JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV AIR POLLUTION Previous Question Paper (July/August - 2022 - R18)

Air pollutants are substances in the atmosphere that can be harmful to human health and the environment. They are broadly classified into two categories: primary and secondary pollutants.

• Primary Air Pollutants: These are emitted directly from a source into the atmosphere. They are the initial substances released. Examples include:
  • Carbon Monoxide (CO): A colorless, odorless gas produced by incomplete combustion of carbon-containing fuels, such as in vehicle engines and industrial processes.
  • Sulfur Dioxide (SO₂): A pungent gas released from the burning of fossil fuels (especially coal and oil) containing sulfur, and from industrial processes like smelting.
  • Nitrogen Oxides (NOx): Primarily nitric oxide (NO) and nitrogen dioxide (NO₂), formed during high-temperature combustion processes in vehicles and power plants.
  • Particulate Matter (PM): Tiny solid particles or liquid droplets suspended in the air, originating from combustion, industrial activities, and natural sources like dust storms.
  • Volatile Organic Compounds (VOCs): Organic chemicals that easily evaporate at room temperature, emitted from sources like paints, solvents, gasoline, and industrial emissions.
  • Lead (Pb): A heavy metal historically emitted from leaded gasoline, and still present in some industrial processes.
• Secondary Air Pollutants: These are not emitted directly but are formed in the atmosphere through chemical reactions involving primary pollutants and other atmospheric constituents (like sunlight, water vapor, and oxygen). Examples include:
  • Ozone (O₃): Ground-level ozone, a major component of smog, is formed when NOx and VOCs react in the presence of sunlight. Stratospheric ozone, however, is beneficial.
  • Sulfuric Acid (H₂SO₄): Formed when SO₂ reacts with water and oxygen in the atmosphere, contributing to acid rain.
  • Nitric Acid (HNO₃): Formed when NOx reacts with hydroxyl radicals and water vapor, also contributing to acid rain.
  • Peroxyacetyl Nitrates (PANs): Formed from the photochemical reactions of NOx and VOCs, contributing to smog and eye irritation.
  • Secondary Particulate Matter: Formed from the condensation of gaseous pollutants like SO₂ and NOx, or through chemical reactions in the atmosphere.

The distinction between primary and secondary pollutants is crucial for understanding atmospheric chemistry and developing effective control strategies.

Sources of air pollution are typically categorized based on their mobility. They can be either stationary (fixed in location) or mobile (capable of moving).

• Stationary Sources: These are fixed facilities or locations from which pollutants are emitted. They can be further subdivided into point sources and area sources.
  • Point Sources: These are single, identifiable sources of emission, such as a smokestack from a power plant, a factory chimney, or an industrial furnace. They are usually easier to monitor and regulate. Examples include:
    • Power plants (coal, oil, natural gas fired)
    • Industrial facilities (chemical plants, refineries, manufacturing units)
    • Incinerators and boilers
    • Commercial and institutional buildings (heating systems)
  • Area Sources: These are numerous, smaller sources of pollution that are spread over a wide area. Their individual emissions may be small, but collectively they can contribute significantly to air pollution. Examples include:
    • Residential heating and cooking
    • Agricultural activities (fertilizer use, livestock)
    • Construction and demolition sites
    • Dry cleaning operations
    • Paints and solvents usage
    • Small commercial boilers
• Mobile Sources: These are sources of pollution that move from place to place, emitting pollutants as they operate. They are a major source of pollutants in urban areas. Examples include:
  • On-road vehicles: Cars, trucks, buses, motorcycles. These are a primary source of CO, NOx, VOCs, and PM in cities.
  • Off-road vehicles: Aircraft, trains, ships, construction equipment, lawnmowers, snowmobiles. These also contribute significantly to air pollution, especially in specific locations or during certain seasons.

Understanding the nature and location of pollution sources is fundamental for implementing targeted air quality management plans and pollution control technologies.