Overview

Air and water pollution are among India's most pressing environmental and public health challenges. India is home to some of the world's most polluted cities -- in recent years, multiple Indian cities have appeared in the top 20 of global PM2.5 rankings. Simultaneously, the CPCB has identified over 350 polluted river stretches across the country, with untreated sewage being the dominant source.

The policy response has been multi-pronged: the National Clean Air Programme (NCAP) targets a 40% reduction in particulate matter by 2026 across 131 non-attainment cities, while Namami Gange has emerged as the flagship river rejuvenation mission. Regulatory frameworks include the Air (Prevention and Control of Pollution) Act, 1981, the Water (Prevention and Control of Pollution) Act, 1974, and the Environment Protection Act, 1986.

For UPSC, this topic is a GS-3 core area. Questions test both factual knowledge (AQI categories, emission norms, BOD/COD) and analytical capacity (policy effectiveness, governance gaps, technology solutions).

Air Pollution — Sources

Vehicular Emissions

  • Transport sector contributes approximately 10-40% of urban air pollution depending on the city
  • Key pollutants: CO, NOx, PM2.5, hydrocarbons, benzene
  • BS-VI emission norms (equivalent to Euro-6) implemented across India from 1 April 2020 -- India leapfrogged from BS-IV directly to BS-VI
  • BS-VI mandates: 80% reduction in NOx for diesel vehicles, sulphur content in fuel reduced from 50 ppm (BS-IV) to 10 ppm (BS-VI), On-Board Diagnostics (OBD) systems mandatory, particulate number limits introduced

Industrial Emissions

  • Thermal power plants (largest industrial source of SO2, NOx, PM, and mercury)
  • Brick kilns (estimated 1.5 lakh units in India; shifting from fixed chimney to zigzag technology)
  • Cement, steel, and chemical industries
  • Flue Gas Desulphurisation (FGD) mandated for all coal-based thermal power plants -- implementation has been delayed multiple times

Crop Residue Burning (Stubble Burning)

  • Concentrated in Punjab and Haryana during the October-November rice harvest season
  • Farmers burn an estimated 15-20 million tonnes of paddy straw annually
  • Contributes up to 30-40% of Delhi's PM2.5 during peak burning weeks
  • Solutions: Happy Seeder (sows wheat directly into rice stubble), Crop Residue Management (CRM) machinery subsidy, bio-decomposer (Pusa Decomposer developed by IARI), ex-situ uses (biomass pellets, bio-CNG, co-firing in power plants)
  • Commission for Air Quality Management (CAQM) in NCR and Adjoining Areas (constituted 2021) has statutory powers to enforce measures

Construction Dust

  • A significant contributor in rapidly urbanising cities
  • Construction and Demolition (C&D) Waste Management Rules, 2016 mandate dust suppression, covered transportation, and recycling of C&D waste

Household Air Pollution

  • Burning of biomass fuels (wood, cow dung, crop residue) for cooking in rural households
  • Affects an estimated 70 crore Indians
  • PM Ujjwala Yojana (PMUY) provides free LPG connections to BPL households; over 10 crore connections distributed

Air Quality Index (AQI)

India's AQI System

Launched by CPCB in 2014 under MoEFCC, the National AQI standardises air quality reporting across India.

Six AQI Categories

Category AQI Range Colour Health Implication
Good 0-50 Green Minimal impact
Satisfactory 51-100 Light green Minor discomfort to sensitive people
Moderate 101-200 Yellow Breathing discomfort for sensitive groups
Poor 201-300 Orange Breathing discomfort on prolonged exposure
Very Poor 301-400 Red Respiratory illness on prolonged exposure
Severe 401-500 Maroon Affects healthy people; serious impact on those with existing diseases

Eight Pollutants Monitored

PM2.5, PM10, NO2, SO2, CO, O3 (ground-level ozone), NH3 (ammonia), and Pb (lead).

The overall AQI is determined by the worst sub-index among all measured pollutants. A minimum of 3 pollutants must be measured, and one must be either PM2.5 or PM10.

National Ambient Air Quality Standards (NAAQS)

Set by CPCB under the Air Act, NAAQS prescribe permissible limits for 12 pollutants in ambient air.

