Singapore Haze Season Guide: Indonesian Peat Fires, PSI vs AQI & Health Protection
Singapore has some of Asia's cleanest urban air year-round — until Indonesia burns. Each dry season, thousands of kilometers of peat fires in Sumatra and Kalimantan send smoke directly over the city-state, turning clear skies grey and pushing health indices into the danger zone. Here's everything you need to understand Singapore's haze crisis and protect yourself.
Why Does Singapore Choke on Indonesian Fires?
Singapore's haze problem is a vivid example of transboundary air pollution — pollution generated in one country that crosses borders to affect others. It's not caused by Singapore's own industries or vehicles; it comes from agricultural burning in Sumatra and Kalimantan (Indonesian Borneo), between 500 and 1,500 km to the northwest.
The root cause is peatland burning. Indonesia has some of the world's largest tropical peat deposits — ancient carbon-rich organic matter accumulated over thousands of years in swampy forest floors. When peatlands are drained for palm oil and paper pulp plantations, the exposed peat becomes flammable. Companies and smallholders use fire as the cheapest method to clear land. Peat fires burn underground, spread slowly and uncontrollably, and can smolder for months — releasing 50–100 times more particulates per hectare than surface vegetation fires.
The southwest monsoon (June–October) creates the delivery mechanism. Prevailing winds during this season blow from the southwest across the Strait of Malacca — exactly from Sumatra toward Singapore and Malaysia. When fires are burning in Riau province or South Sumatra, smoke plumes travel directly on these winds to reach Singapore in 6–24 hours. In 2013, the worst single-day event, PSI reached 401 — the reading instruments at that time could barely register it.
El Niño years dramatically worsen haze because reduced rainfall means more fires burn longer. The 2015 El Niño triggered 261,000 fire hotspots across Indonesia — the equivalent of burning an area larger than Greece. Total health costs to Southeast Asia from that single haze event were estimated at over US$16 billion.
PSI vs AQI: Understanding Singapore's Air Index
Key difference:
- • Singapore's official index
- • 3-hour or 24-hour rolling average
- • Measures PM2.5, PM10, O₃, NO₂, CO, SO₂
- • Reports the highest sub-index
- • Scale: 0–500 (same numbers as AQI)
- • Haze PSI primarily driven by PM2.5
- • US EPA standard (used globally)
- • Reported as real-time or 24-hour
- • Same pollutants, similar breakpoints
- • Used by IQAir, AirVisual, WAQI apps
- • Scale: 0–500+
- • During haze: PSI ≈ AQI (both PM-driven)
During haze events, PSI and AQI are effectively comparable because both are dominated by PM2.5. Singapore's NEA provides both the 3-hour PSI (for immediate conditions) and 24-hour PM2.5 (for health assessment). For daily health decisions, NEA recommends using the 24-hour PM2.5 concentration.
NEA PSI Health Alert Levels
| PSI Band | Category | Recommended Action |
|---|---|---|
| 0–50 | Good | Normal activities. No precautions needed. |
| 51–100 | Moderate | Sensitive groups may reduce prolonged outdoor exertion. |
| 101–200 | Unhealthy | Limit prolonged outdoor activity. Wear N95 if outside for extended periods. |
| 201–300 | Very Unhealthy | Avoid outdoor activities. Stay indoors with windows closed. Wear N95 if must go outside. |
| Above 300 | Hazardous | Stay indoors. Schools may close. Seek medical attention if experiencing symptoms. |
Source: Singapore National Environment Agency (NEA)
Major Singapore Haze Events
| Year | Peak PSI | Fire Region | Notes |
|---|---|---|---|
| 1997 | 226 | Sumatra + Kalimantan | El Niño drought — worst to that date; massive Kalimantan/Sumatra fires |
| 2006 | 150 | South Sumatra, Riau | Dry season fires in South Sumatra and Riau provinces |
| 2013 | 401 | Riau, Sumatra | Historic record — Riau province fires, wind directly over Singapore |
| 2015 | 341 | Sumatra + Kalimantan | El Niño — worst since 1997; 261,000 fires detected in Indonesia |
| 2019 | 188 | Kalimantan, central Sumatra | Kalimantan peat fires during El Niño-adjacent dry conditions |
| 2023 | 139 | Riau, Jambi | El Niño year — moderate haze; NEA activated standby measures |
The ASEAN Haze Treaty: Why It's Not Working
The 2002 ASEAN Agreement on Transboundary Haze Pollution was supposed to solve this. All 10 ASEAN nations signed — including Indonesia — agreeing to prevent and monitor land and forest fires and cooperate on emergency responses. More than two decades later, Singapore still chokes every El Niño year.
