Why PM2.5 Is Low but CO2 Is High on Temtop M10+ Malaysia
Why PM2.5 Is Low but CO2 Is High on Temtop M10+ Malaysia
A Temtop M10+ may show low PM2.5 while the CO2 reading continues to increase.
This is not a contradiction and does not automatically mean that the monitor is faulty.
PM2.5 and CO2 represent different indoor air quality conditions:
- PM2.5 indicates fine airborne particles.
- CO2 is strongly influenced by occupancy and ventilation.
A closed room with an effective air purifier may have low PM2.5 but high CO2 when several people remain inside for a long period.
Why PM2.5 Becomes Low
PM2.5 may decrease when:
- Doors and windows are closed.
- Outdoor haze entry is reduced.
- An air purifier is operating.
- The air conditioner filter captures some particles.
- Cooking and smoking have stopped.
- The room has limited particle sources.
- The room has remained closed for some time.
This can create a cleaner particle environment.
However, removing particles does not automatically remove CO2.
Why CO2 Continues to Increase
People produce CO2 through normal breathing.
CO2 may increase when:
- Several people occupy a small room.
- Doors and windows remain closed.
- Fresh air ventilation is limited.
- A meeting continues for a long time.
- A bedroom is occupied overnight.
- The air conditioner mainly recirculates indoor air.
- The room has poor air exchange.
The more people inside the room, the faster CO2 may increase.
Air Purifiers Usually Do Not Remove CO2
A standard particle air purifier is mainly designed to capture airborne particles.
It may help reduce:
- PM2.5.
- PM10.
- Dust.
- Smoke particles.
- Some airborne material, depending on the filter.
However, a normal particle filter does not provide fresh air and does not generally remove the CO2 produced by occupants.
This means the Temtop M10+ may show:
- Lower PM2.5 after the purifier starts.
- Increasing CO2 while the room remains occupied.
Both readings may be correct.
Air Conditioning Is Not Always Ventilation
Many room air conditioners mainly cool and recirculate indoor air.
They may lower the temperature without bringing in a significant amount of outdoor air.
A cool room can still have increasing CO2.
Do not judge ventilation performance from temperature alone.
The actual result depends on the air-conditioning and ventilation system installed in the building.
Why This Happens During Haze
During haze, users often close doors and windows to prevent outdoor particles from entering.
This may help reduce PM2.5, especially when an air purifier is operating.
However, the same action may reduce fresh air exchange.
This creates a practical trade-off:
- Opening the window may lower CO2 but allow outdoor PM2.5 to enter.
- Closing the window may reduce PM2.5 entry but allow CO2 to increase.
- Running an air purifier may lower particles but not correct the CO2 problem.
Monitoring both parameters helps users see this trade-off instead of focusing on only one reading.
Common Locations Where This Occurs
Bedroom
A closed air-conditioned bedroom may have low PM2.5 but increasing CO2 overnight.
This is especially possible when two or more people occupy the room.
Meeting Room
CO2 may increase during a long meeting even when the office PM2.5 remains low.
The room may appear cool and comfortable while fresh air exchange remains limited.
Classroom
Closing windows during haze may reduce particle entry, but CO2 can rise as students remain in the room.
Clinic or Waiting Room
An occupied waiting room may have low PM2.5 because of filtration while CO2 increases during busy periods.
Factory Office
A factory office may be protected from outdoor dust and haze, but the CO2 reading may rise when several staff members work in a small enclosed area.
Cleaner Indoor Room
A cleaner room created during severe haze may successfully reduce PM2.5. Occupancy and ventilation still need separate attention.
What Should You Check First?
When PM2.5 is low but CO2 is high, check:
- Number of people in the room.
- Room size.
- How long the room has been occupied.
- Whether the door is closed.
- Whether windows are closed.
- Whether the ventilation system provides outdoor air.
- Whether the air conditioner only recirculates indoor air.
