Air Pollution-I

Air pollution is a change in the physical, chemical and biological characteristic of air that causes adverse effects on humans and other organisms. The ultimate result is a change in the natural environment and/or ecosystem.

The substances that are responsible for causing air pollution are called air pollutants. These air pollutants can be either natural (e.g. wildfires) or synthetic (man-made); they may be in the form of gas, liquid or solid.

Types of Air Pollutants:

An air pollutant is known as a substance in the air that can cause harm to humans and the environment. Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition, they may be natural or man-made. Pollutants can be classified as either primary or secondary. Usually, primary pollutants are substances directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulphur dioxide released from factories.

Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground-level ozone — one of the many secondary pollutants that make up photochemical smog.

 Sources of Air Pollution:

Sources of air pollution refer to the various locations, activities or factors which are responsible for the releasing of pollutants in the atmosphere. These sources can be classified into two major categories which are:

Anthropogenic sources (human activity) :

• “Stationary Sources” include smoke stacks of power plants, manufacturing facilities (factories) and waste incinerators, as well as furnaces and other types of fuel-burning heating devices.
• Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.
• Waste deposition in landfills, which generate methane. Methane is not toxic; however, it is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiate and may displace oxygen in an enclosed space.
• Military, such as nuclear weapons, toxic gases, germ warfare and rocketry.
• “Mobile Sources” include motor vehicles, marine vessels, aircraft and the effect of sound etc.
  

  Natural sources: 

• Dust from natural sources, usually large areas of land with little or no vegetation.

• Methane, emitted by the digestion of food by animals, for example, cattle.
• Radon gas from radioactive decay within the Earth’s crust. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking.
• Smoke and carbon monoxide from wildfires.
• Volcanic activity, which produces sulphur, chlorine, and ash particulates.

Major Air Pollutants:

1. Sulphur oxides (SO_x): SO₂ is produced mainly by volcanoes and by burning of fossil fuels. Since coal and petroleum often contain sulphur compounds, their combustion generates sulphur dioxide. It is also produced from various industrial processes like mining and smelting of sulphide ores. Further oxidation of SO₂, usually in the presence of a catalyst such as NO₂, forms H₂SO₄, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources. It causes respiratory problems, severe headache, reduced productivity of plants, yellowing and reduced storage time for the paper, yellowing and damage to limestone and marble, damage to leather, increased rate of corrosion of iron, steel, zinc and aluminium.
2. Nitrogen oxides (NO_x) and Nitrous oxides:  Nitrogen dioxides are emitted from high-temperature combustion, automobile exhausts, burning of fossil fuels, forest fires, electric generation plants, smelting plants, industrial boilers, petroleum refineries and volcanic eruptions.  This air pollutant forms ozone at the ground level upon reacting with other pollutants. Presence of NOx in the atmosphere causes acid rain. It also helps in eutrophication of the lakes and ponds. It forms photochemical smog,  at higher concentrations, causes leaf damage or affects the photosynthetic activities of plants and causes respiratory problems in mammals. Use of catalytic converters at the exhaust reduces the emission of oxides of nitrogen.
3.  Carbon monoxide: It is a colourless, odourless, non-irritating but very poisonous gas. It is a product of incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide. When we let a car engine run in a closed room, CO concentration in the air will rise extensively. it contributes to the greenhouse effect, smog and acidification. the gas can bind to haemoglobin in the blood, preventing oxygen transport to the body. this results in oxygen depletion of the heart, brains and blood vessels, eventually causing death. this gas is highly toxic and poisonous in large quantities. It is a better practice to oxidise CO to CO₂before releasing it into the atmosphere. CO forms naturally in the atmosphere, in the troposphere due to photochemical reactions. Other natural sources are volcanic eruptions, forest fires and combustion. Burning of a stove in a smaller room may pollute the room air with CO as in the closed space the supply of natural air is less.
4. Carbon dioxide (CO₂): A greenhouse gas emitted from combustion but is also a gas vital to living organisms. It is natural gas in the atmosphere but in excess, it contributes to global warming.
5. Volatile organic compounds: VOCs are an important outdoor air pollutant having a range of different contaminants. In this field, they are often divided into separate categories of methane (CH₄) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming.Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukaemia through prolonged exposure. 1, 3-butadiene is another dangerous compound which is often associated with industrial uses.
6. Chlorofluorocarbons (CFCs) – it is an organic compound containing carbon, chlorine and fluorine. they are also known by the DuPont trade name-Freon.  Many CFC s are used as refrigerants,, propellants and solvents. They are harmful to the ozone layer emitted from products currently banned from use. CFCs destroy the ozone layer which then permits harmful UV rays to enter the atmosphere. The ozone layer protects the earth from the ultraviolet rays sent down by the sun. If the ozone layer is depleted by human action, the effects on the planet could be catastrophic.
7.  Ammonia (NH₃) – The continuous release of ammonia from the sources is highly unlikely, but occasional high release or spillage may cause injury to plants and human beings. The extent of injury reduces rapidly with increase in distance from the source. Ammonia is mainly emitted from agricultural activities.  A reduction in livestock numbers, proper management of organic manures and the decreased use of nitrogenous fertilizers may reduce ammonia emission. It is normally encountered as a gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous. ammonia contributes to acid deposition and eutrophication. the subsequent impact of acidification can be on the aquatic ecosystem, lakes and rivers, damage to forests, crops and other vegetations. Eutrophication can lead to bad water quality, decreased biodiversity, changes in species composition and toxicity effects.These are few but the most common air pollutants which are hazardous for plants, animals and human beings. Air is the most essential element for our survival but it seems it has become a garbage bin. Factories are growing like weeds, the sky is choking with smokes and ash, the air is filled with dust, more surprisingly, more than 3000 unwanted compounds are polluting the very basic components of air. Pollutants may cause primary damage, with direct identifiable impact on the environment, or secondary damage in the form of minor perturbations in the delicate balance of the food web that are detectable only over long time periods.An analysis done on the global level revealed a diversification and increasing concentrations are in strict correlation with industrialization and the increasing amount of fossil fuel consumption. Earlier, the air pollution was confined to bigger cities but now, it is spreading across the globe. The air does not obey any boundary, it just sails through the cities after cities. The global phenomenon of air pollution should be managed sincerely when the solutions are known to all of us. Reduce emissions from every source, stop illegal mining, implement the rule strictly, reduce the use of vehicles, encourage people to rely on renewable energy sources and so many more things can be done. Cheating on nature is cheating ourselves. The sooner we realise the better become the living.