Haze Day Why is haze often worse at night and in the early morning?
At night the lowest layer of air cools, becomes stable and shallow, and winds weaken, so smoke collects near the ground. After sunrise the ground warms, the air mixes upwards and readings often ease by midday. Check the hourly PM2.5 before early-morning exercise.
It is a tendency, not a rule
A fresh smoke plume can arrive at any hour if the wind shifts towards the fires, and rain can clear the air at night. That is why the 1-hour reading, not the time of day, should decide.
Planning around it
If you run or cycle before work, check the latest reading first and consider moving to a later or indoor session on hazy days. The next-24-hours chart on each place page shows the cleanest 2-hour window the model expects.
Related guides
Understand the causes
Related questions
Sources
- NEA 1-hour PM2.5 readings (Singapore) — National Environment Agency (NEA), Singapore · official site · API / docs
- CAMS PM2.5 model via Open-Meteo — Copernicus Atmosphere Monitoring Service (ECMWF); served by Open-Meteo · official site · API / docs
- Open-Meteo weather forecast — Open-Meteo (national weather services and ECMWF models) · official site · API / docs
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Haze Day. “Why is haze often worse at night and in the early morning?.” haze.day, updated . https://haze.day/en/faq/haze-worse-at-night
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