Smog, Types, Causes, Composition, Impact, Govt Initiatives

Smog is a type of air pollution formed by a mixture of smoke, harmful gases, and fine particles, reducing air quality and visibility. It is mainly of two types: Classical (Sulphurous) smog and Photochemical (Oxidizing) smog. Smog is caused by vehicular emissions, industrial pollution, stubble burning, and construction dust, often worsened by winter weather conditions. Its composition includes PM2.5, PM10, SO₂, NOx, CO, ozone, and VOCs, leading to serious health, environmental, and economic impacts, which the government addresses through NCAP, GRAP, BS-VI norms, and public awareness initiatives.

What is Smog?

Smog is a type of air pollution formed by the combination of smoke, fog, and harmful chemical pollutants present in the atmosphere. The term “smog” is derived from the words smoke and fog, indicating its composite nature. It develops when pollutants released from vehicles, industries, and burning activities react with atmospheric components under specific weather conditions.

How Smog is Formed?

Smog is formed when pollutants released from vehicles, industries, and burning activities accumulate in the atmosphere and undergo chemical reactions under specific weather conditions. Factors like sunlight, high moisture, and temperature inversion prevent dispersion of pollutants and intensify smog formation.

• Emission of primary pollutants such as PM, SO₂, NOx, CO, and VOCs from human activities.
• Chemical reactions between NOx and VOCs in the presence of sunlight form secondary pollutants like ozone and PAN.
• Unfavourable meteorological conditions (low wind speed, high humidity, temperature inversion) trap pollutants near the ground, creating dense smog.

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Types of Smog

Smog can broadly be classified into two major types based on its composition and formation mechanism.

1. Classical Smog (London Smog / Sulphurous Smog)

1. Formation Conditions: Develops in cold, humid winter conditions, often during temperature inversion, which traps pollutants close to the ground.
2. Primary Source: Caused mainly by burning of coal and heavy fossil fuels in industries and for domestic heating.
3. Major Pollutants: Dominated by sulfur dioxide (SO₂), smoke, soot, and sulfuric acid aerosols formed due to high moisture.
4. Chemical Nature: Known as reducing smog because it contains reducing agents rather than oxidants.
5. Appearance & Effects: Appears as a dense grey-black haze, drastically reducing visibility and creating choking conditions.
6. Impacts: Causes severe respiratory illnesses, corrosion of buildings, and historically led to high mortality (e.g., Great Smog of London, 1952).

2. Photochemical Smog (Los Angeles Smog / Oxidizing Smog)

1. Formation Conditions: Forms in warm, dry, and sunny climates, where strong sunlight triggers chemical reactions in the atmosphere.
2. Primary Sources: Originates mainly from vehicular emissions, especially nitrogen oxides (NOx) and volatile organic compounds (VOCs).
3. Major Pollutants: Contains ground-level ozone (O₃), peroxyacetyl nitrate (PAN), aldehydes, and other secondary oxidants.
4. Chemical Nature: Known as oxidizing smog due to the dominance of strong oxidizing agents like ozone.
5. Appearance & Timing: Appears as a yellowish-brown haze, with peak intensity during afternoon hours.
6. Impacts: Causes eye and throat irritation, aggravates asthma, reduces lung function, and damages crops, rubber, and painted surfaces.

Causes of Smog

Smog is caused by a combination of human activities and unfavourable meteorological conditions that lead to the accumulation and chemical transformation of air pollutants near the Earth’s surface.

