Levels of fine particles in the air – known as “PM2.5” – spiked to the unhealthy range yesterday, triggering warnings for some people to limit outdoor exercise.
This is even as the main Pollutant Standards Index (PSI) stayed in the moderate range. At 9pm last night, the 24-hour PSI in various parts of the island ranged from 48 to 70.
But PM2.5 levels hit 60 micrograms per cubic m at several points in the afternoon, the highest reading this year. A reading above 55 mcg would be considered unhealthy under a new way of calculating the PSI from May.
At these levels, the elderly, children and those with heart or lung disease should reduce prolonged or heavy outdoor exertion, while everyone else should limit it, said an advisory on the National Environment Agency (NEA) website.
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