In Singapore, the 24-hour PSI and the 1-hour PM2.5 reading answer different questions. The 24-hour Pollutant Standards Index is best used with NEA’s health advisory to plan activities over the day. The 1-hour PM2.5 concentration captures short-term changes and is useful for deciding whether to exercise or remain outdoors for the next hour. Both are available from the National Environment Agency (NEA).
If you searched for Singapore PSI today, 1-hour PM2.5, haze Singapore health advisory, what PSI is unhealthy, N95 mask haze or myENV haze forecast, don’t treat a photograph of a hazy skyline or a privately made sensor reading as an official forecast. Check the relevant NEA region, measurement window and current health advisory before adjusting activities.
Quick summary: PSI 0–50 is Good; 51–100 Moderate; 101–200 Unhealthy; 201–300 Very Unhealthy; above 300 Hazardous. One-hour PM2.5 has separate bands: 0–55 Normal, 56–150 Elevated, 151–250 High and 251+ Very High, all in µg/m³. When air pollution worsens, adjust time and intensity outdoors according to your personal health risk and official advice; N95 masks are not routinely necessary for short commutes.
24-hour PSI versus one-hour PM2.5
| Measurement | What is measured | Best practical use |
|---|---|---|
| 24-hour PSI | Composite index calculated from six pollutants over rolling day | Plan daily and prolonged outdoor activities |
| One-hour PM2.5 | Average concentration of fine particles during last hour | Decide on immediate exercise or outdoor exposure |
| NEA forecast | Expected air quality in next period | Prepare tomorrow’s school, sport or work plans |
| Hotspot or satellite image | Possible fires and movement of smoke | Understand sources, not the exact air a person breathes |
54 Singapore haze, PSI and air-quality vocabulary terms
The words below distinguish pollution measurements from warnings and actions. A term like ‘micrometre’ describes particle size, while ‘microgram per cubic metre’ describes how much particulate material is suspended in a volume of air.
| Term | Plain-English meaning | Why it matters |
|---|---|---|
| Haze | Air pollution reducing visibility and air quality | Can arise from regional fires and changing winds |
| NEA | National Environment Agency | Reports Singapore air quality and health advisories |
| PSI | Pollutant Standards Index | Number representing the most significant of six measured pollutants |
| 24-hour PSI | Index based on rolling 24-hour concentrations | Useful for daily activity planning |
| PSI forecast | Prediction over future period | Separate from an observation measured now |
| PM2.5 | Fine particles with diameter no greater than 2.5 micrometres | Important pollutant during haze |
| 1-hour PM2.5 | Average fine particle concentration over the preceding hour | Useful for immediate outdoor decision |
| µg/m³ | Micrograms per cubic metre | Physical unit used for particle concentration |
| PM10 | Particles no greater than 10 micrometres | Included among PSI pollutants |
| SO2 | Sulphur dioxide | One of six PSI pollutants |
| NO2 | Nitrogen dioxide | Pollutant also associated with combustion |
| O3 | Ozone at ground level | One of PSI components |
| CO | Carbon monoxide | One of PSI components |
| Sub-index | Pollutant-specific contribution to PSI | Highest sub-index determines overall PSI |
| Rolling average | Average updated over moving time window | Different from one single instant |
| Five regions | North, South, East, West, Central | NEA reports regional readings |
| North region | Area including Sengkang and Punggol | Check correct region rather than another city |
| South region | Includes Bukit Timah, Orchard, Marina South | NEA-defined reporting region |
| East region | Includes Tampines, Bedok and Hougang | Not necessarily every place popularly called ‘east’ |
| West region | Includes Clementi and Jurong | Select closest relevant reading |
| Central region | Includes Bishan, Ang Mo Kio and Toa Payoh | Different from general downtown label |
| Good PSI | 0–50 | Normal activities for most people |
| Moderate PSI | 51–100 | Usually normal activity under standard guidance |
| Unhealthy PSI | 101–200 | Reduce outdoor exertion according to vulnerability |
| Very Unhealthy PSI | 201–300 | Stronger limitation advised |
| Hazardous PSI | Above 300 | Avoid outdoor activity for vulnerable people |
| PM2.5 Band 1 | Normal, 0–55 µg/m³ | Ordinary immediate activity typically possible |
