SINGAPORE - Air quality hit unhealthy levels on Tuesday (Sept 8) morning before deteriorating further throughout the day.

And it could get worse today (Wednesday, Sept 9).

The hazy conditions are expected to persist as wind from the south or south-west blows smoke haze here from Sumatra, the National Environment Agency (NEA) said on Tuesday night.

The 24-hour Pollutant Standards Index - an air quality measure - is forecast to be in the low- to mid-end of the unhealthy range (101-200) on Wednesday and may deteriorate further if the winds are unfavourable.

The 24-hour PSI first crossed into the unhealthy range at 11am on Tuesday, and as of 8pm stood at between 92 and 105.

The NEA said 38 hot spots were detected in Sumatra on Tuesday, up from nine on Monday, but added that these counts were low, which could have been due to cloud cover.

Tax manager Eileen Seah, 33, said she will take precautions if conditions worsen today, such as wearing a mask outdoors: "I don't want to risk getting health problems."

Continuous exposure to unhealthy PSI levels over a few days is known to cause irritation of the eyes, nose and throat.

Sales executive Steven Ng, 41, found the haze made his eyes itch and plans to avoid outdoor activities in hazy conditions. "I also have a mask in my bag for emergencies."

The elderly, pregnant women and children are advised to minimise prolonged or strenuous outdoor activity, while those suffering from chronic lung or heart disease should avoid these activities when the 24-hour PSI exceeds 100.