Malaysia Haze: Should You Close Windows or Improve Ventilation? Use PM2.5 and CO Monitoring to Decide Introduction When haze affects Malaysia, one of the first pieces of advice people hear is: “Close the windows and doors.” That can make sense when outdoor particulate pollution is elevated. But there is another side to the problem. If a room is occupied and ventilation is reduced for a long period, CO can increase. This creates a practical indoor air quality challenge: How do you reduce outdoor PM2.5 entering the building without creating a poorly ventilated indoor environment? The answer should not be based only on whether the room feels comfortable. A better approach is to monitor both: PM2.5 CO and use actual measurements to understand what is happening inside the building. The Haze Ventilation Dilemma During normal conditions, opening windows may increase natural ventilation. During haze, however, outdoor air can contain elevated particulate matter. This creates two competing considerations. Windows Open Potential advantage: More outdoor air and natural ventilation Potential disadvantage: Outdoor PM2.5 may enter the building Windows Closed Potential advantage: May reduce direct outdoor particulate infiltration Potential disadvantage: CO may increase in occupied rooms if ventilation is insufficient Therefore: “Open the windows” and “Close the windows” are not complete indoor air quality strategies by themselves. Why PM2.5 Matters During Haze PM2.5 refers to fine particulate matter with an aerodynamic diameter of approximately 2.5 micrometres or smaller. During haze events, PM2.5 is one of the important parameters people may want to monitor. Outdoor particles can enter indoor spaces through: Open windows Open doors Building leakage Ventilation systems Outdoor air intakes Frequent movement through entrances Indoor PM2.5 measurement helps show how much particulate pollution is present inside the actual room. Why CO Matters When Windows Are Closed CO is produced by people when they breathe. In an occupied room, CO concentration can increase when ventilation is insufficient relative to occupancy. This means a room may have: Low PM2.5 but Increasing CO after doors and windows remain closed for an extended period. That is why haze management should not focus on particulate matter alone. Example: Meeting Room During Haze Imagine a meeting room in Puchong. Outside: Haze conditions Inside: 10 people The windows are closed to reduce otdoor haze entering the room. At the beginning of the meeting: PM2.5 may be relatively controlled. CO may also be acceptable. But after the room remains occupied: PM2.5 may remain relatively low while CO may gradually increase. If you monitor only PM2.5, you may miss the ventilation issue. Example: Open the Window Now imagine someone opens the window because the room feels stuffy. CO may begin to change because more outdoor air is entering. But during haze: Indoor PM2.5 may also increase. This illustrates why measurement is useful. Instead of guessing which condition is better, monitor both parameters. PM2.5 and CO Tell Different Stories Think of the two parameters separately. PM2.5 Helps you understand fine particulate conditions. During haze, it can help indicate whether outdoor particulate pollution is affecting indoor spaces. CO In suitable occupied indoor environments, CO can provide useful information related to occupancy and ventilation. It does not measure PM2.5. Therefore: PM2.5 ≠ CO and CO ≠ PM2.5 Monitoring both gives a more useful picture. Don't Use CO as a Haze Detector This distinction is important. A low CO reading does not mean outdoor haze pollution is low. Similarly, a high CO reading does not tell you the PM2.5 concentration. If haze is the concern, measure particulate matter directly. If ventilation in an occupied room is also a concern, CO becomes another useful parameter. Don't Use PM2.5 as a Ventilation Indicator The opposite mistake can also happen. A room may show relatively low PM2.5 because: Windows are closed Doors are closed Air purification is operating But the room may still have insufficient ventilation for its occupancy. PM2.5 alone cannot answer that question. This is why multi-parameter monitoring is valuable. What Should You Do During Haze? There is no single answer for every building. The correct strategy depends on: Outdoor conditions Indoor PM2.5 Occupancy CO HVAC design Filtration Air purifier operation Building leakage Room usage Measurement helps facility managers understand these factors. A Practical Monitoring Approach Instead of automatically opening or closing windows, try a structured approach. Step 1 Check Outdoor Conditions Review the current outdoor air quality situation. If outdoor particulate pollution is elevated, be aware that additional outdoor ar may also introduce particulate pollution indoors. Step 2 Measure Indoor PM2.5 Use an indoor air quality monitor to determine actual indoor particulate conditions. Do not assume indoor PM2.5 is identical to the outdoor reading. Step 3 Monitor CO In occupied spaces, observe CO conditions. This can provide additional information about how the room behaves when doors and windows remain closed. Step 4 Review HVAC Operation Determine whether the room depends on: Natural ventilation Mechanical ventilation Air conditioning Outdoor air supply Recirculated air Different buildings require different strategies. Step 5 Review Filtration Where appropriate, evaluate: HVAC filtration Air purifier operation Filter condition Filter replacement Airflow Filtration can play an important role during particulate pollution events. Step 6 Continue Monitoring After making changes, continue measuring. The objective is to determine whether conditions actually improve. Use Measurements to Compare Strategies For example, compare: Condition A Windows closed Air purifier off Condition B Windows closed Air purifier on Condition C Different HVAC setting Condition D Controlled ventilation strategy Observe: PM2.5 CO Temperature Humidity This provides evidence about how the building responds. Test Your Air Purifier During Haze A PM2.5 monitor can help evaluate whether an air purifier is reducing particulate concentration. A simple test is: Record