| PM2.5 Band 2 | Elevated, 56–150 µg/m³ | Reduce or avoid strenuous activities according to risk |
| PM2.5 Band 3 | High, 151–250 µg/m³ | Greater restrictions on outdoor activity |
| PM2.5 Band 4 | Very High, 251+ µg/m³ | Minimise outdoor time, especially vulnerable groups |
| Transboundary haze | Smoke travelling across national borders | Regional source differs from local measured concentration |
| Hotspot | Heat signal detected from possible fire | Does not by itself prove current local air exposure |
| Satellite observation | Remote sensing of smoke or fires | Different from breathing-level air sensor |
| Smoke plume | Visible airborne smoke transport | Wind and weather affect direction |
| Monsoon winds | Seasonal regional wind patterns | Can move pollution toward Singapore |
| Sensitive group | People more vulnerable to haze effects | Includes children, older adults, pregnant people and lung/heart conditions |
| Prolonged exertion | Physical activity outdoors for several hours | Different from walking briefly to a bus |
| Strenuous activity | High-intensity exercise | May be modified during haze |
| Reduce | Do less or for shorter time | Not exactly the same as avoiding all activity |
| Minimise | Do as little as possible | Stronger restriction than reduce |
| Avoid | Do not undertake activity | Stronger than minimise |
| N95 respirator | Close-fitting mask reducing suitable particle inhalation | Needs correct fit and may be inappropriate for some |
| Mask fit | Seal around nose and mouth | Gaps reduce protection |
| Surgical mask | Loose-fitting medical mask | Not equivalent to a properly fitted N95 for fine particles |
| Indoor air | Air inside enclosed building | Affected by ventilation and outdoor air entry |
| Air purifier | Device filtering indoor air | Use appropriate filter and setup |
| HEPA filter | High-efficiency particulate air filter | Can reduce particles when correctly installed |
| Ventilation | Exchange of air between indoors and outdoors | Adapt to circumstances and official advice |
| myENV | Official NEA environmental information app | Provides regional PSI and PM2.5 |
| haze.gov.sg | Official haze information microsite | Use for forecasts and advisory |
| Health advisory | Public guidance linked to air quality category | Depends on current and forecast readings |
| Respiratory symptoms | Breathing or airway discomfort | Seek medical care when severe or persistent |
| Personal risk | Effect of individual health and activity | Same PSI may call for different actions |
| Haze Subsidy Scheme | Separate medical subsidy programme in certain activation situations | Do not assume currently activated automatically |
Singapore PSI levels explained
| 24-hour PSI | NEA category | Everyday interpretation |
|---|---|---|
| 0–50 | Good | Normal activities for most people |
| 51–100 | Moderate | Normal activities under usual health advice |
| 101–200 | Unhealthy | Reduce prolonged/strenuous outdoor exertion; greater caution for vulnerable groups |
| 201–300 | Very Unhealthy | Avoid or minimise outdoor exertion according to health group |
| Above 300 | Hazardous | Avoid unnecessary outdoors, especially vulnerable people |
NEA computes PSI from the sub-indices of six pollutants — PM10, PM2.5, SO2, NO2, O3 and CO — and reports the highest sub-index. This means PSI is not a straight conversion of the current PM2.5 microgram reading. A 24-hour PSI of 110 and a 1-hour PM2.5 of 70 are different units and averaging periods, so their numerical sizes must not be compared directly.
One-hour PM2.5 bands and what to do now
| One-hour PM2.5 | Band | Immediate outdoor guidance |
|---|---|---|
| 0–55 µg/m³ | Normal | Continue normal activities for most people |
| 56–150 µg/m³ | Elevated | Healthy persons reduce strenuous activity for next hour; vulnerable groups avoid strenuous activity |
| 151–250 µg/m³ | High | Healthy persons avoid strenuous activity; vulnerable groups avoid outdoor activity |
| 251+ µg/m³ | Very High | Healthy people minimise all outdoor activity; vulnerable groups avoid outdoor activity |
NEA reports regional 1-hour PM2.5 readings hourly. Weather and wind direction can change the values quickly, so a short-term normal reading during an ongoing episode does not mean the 24-hour PSI has immediately become good. Use the real current data in conjunction with the 24-hour advisory and your symptoms.
