Does an Air Purifier Help With Haze? PM2.5, HEPA & CADR Explained
When Singapore's skies turn hazy, one question tends to come up quickly: does an air purifier actually help?
The short answer is yes. An appropriately sized air purifier with effective particle filtration can help reduce the amount of fine particulate matter in an enclosed indoor space.
But there is a catch.
Not every air purifier will perform the same way, and choosing one based purely on the words "HEPA filter" or a high filtration percentage can be misleading.
To understand what actually makes an air purifier useful during haze, you need to understand three things: PM2.5, HEPA filtration and CADR.
Let's break them down.
Why Is Haze a Problem in the First Place?
Singapore experiences transboundary haze when smoke from regional fires is carried towards the country by prevailing winds.
According to Singapore's National Environment Agency (NEA) , the main pollutant of concern during smoke haze is fine particulate matter known as PM2.5.
These particles are small enough to enter buildings through fresh-air intakes, open windows, doors, gaps and other openings.
This is why staying indoors can reduce exposure, but it does not necessarily mean the air inside your home is completely free from haze particles.
What Is PM2.5?
PM2.5 stands for particulate matter measuring 2.5 micrometres or smaller.
To put that into perspective, these particles are far too small to see individually with the naked eye.
During haze episodes, PM2.5 levels can change relatively quickly depending on factors such as wind direction, rainfall and the movement of smoke plumes.
In Singapore, NEA publishes both 1-hour PM2.5 readings and the 24-hour Pollutant Standards Index (PSI).
NEA recommends using the 1-hour PM2.5 reading when deciding on immediate activities, while the 24-hour PSI forecast is more useful when planning activities ahead.
Current air-quality information can be found through Haze.gov.sg and the myENV app.
So, Does an Air Purifier Help With Haze?
Yes, provided you use the right type of air purifier for the space.
NEA lists portable air purifiers as one way households can further reduce indoor particle levels during haze.
The basic idea is simple.
An air purifier pulls air from the room into the appliance. The air passes through one or more filters, which capture airborne particles, before cleaner air is released back into the room.
As this process repeats, the concentration of airborne particles in an enclosed room can gradually be reduced.
However, how effectively this happens depends on both the filter efficiency and the amount of air moving through it.
This distinction is important, because it explains why HEPA filtration alone does not tell you everything you need to know about an air purifier.
What Does a HEPA Filter Do?
HEPA stands for High Efficiency Particulate Air.
Rather than simply letting air pass through an ordinary mesh screen, HEPA filters use a dense network of fibres designed to capture very small airborne particles as air moves through the filter.
For removing fine particles during haze, NEA recommends highly efficient filters such as HEPA filters.
You can read NEA's household haze and air-purifier recommendations in its air pollution FAQs .
Can HEPA Filters Capture PM2.5?
Yes.
PM2.5 refers to particles measuring 2.5 micrometres and below, while HEPA filters are designed to capture particles across a range of sizes.
One common misconception is that a HEPA filter rated at around 0.3 microns can only capture particles that are 0.3 microns or larger.
That is not how HEPA filtration works.
According to NEA's technical guidance on air-cleaning technologies , the effectiveness of HEPA filtration involves several particle-capture mechanisms.
Around 0.3 microns is commonly used as a reference because it is close to the particle size that is among the most difficult for a filter to capture—not because smaller particles simply pass straight through.
HEPA-13 vs HEPA-14: What's the Difference?
You may also encounter different HEPA classifications when shopping for an air purifier.
For example, products in the NNIO Air Purifier collection include both HEPA-13 and HEPA-14 filtration.
NNIO's HEPA-13 products are rated to capture up to 99.95% of airborne particles at the specified test size, while our HEPA-14 filtration is rated at up to 99.995%.
At first glance, the answer seems simple: pick the higher number.
But that misses an important part of air purification.
A filter can be extremely efficient at capturing particles that pass through it, but the purifier still needs to move enough room air through that filter.
Which brings us to perhaps the most overlooked air-purifier specification.
What Is CADR?
CADR stands for Clean Air Delivery Rate.
In simple terms, it helps describe how much cleaned air an air purifier can deliver.
A purifier with a very effective filter but low airflow may take considerably longer to process the air in a large room than an appropriately sized purifier with a higher CADR.
NEA explains that a higher CADR indicates a greater ability to return clean air to a room.
