Does an Air Purifier Reduce PM2.5? How to Verify It During Haze Malaysia
Meta Description: Does your air purifier really reduce PM2.5 during haze? Learn how to test purifier performance correctly with a PM2.5 air quality monitor in Malaysia.
Does an Air Purifier Reduce PM2.5? How to Verify It During Haze Malaysia
During severe haze in Malaysia, many homes, schools and offices operate air purifiers continuously. However, switching on an air purifier does not automatically prove that the PM2.5 concentration across the room has decreased.
Actual performance depends on several factors:
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Room size
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Purifier capacity
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Filter type and condition
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Fan-speed setting
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Purifier placement
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Open doors and windows
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Outdoor haze intensity
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Building leakage
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Indoor particle sources
A PM2.5 air quality monitor allows users to measure the room before and after operating the purifier. This provides clearer evidence than relying on smell, visibility or the purifier’s fan sound.
Can an Air Purifier Remove Haze Particles?
A suitable air purifier equipped with an effective particulate filter can reduce airborne particles, including PM2.5, within an enclosed space.
However, the result depends on whether the purifier can circulate and filter enough air for that particular room.
Performance may be limited when:
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The room is too large
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The purifier is undersized
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The filter is dirty
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The fan speed is too low
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Doors and windows remain open
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Outdoor particles enter continuously
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Furniture blocks air circulation
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The unit is placed in a corner
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New particles are being generated indoors
Instead of assuming that the purifier is effective, users can verify the result by measuring PM2.5.
Why PM2.5 Should Be Measured
PM2.5 refers to airborne particles with a diameter of 2.5 micrometres or smaller.
During haze, these fine particles may enter buildings through windows, doors, ventilation systems and gaps around the building envelope.
They cannot be assessed accurately through:
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Smell
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Visibility
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Dust seen on furniture
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The purifier’s colour indicator alone
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Whether the room feels comfortable
A room may smell clean while still having elevated PM2.5. A direct numerical measurement provides more useful evidence.
What Equipment Do You Need?
For a basic purifier performance check, you need:
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A PM2.5 air quality monitor
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The air purifier being evaluated
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A clock or timer
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A simple recording sheet
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A reasonably enclosed room
For haze monitoring, choose a meter that displays an actual PM2.5 concentration, normally in µg/m³.
Data logging is useful when users want to observe the complete reduction trend automatically.
Step-by-Step Air Purifier Test
Step 1: Select the Room
Choose the room where the purifier is normally used.
Record:
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Approximate room size
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Number of occupants
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Door and window condition
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Air-conditioning status
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Outdoor haze condition
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Purifier model
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Filter age
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Selected fan speed
Testing conditions should remain as consistent as possible.
Step 2: Position the PM2.5 Monitor
Place the monitor in a representative occupied area.
Do not put it:
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Directly beside the purifier
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In front of the clean-air outlet
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Next to an open window
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Under an air-conditioning outlet
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Beside a kitchen
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Near cigarette smoke
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Against a wall or inside a cabinet
A position near the middle of the occupied area is often more representative than a point immediately beside the purifier.
Step 3: Record the Initial PM2.5
Before starting the purifier, allow the air quality monitor to stabilise.
Record the PM2.5 value as the baseline.
For example:
Initial PM2.5: 85 µg/m³
This is the condition against which later readings will be compared.
Step 4: Switch On the Air Purifier
Operate the purifier at a clearly recorded fan setting.
During severe haze, a low or silent setting may circulate insufficient air for a large room. However, always use the purifier according to its operating instructions.
Keep the doors and windows in the same position throughout the test.
Step 5: Record Readings at Regular Intervals
Record PM2.5 after consistent time intervals, such as:
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10 minutes
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20 minutes
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30 minutes
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45 minutes
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60 minutes
Example:
| Test Time | PM2.5 Reading |
|---|---|
| Before purifier starts | 85 µg/m³ |
| After 10 minutes | 68 µg/m³ |
| After 20 minutes | 52 µg/m³ |
| After 30 minutes | 39 µg/m³ |
| After 45 minutes | 28 µg/m³ |
| After 60 minutes | 22 µg/m³ |
These are example values only. Actual results depend on the room, purifier, outdoor conditions, monitor and test method.
Step 6: Review the Trend
A consistent reduction suggests that the purifier is removing particles faster than they are entering or being generated.
If the PM2.5 reading remains unchanged or increases, further investigation is required.
How to Calculate the Percentage Reduction
A simple percentage reduction can be calculated using:
PM2.5 reduction (%) = [(Initial reading − Final reading) ÷ Initial reading] × 100
For example:
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Initial reading: 85 µg/m³
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Final reading: 22 µg/m³
Reduction = [(85 − 22) ÷ 85] × 100
Reduction = approximately 74%
This calculation describes the reduction observed during that particular test. It should not automatically be treated as the purifier’s certified efficiency because the result is affected by room conditions and measurement procedures.
