Forum: For haze planning, use PM2.5 for immediate activities and PSI forecast for next day’s
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We thank Andre Ching Wei Jie for his letter, “Air quality readings may still leave people in a haze” (Sept 17).
The National Environment Agency (NEA) Pollutant Standards Index (PSI) readings reflect the air quality over the past 24 hours. This is in line with 24-hour air quality indices in the US, EU and UK.
Most health studies on air pollution impact are also based on 24-hour exposure, so PSI readings have health-based descriptors like “Good”, “Moderate”, “Unhealthy”, “Very Unhealthy” and “Hazardous”.
As people with different health and medical conditions are affected to a different extent by poor air quality, the PSI readings are accompanied by health advisories for different groups. When planning activities for the next day, the public can refer to the daily PSI forecast, which assesses the air quality in the coming 24 hours.
The one-hour PM2.5 reading reflects current air quality and supports informed decision-making on immediate activities. It uses non-health-based descriptors such as “Normal”, “Elevated”, “High” and “Very High”, together with guidance on suitable precautions that the public and vulnerable groups should take.
Third-party platforms such as AQICN may use different data sources, averaging periods, index categories and calculation methods to derive their air quality index. Readings by such third-party platforms are not directly comparable with NEA’s air quality indicators.
For accurate information on air quality and health advisories, please refer to NEA’s official readings and guidance on the myENV app, haze microsite (www.haze.gov.sg) and NEA website (www.nea.gov.sg).
Tan Li Yen
Group Director (Clean Environment)
National Environment Agency