Country’s pollution watchdog, CPCB has published air quality indices (AQI) for 24 cities,report says Delhi  is not India’s most polluted city, perhaps not even the second worst. But Central Pollution Control Board’s (CPCB) data for the September 2015-January 2016 period clearly shows that Delhi’s air is far from healthy.

India has set standards for what it thinks are appropriate warnings for a particular level of pollutant.  AQI help in comparing pollution levels at a glance with a colour code and a numerical value. In India, AQIs are determined based on the concentrations of seven pollutants, including PM2.5 (fine, respirable particles), sulphur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO).

There are six AQI categories, namely: Good, Satisfactory, Moderately polluted, Poor, Very poor and Severe. Good air quality days mean minimal health impact. But, on moderately-polluted days, it may cause breathing discomfort in those suffering from lung or heart diseases. On severely-polluted days, pollution may cause respiratory effects even in healthy people and serious health impact in people with lung disease.

The Index is centred around five chief pollutants – Particulate Matter with a diameter less than 10 micrometres (PM10), Particulate Matter with a diameter of less than 2.5 micrometers (PM2.5), ozone (O3), Nitrogen Dioxide (NO2), and Carbon Monoxide (CO). A monitoring station should be able to give you the concentration of a particular pollutant at that moment in time, and its average over a period of time – for CO and O3, the average is taken over eight hours, while for the other three, it is a 24-hour average. The unit of measurement is microgram (or milligram in the case of CO) per cubic meter.

                Carbon monoxide is a gas and is found in air. High levels of carbon monoxide are poisonous to humans and, unfortunately, it cannot be detected by humans as it has no taste or smell and cannot be seen.. Natural sources of carbon monoxide include volcanoes and bushfires.The main sources of additional carbon monoxide are motor vehicle exhaust and some industrial activities, such as making steel. Tobacco smoke is one of the main indoor sources of carbon monoxide. Increased levels of carbon monoxide reduce the amount of oxygen carried by haemoglobin around the body in red blood cells. The result is that vital organs, such as the brain, nervous tissues and the heart, do not receive enough oxygen to work properly.

              Nitrogen dioxide is a nasty-smelling gas. Some nitrogen dioxide is formed naturally in the atmosphere by lightning and some is produced by plants, soil and water. However, only about 1% of the total amount of nitrogen dioxide found in our cities’ air is formed this way. Nitrogen dioxide is an important air pollutant because it contributes to the formation of photochemical smog, which can have significant impacts on human health. The main effect of breathing in raised levels of nitrogen dioxide is the increased likelihood of respiratory problems. Nitrogen dioxide inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis, asthma.

                 Sulfur dioxide is a gas. It is invisible and has a nasty, sharp smell. It reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.About 99% of the sulfur dioxide in air comes from human sources. The main source of sulfur dioxide in the air is industrial activity that processes materials that contain sulfur, eg the generation of electricity from coal, oil or gas that contains sulfur. Sulfur dioxide is also present in motor vehicle emissions, as the result of fuel combustion. Sulfur dioxide affects human health when it is breathed in. It irritates the nose, throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the chest. The effects of sulfur dioxide are felt very quickly and most people would feel the worst symptoms in 10 or 15 minutes after breathing it in.

Airborne particles are sometimes referred to as ‘particulate matter’ or ‘PM’. They include dust, dirt, soot, smoke, and liquid droplets. Some particles are large enough or dark enough to be seen as soot or smoke, while others are so small they can only be detected individually with a microscope. Some particles are emitted directly into the air from a variety of sources that are either natural or related to human activity. Natural sources include bushfires, dust storms, pollens and sea spray. Those related to human activity include motor vehicle emissions, industrial processes (eg electricity generation, incinerators and stone crushing), unpaved roads and woodheaters. Particles can be classified on the basis of their size, referred to as their ‘aerodynamic diameter’. ‘Coarse particles’ are those between 10 and 2.5 micrometres (µm) in diameter; ‘fine particles’ are smaller than 2.5 µm; and ‘ultrafine particles’ are smaller than 0.1 µm. For comparison, the diameter of a human hair is 70 µm and this is seven times the diameter of the largest ‘coarse particles’. Studies have linked exposure to particle pollution to a number of health problems including respiratory illnesses (such as asthma and bronchitis) and cardiovascular disease. In addition, the chemical components of some particles, particularly combustion products, have been shown to cause cancer. These effects are often more pronounced for vulnerable groups, such as the very young and the elderly. Particle pollution is the major cause of reduced visibility. This can be a serious safety issue on roads and in traffic tunnels and can also affect our enjoyment of the natural landscape.

 Lead (or Pb in the periodic table) is a naturally occurring heavy metal that is found in the Earth’s crust. Lead can be released into soil, air and water through soil erosion, volcanic eruptions, sea spray and bushfires;Mining and metal manufacturing ;waste incinerators; battery recycling; the production of lead fishing sinkers; cement, plaster and concrete manufacturing; ceramic products such as garden pots; iron and steel; petroleum and coal products; paper, glass and metal products; motor vehicles and their parts; wood products; and yarn and fabric for making clothes and curtains. Lead is a health hazard. It is stored in your bones and teeth, and may damage parts of your body, including your liver, kidneys and brain. Exposure to lead can affect the health of children, unborn babies and adults. Once in the body, lead circulates in the blood. The amount of lead in a person’s blood gives an indication of how much lead has recently been breathed in or swallowed.