The agreement's fundamental problem is national sovereignty. Indonesia has historically been unwilling to let neighbor nations send surveillance aircraft or ground teams into its territory to identify fire-setters. Companies operating in Sumatra and Kalimantan burn with near-impunity during permissive dry windows. Even when specific companies were identified via satellite fire hotspot data, prosecutions were rare.
Singapore's 2014 Transboundary Haze Pollution Act was a unilateral response — it allows Singapore to fine and prosecute companies operating in neighboring countries if their burning causes haze in Singapore. Indonesia protested this as extraterritorial overreach. No company has yet been successfully prosecuted under it, though several have been issued notices.
Progress has been made in reducing fires when political will aligns. Indonesia banned new peatland concessions in 2016 and President Jokowi's government made reducing fires a priority after the catastrophic 2015 season. The 2021 and 2022 haze seasons were relatively mild. But structural economic incentives — cheap land clearing via fire remains profitable for palm oil expansion — have not changed, and El Niño years continue to create conditions where controls fail.
Singapore Haze Survival Guide: What To Do When PSI Climbs
- •Sensitive groups (asthma, elderly, children, pregnant) reduce prolonged outdoor exertion
- •Download NEA's myENV app for real-time PSI updates
- •Prepare N95 masks at home — conditions can worsen quickly
- •Wear N95 mask for any outdoor activity exceeding 30 minutes
- •Close windows and run air conditioning with fresh air intake minimized
- •Consider HEPA air purifier in bedroom and living room
- •Cancel outdoor sporting events for children and elderly
- •Singapore Airlines / regional airlines may see flight disruptions
- •Minimize all outdoor activity — N95 essential for any outdoor exposure
- •MOE may suspend outdoor activities at schools; check for advisories
- •Keep indoor air clean: seal gaps, run HEPA purifier continuously
- •Healthy adults may feel throat irritation, eye irritation — normal
- •Elderly and cardiac patients should be monitored for chest symptoms
- •Stay indoors. Essential outdoor activities only, with N95 mask
- •Schools may close or shift to home-based learning
- •Seek medical attention if experiencing breathing difficulty, chest pain, palpitations
- •Check on elderly neighbors and vulnerable people
- •Government may issue emergency measures — follow NEA and MOH advisories
N95 vs Surgical Mask: Which Mask Actually Works Against Haze?
Filters ≥95% of airborne particles 0.3 μm and larger when correctly fitted. Effective against PM2.5 haze particles. Must seal tightly to face — no air gaps.
- • Recommended for PSI above 100
- • Replace when breathing becomes difficult (~8 hrs use)
- • Singapore sells at Watsons, Guardian, hardware stores
- • Singapore Standard: SS EN 149 FFP2 equivalent
Designed to stop droplets and large particles, not fine PM2.5. Studies show surgical masks filter only 30–60% of PM2.5 particles, and cloth masks far less — with gaps at the sides allowing unfiltered air in.
- • Not effective for haze protection
- • May reduce particulate load somewhat at low PSI
- • Better than nothing but not a substitute for N95
- • NEA explicitly recommends N95 for PSI above 100
When To Expect Haze in Singapore
Southwest monsoon begins. Some haze possible if fires already burning in Sumatra. Usually manageable (PSI under 80).
Peak haze risk. Southwest monsoon at full strength, winds aligned with Sumatra/Kalimantan fire zones. Major events (PSI 100–400+) most likely during El Niño years.
Southwest monsoon weakening. Fire season winding down in Indonesia. PSI typically below 100 unless late-season fires persist.
Northeast monsoon and inter-monsoon seasons. Wind direction shifts away from Sumatra fire zones. Singapore enjoys its best air quality — consistently AQI 30–50.
El Niño prediction: ENSO forecasts are published 3–6 months ahead by NOAA and the Australian Bureau of Meteorology. El Niño conditions during June–October are the single strongest predictor of severe Singapore haze. Check these forecasts in early 2026 to gauge haze season risk.
Best Apps & Resources for Tracking Singapore Haze
Singapore government app. Real-time PSI, PM2.5 concentration, weather, dengue alerts. Most authoritative for haze decisions.
Global air quality app using US AQI standard. Good for comparing Singapore to other cities and getting real-time sensor data in AQI format.
NASA Fire Information for Resource Management System. Shows active fire hotspots in Sumatra and Kalimantan — early warning for incoming haze plumes.
European satellite PM2.5 and aerosol optical depth maps. Shows smoke plume direction and intensity — useful for understanding if haze will worsen or improve.