• Vehicular Emissions: Exhaust from cars, buses, and trucks releases nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons, which are primary contributors to photochemical smog in urban areas.
• Industrial Activities: Thermal power plants, refineries, brick kilns, and manufacturing units emit sulfur dioxide (SO₂), particulate matter, and toxic gases that intensify smog formation.
• Burning of Fossil Fuels: Extensive use of coal and petroleum for electricity generation, heating, and cooking releases smoke, soot, and sulfur compounds into the atmosphere.
• Agricultural Stubble Burning: Seasonal burning of crop residue, especially in northern India, adds large quantities of particulate matter and gases, worsening smog episodes.
• Construction and Road Dust: Large-scale urban construction, mining, and poorly maintained roads contribute fine dust particles (PM10 and PM2.5) that remain suspended in air.
• Open Waste Burning: Burning of municipal solid waste and landfill fires release toxic fumes, dioxins, and particulate matter, aggravating air pollution.
• Meteorological Conditions: Temperature inversion, low wind speed, high humidity, and calm atmospheric conditions prevent dispersion of pollutants.
• Urbanization and Population Growth: Rapid growth of cities increases energy demand, vehicle density, and industrial output, all of which elevate smog levels.

Composition and Pollutants Involved in Smog

Smog is a complex mixture of primary pollutants released directly into the atmosphere and secondary pollutants formed through chemical reactions under specific climatic conditions.

• Particulate Matter (PM2.5 and PM10): Fine particles originating from vehicle exhaust, coal burning, construction dust, and biomass burning; PM2.5 penetrates deep into the lungs and bloodstream, making it highly harmful.
• Sulfur Dioxide (SO₂): Emitted mainly from coal-based power plants and industries; reacts with moisture in the air to form sulfuric acid aerosols, a key component of classical smog.
• Nitrogen Oxides (NO and NO₂): Released from vehicle engines and industrial combustion; act as precursor pollutants in the formation of photochemical smog.
• Carbon Monoxide (CO): Produced by incomplete combustion of fuels; reduces oxygen-carrying capacity of blood and worsens respiratory stress during smog episodes.
• Ground-Level Ozone (O₃): A secondary pollutant formed by the reaction of NOx and volatile organic compounds in the presence of sunlight; a major irritant in photochemical smog.
• Volatile Organic Compounds (VOCs): Emitted from fuels, solvents, paints, and industrial processes; play a crucial role in ozone and PAN formation.
• Peroxyacetyl Nitrate (PAN): A toxic secondary pollutant responsible for eye irritation and damage to vegetation.
• Smoke and Soot: Carbon-rich particles released from fossil fuel and biomass burning, contributing to reduced visibility and health hazards.
• Trace Heavy Metals: Elements like lead, mercury, and arsenic present in industrial emissions, adding to the toxicity of smog.

Smog Impact

Smog has wide-ranging impacts on human health, environment, economy, and daily life. Prolonged exposure to smog significantly lowers quality of life and poses a major challenge to sustainable urban development.

Health Impacts

• Causes respiratory problems such as asthma, bronchitis, chronic obstructive pulmonary disease (COPD), and lung infections.
• Increases risk of cardiovascular diseases, including heart attacks and strokes.
• Leads to eye irritation, headaches, fatigue, and throat discomfort.
• Affects children, elderly, and pregnant women more severely due to weaker immunity.
• Long-term exposure can result in reduced lung capacity and premature deaths.

Environmental Impacts

• Reduces visibility, disrupting road, rail, and air transport.
• Damages crops and vegetation, especially due to ground-level ozone affecting photosynthesis.
• Leads to acid rain formation, harming soil, water bodies, and forests.
• Alters local climate conditions by trapping heat near the surface.

Economic Impacts

• Increases healthcare expenditure due to rising pollution-related illnesses.
• Causes loss of productivity from sick days and reduced work efficiency.
• Results in school closures, work restrictions, and emergency measures during severe smog episodes.
• Negatively impacts tourism, aviation, and outdoor economic activities.

Social and Urban Impacts

• Reduces overall quality of life in cities.
• Forces vulnerable populations to remain indoors, affecting mental well-being.
• Highlights environmental inequality, as poorer communities are more exposed to polluted environments.

Smog Monitoring and Measurement

Monitoring and measurement of smog are essential for assessing air quality, issuing health advisories, and implementing timely control measures. In India, smog is monitored through a combination of ground-based stations, forecasting systems, and satellite observations.

