How to Measure Indoor PM2.5 Before and After Closing Windows During Haze Malaysia

How to Measure Indoor PM2.5 Before and After Closing Windows During Haze Malaysia

During haze episodes in Malaysia, many homeowners and office managers close their windows to reduce the amount of polluted outdoor air entering their buildings.

But does closing the windows actually reduce indoor PM2.5?

The answer depends on outdoor pollution levels, indoor particle sources, ventilation, air leakage and filtration.

Closing windows may reduce the entry of outdoor haze particles. However, it does not instantly remove particles already suspended in indoor air.

In some buildings, PM2.5 concentrations may decrease gradually after windows are closed. In other situations, particulate concentrations may remain elevated because of indoor pollution sources or continued outdoor air infiltration.

A portable PM2.5 air quality monitor, such as the Temtop S1 Up, can help users observe these changes.

This guide explains how to measure indoor PM2.5 before and after closing windows, how to record useful results and how to interpret particulate concentration trends during haze in Malaysia.

MTM Precision Sdn Bhd supplies portable air quality monitoring instruments for homes, offices and commercial applications throughout Malaysia.

1. Why Do People Close Windows During Haze?

Haze can contain elevated concentrations of fine airborne particles originating from combustion, open burning and other pollution sources.

These particles may enter homes and offices through:

Open windows

Open doors

Outdoor air ventilation

Building gaps

Poorly sealed window frames

Other air leakage pathways

When outdoor PM2.5 concentrations are elevated, reducing unnecessary entry of polluted outdoor air may help limit indoor particulate pollution.

However, closing windows is only one part of managing indoor air quality.

A closed room is not necessarily a clean room.

Particles already present indoors may remain suspended, and additional particles may be generated by indoor activities.

2. What Is PM2.5?

PM2.5 refers to airborne particles with an aerodynamic diameter of 2.5 micrometres or smaller.

Common PM2.5 sources include:

Outdoor haze

Vehicle exhaust

Industrial combustion

Cigarette smoke

Cooking

Burning incense

Candles

Other combustion activities

PM2.5 concentrations are generally expressed in micrograms per cubic metre (µg/m³).

Fine particles can penetrate deeply into the respiratory system.

Exposure to elevated PM2.5 concentrations is associated with respiratory and cardiovascular health risks.

Because these particles cannot reliably be identified by sight, a suitable monitor can provide useful information about indoor particulate conditions.

PM2.5 monitoring helps users observe fine particle concentrations, but it does not measure every indoor air pollutant.

3. Does Closing Windows Immediately Reduce PM2.5?

Not necessarily.

Closing windows may reduce the entry of outdoor particles, but it does not instantly remove particles already inside the room.

After windows are closed, PM2.5 concentrations may change because of several processes.

Reduced Outdoor Particle Entry

Less polluted outdoor air may enter through the previously open window.

Particle Deposition

Some airborne particles gradually settle onto indoor surfaces.

Air Filtration

An operating air purifier or suitable building filtration system may remove particles.

Continued Air Leakage

Outdoor air may still enter through gaps and ventilation pathways.

Indoor Particle Generation

Cooking, smoking and other activities may continue producing particles.

Therefore, closing windows can reduce one pathway for outdoor PM2.5 entry, but the resulting indoor concentration depends on the complete environment.

4. Introducing Temtop S1 Up for Window Closure Monitoring

The Temtop S1 Up Air Quality Monitor is a compact portable instrument suitable for general indoor particulate observations.

Its PM2.5 monitoring capability allows users to observe changes in airborne fine particle concentrations.

Potential applications include:

Comparing PM2.5 before and after closing windows

Monitoring indoor haze infiltration

Observing bedroom particulate concentrations

Checking living room air quality

Investigating office PM2.5 changes

Observing air purifier operation

Comparing particulate conditions between rooms

The Temtop S1 Up can support practical monitoring without requiring a complex fixed installation.

However, customers should refer to the latest manufacturer documentation for exact measurement specifications and operating limitations.

The Temtop S1 Up should not be assumed to measure ozone, carbon monoxide or other gases unless those capabilities are specifically documented.

5. How to Measure PM2.5 Before Closing Windows

The first stage is to establish an indoor particulate baseline.

Step 1 - Select a Representative Location

Place the Temtop S1 Up in the main occupied area.

For example:

Near a living room seating area

At an office workstation

In a bedroom occupied area

In a meeting room

Avoid placing the instrument directly beside an open window, air-conditioning outlet or air purifier discharge unless investigating that specific location.

