SOURCES OF AIR POLLUTION

Air pollution sources are categorized here in five categories. These are as follows:

• Natural Sources
• Domestic Sources
• Agriculture Sources
• Industrial Sources
• Transportation related sources

1) NATURAL SOURCES

Natural sources of pollutants varied from location to location depending on the seasons, vegetation type, meteorological and geological conditions. Human activities may also influence the conditions and enhance the pollutants emerging from natural sources. For example in dust bowl that occurred in 1930 in southwestern United States, the cultivation for agricultural purposes causes the spread of spores of ragweed plant on the unplanted earth banks at construction sites and alongside the roads. These spores contribute to the hey fever. 

Volcanic eruptions are a source of all the pollutant gases. For example Mount St. Helens eruption occurred in May 18, 1990, emitted almost 4 km3 of solids into the atmosphere. This amount is several orders of magnitude higher than the amount of particles discharged from human activities annually in North America.

The chemical composition and particle size o dust (ash) depends upon its distance from the source. This depicts certain chemicals are concentrated in specific particle size ranges. 

2) DOMESTIC SOURCES

In residential areas the domestic activities are the source of air pollution. Some activities and types of pollutants released from the domestic activities are as follows:

Space Heating released the pollutants such as CO, CO2, SO, NOx, soot and smoke.

Cooking emits the fats (solids, liquids, vapors), particles, odors.

Cleaning emits Solvent vapors, dust, lint and spray.

Gardening produce the pollutants pesticides and fertilizers.

Painting produce principally solvent vapors.

Washing releases the detergent particles, soap particles and lint.

Before industrial revolution domestic fires were the source of pollutant in London, England. Modern domestic furnaces are better but pollutants are still released from low chimneys. 

3) AGRICULTURAL SOURCES

Agricultural sources consist of slaughterhouses and animal feedlot operations. For Example chicken production for meat purpose is done on large scale operations. Hundreds or thousands of birds have to be concentrated at one location. At Pennsylvania State University, the observations showed that the pollutants emitted from ventilation system at small house produces more than 40 % of particles smaller than 5 microns in diameter. These are in the range of respiratory size.

4) INDUSTRIAL SOURCES

Industrial sources are noticed because these are emitted from single stack or duct. 

NOx are produced from high combustion units. Main plants of sources are manufacturing fertilizers and explosives.

SOx are released from combustion of fuel oil and coal at stationary sources. Small amount of SOx are emitted from combustion of gasoline and diesel fuels. 

Hydrogen Sulphide are emitted from paper plants, oil refineries, natural gas cleaning and processing plants. 

Carbon Monoxide are released in the production of cast iron and other metallurgical processes. 

Hydrocarbons are released from petroleum and natural gas industries. Hydrocarbons are also released from plastics manufacturing plants and rubber manufacturing and processing plants. 

5) TRANSPORTATION RELATED SOURCES

The spark ignition engine in automobiles released the carbon monoxide, hydrocarbons and Nitrogen Oxides to the North American atmosphere than all other urban and industrial sources. Most hydrocarbons are emitted from tailpipe. Researchers have found the need of nitrogen oxides emissions reduction to reduce the photochemical smog and acid rain precursor emissions. Lead free gasoline has made necessary because lead ( 3 g per gallon in high octane leaded gasoline) poisons the catalysts in the reactors reducing their effectiveness.

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TYPES OF AIR POLLUTANTS AND THEIR EFFECTS

TYPES OF AIR POLLUTANTS

Primary pollutants are those pollutants that are emitted from known sources.

These are for example:

• SO2
• CO2
• NO
• SOx
• Particulates
• Hydrocarbons
• Metals

Secondary pollutants are those pollutants that are formed through chemical reactions in the atmosphere. 

Examples are:

• O3
• PAN
• Oxidized Hydrocarbons

The pollutants described by USA, EPA and EC are:

• CO
• NO2
• O3
• SO2
• PM-10
• Lead

EFFECTS OF POLLUTANTS

1) HUMAN HEALTH

Health effects are given the major consideration while studying the effects of pollutants. The respiratory system of humans is efficient enough for filtering the large particles in air while breathing. The particles that are smaller than 5 µm penetrate in lungs and make deposits in alveoli. For Instance, cigrette smoke particles size is smaller than 1 µm and they are deposited in the alveoli. Some particles are more damaging because of their capability of absorbing gases. Both gases and materials enhance their effect of damage and they enter in deeper lung pockets and affect gastrointestinal system. Lead like chemicals enter in bloodstream via respirator system or by passing through lung membranes. Tritium like substances enter in bloodstream through skin. 

