India’s National Air Quality Index (AQI): Understanding Pollution Levels and Health Impacts

Air pollution is one of India’s most pressing environmental and public health challenges. To help citizens understand what they’re breathing every day, the Indian government launched the National Air Quality Index (AQI) in October 2014. The AQI takes complex pollution data and converts it into a simple, colour-coded number that anyone can understand – no science degree required. But how exactly does this system work, what does it mean for your health, and how does it shape government policy? Let’s break it all down.

What is the National Air Quality Index? 🔗

The National AQI is a standardised tool developed by the Central Pollution Control Board (CPCB) in collaboration with IIT Kanpur and an expert group of medical professionals, air quality scientists, and advocacy groups. It was designed to replace the earlier system of reporting air quality through dense, technical data tables that were difficult for ordinary citizens to interpret.

The concept behind India’s AQI is straightforward: “One Number – One Colour – One Description.” Instead of presenting raw pollutant concentrations across multiple parameters, the AQI distils all that information into a single index value between 0 and 500. Each value falls within a specific category and is assigned a colour, making it easy for people to quickly assess whether the air around them is safe to breathe.

How AQI is calculated and interpreted 🔗

The eight pollutants measured 🔗

India’s AQI framework monitors eight key pollutants: PM10, PM2.5, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ground-level ozone (O₃), ammonia (NH₃), and lead (Pb). This was a significant upgrade from the earlier system, which tracked only three indicators. For each of these pollutants, the CPCB has established short-term National Ambient Air Quality Standards based on 24-hour averaging periods (or 8-hour for ozone and CO).

Sub-index calculation 🔗

The calculation process works as follows. For each pollutant, a sub-index is computed based on the measured ambient concentration and its corresponding health breakpoint. This sub-index is a linear function of concentration – for example, the PM2.5 sub-index would be 51 at a concentration of 31 µg/m³, reach 100 at 60 µg/m³, and fall at 75 for a concentration of 45 µg/m³. Once sub-indices are calculated for all monitored pollutants at a station, the highest (worst) sub-index becomes the overall AQI for that location. This means the AQI always reflects the most problematic pollutant at any given time.

The six AQI categories 🔗

The final AQI value is classified into one of six colour-coded categories:

Good (0-50): Air quality is satisfactory with minimal health impact. No precautions needed.
Satisfactory (51-100): Acceptable air quality, though sensitive individuals may experience minor breathing discomfort.
Moderately polluted (101-200): People with lung conditions like asthma, as well as children and older adults, may experience breathing discomfort.
Poor (201-300): Prolonged exposure can cause breathing difficulty in the general population and discomfort for those with heart disease.
Very poor (301-400): Respiratory illness is likely for people on prolonged exposure, with more pronounced effects on those with existing lung and heart conditions.
Severe (401-500): Even healthy people may experience respiratory distress. Those with existing lung or heart disease face serious health consequences, even during light physical activity.

Impacts of AQI on public health awareness 🔗

Making air pollution visible 🔗

Before the AQI system, air quality information existed mainly in technical reports and research papers – practically invisible to the average person. The AQI changed that by making air pollution data accessible in real time. Today, citizens can check daily AQI bulletins on the CPCB’s online dashboard, through the SAMEER mobile app, and via platforms like SAFAR (System of Air Quality and Weather Forecasting And Research) operated by the Indian Institute of Tropical Meteorology.

This accessibility has fundamentally shifted public awareness. People in cities like Delhi, Mumbai, Kolkata, and Pune now routinely check AQI readings the way they check weather forecasts – before planning outdoor exercise, commutes, or children’s activities.

Protecting vulnerable populations 🔗

The health advisory framework linked to each AQI category is especially critical for vulnerable populations. According to the Government of India’s Advisory on Air Pollution and Health, high-risk groups include elderly individuals, children under five years, pregnant women, and people with pre-existing respiratory or cardiovascular conditions. The advisory also identifies occupational groups – traffic police, construction workers, rickshaw pullers, roadside vendors, and others who work outdoors – as particularly vulnerable due to prolonged exposure.

The health consequences of poor air quality are well-documented. Short-term exposure during high-AQI days can trigger eye and throat irritation, coughing, wheezing, and acute respiratory infections. For vulnerable groups, the effects can be far more severe – including lower respiratory tract infections, asthma exacerbations, and worsening of chronic conditions like COPD and ischaemic heart disease. Long-term exposure, even at moderate pollution levels, has been linked to lung cancer, cardiovascular disease, stroke, and premature death.

The numbers are sobering. According to the World Bank, approximately 1.67 million deaths were attributable to air pollution in India in 2019 alone – that’s roughly 17.8% of all deaths in the country that year. The economic toll was equally staggering, with lost output from premature deaths and illness estimated at US$36.8 billion, or 1.36% of India’s GDP.

Informing daily decisions 🔗

The AQI advisory system provides specific, actionable guidance for both the general public and sensitive groups. For instance, when AQI enters the “Poor” range (201-300), the general population is advised to avoid outdoor physical exertion, while vulnerable individuals should stay indoors altogether. At “Severe” levels, the recommendations include remaining indoors, keeping activity levels low, and avoiding opening doors and windows during morning and evening hours when pollution tends to peak.

