Methodology, data sources, and update policy
This site is designed to help people interpret AQI and make air-quality decisions. The estimate is intentionally simple enough to be understandable, while still tied to recognizable public methodology.
Interactive formula explorer
Follow the estimate one step at a time
Start with a PM2.5 AQI or a direct PM2.5 reading, choose the exposure time, and inspect every value used in Berkeley Earth's rough population-level health-impact comparison.
Berkeley Earth comparison
≈ 2.52 cigarette-equivalents
This is a rough population-level health-impact equivalence for risk communication. It does not measure cigarettes smoked or predict any individual's exposure, diagnosis, or health outcome.
Step 1 · concentration
AQI 150 → 55.4 µg/m³ PM2.5
Interpolation band: AQI 101–150 / PM2.5 35.5–55.4 µg/m³.
Step 2 · concentration-hours
55.4 × 24 = 1,329.6 µg·h/m³
Step 3 · comparison reference
22 × 24 = 528 µg·h/m³
Step 4 · ratio
1,329.6 ÷ 528 = 2.52
1. AQI to PM2.5
The calculator first converts a PM2.5 AQI into an estimated PM2.5 concentration using the current U.S. EPA breakpoints: 0–9.0, 9.1–35.4, 35.5–55.4, 55.5–125.4, 125.5–225.4, and 225.5–325.4 µg/m³ for AQI bands through 500. AQI is easier to look up, while PM2.5 is the concentration used by the Berkeley Earth comparison.
Values above AQI 500 are outside the standard display scale. When such a value is entered, the site follows AirNow's documented approach of extending the 301–500 PM2.5 slope and labels the result as an extrapolation.
Primary references: the current EPA AQI breakpoint table and AirNow technical assistance document, updated May 2026.
2. PM2.5 to a rough health-impact equivalence
After estimating PM2.5, the site applies Berkeley Earth's rough population-level health-impact equivalence as a risk-communication heuristic. Its rule of thumb treats 22 µg/m³ sustained for one day as approximately one cigarette-equivalent in health impact. It does not measure cigarettes smoked or predict an individual's exposure, diagnosis, or health outcome.
Primary reference: Berkeley Earth's air pollution and cigarette equivalence framing.
3. Direct PM2.5 mode
The calculator also accepts PM2.5 directly. In that mode, the rough comparison keeps the entered PM2.5 concentration at its original precision, while the AQI conversion separately follows EPA's requirement to truncate PM2.5 to one decimal before interpolation.
This preserves the source reading for the concentration-time calculation without changing the EPA AQI calculation rule.
4. What the estimate is good for
5. Live city data layer
City pages use EPA AirNow as a live enhancement layer where regional coverage and an API response are available. If the API is unavailable, rate-limited, unsupported for the city, or not configured in the deployment environment, the site falls back to a static planning baseline instead of failing open.
The live layer is designed as a lightweight utility feature, not a hard dependency.
6. Important limitations
- The estimate is not a medical diagnosis and does not predict an individual health outcome.
- AQI is pollutant-specific. An ozone, nitrogen dioxide, sulfur dioxide, or carbon monoxide AQI cannot be treated as a PM2.5 concentration; the conversion tools require a PM2.5 AQI or clearly label the PM2.5 assumption.
- Real-world exposure changes with exertion, indoor leakage, masks, ventilation, and time spent in cleaner or dirtier microenvironments.
7. Update policy
We review the site when the calculator logic changes, when key methodology references materially change, or when new internal content is added. Supporting pages are updated to improve clarity, internal linking, and user decision value.
The city and scenario pages remain planning aids first. The live AQI layer is intended to improve utility, but users should still interpret rapidly changing smoke or pollution events conservatively and cross-check with local authorities when needed.