Which region of Singapore should you check?
| Region | Examples of areas in NEA mapping |
|---|---|
| North | Sengkang, Punggol, Woodlands, Yishun |
| South | Bukit Timah, Orchard, Queenstown, Marina South |
| East | Hougang, Bedok, Tampines, Pasir Ris |
| West | Clementi, Jurong East, Jurong West, Bukit Batok |
| Central | Bishan, Ang Mo Kio, Toa Payoh, Thomson |
The reporting regions are based on NEA’s defined town-centre groupings, not every colloquial use of ‘north-east’ or ‘city centre’. For example, NEA places Punggol in its North region and Hougang in its East region. If your exact location is not listed, use NEA’s nearest relevant region instructions rather than a reading from an unrelated part of the island.
What does an Unhealthy forecast mean for different people?
NEA’s published advisory at 24-hour PSI 101–200 says healthy people should reduce prolonged or strenuous outdoor physical exertion; children, elderly people and pregnant women should minimise it; and people with chronic lung or heart disease should avoid it. When PSI reaches Very Unhealthy (201–300), healthy people should avoid prolonged or strenuous outdoor exertion, while more vulnerable groups should reduce or avoid outdoor activity more strongly.
At Hazardous PSI above 300, authorities advise healthy people to minimise outdoor activity, and vulnerable groups to avoid it. A person with asthma or another respiratory condition should follow individual medical guidance and ensure prescribed medicines are available, rather than use a vocabulary table as a substitute for treatment.
What do reduce, minimise and avoid actually mean?
| Instruction | Plain meaning | Everyday example |
|---|---|---|
| Reduce | Do less or for less time | Shorten a planned outdoor run |
| Minimise | Do only what is necessary | Choose indoor activity instead of prolonged outdoor play |
| Avoid | Do not do that activity | Skip outdoor exercise until guidance improves |
| Strenuous | Demanding physical effort | Running hard or playing a competitive match |
| Prolonged | Continuous exposure for several hours | Long outdoor work shift |
A child walking from home to school is not necessarily experiencing the same exposure as a person doing a long-distance run outdoors for two hours. Health advice distinguishes duration, intensity and personal vulnerability. The safest plan for a specific child or worker should consider all three.
N95 masks: when do they help?
HealthHub explains that N95 masks are not normally needed for ordinary commuting between home, school and work, or for being indoors. They may be considered if a person must remain outdoors during especially high PM2.5 levels and cannot avoid exposure. A properly fitting respirator must seal around the nose and mouth; simply wearing an ill-fitting mask may provide less protection than expected.
Some vulnerable people, including those with significant lung or heart disease, older adults and pregnant people with breathing difficulty, should consult a doctor before prolonged N95 use. Feeling breathless while wearing a mask is not a reason to endure discomfort. N95 masks are not universally suitable for small children, and advice should be age-appropriate.
Indoor air and the difference between a mask and a purifier
A mask filters inhaled air when worn correctly. An indoor air purifier can reduce airborne particles within a room under its rated conditions, especially when it has an appropriate effective filter, but it does not make outdoor air quality readings irrelevant. Keep indoor environments appropriate for occupancy and follow official recommendations on windows, ventilation and exercise during a haze episode.
A portable consumer sensor can help a person notice local variation, but its calibration, placement and accuracy may differ from the regulatory monitoring network. Treat it as supplementary rather than replacing NEA’s official PSI and PM2.5 reports when making public health decisions.
What causes haze in Singapore?
Transboundary haze can occur when smoke from regional vegetation or peat fires travels with winds into Singapore. Satellite images identify potential hotspots and plumes, while local air monitoring instruments measure what reaches Singapore. Rainfall and shifts in wind can reduce or raise observed pollution over a short interval. The underlying fire source and current health risk are related but not identical data.
How to plan a family day during haze
- Check the latest official 24-hour PSI and accompanying NEA/MOH health advisory.
- Check the relevant regional 1-hour PM2.5 band for immediate outdoor decisions.
- Identify who may be more vulnerable: young children, older adults, pregnant people or those with heart/lung problems.
