What is GRAP? A Complete Guide to Delhi-NCR's Emergency Air Quality Plan

The Origins of GRAP

The story of GRAP begins with the Supreme Court of India. In November 2016, as Delhi choked under its worst smog crisis in nearly two decades, the court directed the Environment Pollution (Prevention and Control) Authority (EPCA) to devise a graded plan to tackle the annual air quality crisis. The EPCA — a statutory body established under the Environment Protection Act, 1986 — responded by formulating the first version of GRAP, which was formally notified in January 2017.

The original GRAP framework classified air quality into four categories — Poor, Very Poor, Severe, and Severe+ (Emergency) — and prescribed a corresponding set of actions for each stage. However, the EPCA, despite its quasi-judicial powers, lacked the institutional muscle to enforce compliance across multiple state governments, municipal bodies, and regulatory agencies operating within the NCR.

Recognising this gap, the Indian Parliament enacted the Commission for Air Quality Management in National Capital Region and Adjoining Areas Act, 2021, establishing the CAQM as a permanent statutory body with overriding powers. The CAQM replaced the EPCA and was given authority that superseded state pollution control boards on air quality matters. In its revised avatar, the CAQM overhauled GRAP in 2022 and again in 2024, tightening AQI thresholds, expanding the list of restricted activities, and introducing pre-emptive invocation — allowing stages to be triggered based on weather forecasts, not just real-time readings.

Understanding the Air Quality Index (AQI)

GRAP's trigger mechanism depends entirely on the Air Quality Index (AQI), so understanding how AQI is calculated is crucial. India uses the National Air Quality Index, developed by the Central Pollution Control Board (CPCB), which distils complex pollutant concentration data into a single number on a scale of 0 to 500.

The AQI is computed from eight pollutant parameters: PM2.5, PM10, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), ammonia (NH₃), and lead (Pb). For each pollutant, a sub-index is calculated based on the 24-hour average concentration (or 8-hour average for CO and O₃). The overall AQI is determined by the worst-performing pollutant — whichever sub-index is highest becomes the headline number.

In Delhi-NCR, the dominant pollutants are almost always PM2.5 and PM10 — particulate matter with diameters of 2.5 micrometres and 10 micrometres respectively. PM2.5 is particularly dangerous because particles this small penetrate deep into the lungs and can enter the bloodstream. During winter pollution episodes, PM2.5 concentrations in Delhi routinely exceed 300 µg/m³ — more than 20 times the World Health Organization's guideline of 15 µg/m³ for a 24-hour average.

Data for AQI computation is collected from a network of Continuous Ambient Air Quality Monitoring Stations (CAAQMS) operated by the CPCB, the Delhi Pollution Control Committee (DPCC), and state-level agencies. Delhi alone has over 40 CAAQMS stations spread across residential, industrial, and traffic-heavy zones. For GRAP decisions, the CAQM typically relies on the city-wide average AQI derived from all operational stations, supplemented by 3-day weather and air quality forecasts from the Indian Institute of Tropical Meteorology (IITM) and the SAFAR (System of Air Quality and Weather Forecasting And Research) system.

How GRAP Works in Practice

GRAP is not a self-executing algorithm — it requires human judgement and institutional coordination. Here is how the process works in practice:

1. Forecasting and Early Warning: Starting each October, the CAQM's technical team begins daily monitoring of air quality trends and meteorological forecasts. Data feeds from IITM-Pune and SAFAR project the expected AQI trajectory for the next 72 hours, accounting for wind speed, temperature, mixing height, and emission patterns.
2. Sub-Committee Review: When forecasts suggest AQI will breach a GRAP threshold, the CAQM convenes a meeting of its Sub-Committee for Invoking Actions under GRAP. This sub-committee includes representatives from CPCB, the India Meteorological Department (IMD), and state pollution control boards.
3. Directive Issued: If the sub-committee determines that invoking or escalating GRAP is warranted, it issues a formal directive specifying the stage and the actions required. Since the 2024 revision, GRAP can be invoked pre-emptively — based on forecast data, before real-time AQI actually breaches the threshold.
4. State-Level Enforcement: The directive is transmitted to the Chief Secretaries of Delhi, Haryana, Uttar Pradesh, and Rajasthan, who instruct their respective pollution control boards, district administrations, transport departments, and police forces to implement the mandated actions.
5. Monitoring and Compliance: CAQM field teams, along with DPCC inspectors and district magistrate offices, conduct physical inspections to verify compliance at construction sites, industrial units, transport hubs, and public spaces.

The Science Behind Winter Smog

To understand why GRAP exists, you need to understand why Delhi-NCR's air turns lethal every winter. The answer lies in a convergence of geography, meteorology, and human activity.

Temperature Inversion: During winter, the ground cools rapidly after sunset, creating a layer of cold air near the surface with warmer air above. This phenomenon — called a temperature inversion — acts as a lid, trapping pollutants close to the ground. In summer, convective mixing carries pollutants upward and disperses them; in winter, this mechanism shuts down almost entirely.