                  Ozone is one of the main photochemical oxidants.Photochemical oxidants are formed when sunlight falls on a mixture of chemicals in the air. Other chemicals such as formaldehyde are also found and, like ozone, have adverse health effects. Environment agencies measure the level of ozone because it indicates the total amount of photochemical oxidants in the air. Cities that have abundant sunshine over periods of time, together with moderate winds and high temperatures, are most likely to experience high levels of photochemical oxidants. Ozone is a gas that is formed when nitrogen oxides react with a group of air pollutants known as ‘reactive organic substances’ in the presence of sunlight. The chemicals that react to form ozone come from sources such as: motor vehicle exhaust, oil refining, printing, petrochemicals, lawn mowing, aviation, bushfires and burning off. Motor vehicle exhaust fumes produce as much as 70% of the nitrogen oxides and 50% of the organic chemicals that form ozone.Ozone can irritate the lining of the nose, airways and lungs. People who are exposed to enough ozone might feel some pain in their ears, eyes, nose and throat, and they might start to cough. Chest pains can also occur in some people. People with asthma might have more attacks and athletes might find it harder to perform as well as usual.

Air pollution, several divisions can be made. Primarily air pollutants can be caused by primary sources or secondary sources. The pollutants that are a direct result of the process can be called primary pollutants. A classic example of a primary pollutant would be the sulfur-dioxide emitted from factories

Secondary pollutants are the ones that are caused by the inter mingling and reactions of primary pollutants.

 Air pollution is caused by:

Burning of Fossil Fuels: improper or incomplete combustion and generally emittes Sulfur dioxide, Carbon Monooxide and Nitrogen Oxides. .

Agricultural activities:produce Ammonia( hazardous gases) and  Use of insecticides, pesticides and fertilizers in agricultural  emit harmful chemicals into the air and can also cause water pollution.

Exhaust from factories and industries: Manufacturing industries release large amount of carbon monoxide, hydrocarbons, organic compounds, and chemicals into the air thereby depleting the quality of air. Petroleum refineries also release hydrocarbons and various other chemicals that pollute the air and also cause land pollution.

4. Mining operations: . During the process dust and chemicals are released in the air causing massive air pollution. This is one of the reason which is responsible for the deteriorating health conditions of workers and nearby residents.

5. Indoor air pollution: Household cleaning products, painting supplies emit toxic chemicals in the air and cause air pollution.Suspended particulate matter popular by its acronym SPM, is another cause of pollution. Referring to the particles afloat in the air, SPM is usually caused by dust, combustion etc.

AIR POLLUTION RESULTS IN:

Respiratory and heart problems: The effects of Air pollution are alarming. They are known to create several respiratory and heart conditions along with Cancer, among other threats to the body. Children in areas exposed to air pollutants are said to commonly suffer from pneumonia and asthma.

2. Global warming: Another direct effect is the immediate alterations that the world is witnessing due to Global warming. With increased temperatures world wide, increase in sea levels and melting of ice from colder regions and icebergs, displacement and loss of habitat

Acid Rain: Harmful gases like nitrogen oxides and sulfur oxides are released into the atmosphere during the burning of fossil fuels. When it rains, the water droplets combines with these air pollutants, becomes acidic and then falls on the ground in the form of acid rain. Acid rain can cause great damage to human, animals and crops.

4. Eutrophication: Eutrophication is a condition where high amount of nitrogen present in some pollutants gets developed on sea’s surface and turns itself into algae and and adversely affect fish, plants and animal species. The green colored algae that is present on lakes and ponds is due to presence of this chemical only.

5. Effect on Wildlife: Just like humans, animals also face some devastating affects of air pollution. Toxic chemicals present in the air can force wildlife species to move to new place and change their habitat. The toxic pollutants deposit over the surface of the water and can also affect sea animals.

6. Depletion of Ozone layer: Ozone exists in earth’s stratosphere and is responsible for protecting humans from harmful ultraviolet (UV) rays. Earth’s ozone layer is depleting due to the presence of chlorofluorocarbons, hydro chlorofluorocarbons in the atmosphere. As ozone layer will go thin, it will emit harmful rays back on earth and can cause skin and eye related problems. UV rays also have the capability to affect crops.

TO REDUCE AIR POLLUTION:
Use public mode of transportation: Encourage people to use more and more public modes of transportation to reduce pollution. Also, try to make use of car pooling; implementing national fuel quality standards and supporting the implementation of tighter vehicle emission standards

2. Conserve energy: Switch off fans and lights when you are going out. Large amount of fossil fuels are burnt to produce electricity. One can save the environment from degradation by reducing the amount of fossil fuels to be burned.

3. Understand the concept of Reduce, Reuse and Recycle: Do not throw away items that are of no use to you. In-fact reuse them for some other purpose. For e.g. you can use old jars to store cereals or pulses.

4. Emphasis on clean energy resources: Clean energy technologies like solar, wind and geothermal are on high these days. This will go a long way to curb air pollution.

5. Use energy efficient devices: CFL lights consume less electricity as against their counterparts. They live longer, consume less electricity, lower electricity bills and also help you to reduce pollution by consuming less energy.