How to Check Indoor PM2.5 During Transboundary Haze in Malaysia
How to Check Indoor PM2.5 During Transboundary Haze in Malaysia
Content
Transboundary haze can cause outdoor air quality to deteriorate across Malaysia, but the air inside a home, school or office may be very different from the reading shown by the nearest government monitoring station.
Outdoor API data is useful for understanding regional air quality. However, it does not show the actual PM2.5 concentration inside your room, classroom, office, hotel or factory.
An indoor PM2.5 monitor helps you check whether fine particles are entering the building and whether your air purifier, filtration system or ventilation strategy is working effectively.
What Is PM2.5?
PM2.5 refers to airborne particles with an aerodynamic diameter of 2.5 micrometres or smaller.
These fine particles may come from:
Forest and peat fires
Vehicle exhaust
Industrial emissions
Construction activities
Cooking smoke
Cigarette or vape smoke
Dust entering through doors and windows
Because PM2.5 particles are very small, they can remain suspended in the air and enter deeper into the respiratory system.
Outdoor API Is Not the Same as Indoor PM2.5
Malaysia’s Air Pollutant Index, or API, represents outdoor air quality within a monitoring area. It is not a direct measurement of the air inside your building.
Indoor PM2.5 levels may be lower than outdoor levels when:
Doors and windows remain closed
The air-conditioning system has suitable filtration
A correctly sized air purifier is operating
The building has relatively low air leakage
Indoor levels may remain high when:
Doors are opened frequently
Outdoor air enters through gaps
The filtration system is insufficient
Indoor cooking, smoking or renovation creates additional particles
The air purifier filter is dirty or overdue for replacement
This is why an outdoor API reading cannot confirm whether a particular room is safe or whether an air purifier is performing properly.
How to Measure Indoor PM2.5 Correctly
1. Allow the Monitor to Stabilise
Place the PM2.5 monitor at the selected location and allow its reading to stabilise. Avoid making a decision based only on the first value shown immediately after switching it on.
2. Measure Near the Breathing Zone
For general indoor assessment, position the monitor around the height where occupants normally breathe.
Do not place it directly on the floor, against a wall or very close to the ceiling unless you are specifically investigating those locations.
3. Avoid Direct Airflow
Do not place the monitor directly in front of:
An air-conditioning outlet
A standing fan
An air purifier outlet
An open window
A kitchen exhaust
A humidifier
Strong airflow may produce a reading that is not representative of the rest of the room.
4. Take Measurements at Several Locations
One reading is rarely enough for a large room or building.
Useful measurement points include:
Near the main entrance
At the centre of the occupied area
Near windows facing a road or outdoor haze
Inside a classroom or meeting room
Before and after an air purifier
Near suspected particle sources
Comparing several locations helps identify where outdoor air is entering and whether particle levels are evenly controlled.
5. Record the Time and Building Condition
PM2.5 readings should be recorded together with relevant information, such as:
Date and time
Outdoor API condition
Doors and windows open or closed
Air-conditioning status
Air purifier operating mode
Number of occupants
Cooking, cleaning or renovation activity
Without this information, it may be difficult to explain why the reading increased or decreased.
How to Test Whether an Air Purifier Is Working
A practical test can be conducted using the same PM2.5 monitor:
Close the doors and windows.
Record the starting PM2.5 level.
Switch on the air purifier.
Keep the monitor away from the purifier outlet.
Record the reading at regular intervals.
Compare the reduction over time.
If the reading does not decrease, check:
Whether the purifier is suitable for the room size
Whether the filter needs replacement
Whether outdoor air is continuously entering
Whether an indoor activity is generating particles
Whether the monitor is positioned too close to an air outlet
A sudden lower reading directly beside the purifier does not necessarily mean that the entire room has been cleaned.
Where Should Indoor PM2.5 Be Checked?
Indoor haze monitoring is particularly useful in:
Homes and apartments
Schools and childcare centres
Offices and meeting rooms
Hotels and restaurants
Clinics and waiting areas
Factories and warehouses
Security rooms and control rooms
Data centres and equipment rooms
Schools, offices and commercial buildings should pay particular attention to rooms with high occupancy or limited ventilation.
Can a Low-Cost PM2.5 Monitor Replace Professional Testing?
A portable indoor air quality monitor is useful for:
Identifying changes in PM2.5
Comparing different rooms
Checking before and after filtration
Detecting unusual particle increases
Supporting daily haze management
However, not every portable monitor is suitable for regulatory or occupational exposure assessment.
Sensor readings can be affected by:
Particle type and size distribution
Humidity
Aerosols and vapour
Sensor cleanliness
Instrument age
Calibration and manufacturing variation
Where formal compliance, worker exposure or an important technical decision is involved, the measurement method and instrument capability should be reviewed carefully.
Recommended Monitoring Approach During Haze
A practical indoor haze-monitoring programme can follow this sequence:
Check outdoor API → measure indoor PM2.5 → compare several rooms → investigate entry points → operate filtration → repeat the measurement.
The purpose is not simply to obtain one number. It is to understand whether indoor conditions are improving and what action is producing the improvement.
PM2.5 and Indoor Air Quality Monitors Available from MTM Precision
MTM Precision supplies portable air-quality instruments for homes, schools, offices, hotels and industrial facilities in Malaysia.
Relevant models include:
Temtop P600
Temtop M10i
Temtop M10+
Temtop M100
Temtop S1 up
Temtop C1+
Temtop M2000 2nd Generation
Temtop LKC-1000S 2nd Generation
Different models measure different combinations of PM2.5, PM10, carbon dioxide, formaldehyde, TVOC, temperature and relative humidity. Customers should confirm the required parameters before selecting an instrument.
Contact MTM Precision
MTM Precision Sdn. Bhd. (744811-A)
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com / enquiry@mtmpre.com.my
Website: www.mtmpre.com.my
Visit our Puchong Showroom & Service Centre for product selection, demonstration and technical support.
Operating hours: Monday to Friday, 9:00 AM6:00 PM.
20 Sep 2026