Step 2 - Allow Readings to Stabilise

Switch on the instrument and allow it to stabilise according to the manufacturer's instructions.

Step 3 - Record the Initial PM2.5

Record the displayed concentration in µg/m³.

Step 4 - Document Environmental Conditions

Record:

Date and time

Window position

Door position

Air purifier operation

Air-conditioning operation

Ventilation settings

Recent cooking or smoking activities

Outdoor haze conditions

Step 5 - Record Multiple Readings

Instead of relying on one reading, record several measurements over a consistent period.

A stable baseline provides a more useful starting point for comparison than a single isolated measurement.

6. How to Measure PM2.5 After Closing Windows

Once the initial readings have been recorded, close the selected windows under normal, safe operating conditions.

Avoid deliberately exposing occupants to polluted outdoor air for the purpose of testing.

Step 1 - Close the Windows

Close windows that would normally be shut during a haze episode.

Do not block required ventilation openings or interfere with essential building ventilation systems.

Step 2 - Keep the Monitor in the Same Position

Avoid moving the Temtop S1 Up during the comparison.

Step 3 - Maintain Comparable Conditions

Where practical, keep the following unchanged:

Air purifier fan speed

Air-conditioning operation

Occupancy

Indoor activities

Other ventilation settings

Step 4 - Record PM2.5 at Consistent Intervals

For example:

Immediately before closing windows

10 minutes after closing

20 minutes after closing

30 minutes after closing

60 minutes after closing

Step 5 - Review the Trend

Observe whether PM2.5 decreases, remains stable or increases.

The purpose is to observe indoor particulate changes, not to certify building airtightness or ventilation performance.

7. Example of Indoor PM2.5 Before and After Closing Windows

The following measurements are hypothetical and provided only to demonstrate how a monitoring record might look.

They are not actual Temtop S1 Up test results.

Monitoring conditionExample PM2.5Window open - initial reading48 µg/m³Window closed - 10 minutes43 µg/m³Window closed - 20 minutes37 µg/m³Window closed - 30 minutes31 µg/m³Window closed - 60 minutes24 µg/m³

In this hypothetical example, PM2.5 decreases from 48 µg/m³ to 24 µg/m³.

The observed percentage change can be calculated as:

PM2.5 Reduction (%) = [(Initial PM2.5 - Final PM2.5) / Initial PM2.5] × 100

[(48 - 24) / 48] × 100 = 50%

This indicates that the measured concentration at the monitoring location decreased by 50% during the observation period.

However, this does not prove that closing the windows alone caused the entire reduction.

Other factors may include particle deposition, filtration and changes in outdoor pollution.

An observed PM2.5 decrease is not the same as a controlled measurement of window sealing effectiveness.

8. Why PM2.5 May Stay High After Closing Windows

Some users find that indoor PM2.5 remains elevated even after windows have been closed for an extended period.

Possible reasons include:

Existing Indoor Particles

Particles already inside the room may remain suspended.

Outdoor Air Leakage

Polluted outdoor air may continue entering through gaps or ventilation systems.

Indoor Cooking

Cooking activities can generate fine airborne particles.

Cigarette Smoke

Indoor smoking or smoke entering from adjacent spaces can contribute particulate pollution.

Insufficient Air Filtration

Without effective filtration, airborne particles may decrease more slowly.

Poor Air Purifier Placement

Restricted airflow can affect particle removal throughout the room.

Sensor or Environmental Factors

High humidity, condensation and sensor contamination may affect certain optical particle sensors.

Persistent high PM2.5 should prompt investigation of both indoor pollution sources and outdoor air infiltration.

9. Should You Switch On an Air Purifier After Closing Windows?

A suitable air purifier with effective particulate filtration can help reduce indoor PM2.5.

During haze episodes, combining reduced outdoor particle entry with appropriate filtration may be useful.

However, the purifier must be suitable for the room.

Important considerations include:

Verified particle CADR

Room volume

Filter condition

Fan speed

Airflow distribution

Ongoing particle sources

Outdoor pollution infiltration

An air purifier with insufficient capacity may struggle to reduce PM2.5 in a large room.

Closing windows may reduce incoming outdoor particles, while an air purifier can help remove particles already present indoors.

These are complementary actions, but their effectiveness depends on the actual conditions.

10. How to Compare Window Closure With and Without an Air Purifier

Users may wish to understand the difference between closing windows alone and closing windows while operating an air purifier.

A practical approach is to conduct separate observations under reasonably comparable conditions.

Observation A - Windows Closed, Purifier Off

Record PM2.5 changes after windows are closed while the purifier is not operating.

