Air Quality in Phnom Penh: PM2.5, Dust, Smoke and Choosing a Home

Prepared by the NovAsia Editorial Team

Air quality in Phnom Penh cannot be reduced to a single permanent rating. The city has relatively clear days as well as episodes of elevated fine-particle pollution, with poorer conditions more common during parts of the dry season. For residents, the useful question is not whether Phnom Penh is “clean” or “dirty” in the abstract. It is how to read a nearby monitor, distinguish PM2.5 from visible household dust, choose when to ventilate, and assess how well a particular home is protected from traffic, construction and smoke.

Air pollution is a health issue, but an app reading cannot diagnose the cause of symptoms or replace medical advice. People with asthma, heart or lung disease, pregnancy-related concerns, significant allergies or other health risks should discuss an individual action plan with a qualified clinician.

What air-quality monitors measure

The two particle measurements residents encounter most often are PM2.5 and PM10. These are size categories, not single chemicals.

PM2.5 refers to particles with an aerodynamic diameter of 2.5 micrometres or less. Sources include fuel combustion, vehicle exhaust, open burning, industrial activity and chemical reactions in the atmosphere. Because they are very small, these particles can remain airborne and travel well beyond the source.

PM10 includes larger inhalable particles up to 10 micrometres. In an urban setting, they can be generated by road dust, construction sites, bare ground, damaged surfaces and mechanical disturbance from traffic. Some PM10 settles visibly on balconies and window ledges, but the most health-relevant fine particles cannot be judged reliably by sight.

Monitoring stations may also report:

• nitrogen dioxide, often associated with traffic and combustion;
• sulphur dioxide;
• carbon monoxide;
• ground-level ozone;
• temperature, humidity and wind.

For a practical decision such as whether to run outdoors or open windows, residents commonly look at PM2.5 and an air quality index. These are related but not interchangeable.

PM2.5 concentration is normally expressed in micrograms per cubic metre. AQI is a calculated index that converts one or more pollutant concentrations into a category or colour scale. A reading of 75 AQI does not mean 75 µg/m³ of PM2.5.

Why different apps may show different numbers

Phnom Penh is covered by official monitoring stations as well as private sensors, international platforms and models that combine ground and satellite data. Two apps can therefore show different values at the same time without one necessarily being fraudulent.

Common reasons include:

• different station locations;
• one monitor being close to a road while another is in a quieter area;
• different update intervals;
• different calibration methods;
• one service showing a current reading and another an hourly or daily average;
• different AQI formulas;
• measured data on one platform and modelled data on another.

Cambodia’s Ministry of Environment has encouraged the public to use the national monitoring network and has challenged some conclusions based solely on third-party data. International assessments have also noted the need for continued improvements in coverage, comparability and public access. A resident does not need to choose one side of that debate. The more useful approach is to understand the source and limitations of each number.

A practical checking routine is:

1. Open the Ministry of Environment’s official air-quality portal.
2. Select the station nearest your actual location, not a national average.
3. Compare it with one independent platform.
4. Review the trend over several hours rather than one snapshot.
5. Confirm whether the display is PM2.5, PM10 or AQI.
6. Check the timestamp.

A sharp increase at one monitor, with nearby stations remaining stable, may reflect a local source, a brief event or a sensor problem. A sustained increase across several parts of the city is stronger evidence of a broader urban or regional episode.

Do not make a major decision from a screenshot that lacks a station name and time. Air conditions can change substantially within hours.

How to interpret WHO guideline values

The World Health Organization’s 2021 global air-quality guidelines recommend an annual average of 5 µg/m³ and a 24-hour average of 15 µg/m³ for PM2.5. For PM10, the corresponding guideline levels are 15 and 45 µg/m³.

These are public-health recommendations, not a line below which risk becomes zero. WHO notes that adverse effects can occur at relatively low concentrations.

