Pollutant Standards Index

PSI, the Pollutant Standards Index, is Singapore's official air-quality measure, and searches for it have surged. A haze update from AsiaOne reports that air quality in central Singapore has turned unhealthy, which fits the pattern of people checking the index to see whether it is safe to go outside, exercise, or send children to school. Singapore experiences seasonal haze, often linked to forest fires in neighbouring Indonesia, so the term typically spikes whenever readings deteriorate.