API vs PM2.5 Reading: What Is the Difference During Haze Malaysia?
Meta Description: Understand the difference between Malaysia’s API and PM2.5 readings, why the numbers cannot be compared directly and how to monitor indoor air quality during haze.
API vs PM2.5 Reading: What Is the Difference During Haze Malaysia?
During a haze episode in Malaysia, people commonly check the Air Pollutant Index (API) to determine whether outdoor air quality is good, unhealthy or hazardous.
At the same time, a portable air quality monitor may display a PM2.5 reading, usually expressed in micrograms per cubic metre. Because both numbers relate to air pollution, users sometimes assume that an API reading of 150 should be the same as a PM2.5 reading of 150.
That is incorrect.
API is an index, while PM2.5 is a measured particle concentration. The numbers represent different things and should not be compared directly.
What Is Malaysia’s API?
The Air Pollutant Index, commonly called API in Malaysia, is used to communicate the overall outdoor air-quality condition to the public.
Malaysia’s API categories are generally classified as:
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0–50: Good
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51–100: Moderate
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101–200: Unhealthy
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201–300: Very unhealthy
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Above 300: Hazardous
The API reading is based on data obtained from official air-quality monitoring stations. It provides a useful indication of pollution conditions across a particular area.
During the September 2026 Sarawak haze, for example, Serian and Kuching recorded hazardous API levels. These official readings helped residents understand the seriousness of the regional air-quality situation.
However, an API number is not a direct measurement of the air inside your house, classroom, office or factory.
What Is PM2.5?
PM2.5 means particulate matter with an aerodynamic diameter of 2.5 micrometres or smaller.
These fine particles may come from:
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Forest and peat fires
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Vehicle exhaust
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Industrial combustion
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Open burning
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Power generation
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Cooking smoke
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Tobacco smoke
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Other combustion activities
A PM2.5 monitor normally displays the concentration in:
µg/m³ — micrograms per cubic metre
For example, an air quality monitor might display:
PM2.5: 68 µg/m³
This means the instrument has detected an estimated concentration of 68 micrograms of fine particulate matter in each cubic metre of air at that particular location.
It does not mean that the API is 68.
API vs PM2.5: Key Differences
| Measurement | API | PM2.5 |
|---|---|---|
| What it represents | Overall air-quality index | Concentration of fine particles |
| Typical display | Index number | µg/m³ |
| Main purpose | Public communication of regional outdoor air quality | Measurement of particulate concentration |
| Measurement location | Official monitoring station | Location of the portable or fixed monitor |
| Can it represent your room directly? | Not necessarily | Yes, when measured correctly in that room |
| Can the numbers be compared directly? | No | No |
The official API and a portable PM2.5 reading complement each other, but they do not replace one another.
Why Can the Numbers Be Different?
A resident may see an official API reading of 180 while an indoor monitor shows a PM2.5 concentration of 45 µg/m³.
This does not automatically mean either reading is wrong.
The difference can be caused by:
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Distance from the official monitoring station
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Whether doors and windows are open
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Building airtightness
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Air-conditioning operation
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Air purifier performance
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Type and condition of installed filters
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Indoor cooking or smoking
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Nearby traffic or construction
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Instrument location
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Time of measurement
The official API describes the wider area. A portable monitor measures the air immediately around its sensor.
Therefore, two instruments placed in different rooms may also display different PM2.5 readings.
Why Is PM2.5 Important During Haze?
Haze may contain a high concentration of fine airborne particles. PM2.5 is particularly important because these particles are small enough to remain suspended in the air and enter indoor spaces through gaps, doors, windows and ventilation systems.
You cannot accurately determine PM2.5 concentration from:
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Visibility alone
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The colour of the sky
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Smell
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Dust visible on furniture
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How uncomfortable the room feels
A room may look clear but still have an elevated PM2.5 concentration. Conversely, an enclosed room using effective filtration may have a lower PM2.5 reading than the outdoor environment.
Actual measurement provides stronger evidence than visual observation.
Can a Portable Monitor Replace the Official API?
No.
A portable air quality monitor should not be treated as a replacement for Malaysia’s official API monitoring network.
The official API remains important for:
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Regional air-quality information
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Public warnings
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Government advisories
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School and outdoor-activity decisions
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Understanding wider pollution trends
A portable PM2.5 monitor is more useful for:
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Checking individual rooms
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Comparing indoor and outdoor air
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Detecting haze entering a building
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Evaluating air purifier performance
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Monitoring classrooms or offices
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Identifying pollution near loading bays
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Recording conditions at a specific worksite
For the best understanding, users should refer to the official API while also measuring their immediate indoor environment when necessary.
How to Compare Indoor and Outdoor PM2.5
If you want to determine whether a building is protecting occupants from haze, compare PM2.5 readings under controlled conditions.
Step 1: Measure Outdoors
Take a short measurement in a safe, representative outdoor location. Avoid standing beside vehicle exhaust, generators, smoking areas or other direct pollution sources.
Step 2: Measure Indoors
Move the instrument indoors and allow the reading to stabilise. Position it away from doors, windows, air-conditioning outlets and air purifier exhausts.
Step 3: Record the Conditions
Record:
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Date and time
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Outdoor PM2.5
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Indoor PM2.5
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Room location
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Door and window condition
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Air-conditioning status
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Air purifier status
Step 4: Repeat the Test
Repeat the measurements at different times because haze intensity and indoor conditions can change throughout the day.
This comparison can reveal whether outdoor particles are entering the building and whether filtration measures are working effectively.
Common PM2.5 Monitoring Mistakes
Placing the Monitor Beside an Air Purifier
The reading may appear unusually low because the monitor is measuring freshly filtered air instead of the average room condition.
Measuring Beside an Open Window
The result may be dominated by outdoor air and may not represent conditions across the occupied space.
Taking Only One Reading
A single measurement is only a snapshot. Air quality can change when doors open, ventilation starts or outdoor haze becomes more severe.
Comparing API and PM2.5 as Identical Numbers
API and PM2.5 use different scales. An API reading of 100 does not automatically mean the PM2.5 concentration is 100 µg/m³.
Ignoring Other Indoor Sources
Cooking, smoking, incense, dust-producing work and combustion equipment can raise indoor particulate readings even when outdoor haze improves.
Which Instrument Is Suitable?
For general haze monitoring, choose an instrument that measures at least PM2.5.
Depending on the application, useful functions may include:
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PM10 measurement
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Real-time display
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Audible or visual alarms
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Temperature and humidity
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Data logging
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Historical trend display
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USB data export
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Mobile-app connectivity
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Rechargeable battery
A portable model such as the Temtop LKC-1000S can be used for spot measurements around homes, offices, schools and workplaces.
For longer-term observation, select a model with data-logging capability so that changes can be recorded throughout the day or across several days.
Use the Right Reading for the Right Decision
The simplest way to remember the difference is:
API tells you about the general outdoor air-quality situation in an area.
PM2.5 tells you the fine-particle concentration measured at a particular location.
During haze in Malaysia, check the official API for regional updates and public instructions. Use a PM2.5 air quality monitor when you need to understand conditions inside a specific room, building or workplace.
The two readings answer different questions, but together they provide a more complete understanding of air quality.
Contact MTM Precision
MTM Precision Sdn. Bhd.
Showroom & Service Centre
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia
🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: +6016-660 7346
01 Sep 2026
