2--------------- O3
Nitrogen Dioxide plus Light results in Nitrogen monoxide plus Oxygen Monatomic plus Oxygen Diatomic results in Ozone Triatomic Oxygen
Control of Tropospheric Ozone
Note: The difference between Ozone present in the Stratosphere and Ozone present in the Troposphere is of great importance.
Tropospheric Ozone (O3) is as mentioned secondary pollutant. The only possible way of controlling this pollutant is by reducing the levels of primary pollutants.
An example of these pollutants is: NO2 from vehicles and power stations emissions.
Reduction of Stratospheric Ozone (O3) alters the UV-A (Sun Radiation) which reach the Tropospheric Ozone (O3). This UV-A is the power which drives the photochemical reactions.
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