For smoke haze in particular, the smoke CADR is the most relevant measurement where separate smoke, dust and pollen CADR ratings are provided.
Read more in NEA's guide to air-cleaning devices .
Why CADR and Room Size Need to Be Considered Together
Consider two rooms.
One is a compact bedroom. The other is a large open-plan living and dining area.
Even if both use the same type of HEPA filter, the second room contains considerably more air that needs to be processed.
That means the purifier needs enough airflow and cleaning capacity for the space in which it is operating.
NEA's household guidance recommends that, where smoke CADR is provided, an appropriately sized air purifier should have a smoke CADR of at least three times the volume of the room in cubic metres.
A higher CADR means the purifier is capable of cleaning an enclosed room more quickly.
This is why HEPA + CADR + room size should be considered together.
An Easy Way to Think About It
Imagine an air purifier as a combination of a net and a pump.
The HEPA filter is the net. It determines how effectively particles are captured when air passes through it.
CADR tells you more about the cleaning output. It helps indicate how much cleaned air the appliance can deliver.
You need both working together.
An excellent filter with insufficient airflow can still be slow at cleaning a large room. Strong airflow through an ineffective filter is not particularly useful either.
The goal is to find a purifier with effective filtration and sufficient cleaning capacity for your actual room.
What Should You Look for in an Air Purifier for Haze?
If you're comparing air purifiers during Singapore's haze season, we would focus on these six areas:
- Efficient particle filtration: Look for filtration designed to capture fine airborne particles, such as HEPA.
- CADR: Check how much clean air the purifier can deliver rather than focusing only on filtration percentage.
- Room coverage: Make sure the appliance is appropriately sized for your bedroom, study, living room or other intended space.
- PM2.5 monitoring: A built-in sensor can make it easier to see changes in fine-particle levels indoors.
- Automatic operation: Auto Mode can adjust purification based on detected air quality without requiring constant manual adjustments.
- Replacement filters: Check that compatible replacement filters are readily available before purchasing the purifier.
Do You Still Need an Air Purifier If You Close Your Windows?
Closing your windows can help.
During haze episodes, NEA recommends closing doors and windows when outdoor air quality appears to be worsening, as this can reduce the rate at which haze particles enter the home.
However, a home is not normally completely airtight.
Particles can still enter through gaps, doors being opened, ventilation and other openings. There may also already be particulate matter inside the home.
This is why NEA lists portable air purifiers as an additional measure that can be used to further reduce indoor particle levels.
When outdoor air quality improves, NEA recommends reopening doors and windows to ventilate the home.
Can You Use a Fan During Haze?
Yes, but a fan and an air purifier perform different jobs.
A regular fan circulates air. It does not remove PM2.5 simply by moving air around the room.
An air purifier passes room air through a filtration system designed to capture airborne particles.
NEA notes that fans and air-conditioners may still be used for cooling and air circulation during haze.
If you want both airflow and filtration from one appliance, there are also hybrid appliances such as the NNIO TWOPRO Air Circulator and Purifier or NNIO ZENO Air Purifying Bladeless Fan , which combine HEPA-13 filtration with everyday airflow.
How Long Should You Run an Air Purifier During Haze?
There isn't one fixed number of hours that applies to every home.
Indoor particle levels depend on factors including outdoor air quality, how frequently doors are opened, room size, purifier capacity and other indoor sources of particulate matter.
The key thing to remember is that purification happens while room air is continuously being drawn through the filter.
During periods of poorer air quality, continuous or extended operation may therefore be more useful than switching the purifier on briefly and expecting it to maintain clean air after it has stopped.
An automatic mode can make this easier by adjusting the purifier's operation according to readings from its air-quality sensor.
Do You Need to Run an Air Purifier at Maximum Speed?
Not necessarily.
Higher fan speeds generally allow an air purifier to process more air, but they can also increase noise.
If you need to clean the room more quickly—for example, after a door or window has been open during a haze episode—a higher setting may be useful initially.
Once indoor particle levels have fallen, a lower setting or Auto Mode may be more practical for maintaining air quality.
This is another reason why buying an appropriately sized purifier matters. A unit with sufficient capacity for your room gives you more flexibility than one that needs to operate at maximum speed simply to keep up.
What About PM2.5 Sensors?
