The haze returned to Singapore briefly yesterday.
The pollution was worst in the early afternoon with the three-hour Pollutant Standards Index climbing from 63 at 11am to 92 at 2pm.
It then fell steadily for the rest of the day.
The index is published online hourly from 7am to 7pm and linked to the amount of air pollution in the previous three hours.
At no point did the air here become unhealthy, although there were complaints about the familiar acrid smell and foggy skies.
It seemed like my area was being fumigated.
PUVANA DEVI, Choa Chu Kang resident
Public servant Puvana Devi, 25, who lives in Choa Chu Kang, was surprised by how thick the haze was when she left home in the morning. "It seemed like my area was being fumigated," she said.
Doctors have been put on alert by the Ministry of Health (MOH) to keep a closer eye on patients with asthma, in case they are affected by the haze.
Several general practitioners told The Straits Times that they were advised by the ministry late last month to take measures such as adjusting the dosage of asthma patients' medication if necessary.
They received similar advice last year.
A spokesman for MOH said it wanted to "remind all medical practitioners of the health advisory for the public during the haze season" and "the appropriate management of asthma patients during a haze period".
Earlier this month, the National Environment Agency warned that the Republic might have slight haze on a few days in the first two weeks of this month.
The Meteorological Service Singapore had also forecast that Singapore and the surrounding region can expect the months of June to early October to be drier and warmer than usual, partly due to the El Nino weather phenomenon.
This could increase the risk of haze in the region during this period, it said.
Meanwhile, forest fires in Sumatra, Indonesia - traditionally the source of haze in Singapore - have also been worsening in the past week.
On Thursday, The Straits Times reported that the Indonesian authorities were expanding cloud- seeding operations in Sumatra to artificially induce rain to put out the fires.
The cloud-seeding operations have been taking place over central Sumatra for more than two weeks.