2) EFFECTS ON PLANTS AND ANIMALS

Not only humans but plants and animals are also affected by pollutants. Fluorine for instance is released from fertilizer,, phosphate, aluminium glass and clay baking operations. Fluorine damages the flowers and fruits. It affects the plants at great degree of magnitude. Even at lower concentrations fluorine affects shrubs, tree and grass which are eaten by cattle or other animals. In animals fluorosis can also be occurred. Poor animal health and their low survival is happened. Other heavy metals like mercury and lead also damage the plants and animals. 

Some plants and animals have the susceptibilities to pollutants.Just like angiosperm phylogeny group can tolerate the high concentration of sulphur dioxide alone but if sulphr dioxide and ozone both are exposed than it can not tolerate.

3) EFFECTS ON MATERIALS

Sulphur and Nitrogen oxides reaction in atmosphere made acidic compounds that attacks the metal surfaces. Fluorine is highly reactive and it causes etching of glass at high concentrations. Hydrogen Sulphide in ambient air reacts with lead oxide in white paint and form the lead sulphide that causes white houses to be turned into brownish tint overnight.

The Shish Mahal at Lahore Fort, Shalimar Gardens, Jahangir Tomb and Data Darbar are badly affected by air pollution. 

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AIR POLLUTION AND TERMINOLOGY INVOLVED IN AIR POLLUTION

INTRODUCTION

Air pollution is defined as the presence of non desirable substances in air in the quantities that are high enough to produce harmful effects.

These non desirable substances cause damage to vegetation, health, property, global environment, aesthetic insults in the form of unpleasant smell of brown or hazy air. Many sources of pollutants in the atmosphere are beyond the control of humans. In most densely populated areas and industrialized countries the main sources of pollution are human activities. These activities are linked with the human living style. Without these activities the standard of living reduced to much lower level. 

Another definition of Air Pollution is:

It is defined as the atmospheric conditions in which certain substances are present in such concentrations that cause harmful effects on man and its environment. These substances are gases, particulates, radioactive materials and others. 

AIR POLLUTANTS

Pollutants are the substances that cause the damage to the target in environment. When these materials are introduced in environment, cause the negative effect on the use of resources.

Air pollutants are categorized as physical, biological, chemical an radioactive materials that make the air unhealthy for breathing. 

1) Primary Pollutants

The pollutants that are directly emitted by terrestrial sources are known as primary pollutants.

Examples of primary pollutants are:

• Carbon Monoxide                         
• Carbon Dioxide
• Sulphur Dioxide
• Ammonia
• Nitric Oxide
• Hydrogen Sulphide
• Nitric Oxide
• Hydrogen Fluoride
• Particulates such as dust, ash, fumes, smoke, radioactive substances and hydrocarbons

2) Secondary Pollutants

From the chemical and photochemical interactions between primary pollutants or atmospheric components secondary pollutants are made.

Examples of secondary pollutants are:

• Sulphur Trioxide
• Nitrogen Dioxide
• Sulphates
• Nitrates
• Ozone
• Aldehydes
• PAN (Peroxy Acyl Nitrate)

Secondary pollutants depends upon topographic and meteorological conditions and nature and concentration of primary pollutants and atmospheric components. 

COMPOSITION OF AIR

                         GAS                 CONCENTRATIONS (%)             

                         

                             Nitrogen                                           78.1  

                               Oxygen                                           20.9

                               Argon                                             0.93

                               Carbon Dioxide                          0.033

                               Krypton                                 0.000114

                               Methane                                    0.0002

                               Hydrogen                                0.00005

                               Xenon                                  0.0000087

                               Nitrous Oxide                       0.30 ppm

                               Neon                                    18.18 ppm

PROPERTIES OF POLLUTANTS AND POLLUTION SIGNIFICANCE

Carbon Monoxide

It is a colorless and odorless gas. It is formed during incomplete combustion of hydrocarbons. It causes greenhouse effect and climate changes.

Nitrogen Dioxide

It is a brown orange colored gas. It is a component of photochemical smog and acid deposition.

Ozone

It is highly reactive. It is a secondary pollutant and is produced during photochemical smog. It damages flora and materials.

Sulphur Dioxide

It is a colorless choking gas, soluble in water and produce sulphuric acid. It is a component of acid deposition and damage the flora and fauna.

Lead

It is a heavy metal and it is a source of leaded petrol. Lead pipes, incineration, quarrying are made of lead. It damages fauna and humans. 

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STRUCTURAL BARRIERS TO DISTRIBUTION OF TOXICANTS

The amount and type of chemical varied among different tissues or organs. This depends upon two factors. One is volume of blood flowing through the specific tissue or organ and the other is barriers that slow down the toxicant entrance. Organs that have high blood supply receives the high percentage of toxicants. 