PM2.5 ↓ Turn On Air Purifier ↓ Keep Monitoring ↓ Observe PM2.5 Trend ↓ Compare Before and After This is much more useful than simply assuming the purifier is effective because the fan is running. Air Purification Does Not Replace Ventilation This is another important distinction. An air purifier designed to reduce particles may help lower indoor particulate concentration. But it does not automatically solve every indoor air quality issue. For example, a typical particulate air purifier does not necessarily address increasing CO caused by occupancy. Therefore: Particle filtration and ventilation solve different problems. Air Conditioning Does Nt Automatically Solve Both Problems Many people assume: “The air conditioner is on, so the indoor air must be good.” Not necessarily. An air-conditioning system may: Cool the room Recirculate indoor air Filter some particles but the actual ventilation and filtration performance depends on the system design. Temperature comfort alone is not proof of good indoor air quality. Schools During Haze Schools face a particularly interesting challenge. A classroom may contain many students. During haze: Windows may be closed Doors may remain closed Air conditioning may operate PM2.5 may be one concern. But occupancy-related CO can also become important. This makes combined monitoring useful. Classroom Monitoring A school could monitor: PM2.5 to understand particulate conditions and CO to understand occupied-room ventilation conditions. Additional parameters may include: Temperature Relative humidity This gives school management more useful information than outdoor AQI alone. Offices During Haze The same principle applies to: Meeting rooms Training rooms Open offices Conference rooms Management rooms Different spaces can behave differently because occupancy and ventilation vary. A meeting room with 15 people may have a very different CO pattern from an open office. Factories During Haze Factories may have additional complexity because indoor air quality can be affected by both: Outdoor pollution and Indoor processes Monitoring requirements may therefore include: PM2.5 PM10 CO VOC Temperature Humidity The correct parameters depend on the process and monitoring objective. Temtop M100 for PM2.5 + PM10 + CO Monitoring For haze-related indoor monitoring, the Temtop M100 can be considered where users want to monitor: PM2.5 PM10 CO AQI This combination is useful because it allows users to observe both particulate conditions and CO using one portable monitor. Potential applications include: Homes Offices Schools Universities Public buildings Haze investigations Temtop M10 for Conected Indoor Monitoring The Temtop M10 can be considered where users want monitoring involving: PM2.5 CO VOC Temperature Relative humidity with supported app connectivity. This makes it useful for users who want to observe several indoor environmental parameters and review changes over time. Which Temtop Monitor Should You Choose? For haze applications: Choose Temtop M100 when: Your priority includes: PM2.5 PM10 CO AQI Choose Temtop M10 when: Your priority includes: PM2.5 CO VOC Temperature Humidity Connected monitoring The correct model depends on what you need to understand. One Monitor or Multiple Monitoring Points? A portable monitor is useful when you want to: Check one room Compare rooms Investigate a complaint Test an air purifier Perform a haze survey But a school, office or public building may eventually need continuous information from many rooms. This leads to multi-point monitoring. Example Office Monitoring System A larger office could monitor: Reception PM2.5 + CO Open Office PM2.5 + CO Meeting Room 1 PM2.5 + CO Meeting Room 2 PM2.5 + CO Training Room PM2.5 + CO ↓ Central Monitoring Platform ↓ Historical Data ↓ Facility Management This provides much more useful information than moving one meter around every day. Real-Time Haze Monitoring Continuous monitoring can show what happens: Before haze ↓ As outdoor conditions worsen ↓ During peak haze ↓ After filtration / HVAC adjustments ↓ As outdoor conditions improve This creates a complete environmental trend. Historical Data Helps Identify Patterns Historical monitoring can answer questions such as: When did indoor PM2.5 begin increasing? Which room was affected first? Did PM2.5 increase when doors opened? Did CO rise during meetings? Did air purification reduce PM2.5? How quickly did the room recover? These are much more actionable questions than simply asking: “Is the air good or bad?” From Outdoor AQI to Building Intelligence The monitoring journey can develop from: Outdoor AQI / API ↓ Indoor PM2.5 Measurement ↓ CO Monitoring ↓ Room Comparison ↓ Filtration Evaluation ↓ Historical Data ↓ Multi-Point Sensors ↓ Central Dashboard ↓ Continuous Indoor Air Quality Monitoring This is how haze monitoring can become part of a broader building environmental management strategy. Information Needed for a Haze Monitoring Project For schools, offices, factories and public buildings, customers can provide: Building type Location Number of floors Number of rooms Approximate occupancy PM2.5 requirement PM10 requirement CO requirement VOC requirement Portable or fixed monitoring Number of monitoring points Historical data requirement 24/7 monitoring requirement Dashboard requirement Alarm requirement HVAC information if available Floor plan if available This helps determine whether the application requires portable Temtop instruments or a larger continuous monitoring solution. Why Choose MTM Precision? MTM Precision Sdn. Bhd. supplies Temtop air quality monitors and professional environmental monitoring solutions throughout Malaysia. We support applications involving: Haze monitoring PM2.5 monitoring PM10 monitoring CO monitoring Indoor air quality assessment School air quality monitoring Office air quality monitoring Factory environmental monitoring Multi-point monitoring Historical data Continuous environmental monitoring Central dashboards The objective is not simply to sell an air quality meter. The objective is to help customers understand: What is happening in the building, why it is happening, and what should be monitored next. 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 Copy Link