Dewās — WHO vs EPA vs NAQI
Dewās sits at the centre of a benchmark gap. Across 2,447 days of CPCB monitoring, 47.7% land in NAQI's Good or Satisfactory bands, but only 20.6% would clear the US EPA's Good-or-Moderate bar — and 99.5% of days exceed the WHO 24-hour PM2.5 guideline of 15 µg/m³. Annual mean PM2.5 (estimated) sits at 56.7 µg/m³, 11.3× over the WHO long-term guideline.
Three rule books, three verdicts
The three charts below judge the same air quality data three different ways. India NAQI is the official Indian scale (CPCB) and is the most lenient on PM2.5. US EPA AQIuses the same 0–500 scale but with stricter thresholds, so the same day usually lands a category higher. WHO 2021is the strictest of all — health-based limits of 5 µg/m³ annually and 15 µg/m³ per day. They disagree because each scale has a different goalpost; the breakdown below shows how often, and by how much, for Dewās.
100% stacked. Each row covers the same set of CPCB monitoring days, classified under a different rule book.
PM2.5 estimated by inverse-mapping daily NAQI through the CPCB PM2.5 breakpoint table. WHO 2021 air quality guideline (AQG) and four interim targets shown.
Where the rule books disagree
On 27.1% of Dewās's days, NAQI says "Good" or "Satisfactory" while US EPA flags the same air as Unhealthy for Sensitive Groups or worse. EPA AQI averages 32 points higher than NAQI — that gap is the structural difference between the two scales, not a measurement error. India's NAQI was calibrated for higher background concentrations: its Moderate band stretches from AQI 101 to 200 and accepts PM2.5 up to 90 µg/m³, where US EPA already calls 35.4 µg/m³ the boundary of "Unhealthy for Sensitive Groups."
Per-NAQI-band crossover — what does each Indian category really mean?
For every NAQI band, here is how the same days distribute across US EPA bands. Rows sum to that NAQI band’s share of 2,447 days.
| NAQI band | Good | Moderate | USG | Unhealthy | Very Unhealthy | Hazardous | Total |
|---|---|---|---|---|---|---|---|
| Good | — | 14.1% | — | — | — | — | 14.1% |
| Satisfactory | — | 6.5% | 20.9% | 6.1% | — | — | 33.6% |
| Moderate | — | — | — | 47.8% | — | — | 47.8% |
| Poor | — | — | — | 4.3% | — | — | 4.3% |
| Very Poor | — | — | — | — | 0.2% | — | 0.2% |
| Severe | — | — | — | — | — | — | 0.0% |
Against WHO 2021 — the international yardstick
Against the WHO 2021 guidelines, Dewās runs squarely outside safety. 0.0% of days fall within the WHO annual mean (5 µg/m³); another 0.5% land between annual and 24-hour ceilings (5–15 µg/m³); the remaining 99.5% breach WHO's 24-hour limit. That single number — share of days above 15 µg/m³ — is the cleanest international comparison: it puts Dewās's record on the same axis as London, Beijing, or Dakar, regardless of which national AQI you trust.
What to do with this
For personal decisions in Dewās, treat WHO 24-hour (15 µg/m³) as your floor for "outdoor exercise OK," not NAQI's Good band. Use a HEPA purifier sized so indoor PM2.5 stays under 5 µg/m³ year-round. For policy and journalism, lead with the WHO daily-exceedance number (99.5%) and the EPA-vs-NAQI re-classification number (27.1%) — they survive scale arguments because they are direct day-counts, not category labels.
Frequently asked questions
More Dewās analytics
PM2.5 estimated by inverse-mapping daily NAQI through the CPCB PM2.5 sub-index breakpoint table; EPA AQI then forward-mapped from that estimate. Reliable when PM2.5 is the dominant pollutant (true for the vast majority of polluted Indian station-days). Source: CPCB station-level daily readings.