The concentration of toxicant in a tissue depends upon the tissue affinity for chemicals. These toxicants accumulate in high concentrations inspite of low flow of blood. For instance adipose tissues which have low flow of blood accumulates the high concentration of lipid soluble toxicants. These toxicants remain for long time in tissues due to their solubility in tissues and low blood flow. 

The distribution of toxicants from capillaries to the organs is not even. The structural barriers exist that restrict the entry of toxicant in the organ or tissue. These are e.g. brain, placenta and testes. 

BLOOD- BRAIN BARRIER

The main barrier in human body is blood-brain barrier that restricts the toxicants from entering in the brain. The astrocytes cells consisting of small branches acted as barrier between capillary endothelium and neurons of the brain. Lipids in astrocyte cell wall and tight junctions between adjacent endothelial cells restricts the passage of water soluble molecules. This barrier is not totally non penetateable. It slow down the rate of toxicant passing in the brain tissues and allows the transfer of necessary nutrients such as oxygen. 

Blood Brain Barrier

PLACENTAL BARRIER

The placental barrier protects the developing fetus from toxicants distributed in maternal circulation. This barrier consist of layers of cells between the maternal and fetus circulatory vessels in the placenta. The water soluble toxicants diffusion are inhibited by lipids present in cell membranes. But the waste, nutrients and gases of fetus can pass through placental barrier. It is not totally impenetrable but slow the rate of transfer of toxicants from mother to fetus. 

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EXPOSURE OF TOXICANTS TO HUMANS

INFLUENCE OF ROUTE OF EXPOSURE

The route of exposure is important parameter that affect the concentration of toxicants at any specific location in the blood or lymph of human body. The time exposure and path of toxicant affects the rate of biotransformation, storage and elimination of chemicals. For Example if a chemical first enters in the liver before moving to the other parts of body than it is biotransformed rapidly and the levels of toxicants downstream are eliminated. This affects the potential toxicity.

The toxicants that enter through Gastrointestinal tract are carried by blood via vascular system to the liver. The rare drugs given by intrapertinocal injection also enters through portal system to the liver. Blood from liver flows to the heart and then goes to lungs before moving to the other organs. The toxicants that enter through GI tract or peritonium are subject to biotransformation or excretion by the liver or elimination by lungs. This is known as first pass effect.

The toxicants enter through lungs or skin enter in blood and go directly to heart and systematic circulation. The toxicant then moves to other organs before going to other liver and it is not first pass effect. A toxicant that enter through the lymph of intestinal tract also don not go in  liver first. Instead it is transported in systematic circulation. 

The blood level of toxicant depends on site of absorption and rate of biotransformation and excretion. 

DISPOSITION MODELS

The integration of all the processes such as distribution, biotransformation and elimination is known as Disposition. Disposition models are used to describe how a toxicant moves in the body with time.  These models are also known as Kinetic Models. The types of disposition models are named for the areas of body (compartments) where chemical moves. Examples of compartments are blood, adipose tissue, liver, kidney, bones and brain. 

1) ONE COMPARTMENT OPEN MODEL

It describes the disposition of a material rapidly and consistently in the body at a rate and amount that is proportional to the amount that is left in the body. It is known as first order rate and shown as logarithm of concentration of substance in blood as linear function of time. 

The half life of the chemical is defined as time required for half of the chemical to be lost in the plasma. Few chemicals follow this one compartment open model.

2) TWO COMPARTMENT OPEN MODEL

In this model the chemical first enters in the first compartment which is blood than it enters into second compartment that is any organ from where it can be eliminated or it returns to the first compartment. As the concentration in first compartment decreases, the concentration in the other compartment increases. The concentration in second compartment decreases when the chemicals is excreted from the body. 

The half life of chemical in two compartment open model is known as biological half life. this is the measure for kinetic behavior of a xenobiotic.   

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TROPHIC LEVEL PYRAMIDS AND THEIR TYPES

Trophic level is defined as the position of organism in the food chain. Food chain is a sequence of organisms that eat the other organism and in turn are eaten themselves. At base level are primary producers that are plants, they are eaten by second level herbivores, At third level are predators or 1st level carnivores that eat herbivores. At 4 and 5 level apex predators or carnivores are present. 

TROPHIC PYRAMIDS

Trophic pyramids are the graphical representation designed to show the number, biomass, bio productivity and energy at each trophic level. These pyramids are divided into 3 types: pyramids of biomass, pyramids of numbers and pyramids of energy.