A national monitoring system may use different regulatory thresholds and its own labels such as good, moderate or unhealthy. An official “good” category and a concentration above the more stringent WHO guideline can therefore appear at the same time. They answer different questions:

• the national category reflects the adopted national assessment system;
• the WHO guideline indicates a health-protective target;
• an individual decision also depends on health status, exposure duration and activity level.

Do not automatically apply a US AQI colour scale to every Cambodian app. First confirm which formula the platform uses.

For everyday decisions, changes relative to the local baseline can be more actionable than arguments about one universal threshold. If a neighbourhood usually records one range and PM2.5 suddenly rises several-fold, it is reasonable to shorten hard outdoor exercise, close windows facing the source and reassess later.

When Phnom Penh’s air is more likely to be worse

Cambodia-focused monitoring assessments report that higher PM2.5 concentrations are often observed during the dry season. The pattern is plausible: there is less rain to remove particles, dry surfaces produce more dust and stagnant conditions may allow pollution to accumulate.

The wet season does not guarantee clean air. A downpour may reduce particle levels temporarily, but dust can return when roads dry. High humidity can also make the air feel heavy without necessarily indicating high PM2.5.

More difficult episodes can occur when several factors coincide:

• prolonged dry weather;
• weak wind;
• heavy urban traffic;
• construction dust;
• waste burning;
• agricultural or vegetation fires in the region;
• smoke transported from elsewhere in Cambodia or neighbouring countries.

Fine particles do not respect city boundaries. A smoky day cannot always be explained by the nearest construction site or junction.

For a resident, it helps to distinguish three scales of exposure:

A local source may be reduced by closing one side of the home or changing route. During a regional smoke episode, moving one street away is unlikely to solve the problem.

Morning is not automatically cleaner than evening

It is tempting to assume that dawn is always the best time to exercise. Weather and atmospheric mixing make the reality less predictable.

Pollution can accumulate near ground level overnight when wind is weak. Morning traffic then adds fresh emissions, so early hours may occasionally be worse than midday. On another day, overnight rain or stronger wind may make morning the best period.

Evenings also vary. Daytime heating can improve mixing, but rush-hour traffic can raise roadside pollution.

A rule such as “always run at 6 am” is therefore unreliable. Before a hard session, look at the hourly trend from a nearby station. Moving an activity by two hours may reduce exposure without cancelling it.

Wind direction also matters. A flat or running route downwind from a construction site, generator, road or burning area may experience higher local levels than the citywide reading suggests.

Choosing a home with air quality in mind

Assess air in the same way as noise: at the exact building, at different times, and both inside and outside.

Look for sources within the immediate block:

• a congested road below the windows;
• an intersection where traffic idles;
• an active construction site;
• an unpaved parking area;
• workshops;
• restaurant exhaust outlets;
• waste-storage areas;
• habitual open burning;
• a standby generator close to the façade or air intake.

Visit in the morning and evening. A road that is quiet at midday may become a queue after work. Construction may be inactive on Sunday, making a weekend-only viewing misleading.

A higher floor can reduce some direct exposure to coarse road dust and immediate exhaust, but it does not create a separate atmosphere. PM2.5 from citywide or regional sources reaches upper floors.

Examine the windows. Large gaps, poorly fitting sliding frames and permanent openings increase the amount of outdoor air entering. At the other extreme, a tightly sealed flat without managed ventilation can accumulate carbon dioxide, moisture, odours and indoor pollutants. The goal is not perfect isolation but controllable ventilation.

A standard split air conditioner usually recirculates indoor air. Its washable mesh filter catches coarse dust and protects the unit, but it is not equivalent to a HEPA filter designed for fine particles.

Where air quality is an important health factor, a small personal PM2.5 monitor can help compare several flats using the same instrument. It is not a professional reference station, but it can show meaningful relative differences.

A simple in-home test during a viewing

One measurement cannot establish a flat’s long-term air quality. Readings depend on whether windows were open, whether someone was cooking or cleaning, and whether a purifier had been running.