Observation B - Windows Closed, Purifier On

On another suitable occasion, record PM2.5 changes with the purifier operating at a consistent setting.

Compare the Results

Review whether the concentration decreases more rapidly when the purifier is operating.

However, outdoor PM2.5, indoor particle sources and ventilation conditions may differ between observations.

This informal comparison cannot independently establish the purifier's CADR or certified filtration efficiency.

For accurate performance testing, controlled methods and suitable equipment are required.

11. How Long Does It Take for PM2.5 to Decrease After Closing Windows?

There is no universal time that applies to every room.

The reduction rate depends on:

Initial PM2.5 concentration

Outdoor pollution concentration

Room volume

Air leakage

Particle deposition

Air purifier capacity

Ventilation

Indoor particle generation

In some environments, concentrations may decrease relatively quickly.

In other cases, they may remain elevated for an extended period.

Do not assume that waiting 30 minutes or one hour will always produce a particular PM2.5 concentration.

A monitor can help users observe the actual trend in their own environment.

12. Can Air Conditioning Reduce PM2.5?

An air conditioner primarily controls indoor temperature and, depending on its design, humidity.

Some air-conditioning systems include particulate filtration.

However, filtration performance varies between models.

A conventional recirculating split-unit air conditioner does not necessarily introduce fresh outdoor air.

It should not automatically be treated as equivalent to a dedicated HEPA air purifier.

Similarly, an air purifier does not automatically provide adequate fresh-air ventilation.

EquipmentMain functionAir conditionerTemperature controlAir purifierRemoval of specified airborne pollutantsVentilation systemAir exchangePM2.5 monitorParticulate concentration observation

Good indoor air quality management requires appropriate ventilation, source control and filtration rather than relying on one device alone.

13. Important Ventilation Considerations When Windows Are Closed

Closing windows may help reduce outdoor particulate infiltration during severe haze.

However, adequate ventilation remains important.

Poor ventilation can allow certain indoor-generated pollutants to accumulate.

These may include:

Carbon dioxide from occupants

VOCs from indoor sources

Moisture

Cooking-related pollutants

Other gases

A PM2.5 monitor cannot determine whether ventilation is adequate.

For example, a room may have low PM2.5 but elevated CO2.

Similarly, a room may have low PM2.5 while containing other pollutants that require different measurement methods.

Do not use PM2.5 readings alone to determine whether a closed room has sufficient ventilation.

Buildings with filtered mechanical ventilation may be better equipped to manage outdoor particulate pollution while maintaining fresh-air supply.

14. Indoor PM2.5 vs Outdoor API During Haze

Malaysia uses an official Air Pollutant Index (API) for reporting outdoor air quality.

PM2.5 concentration and API are not the same measurement.

PM2.5: A concentration of fine airborne particles, commonly expressed in µg/m³.

API: A calculated outdoor air quality index based on the official methodology.

A portable monitor's indoor PM2.5 reading should not be directly compared numerically with an official API value.

For current outdoor air quality information, users should refer to Malaysia's official Department of Environment monitoring service.

Official outdoor API provides regional pollution information, while indoor PM2.5 monitoring helps users observe particulate conditions inside their own buildings.

15. How to Interpret PM2.5 Measurements

The World Health Organization's 2021 PM2.5 air quality guideline values include:

Averaging periodWHO guidelineAnnual average5 µg/m³24-hour average15 µg/m³

These are health-based guidelines for the stated averaging periods.

They are not instantaneous thresholds that establish whether a room is safe.

For example, a single reading of 20 µg/m³ does not by itself establish the 24-hour average.

Similarly, a low reading after closing windows does not confirm that all indoor pollutants have been removed.

Always interpret PM2.5 readings according to their measurement units, averaging periods and instrument limitations.

16. Common Mistakes When Comparing Open and Closed Windows

Mistake 1 - Moving the Monitor Between Measurements

Different positions may have different particulate concentrations.

Solution: Keep the instrument in a consistent representative location.

Mistake 2 - Switching Multiple Devices On and Off

Changing the air purifier, air conditioner and ventilation simultaneously makes interpretation more difficult.

Solution: Change one factor at a time when practical.

Mistake 3 - Measuring During Indoor Cooking

Cooking can generate particles and distort the comparison.

Solution: Record indoor activities and avoid uncontrolled particle sources.

Mistake 4 - Assuming Closed Windows Stop All Outdoor Pollution

Air leakage and ventilation can still introduce outdoor particles.

Solution: Investigate building conditions and filtration.