Air Quality Index (AQI): AQI is a standardized numerical scale used to communicate air pollution levels and associated health risks. It integrates concentrations of major pollutants like PM2.5, PM10, NO₂, SO₂, CO, O₃, Lead, and NH₃ into a single value.

Government Initiatives and Policy Measures

• National Clean Air Programme (NCAP): Aims to reduce particulate matter (PM2.5 and PM10) concentrations by a targeted percentage through city-specific action plans.
• Graded Response Action Plan (GRAP): Implements emergency measures in Delhi-NCR during severe smog episodes, such as restricting vehicles, banning construction, and closing schools.
• Bharat Stage VI (BS-VI) Emission Norms: Introduced stringent vehicular emission standards to reduce NOx, SO₂, and particulate emissions from vehicles.
• Commission for Air Quality Management (CAQM): Ensures coordinated and integrated management of air pollution across Delhi-NCR and adjoining states.
• Promotion of Electric Vehicles: FAME scheme and state EV policies encourage cleaner transportation to reduce vehicular pollution.
• National Electric Mobility Mission (NEMM): Supports transition to electric and hybrid vehicles to curb emissions.
• Control of Industrial Emissions: Mandates installation of pollution control devices and adoption of cleaner fuels in industries and power plants.
• Stubble Burning Management Measures: Provides incentives, machinery, and alternatives to farmers to discourage crop residue burning.
• Expansion of Public Transport: Investments in metro rail, buses, and non-motorized transport to reduce private vehicle dependence.

Challenges in Smog Management

• Inter-State Nature of Air Pollution: Smog often results from pollutants transported across state boundaries, making coordinated action and accountability difficult.
• Weak Enforcement of Pollution Norms: Poor monitoring, limited manpower, and regulatory gaps reduce the effectiveness of existing environmental laws.
• Rapid Urbanization and Vehicle Growth: Increasing population, urban sprawl, and rising vehicle ownership continuously add to emission levels.
• Economic Dependence on Polluting Activities: Industries, construction sector, and farmers rely on practices that contribute to smog, limiting strict action.
• Seasonal Agricultural Practices: Crop residue burning remains prevalent due to time constraints and lack of affordable alternatives for farmers.
• Inadequate Public Awareness: Limited understanding of pollution sources and health impacts hinders behavioral change at the individual level.

Way Forward

• Strengthen Regional & Inter-State Coordination: Studies show that 30–40% of Delhi-NCR’s winter smog originates from outside the city, highlighting the need for coordinated action among Punjab, Haryana, UP, Rajasthan, and Delhi through bodies like CAQM.
• Accelerate Clean Energy Transition: India still derives over 70% of its electricity from coal, a major source of SO₂ and PM emissions. Rapid expansion of renewables (India’s target: 500 GW non-fossil capacity by 2030) can significantly reduce smog-forming pollutants.
• Improve Urban Transport Systems: Vehicular emissions contribute nearly 40% of PM2.5 pollution in major cities. Expanding metro networks, electric buses, and EV adoption (target of 30% EV penetration by 2030) can substantially cut NOx and VOC emissions.
• Address Agricultural Stubble Burning: Satellite data indicates that stubble burning accounts for 20–35% of peak PM2.5 levels in North India during October–November. Scaling alternatives like Happy Seeders, bio-decomposers, and biomass-based power plants is critical.
• Strengthen Industrial Emission Controls: Thermal power plants contribute around 50% of SO₂ emissions in India. Enforcing flue gas desulfurization (FGD) units and cleaner fuels can reduce classical smog components.
• Enhance Air Quality Monitoring & Forecasting: Currently, India has air quality monitoring stations in only ~800 locations, which is insufficient for a country of its size. Expanding real-time monitoring and early-warning systems like SAFAR can enable timely preventive measures.