A PM2.5 sensor doesn't clean the air by itself, but it can make an air purifier much easier to use.
Rather than guessing whether indoor particle levels are increasing or decreasing, the sensor detects fine particles and gives you an indication of changing indoor air quality.
Some purifiers can also use this information automatically.
For example, the NNIO HEPA-14 Air Purifier (NH14PRO) includes a PM2.5 sensor and Auto Mode, allowing the purifier to adjust its speed according to detected air quality.
The NH14PRO has a stated 400m³/h CADR and coverage of up to 520 sq ft.
What If You Have Pets During Haze Season?
Pet households can have another layer of indoor particles to think about.
In addition to particles coming from outdoors, there may be pet fur, dander and other household debris inside the home.
A pre-filter can be useful here because it captures larger particles such as fur before they reach the finer HEPA filtration stage.
The NNIO PET-PRO HEPA-14 Air Purifier for Pets combines a fabric pre-filter for larger pet debris with HEPA-14 filtration, a PM2.5 sensor, 400m³/h CADR and coverage of up to 520 sq ft.
For a more detailed look at choosing a purifier for a pet household, read our guide to the best air purifier for pets in Singapore .
Air Purifiers Are Only One Part of Managing Haze Indoors
An air purifier can help reduce indoor particle concentrations, but it should not be treated as a force field around your home.
During haze episodes, NEA also recommends practical measures including:
- Closing windows and doors when outdoor air quality worsens
- Reducing sources of indoor air pollution
- Using wet-cleaning methods such as mopping and wiping for settled dust
- Reopening doors and windows when outdoor air quality improves
- Checking current PM2.5 readings and health advisories
For the latest official recommendations, refer to NEA's haze FAQs .
So, Does an Air Purifier Help With Haze?
Yes—but the details matter.
During haze, the pollutant of greatest concern is PM2.5. An effective air purifier can help lower concentrations of these fine particles inside an enclosed room by repeatedly drawing air through an efficient filtration system.
But don't choose your purifier based on HEPA grade alone.
Look at the complete picture:
- HEPA filtration tells you about particle filtration efficiency.
- CADR helps indicate how much cleaned air can be delivered.
- Room size determines how much air needs to be cleaned.
- PM2.5 monitoring helps you understand what's happening indoors.
Put those together, and you'll have a much better idea of whether an air purifier is actually suitable for your home.
If you're currently comparing models, read our 2026 guide to choosing the best air purifier for haze in Singapore for a more detailed buying guide.
Or explore the NNIO Air Purifier collection → to compare dedicated HEPA-14 air purifiers with HEPA air-purifying fans and circulators.
Frequently Asked Questions
Can an air purifier remove haze particles?
An appropriately sized air purifier with efficient particle filtration such as HEPA can help reduce fine particulate matter in an enclosed indoor space. NEA recommends HEPA-type filtration for removing fine particles during haze.
Does HEPA remove PM2.5?
Yes. HEPA filters are designed to capture airborne particles across a range of sizes, including particles within the PM2.5 category.
Is HEPA-13 or HEPA-14 better for haze?
HEPA-14 has a higher rated filtration efficiency, but HEPA classification is only one consideration. CADR and room coverage are also important because they affect how quickly room air can be processed.
What CADR is good for haze?
NEA recommends using smoke CADR where available because it is the most relevant CADR measurement for haze pollutants. Its household guidance states that the smoke CADR should be at least three times the room volume in cubic metres.
Should I close my windows when using an air purifier during haze?
When outdoor air quality worsens, NEA recommends closing doors and windows to help reduce the rate at which haze particles enter the home. Windows can be reopened when outdoor air quality improves.
Does a fan remove PM2.5?
A conventional fan circulates air but does not remove PM2.5 simply by moving it around. Particle removal requires filtration or another appropriate air-cleaning technology.
Where can I check Singapore's current haze readings?
Check the latest 1-hour PM2.5 readings, 24-hour PSI and haze advisories through Haze.gov.sg , the NEA website or the myENV app.
Sources & further reading
- National Environment Agency: Managing Haze
- National Environment Agency: Air Pollution & Haze FAQs
- National Environment Agency: Air Cleaning Devices
- Haze.gov.sg: Singapore Air Quality & Haze Updates
Air-quality conditions can change throughout the day. Refer to NEA, Haze.gov.sg and myENV for current readings and official health advisories.