- Reduce, minimise or avoid outdoor activities according to the applicable health group.
- Prefer suitable indoor activities when air is poor and monitor symptoms.
- Do not assume a brief visually clear sky means the day’s air quality forecast is good.
- If anyone develops significant or persistent respiratory symptoms, seek appropriate medical care.
- Review the forecast again before committing to longer outdoor plans.
Four scenarios: turning vocabulary into decisions
| Scenario | Correct first question | What the answer changes |
|---|---|---|
| A teacher planning sports day | What is the PSI forecast and students’ vulnerability? | Whether to modify, postpone or move activities |
| A parent planning a short walk | What is current 1-hr PM2.5 in our region? | The immediate exposure decision |
| A runner with asthma | What does medical advice say for this level? | Avoiding risky exertion |
| A commuter seeing a viral haze photo | What are NEA’s latest measurements and date? | Avoiding mistaken claims from old images |
Common misconceptions corrected
| Misleading statement | More accurate version |
|---|---|
| 24-hour PSI and 1-hour PM2.5 are the same reading. | Different pollutants/time windows and units are involved. |
| A screenshot of last night’s PSI proves today’s condition. | Check current official time and region. |
| Haze visible in a skyline proves every region is Hazardous. | Use measured local pollution and advisory. |
| All people must stop going outside at PSI 101. | Recommendations depend on intensity, duration and vulnerability. |
| Every citizen must wear N95 when haze appears. | N95 is not routinely needed for short commutes. |
| A home sensor automatically overrides NEA. | Private sensors vary in calibration and siting. |
| A low current PM2.5 means the 24-hour PSI is instantly normal. | The 24-hour index changes on a rolling average. |
Frequently searched Singapore haze questions
What PSI is considered unhealthy in Singapore?
The 24-hour PSI category becomes Unhealthy from 101 to 200; 201–300 is Very Unhealthy and above 300 is Hazardous.
What is the difference between PSI and PM2.5?
PSI is a 24-hour multi-pollutant index; the one-hour PM2.5 value is a concentration of fine particles during a recent one-hour period.
What is the normal one-hour PM2.5 band?
NEA defines Normal as 0–55 micrograms per cubic metre in its current short-term guidance.
What does Elevated PM2.5 mean?
Band 2 is 56–150 µg/m³; healthy people should reduce strenuous activity for the next hour while vulnerable people should avoid strenuous activity.
Where can I find Singapore’s current haze reading?
Use NEA’s myENV app, official NEA website or haze.gov.sg, looking at the appropriate region and timestamp.
Do I need an N95 mask for the MRT commute?
HealthHub says N95 masks are generally unnecessary for an ordinary commute. Certain people unable to avoid outdoor exposure at high levels may benefit from appropriately fitted respirators.
Why does haze change quickly during the day?
Winds, rainfall, the movement of smoke plumes and local conditions cause short-term concentration to fluctuate.
Does PSI 150 mean every person has the same health risk?
No. Healthy persons, children, older adults, pregnant women and persons with chronic heart/lung disease are advised differently.
Can I use a consumer particle monitor instead of NEA?
It can be supplementary, but NEA’s calibrated monitoring network and official public-health advice remain the primary Singapore reference.
What should I do if someone has breathing difficulty during haze?
Seek appropriate medical assessment promptly, particularly if symptoms are severe or persistent. Do not use general air-quality numbers to delay necessary care.
Connected eduKateSG reading
- How Singapore Works | Haze, PSI and PM2.5 — system explanation.
- Everything We Need to Know About Singapore | Weather and Haze — wider weather context.
- Singapore Vocabulary | Healthcare Subsidies — care and financing terminology.
- Vocabulary Hub — more Singapore terms.
Official sources and health guidance
- NEA: Air Quality FAQs — PSI method, five regions and one-hour PM2.5.
- NEA: Managing Haze — current health advisory table.
- HealthHub: Protecting Yourself Against Haze — immediate bands and mask advice.
- Singapore Haze Microsite — current readings and forecasts.
Reviewed 4 November 2026. This is a vocabulary guide, not a real-time air-quality report or diagnosis. For an immediate decision, look up the newest NEA reading and follow the official health advisory.