Pollutant Annual average (micrograms per cubic metre) 24-hour average
PM2.5 40 60
PM10 60 100
SO2 50 80
NO2 40 80
CO -- 2 mg per cubic metre (8-hour)
O3 -- 100 (8-hour)
Pb 0.5 1.0
NH3 100 400

Non-attainment cities are those that consistently fail to meet NAAQS for PM10 and/or NO2. These cities form the target group for NCAP.

National Clean Air Programme (NCAP)

Key Features

Parameter Detail
Launched January 2019 by MoEFCC
Cities covered 131 non-attainment cities across 24 states/UTs
Target 40% reduction in PM10 and PM2.5 concentrations by 2025-26 (from 2017 baseline); revised upward from the initial 20-30% target
Approach City-specific clean air action plans; sector-wise interventions
Budget Rs 10,566 crore allocated to 131 cities for implementation

Progress and Challenges

  • As of 2025, 95 of 131 cities showed improvement in PM10 levels compared to 2017
  • However, only 51 cities achieved the initial 20-30% reduction target, and only 23 cities met the revised 40% target
  • A 2025-26 assessment found that meeting the 40% reduction target across all 131 cities remains unlikely within the timeline
  • Key challenges: insufficient monitoring infrastructure in smaller cities, lack of source apportionment studies, poor enforcement of construction dust norms

GRAP — Graded Response Action Plan (Delhi-NCR)

Structure

GRAP is an emergency response mechanism for the NCR region, implemented by the Commission for Air Quality Management (CAQM). It is triggered based on AQI levels and weather forecasts.

Stage AQI Range Key Actions
Stage I (Poor) 201-300 Ban on open burning, water sprinkling on roads, enforce emission norms
Stage II (Very Poor) 301-400 Restrict diesel generator use, enhanced road sweeping, control pollution hotspots
Stage III (Severe) 401-450 Restrict certain vehicles, halt construction at non-compliant sites, remote schooling measures
Stage IV (Severe+) Above 450 Ban entry of non-essential heavy vehicles, close schools, shut non-essential industries, ban truck entry except essential goods

GRAP measures are cumulative -- actions under all previous stages continue when a higher stage is invoked. CAQM revised GRAP in 2024 to make it more stringent, with a pre-emptive approach based on AQI forecasts rather than waiting for deterioration to occur.

Bharat Stage Emission Norms

Norm Implementation date Equivalent to Key improvement
BS-I 2000 Euro-1 First emission standards for vehicles
BS-II 2005 Euro-2 Stricter limits on CO, HC, NOx
BS-III 2010 Euro-3 Catalytic converters mandatory
BS-IV 2017 (nationwide) Euro-4 Significant PM and NOx reduction
BS-VI 1 April 2020 Euro-6 80% NOx reduction (diesel); 10 ppm sulphur; OBD mandatory; real driving emission (RDE) tests

India skipped BS-V entirely, leapfrogging directly from BS-IV to BS-VI. This was a landmark regulatory decision that brought India's emission standards on par with European norms.

Water Pollution — Sources and Indicators

Major Sources

Source Contribution Key pollutants
Domestic sewage ~80% of river pollution Organic matter, pathogens, nutrients (N, P)
Industrial effluents ~15% Heavy metals, toxic chemicals, acids/alkalis
Agricultural runoff ~5% Fertilizers (N, P causing eutrophication), pesticides
Urban stormwater Variable Oil, grease, suspended solids, microplastics

Water Quality Indicators

Indicator Meaning Clean water range
BOD (Biochemical Oxygen Demand) Oxygen consumed by microbes to decompose organic matter (5 days, 20 degrees C) Less than 3 mg/L
COD (Chemical Oxygen Demand) Oxygen needed to chemically oxidise all organic and inorganic matter Less than 10 mg/L
DO (Dissolved Oxygen) Oxygen available for aquatic life More than 6 mg/L
Faecal Coliform Indicator of pathogenic contamination from human/animal waste Less than 500 MPN/100mL
Total Dissolved Solids (TDS) Dissolved salts and minerals Less than 500 mg/L (drinking)

