How to Compare Indoor and Outdoor PM2.5 with Temtop S1-UP Malaysia
Why is the PM2.5 reading inside your home different from the outdoor AQI shown on a weather App?
Is indoor air always cleaner during Malaysian haze?
Can you move the Temtop S1-UP outdoors to compare readings?
How long should you wait after moving the monitor?
Why does the reading change near a window or external door?
The Temtop S1-UP can help users understand how particle conditions differ between:
Indoor occupied areas
Areas near windows and doors
Different rooms
Sheltered outdoor locations
However, indoor and outdoor comparisons must be made carefully.
A monitor reading from one location should not automatically be expected to match a distant outdoor monitoring station.
What Does the Temtop S1-UP Measure?
The S1-UP monitors:
PM2.5
AQI
Temperature
Humidity
It is suitable for general environmental monitoring in:
Homes.
Bedrooms.
Offices.
Classrooms.
Tuition centres.
Clinics.
Retail shops.
The S1-UP does not measure:
CO2.
PM10.
TVOC.
Formaldehyde.
Specific gases.
Its indoor-outdoor comparison is therefore focused mainly on PM2.5 and basic environmental conditions.
Why Compare Indoor and Outdoor PM2.5?
During Malaysian haze, users may want to know:
Is indoor PM2.5 lower than outdoors?
Are particles entering through the windows?
Does closing the room reduce particle entry?
Is the air purifier improving indoor conditions?
Which room provides better protection from haze?
A structured comparison can provide more useful information than simply assuming the indoor environment is clean.
Why Can Indoor and Outdoor PM2.5 Be Different?
Indoor PM2.5 depends on:
Outdoor pollution.
Building design.
Window condition.
Door-opening frequency.
Air leakage.
Mechanical ventilation.
Air conditioning.
Air purifier operation.
Indoor particle sources.
Room size.
Indoor and outdoor readings may therefore be very different.
Outdoor Particles Entering Indoors
Outdoor particles may enter through:
Open windows.
Balcony doors.
Main entrances.
Ventilation openings.
Building gaps.
Mechanical ventilation.
Frequent movement of people.
A room does not need to have a fully open window for outdoor PM2.5 to affect indoor conditions.
Indoor Sources Affecting the Comparison
Indoor PM2.5 may be produced by:
Cooking.
Smoking.
Burning incense.
Candles.
Cleaning.
Vacuuming.
Dusting.
Renovation work.
Dust disturbance.
If indoor PM2.5 is high, do not immediately assume that all particles came from outdoors.
Record indoor activities during the comparison.
Why Does S1-UP Not Match a Weather App?
A weather App may obtain information from an outdoor monitoring station that is:
Several kilometres away.
At a different height.
Near a different road.
Exposed to different wind conditions.
Using a different sensor or measurement method.
Using a different averaging period.
The S1-UP measures the air directly around the instrument.
Therefore:
A local indoor reading should not be expected to match a wider outdoor report exactly.
Outdoor AQI vs Indoor AQI
AQI is an index used to communicate air-quality conditions.
Different devices or authorities may use:
Different pollutants.
Different calculation methods.
Different averaging periods.
Different breakpoints.
The outdoor AQI and the AQI displayed by the S1-UP may therefore differ.
For room monitoring, focus on consistent measurements with the same instrument and procedure.
Is Indoor Air Always Cleaner?
No.
Indoor PM2.5 may be lower when:
Windows remain closed.
External doors open less frequently.
An appropriate air purifier operates.
The building has effective particle filtration.
Indoor particle sources are controlled.
Indoor PM2.5 may be higher when:
Cooking occurs.
People smoke indoors.
Incense burns.
Cleaning disturbs dust.
Renovation work takes place.
Outdoor particles enter and become trapped.
The purifier is too small or requires maintenance.
The result depends on actual conditions.
Can S1-UP Be Used Outdoors?
The S1-UP may be used for a brief comparison in a suitable sheltered environment.
However, protect it from:
Rain.
Water.
Direct sunlight.
Excessive heat.
Strong wind.
Condensation.
Unsuitable humidity.
Heavy dust.
Do not leave the monitor exposed outdoors as though it were a weatherproof fixed monitoring station.
Follow the manufacturer’s operating instructions and environmental limitations.
Avoid Direct Sunlight
Direct sunlight may heat the instrument and affect its temperature reading.
It may also create a comparison that is not representative of the surrounding shaded air.
For an outdoor spot check, choose a suitable sheltered position away from direct sunlight.
Avoid Rain and Water
The S1-UP should not be exposed to:
Rain.
Water splashes.