Use the same sequence for each property:

1. Check the nearest official outdoor reading.
2. Measure in the lobby and inside the flat.
3. Close the windows for 20–30 minutes.
4. Run the air conditioner without a purifier.
5. Measure again.
6. Open the window facing the road and observe how quickly the reading changes.
7. Inspect the air-conditioner filters.
8. Check for odours around the kitchen extract and bathroom ventilation.

A low indoor reading can be encouraging, but ask whether a purifier had been operating before the visit. Also remember that low PM2.5 says nothing about mould, volatile organic compounds or carbon dioxide.

Consumer optical sensors can be affected by humidity, placement and calibration. They are most useful for comparing trends with one device, not for claiming laboratory-level accuracy.

Reducing particles indoors

The most effective household approach begins with source control.

Do not smoke indoors or burn rubbish. Avoid frequent incense, candles and smoky mosquito products in closed rooms. Use a kitchen hood when it genuinely vents outdoors. A weak recirculating hood does less to remove combustion particles than a properly ducted extract system.

During an elevated-PM2.5 episode, close windows facing the source. Ventilate when outdoor readings improve. Keeping a home sealed indefinitely without monitoring humidity and carbon dioxide can create other problems, so the ventilation strategy should change with outdoor conditions.

Maintain the air conditioner. A dirty filter reduces airflow, while damp internal components can develop odours and microbial growth. Cleaning the filter still does not turn the air conditioner into a fine-particle purifier.

Use damp cleaning methods instead of aggressive dry sweeping. Dry brooms can resuspend settled dust. A vacuum with good filtration, followed by a damp cloth or mop, generally reduces this effect.

Carpets, heavy curtains and upholstered furniture collect dust. They do not have to be eliminated, but a home beside a busy road may require more frequent cleaning.

Choosing an air purifier

For PM2.5, look for a purifier designed to remove fine particles, normally with a genuine high-efficiency particle filter and a stated clean-air delivery rate.

Do not rely only on the room-size claim printed on the box. Manufacturers may calculate floor area using different fan speeds and air-change assumptions. CADR—clean air delivery rate—is a more transparent comparison.

For a room with a volume of 75 m³ and a target of four air changes per hour, an indicative requirement is:

75 × 4 = 300 m³/h

This is a sizing method, not an individual medical prescription. It helps compare products on the same basis.

For a bedroom, examine output at the speed you can tolerate overnight. A purifier with an excellent maximum CADR may be too noisy on high and much less effective on its quietest setting.

Check:

• CADR for smoke or fine particles;
• the price and local availability of replacement filters;
• how quickly filters can be delivered in Cambodia;
• noise levels at different speeds;
• electricity consumption;
• space around the air intake and outlet;
• whether any ionisation or ozone-generating mode can be disabled;
• whether display lights can be turned off.

The US Environmental Protection Agency warns that ozone-generating devices can produce a gas that irritates the lungs and are not a safe substitute for particle filtration in occupied rooms.

Place the purifier where air can move freely around it, not behind a sofa or inside a tight corner. A dedicated unit in the bedroom is often more useful than one undersized machine expected to clean an entire flat with closed doors.

Filter life depends on actual use. In a dusty or smoky period, a filter may load faster than the calendar estimate. Reduced airflow, odour or heavy visible discolouration are reasons to inspect it sooner.

Is a separate PM2.5 monitor worthwhile?

A household monitor can help residents decide when to ventilate and whether the purifier is working. Without feedback, people may run a purifier at full speed unnecessarily or leave it off during a poor-air episode.

Useful questions include:

• when can the windows be opened;
• how quickly does the purifier reduce particles;
• does cooking create a spike;
• is smoke entering from another unit;
• how different are the bedroom and balcony;
• is a filter change affecting performance.