River Pollution in India

Scale of the Problem

  • CPCB has identified 351 polluted river stretches on 323 rivers across India
  • Ganga and Yamuna are the most critically studied
  • The Yamuna in the Delhi stretch (22 km, representing less than 2% of total length) receives approximately 58% of Delhi's wastewater, resulting in near-zero dissolved oxygen levels during lean flow months

Sewage Treatment Capacity Gap

Parameter Data
Urban sewage generation ~72,368 MLD (million litres per day)
Installed treatment capacity ~26,665 MLD
Actual treatment ~20,235 MLD (approximately 28% of generation)
Untreated discharge ~52,133 MLD

Five states -- Maharashtra, Gujarat, Uttar Pradesh, Delhi, and Karnataka -- account for 60% of total installed treatment capacity, while Bihar, Assam, and northeastern states have negligible infrastructure.

Namami Gange Programme

Overview

Feature Detail
Launched June 2014 as a flagship programme under Ministry of Jal Shakti
Implementing body National Mission for Clean Ganga (NMCG)
Budget Allocated Rs 23,424.86 crore from FY 2014-15 to FY 2024-25; Namami Gange Mission-II approved with Rs 22,500 crore till 2026
Coverage Five main-stem states -- Uttarakhand, UP, Bihar, Jharkhand, West Bengal; and tributaries

Key Components

Component Focus
Sewage treatment Creation of new STPs; rehabilitation of existing non-functional STPs
Industrial pollution Monitoring and closure of Grossly Polluting Industries (GPIs); real-time effluent monitoring
River surface cleaning Removal of floating solid waste using trash skimmers
Biodiversity conservation Conservation of Gangetic dolphins, turtles, and other aquatic fauna
Afforestation Plantation drives along river banks to prevent erosion
Ganga rejuvenation Maintaining ecological flow (e-flow) -- minimum environmental flow standards notified

Progress (as of 2025)

  • Over 300 projects completed; total investment of approximately Rs 40,000 crore
  • 25 Sewage Treatment Plants (STPs) commissioned in 2025, treating 530 MLD daily
  • Number of GPIs identified and brought under real-time monitoring increased significantly
  • Improvement in DO levels observed at several monitoring stations

Challenges

  • Sewage infrastructure in smaller towns along tributaries remains weak
  • State-level implementation varies significantly
  • Encroachments on floodplains continue in several stretches
  • River e-flow standards are difficult to enforce when dam operators prioritise irrigation and power

Groundwater Contamination

Arsenic Contamination

  • Detected in groundwater in parts of 230 districts across 25 states
  • Most affected: West Bengal, Bihar, Jharkhand, Uttar Pradesh, Assam, Manipur
  • Source: Natural geological -- dissolution of arsenic-bearing minerals in alluvial aquifers of the Ganga-Brahmaputra-Meghna basin
  • Health effects: Arsenicosis (skin lesions, keratosis), increased risk of cancer (bladder, lung, skin)
  • WHO permissible limit: 10 micrograms per litre

Fluoride Contamination

  • Found in 469 districts across 27 states
  • Most affected: Rajasthan, Haryana, Karnataka, Telangana, Gujarat, Punjab, Andhra Pradesh
  • Source: Natural dissolution of fluoride-bearing minerals (fluorite, apatite) in hard-rock aquifers
  • Health effects: Dental fluorosis (mottled teeth), skeletal fluorosis (bone deformation, crippling)
  • Permissible limit: 1.5 mg/L (BIS)

Nitrate Contamination

  • 19.8% of groundwater samples exceed permissible limits
  • Source: Fertilizer overuse, septic tank leachate, animal waste
  • Health effects: Blue baby syndrome (methemoglobinemia) in infants

CPCB and SPCB — Regulatory Framework

Central Pollution Control Board (CPCB)

  • Constituted under the Water (Prevention and Control of Pollution) Act, 1974
  • Functions: set ambient quality standards (NAAQS, water quality), coordinate with SPCBs, advise the central government, operate national monitoring networks (NAMP for water, CAAQMS for air)
  • Chairman appointed by the Central Government

