BEIJING • While Singapore experienced a severe bout of haze earlier this year, the cause of the air pollution differs from China's persistent battle with smog.
Haze consists of sufficient smoke, dust, moisture and vapour suspended in air to impair visibility.
For Singapore, this was caused mainly by forest and plantation fires in Central Kalimantan and South Sumatra. The fires were caused by the slash-and-burn method used to clear forested land for farming.
As such, larger particulate matter (PM10) makes up a major component of the haze as PM10 can occur naturally or is produced by burning wood and other vegetation.
The Pollutant Standards Index used in Singapore to measure air pollution reflects six pollutants: sulphur dioxide, particulate matter (PM10), fine particulate matter (PM2.5), nitrogen dioxide, carbon monoxide and ozone.
A 24-hour reading above 100 is unhealthy, and anything higher than 300 is defined as hazardous.
In China, six main sources have been identified for smog in Beijing, with coal burning identified by experts as the main culprit.
The others are soil dust, biomass burning, traffic and waste incineration emission, industrial pollution and secondary inorganic aerosol. This complex mixture makes up PM2.5, the most hazardous of fine particulate matter.
The Air Quality Index used by China specifies PM2.5 concentrations in the air. A reading above 300 is considered hazardous while one above 500 is classified as "beyond index".