Air Pollution

Air pollution can be defined as the mixing of harmful gases or chemical substances in the air, that results into harmful effects on flora as well as fauna. The major pollutants of air pollution includes the harmful untreated gases that are released into the atmosphere from factories, also the carbon monoxide gas released from the burnt fuel in the automobiles. Sometimes the leakage of radioactive substance also led to adverse effects on living organism.

Burning of fossil fuels leads to their combustion causing the release of carbon dies oxide in air. It also releases other harmful gases that cause air pollution. So, option B " Automobile exhausts and industrial wastes" is the correct answer.

The air around us has various types of unwanted suspended particles like- smoke, dust, pollens etc. When we inhale these particles get trapped in the hair present in our nasal cavity. However, sometimes these particles may get past the hair present in our nasal cavity. Then they irritate the lining of the cavity as a result of which we sneeze. Sneezing expels these foreign particles from the inhaled air and a dust-free, clean air enters our body. 

Air pollution is due to various substances that holds the potential to hinder the atmosphere or the well  being of the living beings surviving in it. The sustainment of all things living is due to a combination of gases  that collectively form the atmosphere; the imbalance caused by the increase or decrease of the percentage  of these gases can be harmful for survival. All the above mentioned a, b & c points are the cause of air  pollution.

The use of excessive chemical fertilizers and pesticides results in the water pollution and soil pollution. The construction of the housing estates results in air pollution. The quarrying of the limestone also results in the release of the particles causing air pollution. The increase in the forest reserves does not result in any kind of pollution. 

Hydrogen sulphide is a known irritant to the mucous membranes of the respiratory tract and eyes. While other gases listed are pollutants, hydrogen sulphide is specifically noted for this physiological effect.

Automobiles are a major source of air pollution due to the combustion of fossil fuels, which releases carbon monoxide, nitrogen oxides, and particulate matter. Pesticides and sewage are primarily associated with land and water pollution.

• Compressed natural gas (CNG) (methane stored at high pressure) is a fuel which can be used in place of gasoline, diesel fuel, and propane/LPG. CNG combustion produces fewer undesirable gases than gasoline.
• Hence In Delhi, CNG vehicles are used to control air pollution.
• So, the correct answer is 'CNG vehicles'.

Aerosols are the minute particles that are released with the pressure and remain suspended in the air. These can be sold particles or liquid droplets. The natural aerosols appear in the form of the fog, dust, forest exudates, geyser steams etc. The anthropogenic aerosols are more harmful and persist for the longer duration, like smoke, particulate matter etc. The emission from the jets comprises mainly of the fluorocarbons that are emitted with an immense pressure to provide propulsion to the engine.

Hydroelectric power is the cleanest form of electricity generation without contributing to the air pollution as it does not require the burning of fuel for working and water is provided by a natural force and moreover, it is renewable by rainfall causing refilling of reservoir. The dams are built which provide storage and it helps in reducing greenhouse gases emissions apart from the fact that once it becomes operative these have a low maintenance cost.

Electrostatic precipitators use the principle of electrically charging particles in an exhaust and then allowing them to settle on variably charged platforms. It is done primarily for control of SPM or suspended particulate matter such as dust, fumes, smoke etc.

PM or particulate matter of diameter $2.5\,\,\mu$m or less is the most harmful as they are inhaled deep into the lungs causing serious lung damages, deposition in respiratory tracts and even death of the person.

Forests act as natural filters for air pollution, as trees and leaves capture particulate matter and absorb various gaseous pollutants from the atmosphere.

The aircraft or jet planes engine emit certain particles and gases like carbon dioxide, hydrocarbons, nitrogen oxides, lead, black carbon, aerosols etc. These are basically greenhouse gases and anthropogenic compounds which have the tendency to react among themselves and with gases present in the atmosphere. Greenhouse effect, ozone depletion activities can be related to the emission of these gases.