Wet surfaces.
Condensation.
Heavy steam.
If outdoor conditions are wet or unsuitable, do not conduct the comparison.
Instrument protection is more important than collecting one extra reading.
Avoid Strong Wind
Strong airflow may create rapidly changing conditions around the monitor.
It may also make the outdoor location difficult to compare with the calmer indoor environment.
Choose a stable, sheltered position when making a general comparison.
Step 1: Define the Question
Before measuring, decide what you want to know.
Examples include:
Is indoor PM2.5 lower than the sheltered outdoor area?
Does PM2.5 increase when the window opens?
Does the purifier improve indoor conditions?
Which room has the lowest PM2.5?
Is haze entering through the main door?
A clear question helps you select the correct measurement position.
Step 2: Begin with the Indoor Reading
Place the S1-UP in a representative occupied area.
Avoid:
Air purifier outlets.
Air-conditioner outlets.
Open windows.
External doors.
Cooking areas.
Direct sunlight.
Allow the reading to stabilise.
Record:
PM2.5.
AQI.
Temperature.
Humidity.
Time.
Room.
Door condition.
Window condition.
Purifier status.
Indoor activity.
Step 3: Select a Suitable Outdoor Position
Choose a sheltered outdoor position that is:
Protected from rain.
Away from direct sunlight.
Away from cooking smoke.
Away from vehicle exhaust outlets.
Away from smoking areas.
Safe for the instrument.
Do not place the monitor directly beside a running vehicle or another intense local source unless that is the specific investigation objective.
Step 4: Allow the Monitor to Respond
After moving from indoors to outdoors, do not treat the first displayed number as the final outdoor result.
The instrument has entered a different environment.
Changes may include:
PM2.5.
Temperature.
Humidity.
Airflow.
Allow the reading time to respond before recording it.
Step 5: Record the Outdoor Condition
Record:
PM2.5.
AQI.
Temperature.
Humidity.
Time.
Location.
Weather condition.
Distance from roads.
Nearby activity.
Whether the position is sheltered.
This creates context for the comparison.
Step 6: Return Indoors
Move the S1-UP back to the original indoor location.
Keep the room conditions recorded.
Allow the monitor to respond again.
Observe whether the indoor reading returns to a similar pattern.
This helps identify whether the difference was related to the environment rather than an instrument problem.
Use A Mode for Active Comparison
The S1-UP provides A Mode for more immediate monitoring.
A Mode is more suitable when moving the instrument between locations and actively checking changes.
According to Temtop, standby duration in A Mode may reach approximately 20 days, depending on use and battery condition.
Use ECO Mode for Longer Indoor Monitoring
ECO Mode prioritises longer battery endurance.
According to Temtop, standby duration may reach approximately 60 days, depending on use and battery condition.
ECO Mode is better suited to general indoor monitoring in one location.
For an active indoor-outdoor comparison, A Mode is the more practical choice.
Indoor vs Window-Area Comparison
Before moving fully outdoors, users may first compare:
The occupied room.
An area near the closed window.
An area near the open window.
Keep the S1-UP in each position long enough to respond.
Label the readings correctly.
A window-area reading does not necessarily represent the whole room.
Indoor vs External-Door Comparison
External doors can allow particles to enter when:
Customers arrive.
Students enter.
Employees enter or leave.
Deliveries occur.
The door remains open.
A shop, clinic or office may show changing PM2.5 near the entrance.
For general indoor monitoring, position the S1-UP farther inside the occupied area.
For door-entry investigation, take a separate reading near the door.
Bedroom Comparison
For a bedroom during haze:
Record PM2.5 in the occupied area.
Record whether the window is open or closed.
Record whether the bedroom door is open.
Record the purifier status.
Conduct an outdoor check only in a safe sheltered location.
Return the S1-UP to the same bedroom position.
Observe whether indoor PM2.5 remains lower over time.
Living-Room Comparison
A living room may be affected by:
The main entrance.
Balcony doors.
Kitchen activity.
Visitors.
Open-plan connections.
Record these conditions carefully.
A high living-room reading may come from outdoor haze or indoor cooking.
Home-Office Comparison
A home office may remain closed for many hours.
The S1-UP can help compare particle conditions, but it does not measure CO2.
A closed room may have low PM2.5 while CO2 increases because of occupancy.
Use a CO2-capable monitor when ventilation awareness is also required.
Office Comparison
An office may not have openable windows.
Outdoor air may enter through:
Mechanical ventilation.
Building entrances.
Loading areas.
Doors.
Air leakage.
Compare representative indoor positions instead of assuming that one entrance reading represents the entire office.