Mistake 5 - Assuming Low PM2.5 Means Good Ventilation

PM2.5 does not directly measure ventilation adequacy.

Solution: Consider CO2 monitoring or professional ventilation assessment when appropriate.

Mistake 6 - Using a Consumer Monitor for Formal Building Testing

A portable PM2.5 monitor cannot independently certify building airtightness or ventilation performance.

Solution: Use appropriate professional methods for formal assessments.

17. Practical Monitoring Checklist for Homes and Offices

CheckpointRecommended actionOutdoor hazeCheck official air quality informationInitial indoor PM2.5Record baseline concentrationWindow positionDocument open or closed conditionMonitor placementKeep location consistentAir purifierRecord operating modeAir-conditioningDocument operationVentilationMaintain necessary fresh-air provisionIndoor pollution sourcesRecord cooking, smoke and other activitiesMonitoring intervalUse consistent measurement timesFinal PM2.5Compare with initial readingUnexpected resultsInvestigate sources and environmental changes

This checklist supports general particulate observations rather than formal environmental certification.

18. Frequently Asked Questions

Does closing windows reduce PM2.5 during haze?

It may reduce outdoor particle entry, but the actual indoor concentration depends on filtration, air leakage, indoor sources and other conditions.

How quickly will PM2.5 decrease after closing windows?

There is no fixed time. The rate depends on room conditions, particle removal and continuing pollution sources.

Can Temtop S1 Up measure PM2.5 before and after closing windows?

Yes. It can be used for general indoor particulate observations according to its supported measurement functions.

Should I run an air purifier after closing windows?

A suitable air purifier can help reduce airborne particles, but it must be appropriately sized and maintained.

Why is PM2.5 still high after closing all windows?

Possible reasons include existing particles, outdoor air leakage, indoor smoke, cooking or insufficient filtration.

Can air conditioning replace an air purifier?

Not necessarily. Air conditioners and air purifiers have different primary functions, and filtration performance varies.

Does low PM2.5 mean my room has enough fresh air?

No. PM2.5 monitoring does not directly measure ventilation adequacy.

Can Temtop S1 Up measure CO2 or ozone?

Customers should verify the exact manufacturer's specifications. PM2.5 measurement does not imply CO2 or ozone measurement capability.

Can one monitor be used in different rooms?

Yes, for sequential spot checks. However, readings taken at different times may reflect changing environmental conditions.

Where can I buy Temtop S1 Up in Malaysia?

Customers can contact MTM Precision Sdn Bhd in Puchong, Selangor, for pricing and current stock availability.

19. Buy Temtop S1 Up PM2.5 Air Quality Monitor Malaysia

MTM Precision Sdn Bhd supplies portable air quality monitoring instruments for residential, office and commercial applications throughout Malaysia.

The Temtop S1 Up Air Quality Monitor is suitable for general indoor PM2.5 monitoring applications, including observing particulate changes before and after closing windows during haze.

Potential applications include:

Indoor haze monitoring

Bedroom PM2.5 observation

Living room air quality checks

Office particulate monitoring

Air purifier performance observation

Window closure comparison

General indoor environmental monitoring

Customers may contact MTM Precision for:

Temtop S1 Up pricing

Current stock availability

Product specifications

Home and office PM2.5 applications

Air quality monitor comparisons

General product selection assistance

MTM Precision serves customers throughout Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kelantan, Terengganu, Kedah, Perlis, Sabah and Sarawak.

Contact MTM Precision Sdn Bhd

Showroom & Service Centre

No. 29-1 & 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

Want to Check Whether Closing Your Windows Reduces Indoor PM2.5?

Contact MTM Precision for Temtop S1 Up pricing, stock availability and assistance selecting a suitable portable PM2.5 monitoring instrument.

You may send us your room dimensions, air purifier model or intended monitoring application through WhatsApp for an initial product recommendation.

Conclusion

Closing windows during haze may help reduce the entry of outdoor fine particles into homes and offices.

However, it does not instantly remove existing indoor PM2.5 or prevent all outdoor pollution infiltration.

The Temtop S1 Up Air Quality Monitor provides a convenient way to observe particulate concentration changes before and after closing windows.

By recording measurements under comparable conditions, users can better understand how window position, filtration, ventilation and indoor activities influence particulate concentrations.

Effective haze management combines reduced outdoor particle entry, suitable air filtration, indoor pollution source control and appropriate ventilation.

For Temtop S1 Up Malaysia enquiries, contact MTM Precision Sdn Bhd in Puchong, Selangor.