- Whether the monitor is placed near occupants.
- Whether the monitor was moved recently.
- Whether the CO2 reading changes when the room becomes empty.
Record the conditions instead of relying on one isolated number.
How to Perform a Simple Room Test
Step 1: Record the Starting Conditions
Record:
- PM2.5.
- CO2.
- Number of occupants.
- Door and window status.
- Air conditioner operation.
- Air purifier operation.
Step 2: Keep the Monitor in One Position
Place the Temtop M10+ in a representative occupied area.
Keep it away from direct breathing, air conditioner outlets, open windows, and purifier outlets.
Step 3: Observe the Trend
Check whether CO2 increases as the room remains occupied.
Step 4: Empty the Room
If practical, allow the room to remain unoccupied and observe whether the CO2 trend changes.
Step 5: Review Ventilation
Check whether the building ventilation system is operating and whether it provides outdoor air.
Step 6: Compare With Outdoor Conditions
Before opening windows during haze, consider the outdoor particle condition.
Do not solve a CO2 problem by allowing heavily polluted outdoor air to enter without considering filtration and building requirements.
Where Should the M10+ Be Positioned?
For more representative readings:
- Place it near breathing height.
- Keep it away from a persons face.
- Avoid direct exhaled breath.
- Avoid direct air conditioner airflow.
- Avoid the immediate outlet of an air purifier.
- Keep it away from open windows.
- Keep the air inlet unobstructed.
- Use a stable location.
- Allow readings to respond after moving the unit.
A monitor placed directly beside a person may show a locally higher CO2 reading because of exhaled air.
Do Not Use Only the AQI Display
AQI normally focuses on air pollution indicators and does not replace checking the individual CO2 value.
A room may show acceptable particle conditions while CO2 is increasing.
Always review the actual parameters separately:
- PM2.5 for fine particles.
- CO2 for occupancy and ventilation information.
- TVOC for a broad volatile organic compound indication.
- Temperature and humidity for indoor environmental conditions.
Practical Responses for Facilities Teams
Possible actions depend on the building design and outdoor conditions.
Facilities teams may consider:
- Checking whether mechanical ventilation is operating.
- Reviewing fresh air intake and filtration.
- Reducing room occupancy where appropriate.
- Scheduling breaks between long meetings.
- Keeping ventilation openings unobstructed.
- Operating the air purifier for particle control.
- Monitoring PM2.5 and CO2 together.
- Consulting the building ventilation contractor when the pattern is repeated.
- Following applicable building and workplace requirements.
Do not block, modify, or shut down a building ventilation system without proper assessment.
When the CO2 Reading May Need Further Checking
Further investigation may be appropriate when:
- The CO2 reading does not respond after moving outdoors to suitable fresh air.
- The reading remains unusually high in an unoccupied and ventilated room.
- The display is frozen.
- The monitor shows an error.
- The unit was dropped or exposed to water.
- The value changes abnormally without any environmental change.
- A controlled comparison with another suitable CO2 monitor shows a large persistent difference.
Allow the monitor time to respond when moving between locations.
Comparison Is Not Calibration
Placing two CO2 monitors beside each other is a comparison check.
It may show whether both units follow a similar trend, but it does not confirm accuracy against a traceable reference.
Calibration requires a defined method, controlled conditions, and an appropriate reference.
Temtop M10+ Support in Malaysia
Low PM2.5 and high CO2 can occur naturally in a closed occupied room.
The correct response is to review particle control and ventilation as two separate requirements.
If the Temtop M10+ reading remains unusual after a controlled check, WhatsApp MTM Precision with:
- A clear photo of the monitor.
- The complete model label.
- The displayed PM2.5 and CO2 readings.
- The room location.
- The number of occupants.
- The door and window condition.
- A short video showing the visible error or symptom.
MTM Precision Sdn Bhd
Showroom and Service Centre: No. 29-1 and 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