These simple, category-specific advisories empower people to make informed decisions about their daily routines – whether it’s choosing to exercise indoors, rescheduling outdoor activities, or ensuring children with asthma have their medications readily available.

Supporting policy and regulatory action 🔗

The Graded Response Action Plan (GRAP) 🔗

One of the most direct ways AQI data drives policy is through the Graded Response Action Plan (GRAP), a stage-wise emergency framework specifically designed for the Delhi-NCR region. Originally formulated in 2016 and later revised, GRAP mandates pre-defined preventive and restrictive actions that are triggered automatically based on AQI thresholds.

GRAP operates across four stages. Stage I is activated when AQI falls in the “Poor” range (201-300), with 24 action points including intensified inspections and prevention of open burning. Stage II kicks in at “Very Poor” levels (301-400), adding 12 more action points. Stage III at “Severe” (401-450) and Stage IV at “Severe+” (above 450) bring progressively stricter measures – from halting construction work to implementing traffic restrictions and closing schools.

A key improvement in the revised GRAP framework is the use of air quality forecasting. Actions under Stages II, III, and IV are now triggered at least three days in advance based on AQI projections from the India Meteorological Department (IMD) and IITM. This pre-emptive approach allows authorities to act before pollution peaks rather than merely reacting after conditions deteriorate.

The National Clean Air Programme (NCAP) 🔗

At a broader scale, AQI data underpins the National Clean Air Programme (NCAP), launched by the Ministry of Environment, Forest and Climate Change in January 2019. The NCAP targets a 40% reduction in particulate matter concentrations by 2026 compared to 2017 baselines, covering over 130 non-attainment cities across 24 states and union territories.

AQI monitoring stations – both manual and continuous – form the data backbone of this programme. Cities are evaluated on their ability to reduce PM10 levels, and access to central funding is tied to demonstrated improvement. The programme has also led to a significant expansion of India’s monitoring infrastructure. According to a CREA progress report, national data indicate roughly a 25-27% reduction in particulate matter levels between 2019 and 2024, though challenges persist – particularly with episodic spikes from stubble burning, construction dust, and vehicular emissions.

Health sector integration 🔗

AQI data is also increasingly informing public health policy. The National Programme on Climate Change and Human Health (NPCCHH) under India’s Ministry of Health and Family Welfare uses AQI data to issue health advisories, guide hospital preparedness during high-pollution episodes, and develop city-specific health action plans. State health departments are directed to establish sentinel surveillance systems that correlate acute respiratory and cardiac events with daily AQI levels – creating a direct feedback loop between pollution data and healthcare response.

Additionally, during severe pollution episodes, authorities issue specific instructions for schools, hospitals, and workplaces. These include closure orders, mandatory use of air purifiers in classrooms, and alerts to medical facilities to prepare for an anticipated increase in emergency admissions.

Limitations and the path forward 🔗

Despite its transformative role, the AQI system has limitations. A 2025 study highlighted by Health Policy Watch pointed out that India’s current AQI health advisories are relatively generic and do not adequately communicate the risk of mortality – describing consequences in terms like “breathing discomfort” rather than explicitly warning about premature death risks. The study proposed replacing the AQI with a city-specific Air Quality Health Index (AQHI) that would reflect localised mortality data, arguing that a one-size-fits-all national index doesn’t account for India’s demographic and epidemiological diversity.

There are also ongoing debates about the emphasis on PM10 as the primary performance metric under NCAP, with experts arguing that PM2.5 – which is more harmful due to its ability to penetrate deep into the lungs and enter the bloodstream – should be the primary benchmark for policy action. Expanding the network of continuous ambient air quality monitoring stations (CAAQMS) remains another priority, as many cities still lack real-time monitoring infrastructure.

Why AQI matters for every Indian citizen 🔗

The National AQI is more than just a number on a dashboard. It is a communication bridge between scientific data and everyday decision-making. For citizens, it provides the information needed to protect personal and family health. For policymakers, it serves as both an early warning system and a performance metric. And for the healthcare sector, it offers a framework to anticipate and respond to pollution-driven health crises.

As India’s air quality monitoring network expands and the index potentially evolves to incorporate mortality-linked health indicators, the AQI will only grow in importance as a tool for environmental governance and public health protection.

What do you think? Should India move toward a city-specific Air Quality Health Index that communicates mortality risk more directly, or does the current national AQI system serve its purpose well enough? And in your city, how often do you check the AQI before planning your day?

References

1. https://cpcb.nic.in/National-Air-Quality-Index/
2. https://www.pib.gov.in/newsite/printrelease.aspx?relid=110654&reg=3&lang=2
3. https://airquality.cpcb.gov.in/AQI_India/
4. https://safar.tropmet.res.in/AQI-47-12-Details
5. https://ncdc.mohfw.gov.in/wp-content/uploads/2024/05/1-ADVISORY-ON-AIR-POLLUTION-AND-HEALTH.pdf
6. https://www.worldbank.org/en/country/india/publication/catalyzing-clean-air-in-india
7. https://www.pib.gov.in/PressReleaseIframePage.aspx?PRID=1909910&reg=3&lang=2
8. https://energyandcleanair.org/publication/tracing-the-hazy-air-2025-progress-report-on-national-clean-air-programme-ncap/
9. https://healthpolicy-watch.news/indian-study-calls-for-air-quality-index-to-be-linked-to-health-risk/