Classroom Comparison
During haze, a classroom may have:
Closed windows.
Frequent door movement.
Air conditioning.
An air purifier.
The S1-UP can help compare indoor PM2.5 with a suitable sheltered outdoor location.
However, it does not measure classroom CO2.
High occupancy and closed windows may require separate CO2 monitoring.
Air Purifier Comparison
To evaluate an air purifier:
Keep the S1-UP indoors.
Record the initial PM2.5.
Switch on the purifier.
Keep the windows and doors consistent.
Record the purifier speed.
Observe the PM2.5 trend.
Do not place the S1-UP beside the clean-air outlet.
The purpose is to understand the occupied room, not the purifier discharge.
Why Is Indoor PM2.5 Lower but Not Zero?
Possible reasons include:
Particles remain inside.
The building is not perfectly sealed.
Doors open occasionally.
The purifier cannot remove every particle immediately.
Indoor activities continue.
Air enters from other rooms.
A low but non-zero reading can be expected in normal environments.
Focus on the trend and application rather than expecting a permanent zero reading.
Why Is Outdoor PM2.5 Lower Than Indoors?
Possible reasons include:
Indoor cooking.
Smoking.
Incense.
Cleaning.
Renovation dust.
Poor indoor filtration.
Particles trapped indoors.
The outdoor location being away from the main pollution source.
Outdoor conditions changing during the test.
Review indoor activities before assuming that the monitor is incorrect.
Why Does the Reading Change Quickly Near a Door?
Door movement can create changing airflow.
The monitor may alternately sample:
Indoor air.
Corridor air.
Outdoor-influenced air.
This can cause fluctuations.
A doorway is useful for investigating particle entry but is not usually the best location for general room monitoring.
Why Does the Reading Change After Moving?
The S1-UP has entered a different air environment.
This is expected.
The instrument must respond to new:
Particle conditions.
Temperature.
Humidity.
Airflow.
Do not interpret the first number after moving as the final stable reading.
Can One Reading Prove the Building Is Protected from Haze?
No.
One reading represents one location and time.
Building performance may change according to:
Outdoor haze.
Wind.
Door activity.
Ventilation operation.
Purifier operation.
Occupancy.
Different rooms.
Longer monitoring and multiple representative locations provide more useful information.
Formal building-performance assessment may require specialised methods.
Common Indoor-Outdoor Comparison Mistakes
Mistake 1: Comparing S1-UP with a Distant Weather Station
The locations and methods are different.
Mistake 2: Placing the Monitor in Direct Sunlight
This creates unsuitable comparison conditions.
Mistake 3: Exposing It to Rain
The instrument must be protected.
Mistake 4: Recording the First Number After Moving
Allow the monitor to respond.
Mistake 5: Ignoring Indoor Particle Sources
Cooking and cleaning may dominate the indoor reading.
Mistake 6: Comparing Different Operating Modes
Use the same mode throughout the comparison.
Mistake 7: Moving the Monitor to an Extreme Outdoor Source
A vehicle exhaust location does not represent general outdoor air.
Mistake 8: Treating PM2.5 as CO2
The S1-UP does not measure ventilation-related CO2 changes.
Indoor-Outdoor Monitoring Checklist
Indoor
Use a representative occupied position.
Record doors and windows.
Record purifier and air-conditioner status.
Record indoor activity.
Allow the reading to stabilise.
Outdoor
Use a sheltered location.
Avoid rain and direct sunlight.
Avoid strong local pollution sources.
Record traffic and weather conditions.
Allow the reading to respond.
Comparison
Use the same instrument and mode.
Record time and location.
Observe the trend.
Return to the original indoor position.
Do not rely on one number.
Indoor vs Outdoor PM2.5 Final Summary
The Temtop S1-UP can help Malaysian users understand whether indoor PM2.5 differs from the surrounding outdoor environment.
For a useful comparison:
Measure indoors from a representative occupied position.
Use a safe sheltered outdoor location.
Protect the instrument from rain, sunlight and strong wind.
Allow the reading to respond after moving.
Record indoor activities, windows, doors and purifier operation.
Most importantly:
Do not expect a local indoor monitor to match a distant outdoor AQI station exactly.
The S1-UP is most useful for answering practical room-level questions such as:
Is haze entering?
Is indoor PM2.5 lower?
Does closing the window help?
Is the purifier improving the room?
Contact MTM Precision
Contact MTM Precision for Temtop S1-UP Malaysia price and quotation, or for assistance selecting Temtop monitors for indoor and outdoor PM2.5 comparison, haze, air purifiers, homes, offices and classrooms.
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