State Pollution Control Boards (SPCBs)

  • Implement and enforce pollution control laws at the state level
  • Grant Consent to Establish (CTE) and Consent to Operate (CTO) to industries
  • Monitor industrial effluent compliance
  • Powers to issue closure orders against polluting units
  • Key challenge: SPCBs are often understaffed, underfunded, and subject to political pressure

National Green Tribunal (NGT)

  • Established under the NGT Act, 2010 for effective and expeditious disposal of cases relating to environmental protection
  • Has heard numerous cases on river pollution, air quality, and industrial contamination
  • Can impose substantial penalties and direct remedial action
  • Proactively monitors Namami Gange, NCAP implementation, and groundwater contamination issues

Remediation Technologies

Air Pollution Control

Technology Application
Electrostatic Precipitators (ESP) Remove PM from flue gases in thermal power plants; efficiency up to 99%
Bag filters/Fabric filters Capture fine particles in cement, steel, and chemical industries
Flue Gas Desulphurisation (FGD) Remove SO2 from power plant emissions using limestone slurry (wet FGD)
Selective Catalytic Reduction (SCR) Reduce NOx emissions using ammonia as a reductant
Catalytic converters Fitted in vehicle exhaust to convert CO, NOx, and HC to harmless gases
Smog towers Experimental large-scale air purifiers (Delhi installed two); effectiveness debated

Water Pollution Treatment

Technology Application
Activated Sludge Process (ASP) Most common biological treatment for domestic sewage
Sequential Batch Reactor (SBR) Modified ASP with batch processing; compact footprint
Moving Bed Biofilm Reactor (MBBR) Uses biofilm carriers for high-efficiency biological treatment
Constructed Wetlands Nature-based solution using natural filtration by plants (phytoremediation)
Membrane Bioreactor (MBR) Combines biological treatment with membrane filtration; highest quality effluent
Common Effluent Treatment Plant (CETP) Shared treatment for industrial clusters (mandated for polluting industries)

Phytoremediation

  • Use of plants to absorb, concentrate, or detoxify pollutants from soil and water
  • Hyperaccumulator plants like Thlaspi caerulescens (zinc, cadmium) and water hyacinth (heavy metals from water bodies)
  • Cost-effective and eco-friendly but slow compared to engineered solutions

Key Government Schemes and Policies Summary

Scheme/Policy Year Focus
Water Act 1974 Prevention and control of water pollution
Air Act 1981 Prevention and control of air pollution
Environment Protection Act 1986 Umbrella legislation for environmental protection
National River Conservation Plan 1995 Conservation of major rivers
NAMP (National Air Monitoring Programme) 1984 Ambient air quality monitoring network
NCAP 2019 40% PM reduction in 131 cities by 2026
Namami Gange 2014 Ganga rejuvenation flagship programme
BS-VI Norms 2020 Vehicular emission standards at par with Euro-6
GRAP 2017 (revised 2024) Emergency air quality response for Delhi-NCR
CAQM Act 2021 Statutory body for air quality management in NCR

Exam Strategy and Previous Year Relevance

Air and water pollution is a high-frequency topic across both Prelims and Mains.

Prelims focus areas:

  • AQI categories and pollutants (6 categories, 8 pollutants)
  • BOD vs COD definitions
  • NAAQS values for PM2.5 and PM10
  • BS-VI implementation date and key features
  • NCAP target and number of cities
  • GRAP stages and corresponding AQI ranges
  • CPCB vs SPCB roles

Mains question patterns:

  • "Examine the effectiveness of the National Clean Air Programme in addressing urban air pollution. What reforms are needed?" (GS-3)
  • "Discuss the causes of river pollution in India. Critically evaluate the Namami Gange Programme." (GS-3)
  • "Stubble burning is a governance failure, not just an environmental problem. Discuss." (GS-3)
  • "What is GRAP? How effective has it been in managing Delhi's air quality crisis?" (GS-3)

Key tip: For Mains answers on pollution, always structure your response with: sources of pollution, health/environmental impact, existing policy framework, implementation gaps, and way forward with specific suggestions.

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