Trophic Pyramids

PYRAMIDS OF NUMBERS

Food webs describes the relation of feeding among the organisms in a community. But these are not quantitative. The first time concept of quantitative study of trophic levels was given by Elton. By studying a wood oak we see increase number of small herbivorous insects such as aphids, good number of small warblers, large number of carnivores ground beetles and spiders and one or two hawks. In same way in a small pond protozoa number goes to million. Daphnia and Cyclops number is in thousands, and few fishes. The animals at the base are comparatively high  and at the end they are fewer. Small herbivores can increase their number They could enhance their number they have margin to increase their number above which they they maintain their population in absence of enemies. This margin supports carnivores that are larger in size but low in numbers. These carnivores further have low margin owing to their large size and make them increase slowly and low in numbers.

Elton in his observation pointed neither producers or decomposers. He pointed the term pyramid of numbers. He found that it is difficult to get actual number of individuals at different stage of food chain. Pyramids of numbers have the units of individuals/area.

PYRAMIDS OF BIOMASS

Ecologists find that some pyramids are inverted due to large size of producers or small size of parasites. So they need to determine pyramids of biomass. 

Pyramids of Biomass are calculated by calculating the biomass of producers, biomass of herbivores, biomass of 1 st level carnivores and so on.

Pyramid of Biomass can never be inverted. The reason behind this are not theoretical. One reason is in case of phytoplankton are source of food for zooplankton. The mass of phytoplankton best supports the large number of zooplankton. The rate of reproduction of phytoplankon is much higher because of its small size. The turnover of phytoplankton is much higher than the turnover of zooplankton. Pyramids of biomass have the units of mass/area.

PYRAMID OF ENERGY

The flow of energy from one trophic level to the other is described by the Pyramid of Energy. 

The units are energy/area/time, e.g. kJ/ha/yr. It shows the rate of flow of energy in food web. Pyramids of Energy can not be inverted because it follows the first law of thermodynamics that states  energy is neither created nor destroyed and it is always conserved. 

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URBAN PROBLEMS FACED BY THE DEVELOPED WORLD

The rapid growth of  most developed countries in 19th an 20th centuries such as Europe and North America is now slowing down. For Example, London population in 1939 was 8.6 million which has been dropped now to a 6.7  million people. Almost 2 million people have been lost. The large areas surrounding the London have many of residents  but the city of London itself now remained 12th largest city in the world. 

Now the environmental problems in developed countries have been reduced frequently. Sanitation and medical care have been improved to much extent. Air and water quality have been improved intensely as the industries such as steel smelting and chemical manufacturing have been moved to the developing countries. The people in field of consumer and information economies now have no need to be gathered in central cities as they can do this in any of the city. Now the working class also has access to recreation, enjoy the yards and single family homes by vehicles just like elite class.

Due to the shift of industries to the developing countries people also moved from the areas to the developing countries because to get employment sources. For Example, in US old cities Philadelphia and Detroit have now less population because of demographic shift due to business and industrial shift. Some growing metropolitan areas are Colorado, Texas, Arizona, Phoenix, California, Austin and San Jose.

Urban Sprawl

Where the movement of the people towards suburbs and rural areas provide the benefit to the citizens, there many urban problems also have raised. Due to the compact nature of cities people start moving toward landscape, consuming open spaces and wasting the resources. This pattern of growth is known as sprawl.

A former Maryland Governor Parris N. Glendening  said that:

"In its path, sprawl consumes thousands of acres of forests and farmlands, woodlands and wet lands. It requires government to spend millions extra to build new schools, streets, water and sewer lines."

Christine Todd Whitman, governor of New Jersey and head of Environmental Protection Agency said that:

"Sprawl eats up our open space. It creates traffic jams that boggle the mind and pollute the air. Sprawl can make one feel downright claustrophobic about our future."

The U.S. Development of Housing and Urban Development predicted that due to urban sprawl every year 200,000 ha of farmland is consumed. The cities also live on fertile river valleys and shorelines. That land is useful for crops production for local communities. 

Landowners, builders claim that growth provide benefit to suburbs in which they live. They said that increase number of residents decreases the taxes on everyone. but the opposite is true. 

Sprawl causes the problems in central cities from where the inhabitants and business have moved out. The city is not able to maintain the infrastructure with less tax base and less number of civic leaders working in downstream areas. It is bad for health. By promoting driving and not the walking many health problems just as diabetes, heart attack occurs. 

The alternative of urban sprawl is smart growth. The smart growth is characterized by effective and efficient land resources and present infrastructure. Smart Growth purpose is to give mix land uses to promote affordable housing choices and opportunities. It also provides choices of transportation entertaining pedestrian friendly neighborhoods. 

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