How Often Should You Check Indoor PM2.5 During Haze Malaysia
How Often Should You Check Indoor PM2.5 During Haze Malaysia
During a haze episode, checking indoor PM2.5 only once may not provide enough information.
Conditions can change when:
Outdoor API rises
Wind direction changes
Rain starts or stops
Windows are opened
People enter or leave
Cooking begins
An air purifier is switched on
Homes, schools and offices in Banting, Klang, Shah Alam, Kuala Lumpur and other affected areas should monitor according to how the room is used rather than checking randomly.
Is One PM2.5 Reading Enough?
No.
A single reading is only a snapshot of the condition around the monitor at that moment.
It does not show:
- Whether PM2.5 is increasing or decreasing
- Whether the air purifier is effective
- Whether smoke enters when doors open
- Whether one room is cleaner than another
- Whether morning and evening conditions differ
- Whether indoor activities are producing particles
Repeated measurements provide a clearer trend.
Basic Schedule for a Home
For simple household monitoring, check at least:
Morning
Check the bedroom and living room before opening windows or external doors.
This provides a reference for overnight conditions.
Afternoon
Outdoor conditions and household activities may have changed.
Check again after:
- Cooking
- Cleaning
- Opening the main door
- Operating the air purifier
- Changes in outdoor haze
Evening
Check the bedroom before sleeping, especially if the room was unoccupied or the door remained open during the day.
A simple morning, afternoon and evening schedule can provide more useful information than frequent random checks.
When Should You Check More Frequently?
Additional measurements may be useful when:
- Outdoor API changes significantly
- Smoke becomes visible
- A burning smell enters the building
- Windows or doors were left open
- The air purifier was switched off
- The purifier filter was replaced
- Cooking or cleaning caused a sudden increase
- The monitor was moved to another room
- The building ventilation system changed
- Employees or occupants report a change in conditions
Record what happened before the reading changed.
Monitoring Schedule for an Office
An office may check:
Before Employees Arrive
This establishes the condition before normal occupancy.
Mid-Morning
Check after employees have entered and the air-conditioning system has been operating.
During Peak Occupancy
Meeting rooms and training rooms may change quickly when several people occupy the space.
If the monitor also measures CO₂, observe both parameters separately.
After Lunch
External doors, lifts, corridors and pantry activities may influence the reading.
Before the Office Closes
This final reading helps management understand whether conditions improved or worsened throughout the day.
Monitoring Schedule for Schools
Schools and childcare centres may check:
- Before students enter
- During the first occupied session
- Before outdoor activities
- After doors or windows are opened
- After operating air purification
- Before afternoon classes
- When outdoor haze visibly worsens
Do not rely only on a monitor placed in the office.
Classrooms near roads, open corridors or drop-off areas may record different conditions.
Monitoring Schedule for Factories and Warehouses
Factories should measure according to zones and activities.
Useful times include:
- Before the production shift
- After external doors open
- During loading activity
- While major equipment operates
- During lunch or rest periods
- After air filtration is activated
- Before the end of the shift
Record whether the particles may come from outdoor haze or an internal process.
A general PM2.5 monitor supports screening and trend comparison. It does not replace occupational dust sampling or process-specific measurement.
How Long Should You Observe the Monitor?
Avoid recording only the first number displayed immediately after switching on or moving the instrument.
Allow the monitor to respond to the new environment.
The required stabilisation time depends on the instrument, airflow and how different the new location is from the previous one.
When comparing rooms:
- Use the same monitor
- Use a similar measurement height
- Keep the instrument away from vents
- Do not block the air inlet
- Record after the reading begins to stabilise
- Use the same method at every location
What Should Be Recorded?
A practical PM2.5 record may include:
Item Information
Date and time When the measurement was taken
Location Bedroom, office, classroom or factory zone
PM2.5 reading Displayed particle concentration
Outdoor API Latest official regional condition
Doors and windows Open or closed
Air purifier On, off or operating speed
Air-conditioning On or off
Occupancy Approximate number of people
Activity Cooking, cleaning, production or loading
Remarks Smoke smell, rain or unusual event
A short, consistent record is more useful than a complicated form that employees do not complete.
Continuous Monitoring or Manual Spot Checks?
Manual Spot Checks Are Suitable When:
- The monitor is shared between rooms
- Only basic comparisons are required
- The premises are small
- Users can follow a consistent schedule
- Historical data is not essential
Continuous Monitoring Is More Suitable When:
- Conditions change frequently
- The room is occupied for long periods
- Management needs trend records
- Filtration performance must be reviewed
- A critical room requires regular observation
Select the monitoring method according to the application rather than assuming continuous monitoring is always necessary.
Do Not React to Every Small Change
PM2.5 readings may fluctuate because particles and air are constantly moving.
Before taking action, ask:
- Is the increase sustained?
- Did someone open a door?
- Did cooking or cleaning begin?
- Was the monitor moved?
- Did the air purifier stop?
- Did outdoor haze worsen?
Look for repeatable patterns and consistent trends.
Choosing a Monitor for Repeated Checking
For simple haze monitoring, prioritise:
- PM2.5 measurement
- Clear display
- Portable design
- Convenient power arrangement
- Easy operation
A multi-parameter monitor may be considered when users also need:
- CO₂
- PM10
- TVOC
- Formaldehyde
- Temperature
- Humidity
MTM Precision supplies Temtop air-quality monitors for homes, schools, offices, factories and other workplaces.
Customers may WhatsApp us their intended monitoring schedule, required parameters and number of locations for suitable model selection.
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
06 Oct 2026