The most expensive monitor is not automatically necessary. Consistency matters more than an impressive app. Compare the device periodically with the nearest official outdoor station. If it always reads several times higher or lower, reconsider placement, humidity and sensor quality.

Do not place it directly beside the purifier outlet, air conditioner, cooker or open window. That measures one local stream rather than the air in the occupied zone.

Respirators and outdoor exposure

A loose cloth covering or ordinary loose-fitting surgical mask is not designed to provide reliable PM2.5 protection. A certified particulate respirator can reduce exposure only when it fits correctly.

WHO guidance emphasises that the respirator should cover the nose and mouth and seal closely to the face. Gaps around the cheeks or nose substantially reduce protection, and facial hair can prevent a reliable seal.

During a significant smoke or dust episode, people commonly look for certified N95, FFP2 or comparable particulate respirators. Certification and provenance matter; printed markings alone do not prove that a counterfeit product performs as claimed.

A particulate respirator does not protect against every gas or unknown chemical. If there is a nearby chemical release or unidentified heavy smoke, leaving the area and following official emergency advice is safer than relying on an N95.

People with heart or lung conditions, pregnant people and anyone who struggles to breathe while wearing a respirator should seek individual medical advice. A mask should not create false confidence to continue strenuous exercise during severe pollution.

Adjusting physical activity on a poor-air day

During exercise, breathing becomes faster and deeper, increasing the dose of polluted air. This does not mean every departure from an ideal guideline requires cancelling all activity.

A proportionate sequence is:

• move exercise to a time with lower readings;
• choose a park or quieter street away from traffic;
• shorten the session;
• replace running with lighter activity;
• train indoors where air is filtered;
• stop and seek medical help for unusual shortness of breath, chest pain, wheezing or a marked deterioration in health.

Children, older adults, pregnant people and those with asthma, chronic lung disease or cardiovascular disease may be more sensitive.

Parents should ask schools how air quality is monitored, whether classrooms have suitable filtration, where activities move during smoke episodes and who decides when outdoor sport is changed or cancelled.

Do not alter prescribed medication solely because of an app reading. Asthma and other condition-specific action plans should be agreed with a clinician in advance.

Air pollution, mould and allergies are not the same problem

PM2.5, coarse dust, mould and allergens can cause overlapping complaints such as irritated eyes, cough, nasal symptoms and throat discomfort. The appropriate response depends on the source.

If symptoms are worse in only one room, inspect:

• mould behind furniture and around the air conditioner;
• indoor humidity;
• a persistent damp smell;
• dust in bedding and curtains;
• pest allergens;
• the condition of the air-conditioner filter;
• cleaning products and fragrances;
• smoke from neighbours.

A citywide PM2.5 episode usually appears across several outdoor stations and may also raise indoor sensor readings. Mould can exist when outdoor particle levels are low and may not create an obvious PM2.5 spike.

A dehumidifier does not remove fine particles, and a HEPA purifier does not repair a leak or wet wall. The source of moisture must be fixed.

Persistent or significant symptoms need medical assessment. Their cause cannot be determined from timing or one sensor number alone.

What to do when you smell burning

A burning smell indicates combustion somewhere nearby or upwind, but odour intensity does not quantify PM2.5. Some harmful particles have little smell, while a strong local smell may appear before a city monitor reflects the event.

If smoke appears suddenly:

1. Close windows on the affected side.
2. Turn off any extract system that is pulling outdoor air inside.
3. Check official data and nearby monitors.
4. Observe the area without approaching the source.
5. Run the purifier.
6. Avoid hard outdoor exercise.
7. Report a fire or unlawful burning to building management or the relevant authorities.

Do not attempt to tackle a substantial waste, electrical or unknown-material fire yourself. The smoke may contain hazardous substances.

If the smell enters through the building ventilation, notify management. The source may be another kitchen, a generator, a car park or a technical-room incident. Blocking a vent without understanding the system can create a different safety problem.

Auditing a neighbourhood before a long lease

A one-week observation is more informative than a citywide annual average.

