The spread of transboundary haze across South-East Asia from ongoing wildfires in Indonesia has historically caused confusion over the different ways air quality is reported.
As of October 10, 2026, Singapore's National Environment Agency (NEA) reported that most Singapore regions were in the "unhealthy" category. The reported 24-hr PSI at 6:00 AM (local time) was 127-177 (1). At the same time, IQAir reported a U.S. Air Quality Index (AQI) value of 197, or “unhealthy.”
While both indexes reported the air quality as being in the unhealthy range at that time, there are times when the two indexes will display different ranges.
Singapore was ranked the second most polluted major city in the world as of October 10, 2026, at 6:00 AM (local time). Source: IQAir.
Air quality map of Singapore, as of October 10, 2026, at 6:00 AM Source: IQAir.
In Singapore, the NEA uses the Pollutant Standards Index (PSI). It has five categories from “good” to “hazardous.”
PSI Categories:
- 0 – 50: Good
- 51 – 100: Moderate
- 101 – 200: Unhealthy
- 201 – 300: Very Unhealthy
- Above 300: Hazardous
The IQAir AirVisual platform uses the U.S. Air Quality Index (AQI). It has six categories which also range from “good” to “hazardous.”
U.S. AQI Categories:
- 0 – 50: Good
- 51 – 100: Moderate
- 101 – 150: Unhealthy for Sensitive Groups
- 151 – 200: Unhealthy
- 201 – 300: Very Unhealthy
- 301 – 500+: Hazardous
Why are the Singaporean and U.S. AQI different?
There are two main reasons for the differences between AQIs.
The timeframe: Singapore’s NEA updates the PSI on its website every hour, but each new reading is actually an average of the previous 24 hours. This means that the PSI figure of 127 (unhealthy) at 6:00 AM was an average of the previous 24 hours. It doesn’t tell you what the air was like at 6:00 AM.
In contrast, the IQAir AirVisual platform reports Singapore's air quality data every hour, or in real time. As a result, if there is a sudden dangerous spike in air pollution, the value will reflect this. That information is then available to you immediately, and you can act to protect yourself, for example, by wearing an air pollution mask, limiting outdoor activities, or running an air purifier.
The index: the IQAir AirVisual platform uses the U.S. Air Quality Index, which is one of the world's most stringent indexes and a widely used international standard.
The US AQI and the Singaporean PSI are both calculated from the same six pollutants, with the dominant pollutant determining the final value.
When PM2.5 density is between 13-55 micrograms per cubic meter (µg/m³), the Singapore PSI reports the air quality as “moderate.” But the US AQI considers roughly half of the Singapore “moderate” category (35.5-55.4 µg/m³) to be “unhealthy for sensitive groups,” providing guidance for more vulnerable groups, including children, the elderly, and people with heart and lung disease.
What is AQI+?
To make it even clearer that IQAir's AQI is updated hourly, the IQAir website, the IQAir AirVisual app, and the IQAir Dashboard display a U.S. AQI⁺ label. Conventional U.S. AQI calculations typically depend on 24-hour pollutant averages (for PM2.5, for instance) which can fail to capture sudden shifts in air quality. While some platforms offer AQI readings built on shorter averaging windows, even these update less frequently than IQAir's hourly reporting.
How does IQAir report air quality data?
Using the U.S. AQI, IQAir reports data from air monitoring stations operated by the Singapore NEA and from local contributors.
IQAir validates all data before publishing it on its AirVisual platform, filtering out anomalous readings. That means if a faulty air quality monitor suddenly reports unusually high readings, AirVisual’s AI system would spot the fault and it would not affect that city’s overall air quality reading.
To access the fastest, most up-to-date information, see Singapore's air quality map or download the free IQAir AirVisual app.
