Why Does Indoor PM2.5 Rise Again After the Air Purifier Is Switched Off Malaysia
Why Does Indoor PM2.5 Rise Again After the Air Purifier Is Switched Off Malaysia
During haze conditions, an air purifier may gradually reduce the indoor PM2.5 reading.
However, some users notice that the reading begins increasing again shortly after the purifier is switched off.
This does not automatically mean the PM2.5 monitor or air purifier is faulty.
It usually means that particles are still entering the room, remaining suspended indoors or being generated by an internal activity.
The Air Purifier Stops Removing New Particles
An air purifier removes airborne particles only while it is operating.
When the purifier is switched off:
- Outdoor smoke may continue entering
- Particles may move between rooms
- Settled dust may become airborne again
- Cooking or cleaning may generate new particles
- People may open doors and windows
- Air-conditioning or ventilation may bring in outdoor air
If the pollution source continues, the PM2.5 level can rise again.
Outdoor Haze Is Still Entering the Building
Closing the windows may reduce smoke entry, but many buildings are not completely sealed.
Outdoor particles can enter through:
- Door gaps
- Window-frame gaps
- Ventilation openings
- Air-conditioning systems
- Corridors
- Balconies
- Loading bays
- Frequently opened entrances
The purifier may have been removing particles at the same time that new particles were entering.
Once it stops, the indoor concentration may begin increasing.
The Door Was Opened
A brief door opening can cause the reading to change, especially when the outdoor air is heavily polluted.
Check whether PM2.5 increases after:
- Someone enters the room
- The main entrance opens
- A delivery arrives
- A balcony door opens
- Employees move between indoor and outdoor areas
- The office connects to a warehouse or loading bay
Record the reading before and after the door opens.
Particles Move From Another Room
A cleaner room can be affected by air from:
- The kitchen
- Living room
- Corridor
- Pantry
- Smoking area
- Workshop
- Production area
- Warehouse
If the room door remains open, particles may move from a more polluted area into the cleaner space.
Cooking Causes PM2.5 to Increase
Cooking can produce fine particles, especially during:
- Frying
- Grilling
- High-temperature cooking
- Food burning
- Heavy oil use
A monitor located outside the kitchen may still respond when cooking emissions spread through the building.
Do not assume that every PM2.5 increase during a haze episode comes from outdoor smoke.
Cleaning and Movement Can Disturb Dust
PM2.5 may rise during:
- Sweeping
- Dusting
- Vacuuming
- Moving boxes
- Handling dusty materials
- Renovation work
- People walking through dusty areas
Some activities can disturb settled particles and return them to the air.
Record what was happening when the reading increased.
The Air Purifier May Be Too Small
A purifier designed for a small bedroom may struggle to maintain lower PM2.5 in:
- A large living room
- An open-plan office
- A classroom
- A factory office
- A warehouse
- A room connected to other spaces
The reading may improve while the purifier runs at high speed but rise quickly after it is switched off.
Check the manufacturer’s recommended room coverage and operating instructions.
The Filter May Require Attention
Possible filter-related issues include:
- Dirty filter
- Incorrect installation
- Filter not replaced according to instructions
- Air intake blocked
- Air outlet obstructed
- Unsuitable replacement filter
- Heavy particle loading during prolonged haze
Follow the purifier manufacturer’s maintenance procedure.
Do not clean or modify a filter unless the manufacturer allows it.
The Monitor May Be Too Close to the Purifier
A PM2.5 monitor placed directly beside the purifier outlet may show a low reading while the purifier is operating.
After the purifier stops, the monitor may begin detecting the general room condition again.
For a more representative measurement, place the monitor:
- Away from the clean-air outlet
- Away from the purifier intake
- Away from the window
- Away from the door
- Away from air-conditioning vents
- Around normal breathing height
The monitor should represent the occupied area rather than one concentrated airflow.
A Simple Troubleshooting Test
Step 1: Record the Starting Reading
Before operating the purifier, record:
- PM2.5
- Time
- Room location
- Doors and windows status
- Outdoor API condition
- Any cooking or cleaning activity
Step 2: Operate the Purifier
Keep the doors, windows and monitor position consistent.
Observe whether the PM2.5 reading decreases.
Step 3: Switch Off the Purifier
Continue observing the monitor without changing other conditions.
Record:
- How quickly PM2.5 rises
- Whether anyone opened the door
- Whether the air-conditioner remained on
- Whether an indoor activity started
- Whether outdoor haze worsened
Step 4: Repeat the Test
Repeat the procedure at a different time.
A repeated pattern is more meaningful than one isolated event.
What Does a Rapid Increase Suggest?
A rapid increase after switching off the purifier may indicate:
- Continuous outdoor particle entry
- An active indoor particle source
- Frequent door opening
- A purifier that is too small for the room
- A monitor positioned too close to the purifier
- Air movement from a more polluted area
Further checking may be needed before blaming the instrument.
Should the Purifier Run Continuously?
Operating requirements depend on:
- Outdoor haze condition
- Room size
- Occupancy
- Building sealing
- Purifier design
- Filter condition
- Manufacturer instructions
- Indoor particle sources
Follow the purifier manufacturer’s guidance and use PM2.5 trends to understand what happens when operating conditions change.
PM2.5 Monitoring Does Not Measure Everything
A PM2.5 monitor does not indicate:
- Carbon dioxide
- Oxygen
- Combustible gas
- Carbon monoxide
- Every chemical pollutant
- Whether ventilation is sufficient
A multi-parameter monitor may be considered when the user also needs to check COâ‚‚, PM10, TVOC, formaldehyde, temperature or humidity.
MTM Precision supplies Temtop air-quality monitors for homes, offices, schools, clinics, factories and other workplaces.
Customers experiencing unusual readings may WhatsApp us a clear photo of the monitor, model label, display and measurement location for initial checking and model-selection assistance.
MTM Precision Sdn Bhd
Showroom & Service Centre: No. 29-1 & 29-2, Jalan Bandar 18, Pusat Bandar Puchong, 47160 Puchong, Selangor, Malaysia
Tel: 03-8080 7172
WhatsApp: +6016‑660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
07 Oct 2026