Save the three nearest monitoring stations and check them morning, afternoon and evening. Note dry days, wind, rain and visible smoke. Then compare the data with what you experience on the street.

Look for:

• heavy-vehicle traffic;
• recurring congestion;
• poor road surfaces and loose dust;
• exposed ground;
• active construction;
• waste areas;
• generators;
• workshops;
• restaurant exhaust aimed at homes;
• repeated open burning.

Two buildings in the same neighbourhood may differ more than two neighbourhood averages. A second-line building with good windows and controllable ventilation may be more comfortable than a prestigious tower directly above a junction.

Do not judge by sky colour alone. Humidity can create haze without extreme particle pollution, while PM2.5 may be elevated on a visually clear day.

A practical poor-air-day routine

A simple plan reduces both exposure and anxiety.

In the morning:

1. Check the nearest official station.
2. Compare it with one independent source.
3. Review the trend over recent hours.
4. Decide when to ventilate.
5. Reschedule prolonged outdoor exercise if necessary.

At home:

• close windows facing the source;
• run an appropriately sized purifier;
• avoid smoking and incense;
• use effective kitchen extraction;
• monitor particles and humidity;
• do not keep the home excessively damp.

Outside:

• choose lower-traffic streets;
• minimise time beside stationary queues;
• use a suitable respirator during a pronounced particle episode where appropriate;
• avoid strenuous exercise beside major roads;
• pay particular attention to children and medically vulnerable household members.

The aim is not to create a sterile environment. It is to reduce cumulative exposure at the times when doing so is straightforward.

Conclusion

Air quality in Phnom Penh varies by season, neighbourhood and hour. Dry periods are more likely to bring elevated PM2.5 episodes, but there is no universal best time of day. Use the nearest official station, read the trend rather than a single number and confirm which AQI scale an app uses.

When choosing a home, assess the actual façade, road, construction sites, generators, windows and ventilation. A high floor may reduce some local coarse dust but does not protect against citywide or regional smoke.

At home, the most practical measures are source control, ventilation timed to outdoor conditions, proper air-conditioner maintenance, a suitably sized HEPA purifier and a basic PM2.5 monitor. On poorer days, changing the time and location of exercise can often reduce exposure more effectively than relying on one mask or gadget.

Sources

1. Ministry of Environment of Cambodia — official air-quality monitoring portal and national monitoring network. Reviewed 25 June 2026.
2. Global Green Growth Institute — *Situation Assessment Report: Air Quality Monitoring in Cambodia*, 3 September 2025.
3. United Nations Economic and Social Commission for Asia and the Pacific — *Assessment of Air Quality Remote Sensing in Cambodia*, 2025.
4. World Health Organization — *WHO Global Air Quality Guidelines: PM2.5, PM10, Ozone, Nitrogen Dioxide, Sulfur Dioxide and Carbon Monoxide*, 22 September 2021.
5. World Health Organization — *Personal-level Actions to Reduce Air Pollution Exposure in the WHO European Region*, 2024.
6. United States Environmental Protection Agency — *Guide to Air Cleaners in the Home*. Current version reviewed 25 June 2026.
7. World Health Organization — *Ambient (Outdoor) Air Pollution: Health Impacts and Sensitive Groups*, updated 24 October 2024.

Frequently asked

Will living on a high floor completely avoid air pollution?

No. Height may reduce some immediate roadside dust and exhaust exposure, but PM2.5 circulates through the wider urban air and can enter through windows, doors and ventilation.

Does an air conditioner remove PM2.5?

A standard split air conditioner mainly cools and recirculates indoor air. Its washable mesh filter is not normally a substitute for a properly sized HEPA air purifier.

Can air quality be judged by smell or visibility alone?

No. PM2.5 can be elevated without a strong smell or obvious haze. For decisions about ventilation or outdoor exercise, use recent data from a nearby monitoring station as well as local observations.