What do these numbers mean?
Singapore reports haze with two readings. They measure different things and answer different questions, so it helps to know which to look at.
The short version
1-hr PM2.5
Should I go out now?
Fine particles in the air over the last hour, in µg/m³. It changes quickly, so use it for plans in the next few hours, like a run or a walk to the bus stop.
24-hr PSI
What's today like overall?
An index built from the last 24 hours of pollution. It moves slowly and lags behind, so use it to plan the day, or the next day.
When they disagree, the 1-hr PM2.5 tells you about the air right now. A PSI of 168 with a PM2.5 of 251 means the past day was unhealthy and this hour is much worse.
1-hr PM2.5 bands
PM2.5 are particles smaller than 2.5 microns, small enough to reach deep into the lungs. In haze, they're mostly smoke.
| Band | µg/m³ | NEA: everyone | NEA: vulnerable persons |
|---|---|---|---|
| Normal | 0–55 | Continue with normal activities | As above |
| Elevated | 56–150 | Reduce strenuous outdoor activity for the next hour | Avoid strenuous outdoor activity for the next hour |
| High | 151–250 | Avoid strenuous outdoor activity for the next hour | Avoid all outdoor activity for the next hour |
| Very high | 251+ | Minimise all outdoor activity for the next hour | Avoid all outdoor activity for the next hour |
24-hr PSI bands
The Pollutant Standards Index combines six pollutants. During haze, PM2.5 almost always sets the number.
| Band | PSI | Healthy persons | Elderly, pregnant women, children | Persons with chronic lung disease, heart disease |
|---|---|---|---|---|
| Good | 0–50 | Normal activities | Normal activities | Normal activities |
| Moderate | 51–100 | Normal activities | Normal activities | Normal activities |
| Unhealthy | 101–200 | Reduce prolonged or strenuous outdoor physical exertion | Minimise prolonged or strenuous outdoor physical exertion | Avoid prolonged or strenuous outdoor physical exertion |
| Very unhealthy | 201–300 | Avoid prolonged or strenuous outdoor physical exertion | Minimise outdoor activity | Avoid outdoor activity |
| Hazardous | 301+ | Minimise outdoor activity | Avoid outdoor activity | Avoid outdoor activity |
Who counts as vulnerable?
NEA's advice uses this term for the elderly, pregnant women, children, and persons with chronic lung disease or heart disease.
Good to know
- Sheltered isn't indoors. Void decks, covered walkways and open-air hawker centres have the same air as outside.
- Masks: N95 masks filter PM2.5; surgical masks don't. N95s aren't designed for young children.
- At home: close windows, run an air purifier with a HEPA filter, and set aircon to recirculate.
- Feeling unwell? Throat or eye irritation usually clears once you're out of the haze. See a doctor for breathlessness, chest tightness or wheezing.
Bands and advice follow NEA's haze health advisory. For official updates, see haze.gov.sg. Not medical advice.
See the latest readings