Why Is the PM2.5 Reading Not Decreasing?
The Purifier Is Too Small
A purifier designed for a small bedroom may not circulate enough air for a large classroom, meeting room or open office.
The Filter Is Dirty
A loaded filter may restrict airflow and reduce performance. Check the manufacturer’s replacement recommendations and the actual filter condition.
The Fan Speed Is Too Low
Quiet mode may be suitable for normal conditions but insufficient during severe haze or in a large room.
Doors or Windows Are Open
If outdoor PM2.5 continuously enters the room, the purifier may not reduce the concentration effectively.
The Purifier Is Poorly Positioned
Air intake or outlet airflow may be blocked by furniture, curtains or walls.
The Monitor Is Incorrectly Positioned
A monitor placed next to a window may mainly measure incoming outdoor pollution. One placed beside the purifier outlet may show artificially low readings.
The Room Has an Indoor Particle Source
Cooking, smoking, candles, incense, cleaning and dust-producing work can increase PM2.5 while the purifier is operating.
The Purifier Needs Maintenance
The filter may be incorrectly fitted, packaging may still cover a new filter, or the unit may have an airflow problem.
Why the Purifier’s Built-In Reading May Differ
Some air purifiers include a built-in PM2.5 display. Its reading may differ from a separate monitor because:
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The sensors are in different locations
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The purifier measures air near its own intake
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Each sensor has a different response time
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Air is not evenly mixed throughout the room
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One display may apply smoothing or averaging
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Sensor contamination may affect the reading
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The two instruments may use different algorithms
Different readings do not automatically mean one device is defective.
For a more representative check, use the portable monitor away from the purifier and repeat measurements at several locations.
Should the Purifier Be Placed Beside a Window?
Not necessarily.
The best position depends on room layout and airflow. General considerations include:
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Do not block the air intake
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Keep the outlet clear
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Avoid placing the unit behind furniture
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Allow air to circulate across the occupied space
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Follow the manufacturer’s clearance instructions
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Consider where outdoor particles are entering
Use PM2.5 measurements at different points to determine whether the selected position produces a more consistent reduction throughout the room.
How to Compare Two Air Purifiers
If comparing two units, use the same:
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Room
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Starting conditions
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Monitor
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Monitor position
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Door and window status
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Fan-speed basis
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Test duration
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Measurement intervals
Test each purifier separately.
Do not operate both simultaneously unless the objective is to evaluate their combined performance.
Because outdoor haze and starting concentrations can change, results from tests conducted on different days should be interpreted carefully.
Testing Air Purifiers in Schools and Offices
For larger occupied areas, measure more than one point.
Suggested locations include:
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Centre of the room
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Area furthest from the purifier
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Near the main entrance
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Typical occupant location
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Area close to suspected particle entry
A low reading beside the purifier does not prove that the opposite side of a classroom or meeting room has the same air quality.
A data-logging monitor can help facility managers determine whether PM2.5 remains controlled throughout the school or working day.
Common Testing Mistakes
Testing With the Monitor Beside the Outlet
This measures freshly filtered air rather than the average room condition.
Opening Doors During the Test
Changing the room condition makes the before-and-after comparison less reliable.
Recording Only the Final Reading
Without a baseline, the amount of improvement cannot be determined.
Changing Several Factors at Once
If the purifier speed, window position and air-conditioning settings are all changed together, it becomes difficult to identify which action affected the reading.
Testing for Only a Few Minutes
A purifier may require time to circulate and filter the room air.
Assuming One Successful Test Applies Everywhere
Performance can differ in another room, building or haze condition.
Choosing a PM2.5 Monitor for Purifier Testing
Useful features include:
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PM2.5 measurement
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PM10 measurement
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Clear numerical display
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Fast response
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Data logging
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Rechargeable battery
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Historical trend display
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Downloadable records
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Portable design
The Temtop LKC-1000S is one option for portable particulate spot checks and basic air purifier comparisons.
For schools, offices or facilities requiring longer-term records, consider a monitor with data-logging and export functions.
Measure the Result, Not Just the Fan Operation
An operating fan confirms only that the purifier is switched on. It does not show how much PM2.5 has been reduced throughout the room.
A structured test using a PM2.5 monitor can help users:
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Establish the initial concentration
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Observe the reduction trend
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Compare purifier settings
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Detect dirty-filter performance
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Evaluate purifier placement
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Identify particle infiltration
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Document changes during haze
The test should be treated as a practical performance check rather than formal laboratory certification.
Always follow official Malaysian haze advisories and the purifier manufacturer’s operating and maintenance instructions.
Contact MTM Precision
Contact MTM Precision for assistance selecting a PM2.5 air quality monitor to test air purifier performance during haze in Malaysia.
MTM Precision Sdn. Bhd.
Showroom & Service Centre
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia
🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: +6016-660 7346
01 Sep 2026
