China's Air Quality Index Explained
China reports air quality on a 0-to-500 AQI that looks much like the US scale — same range, "worst pollutant wins," colour-coded — but with six differently named categories and more lenient breakpoints. Introduced in 2012 (and, for the first time, including PM2.5 and ozone), it became the public face of China's "war on pollution." This guide breaks it down.
What China's AQI is
Defined by national standard HJ 633-2012, China's AQI summarises six pollutants: PM2.5, PM10, sulphur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), and ozone (O₃). Each pollutant gets an Individual Air Quality Index (IAQI) from its own breakpoint table, and the reported AQI is the maximum. When the AQI exceeds 50, the pollutant with the highest IAQI is named the "primary pollutant."
The six categories
| AQI | Category | Colour | In plain English |
|---|---|---|---|
| 0–50 | Excellent | Green | Air quality is satisfactory; no health impact. |
| 51–100 | Good | Yellow | Acceptable; a few unusually sensitive people may feel mild effects. |
| 101–150 | Lightly Polluted | Orange | Sensitive groups should reduce prolonged outdoor exertion. |
| 151–200 | Moderately Polluted | Red | Sensitive groups feel effects; the general public may begin to. |
| 201–300 | Heavily Polluted | Purple | Everyone may experience effects; sensitive groups should avoid outdoor activity. |
| 301–500 | Severely Polluted | Maroon | Health warnings of emergency conditions; everyone should stay indoors. |
The particulate breakpoints
PM2.5 and PM10 — the pollutants that dominate China's AQI in practice — use a 24-hour average:
| Category | PM2.5 (24-hr, µg/m³) | PM10 (24-hr, µg/m³) |
|---|---|---|
| Excellent | 0–35 | 0–50 |
| Good | 36–75 | 51–150 |
| Lightly Polluted | 76–115 | 151–250 |
| Moderately Polluted | 116–150 | 251–350 |
| Heavily Polluted | 151–250 | 351–420 |
| Severely Polluted | 251+ | 421+ |
How it compares to the US AQI
The two 0–500 scales are structurally alike but China's bands are more lenient at the clean end. China's "Excellent" tops out at 35 µg/m³ PM2.5 — roughly where the modern US scale already reaches "Moderate" — and China's "Good" (up to 75 µg/m³) extends well into what the US calls "Unhealthy for Sensitive Groups." So a Chinese AQI of 100 is meaningfully dirtier air than a US AQI of 100. The category interpretation translates better than the numbers do.
Context: a scale tied to a national clean-up
The 2012 revision — adding PM2.5 monitoring after intense public pressure — coincided with Beijing's "Airpocalypse" and helped launch China's "war on pollution." Concentrations in major cities have fallen substantially since, though winter heating-season episodes and spring dust persist. See Beijing air quality.
Air quality on your iPhone — free
Smog Report shows real-time air quality with widgets, Live Activities, and Apple Watch. Free, no account, no tracking.
Download for iOSPrimary sources: China Air Quality Standards (HJ 633-2012 / GB 3095-2012)