Most Indians check air quality only during the Delhi smog season. The rest of the year, the assumption is simple: if the AQI app says "satisfactory," the air is fine. We wanted to test that assumption with data.
We collected cleaned sensor readings from 41 CPCB monitoring stations across 16 Indian cities for the entire month of April 2025, a month that isn't considered a "pollution season." We measured every single day against two standards: the WHO Global Air Quality Guidelines (2021) and India's own National Ambient Air Quality Standards (NAAQS, 2009).
What we found challenges the way most people think about air quality in India.
The two standards, and the gap between them
The WHO 2021 guidelines recommend PM2.5 should not exceed 5 µg/m³ annual or 15 µg/m³ 24-hour. For PM10: 15 µg/m³ annual and 45 µg/m³ 24-hour.
India's NAAQS (2009) allows 40 µg/m³ annual and 60 µg/m³ 24-hour for PM2.5. For PM10: 60 µg/m³ annual and 100 µg/m³ 24-hour.
The gap: India's PM2.5 standard is 8× more lenient than WHO's annual guideline and 4× more lenient for 24-hour exposure. Neither defines an hourly limit for particulate matter.
What April 2025 data shows across 16 cities
| City | PM2.5 avg | × WHO | WHO breach | NAAQS breach | False safety |
|---|---|---|---|---|---|
| Delhi | 83 | 5.5× | 100.0% | 92.0% | 8.0% |
| Gurugram | 76.3 | 5.1× | 100.0% | 78.6% | 21.4% |
| Lucknow | 71.8 | 4.8× | 100.0% | 69.6% | 30.4% |
| Patna | 61.9 | 4.1× | 100.0% | 43.6% | 56.4% |
| Indore | 56.5 | 3.8× | 100.0% | 27.6% | 72.4% |
| Noida | 56.3 | 3.8× | 98.3% | 36.2% | 62.1% |
| Jaipur | 55 | 3.7× | 100.0% | 24.4% | 75.6% |
| Pune | 51.8 | 3.5× | 98.7% | 31.6% | 67.1% |
| Nagpur | 48 | 3.2× | 100.0% | 20.7% | 79.3% |
| Bhopal | 43.9 | 2.9× | 100.0% | 15.5% | 84.5% |
| Ahmedabad | 36.2 | 2.4× | 100.0% | 3.8% | 96.2% |
| Hyderabad | 35.3 | 2.4× | 92.9% | 5.4% | 87.5% |
| Kolkata | 32.3 | 2.2× | 91.7% | 0.9% | 90.8% |
| Bengaluru | 29 | 1.9× | 97.3% | 0.0% | 97.3% |
| Mumbai | 19.3 | 1.3× | 57.4% | 0.9% | 56.5% |
| Chennai | 19.3 | 1.3× | 73.7% | 0.0% | 73.7% |
Data analysis by Prithvi Mehta.
The false safety zone
The most important column: the percentage of days within India's NAAQS (≤60 µg/m³) but above WHO (>15 µg/m³). On these days, India's AQI shows "satisfactory" while WHO considers the air unhealthy.
Bengaluru has the highest false safety rate at 97.3%. Zero NAAQS breaches, technically "clean air" under Indian law. Yet 97.3% of days exceeded WHO limits. Ahmedabad follows at 96.2%, Kolkata at 90.8%.
Four tiers of Indian cities
Crisis cities (>60 µg/m³)
Delhi (83.0), Gurugram (76.3), Lucknow (71.8), Patna (61.9). All on or near the Indo-Gangetic Plain or NCR. Air purification is a baseline necessity.
High but invisible (40–60 µg/m³)
Indore (56.5), Noida (56.3), Jaipur (55.0), Pune (51.8), Nagpur (48.0), Bhopal (43.9). Rarely trigger NAAQS alerts, but false safety zones are massive (62–85%).
Moderate but chronic (25–40 µg/m³)
Ahmedabad (36.2), Hyderabad (35.3), Kolkata (32.3), Bengaluru (29.0). Zero or near-zero NAAQS breaches in most cases. Yet 92–100% of days exceeded WHO guidelines.
Cleanest but not clean (<25 µg/m³)
Mumbai (19.3), Chennai (19.3). Even here, 57–74% of days exceed WHO limits.
Your neighbourhood matters more than your city
In Pune, Revenue Colony averaged 63.7 µg/m³ while Transport Nagar was 29.6. In Hyderabad, Zoo Park averaged 53.5 while Central University was 20.2. The station nearest your home determines your actual exposure.
Why this matters for indoor air
The WHO steering group concluded that PM guidelines are equally applicable to indoor spaces. In Indian homes with natural ventilation, outdoor PM2.5 enters with minimal filtration (I/O ratios of 0.7–1.0+). Indoor sources add to the outdoor baseline. WHO estimates combined ambient and household air pollution cause 6.7 million premature deaths annually.
The outdoor data represents the minimum pollution your home is exposed to.
What this means for you
For Delhi, Gurugram, Lucknow, Patna, the data shows year-round exposure well above both WHO and NAAQS thresholds. For Indore, Noida, Jaipur, Pune, Nagpur, Bhopal, the false safety zone is the key finding: most unsafe days go undetected by India's AQI. For Ahmedabad, Hyderabad, Kolkata, Bengaluru, the gap between domestic and international standards is largest. For Mumbai, Chennai, even in India's cleanest months and cities, WHO limits are exceeded more often than not.
This data suggests that informed decisions about indoor air management, whether through ventilation timing, filtration, or monitoring, are relevant across all Indian cities, not just during winter smog season.
Data & methodology
Data: 41 CPCB stations across Delhi (4), Gurugram (1), Lucknow (2), Patna (3), Indore (1), Noida (2), Jaipur (3), Pune (3), Nagpur (1), Bhopal (2), Ahmedabad (1), Hyderabad (4), Kolkata (4), Bengaluru (4), Mumbai (4), Chennai (2). April 2025, cleaned.
References
- [1] WHO Global Air Quality Guidelines 2021
- [2] India NAAQS 2009
- [3] WHO Indoor AQ Guidelines 2010
- [4] WHO Fact Sheet Oct 2024
- [5] Massey et al. (2009, 2012), Building and Environment
- [6] CARB, Inhalable Particulate Matter and Health
All references collated on the Reference Papers page.
Related reading: India AQI vs US AQI — why the PM2.5 numbers in this analysis look very different on a US-scaled app like AirVisual, and which scale to use for what.
Email us at indoorairguide@outlook.com