Haze disrupts daily routines, hits businesses in Singapore's west as PSI reaches very unhealthy level

The Pollutant Standards Index, or PSI, is a number used to describe overall air quality. It combines pollution measurements into a scale that helps people understand how polluted the air is and what it may mean for daily activities. A higher PSI indicates worse air quality.

A reading of 230 is classified as very unhealthy. In the article, the western region reached 230 at 10am on Sunday, October 18. Residents reported eye irritation, breathing discomfort and reduced outdoor activity as the haze worsened.

The figure was a regional reading, not necessarily the same across the whole island. Air quality can change between regions and even within a single day. Wind, smoke-plume movement, rainfall and local pollution can all cause PSI levels to rise or fall.

The haze was widespread across Singapore, but its severity varied sharply between regions. The west recorded a 24-hour PSI of 230 at 10am on October 18. That was the highest reading recorded islandwide that year and placed western Singapore in the very unhealthy range.

The west had the poorest daily air quality from October 12 onward, except on October 16, when central Singapore ranked worst. It also recorded the highest one-hour PM2.5 readings on most of those days. Its one-hour PM2.5 reading reached 288 on October 14, the highest recorded that year.

Earlier in September and October, central Singapore had recorded higher haze readings. Experts warned that conditions could change because smoke plumes, wind, atmospheric mixing, rainfall and local emissions affect different parts of the island differently.

The haze disrupted ordinary routines and reduced outdoor activity in western Singapore. Residents stayed indoors more often, used masks and eye drops, and experienced eye irritation or breathing difficulty. The conditions affected adults, children and businesses, not only people with outdoor jobs.

Jurong West resident Yong Yoon Chin and his wife stopped evening walks and paused other activities, including golf. Their children’s clothing shop saw business fall by about 70 per cent over two weeks. They sometimes closed at 4.30pm instead of 8pm. Eight-year-old Eashan also stopped visiting the playground with his younger brother and said the change was boring.

These effects came from fewer people venturing outside and discomfort caused by polluted air. The disruption could continue while haze levels remain high, but experts said conditions are dynamic and may improve with changing winds, rainfall and the coming monsoon transition.

Air quality differs across Singapore because pollution is constantly transported, diluted, removed or added. Smoke plumes may move toward one region while another receives cleaner air. Dense buildings can also create varied airflow patterns. As a result, the highest PSI reading can appear in different parts of Singapore at different times.

The article gives several controls on this process. Wind direction moves smoke, while wind speed and atmospheric mixing affect how concentrated it becomes. Rain can wash pollutants from the air. Local urban emissions add more pollution, and topography affects how particles travel, spread and settle. These processes can dominate at different moments.

That is why the west’s recent lead may not last. Central Singapore had the highest readings earlier in the season, and it led again on October 16. Experts said hourly PM2.5 trends are difficult to generalise for any specific area.

The article links Singapore’s haze to transported smoke from fire hotspots in Indonesia. Smoke can cross borders and travel long distances, especially when large plumes are carried by prevailing winds. However, Singapore’s air is not affected by one source alone. Local urban emissions also contribute to the pollution measured at monitoring stations.

Fires release fine particles into the atmosphere. Their impact depends on the amount emitted, the number and location of hotspots, and the direction of the wind. Chemical reactions can form additional particles. Local emissions then combine with incoming smoke, while atmospheric mixing may dilute or spread the pollution.

This combination explains why conditions differ across Singapore. Professor Rajasekhar Balasubramanian said sporadic smoke plumes and changing atmospheric conditions make consistent hourly trends difficult to predict. The article does not identify one single fire as the source of each reading.

Weather controls how intense the haze becomes. Wind direction determines where smoke travels, while wind speed and atmospheric mixing affect whether particles remain concentrated or become more diluted. If smoke is carried toward a region and mixing is weak, pollution can build there. Stronger mixing can distribute particles more widely.

Rain can reduce pollution by washing airborne particles from the atmosphere. Associate Professor Yu Liya said rainfall may dominate over incoming smoke, producing fewer pollutants and a lower PSI. By contrast, continued smoke transport, limited mixing or unfavourable winds can intensify readings. Temperature and local airflow also influence the final concentration.

The article looked ahead to a monsoon transition in the coming month. During the northeast monsoon, likely starting in December, transported smoke was expected to weaken and rainfall to increase. Those changes could help cleanse Singapore’s ambient environment, although conditions remained dynamic.

PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometres or less. These particles are much smaller than visible dust. Because of their tiny size, they can remain airborne and travel with smoke. They are tracked separately from the broader PSI because they provide specific information about fine-particle pollution.

The article reports that western Singapore recorded a one-hour PM2.5 reading of 288 on October 14. Residents described eye irritation and breathing difficulty, while Yong said wearing a mask made breathing harder. Fine particles can reach deep into the lungs, where they may inflame airways and worsen breathing problems, especially during heavy pollution.

PM2.5 levels depend on fires, wind, chemical reactions, atmospheric mixing and local urban sources. Readings can therefore change quickly. Rain and improved atmospheric conditions may lower concentrations, while incoming smoke can raise them again.