How AirAware works

Where AirAware’s readings come from, how the PM2.5 US AQI estimate is calculated, why PSI and AQI can disagree, and the limits of five regional readings.

What AirAware shows

Official 24-hr PSI and 1-hr and 24-hr PM2.5 for five regions, from NEA via data.gov.sg, shown exactly as published and updated hourly. One figure is calculated by AirAware: a PM2.5-only US AQI, from NEA’s 24-hr PM2.5 using the US EPA’s May 2024 breakpoints (concentration truncated to 0.1 µg/m³, linear interpolation, rounded to the nearest whole number). It is an estimate, not an official Singapore index. Singapore-wide figures are the highest regional reading, not an official national average.

Limitations

Five regional readings can’t describe individual streets or neighbourhoods. Map zones are approximate. PSI and AQI use different scales and aren’t interchangeable. Readings can be delayed, missing or revised. Fresh means received within 75 minutes; delayed, up to 3 hours; older values are labelled “last known”.

Common questions

Why can AQI and PSI disagree?

They turn the same 24-hr PM2.5 concentration into a number using different breakpoints. The US EPA tightened its PM2.5 breakpoints in 2024, so the same air can read as a worse category on the US AQI than on Singapore’s PSI. The PSI also reports the worst of six pollutants, while the AQI shown on AirAware covers PM2.5 only.

What is the PSI?

The Pollutant Standards Index is Singapore’s official air-quality index, published hourly by NEA for five regions. NEA calculates a sub-index for six pollutants (PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide) and reports the highest. 0–50 is Good, 51–100 Moderate, 101–200 Unhealthy, 201–300 Very unhealthy and 301+ Hazardous. Singapore’s health advisory is based on the 24-hr PSI.

What is the AQI?

The US Air Quality Index converts pollutant concentrations into one 0–500 scale with six categories. A value of 100 corresponds to the US short-term health standard. AirAware calculates a PM2.5-only AQI from NEA’s 24-hr PM2.5 using the EPA’s 2024 breakpoints. It is an estimate, not an official Singapore index.

What is PM2.5?

Fine particles 2.5 micrometres across or smaller, the main pollutant in haze smoke. They are small enough to reach deep into the lungs. PM2.5 is a measured concentration in micrograms per cubic metre (µg/m³), not an index.

How often is Singapore’s air-quality data updated?

NEA publishes new readings every hour. Each update adds one new 1-hr PM2.5 value and recalculates the 24-hr PSI over the latest 24 hours, so the 24-hr figure moves slowly even when the air changes quickly. AirAware checks for new readings every five minutes.

Source: National Environment Agency (NEA) via data.gov.sg, Singapore Open Data Licence v1.0. Health guidance: Ministry of Health (MOH) and US EPA. AirAware is not affiliated with NEA, MOH or the US EPA and does not provide medical advice. For official information, see haze.gov.sg.

Data: latest readings (JSON) · 7-day history (JSON) · llms.txt