The Indo-Gangetic Plain: Delhi sits at the western edge of the vast Indo-Gangetic Plain, a flat alluvial expanse stretching over 700,000 square kilometres. This flat terrain offers no natural barriers to funnel or disperse pollution. In winter, cold north-westerly winds sweep pollutants from Punjab, Haryana, and western Uttar Pradesh directly into the NCR, where they accumulate.

Crop Residue Burning: Between October and November, farmers in Punjab and Haryana burn an estimated 20-25 million tonnes of paddy stubble to clear their fields before the rabi (winter) sowing season. Satellite imagery from NASA's VIIRS and MODIS instruments regularly shows thousands of fire hotspots across the region. Studies by the Indian Agricultural Research Institute have estimated that stubble burning contributes between 25% and 45% of Delhi's PM2.5 load during peak burning weeks.

Low Wind Speeds and Boundary Layer Compression: Winter brings a dramatic drop in wind speeds across the NCR — average wind speeds fall below 5 km/h during November and December, compared to 15-20 km/h in summer. Simultaneously, the atmospheric boundary layer — the lowest layer of the atmosphere where mixing occurs — compresses from roughly 2-3 kilometres in summer to as low as 200-400 metres in winter. This means the same volume of emissions is being trapped in a dramatically smaller atmospheric volume.

Who Enforces GRAP?

GRAP enforcement is a multi-agency operation spanning four states and dozens of government bodies. Here is how responsibility is distributed:

• Commission for Air Quality Management (CAQM): The apex body. Issues directives, monitors compliance, and has the authority to impose penalties of up to ₹1 crore or initiate prosecution for non-compliance. Its orders override those of state pollution control boards.
• Delhi Pollution Control Committee (DPCC): The state pollution control board for Delhi. Responsible for enforcing GRAP at industrial units, construction sites, and commercial establishments within Delhi. Conducts inspections, issues closure orders, and imposes environmental compensation.
• Haryana State Pollution Control Board (HSPCB) and UPPCB: Enforce GRAP provisions within NCR districts of Haryana (Gurugram, Faridabad, Sonipat, Jhajjar, Panipat, etc.) and Uttar Pradesh (Noida, Ghaziabad, Greater Noida, Bulandshahr, etc.) respectively.
• District Administrations: District Magistrates in each NCR district play a critical role in coordinating enforcement across departments, deploying anti-smog guns, ensuring road-watering operations, and shutting down non-compliant activities.
• Traffic Police: Enforce vehicle-related restrictions — checking for BS-III/BS-IV compliance, implementing entry restrictions on trucks, issuing challans for polluting vehicles, and managing enhanced public transport corridors during Stage III and Stage IV.
• Municipal Corporations: Responsible for mechanised sweeping of roads, elimination of open burning and garbage fires, management of landfill-related emissions, and maintenance of green belts and dust-suppression activities.

Impact on Daily Life

GRAP is not an abstract policy document — its effects ripple through every aspect of daily life in the NCR when activated.

Commuters: GRAP's vehicle restrictions hit commuters hardest. Under Stage III, all BS-III petrol and BS-IV diesel vehicles are banned from Delhi's roads, affecting lakhs of car owners. Under Stage IV, truck entry into Delhi is banned entirely (except for essential goods and CNG/electric vehicles), causing traffic rerouting and congestion on bypass highways. Parking fees are hiked to discourage private vehicle use, and metro and bus services are augmented with additional trips.

School Children: When Stage IV is invoked, physical classes for all students up to Class XII are suspended, and schools must shift to online instruction. Even under earlier stages, schools are directed to suspend outdoor activities, sports days, and excursions. The health implications are profound — children breathe at a faster rate than adults and absorb proportionally more pollutants per kilogram of body weight.

Construction Workers: The construction industry bears a disproportionate burden. Under Stage III, all construction and demolition (C&D) activities are halted entirely — affecting an estimated 1.5 to 2 million daily-wage workers in the NCR. Even under Stage I, projects with sites larger than 500 square metres must implement stringent dust-control measures including anti-smog nets, wind-breaking walls, and water sprinklers, with sites facing closure and penalties for non-compliance.

Factory and Industrial Workers: Industries operating in non-conforming areas face closure orders. Brick kilns that have not transitioned to zig-zag technology are shut down. Small-scale manufacturing units using coal or biomass as fuel are ordered to cease operations. For the workers employed in these units — often migrant labourers — a GRAP escalation can mean sudden loss of income with little warning or support.

GRAP remains a necessary, if imperfect, tool in the fight against Delhi-NCR's air pollution crisis. It cannot solve the structural problems — the region's dependence on thermal power, the absence of adequate public transport, the slow pace of industrial transition, or the entrenched practice of stubble burning. But when winter closes in and the AQI climbs toward emergency levels, GRAP is the frontline defence that determines what restrictions are imposed, how quickly they take effect, and how millions of people navigate their daily lives under a poisoned sky.