Air quality comparison · Cambodia, 231 km apart
Phnom Penh vs Siem Reap Air quality index (AQI) today
Phnom Penh has cleaner air than Siem Reap right now: AQI 28 (Good) against 47 (Good).
Both sit in the same EPA band, so the health advice is the same for each today. But over the past 7 days, on modeled daily averages, Siem Reap averaged AQI 30 against 52, and it was the cleaner of the two on 7 of those days. Phnom Penh has lost more forest since 2001. Siem Reap has more tree cover.
Cambodia
AQI 28
Good
Cleaner right now
- PM2.5
- 5.1 µg/m³
- Main pollutant
- PM2.5
- Source
- Ground station
- Reading
- Nov 12, 01:00 local
Cambodia
AQI 47
Good
Cleaner right now
- PM2.5
- 8.4 µg/m³
- Main pollutant
- PM2.5
- Source
- Ground station
- Reading
- Nov 12, 01:00 local
Updated . Lower is better on the US EPA index: 0–50 is Good, above 300 is Hazardous. Measured by Airleaf.
Phnom Penh28Siem Reap47
Head to head
Phnom Penh vs Siem Reap at a glance
Siem Reap is ahead on 4 of 6 measures, and Phnom Penh on 2. The better figure in each row is marked.
| Phnom Penh | Siem Reap | |
|---|---|---|
| Air quality nowUS AQI. Lower is better. | 28 (better) | 47 |
| PM2.5Fine particles, µg/m³. | 5.1 (better) | 8.4 |
| Past week's averageUS AQI, 7 days. | 52 | 30 (better) |
| Forest lost since 2001Within 10 km of the center. | 158 ha | 64 ha (better) |
| Tree coverWithin 2 km of the center. | 7.0% | 31.6% (better) |
| Trees still neededTo reach a healthy canopy. | 71.2K | 0 (better) |
Air quality today
What is the air like in Phnom Penh and Siem Reap right now?
Phnom Penh has cleaner air than Siem Reap right now: AQI 28 (Good) against 47 (Good). PM2.5 is setting the index in both.
Both readings come from nearby ground stations.
Phnom PenhSiem Reap
Concentrations at the same moment as the index above, for the pollutants both places report. Lower is better. The dark marks on the PM2.5 and PM10 rows show the WHO's 24-hour guidelines (15 and 45 µg/m³).
The past week
Which had cleaner air over the past 7 days?
But over the past 7 days, on modeled daily averages, Siem Reap averaged AQI 30 against 52, and it was the cleaner of the two on 7 of those days. A single reading can catch a city on a bad afternoon; the week says whether it was the weather or the place.
- Cleaner days
- Phnom Penh0Siem Reap7
- Average AQI
- Phnom Penh52Siem Reap30
- Worst day, AQI
- Phnom Penh66Siem Reap45
The daily numbers (7 days)
| Day | Phnom Penh | Siem Reap |
|---|---|---|
| Nov 5 | 66 | 44 |
| Nov 6 | 63 | 45 |
| Nov 7 | 56 | 27 |
| Nov 8 | 62 | 38 |
| Nov 9 | 49 | 24 |
| Nov 10 | 38 | 12 |
| Nov 11 | 30 | 17 |
Daily averages from the CAMS atmospheric model for both places, so the week compares like with like. They can differ from today's reading at the top of the page wherever that comes from a ground station.
What it means today
Is it safe to go outside in Phnom Penh and Siem Reap today?
Air quality is satisfactory for everyone. Both are in the same EPA band today (Good), so the advice is the same.
Exercise outdoors
A good day to be active outside.
Windows
Open them to air the house.
Masks
Not needed.
Air purifier
Not needed.
Against everywhere else
How do Phnom Penh and Siem Reap compare with the rest of the world?
Right now Phnom Penh's air is cleaner than 81% of the 5,420 places Airleaf tracks, and Siem Reap's is cleaner than 64%. Within Cambodia, that is 50% and 0% of its 5 measured places.
Cleaner air than…
- Phnom Penh
- Beats 81%
- Siem Reap
- Beats 64%
More tree cover than…
- Phnom Penh
- Beats 14%
- Siem Reap
- Beats 72%
Includes model estimates as well as station readings, so it can differ from our most polluted and cleanest air rankings, which use station readings only.
Deforestation · 2001–2025
Which has lost more forest, Phnom Penh or Siem Reap?
Phnom Penh has lost more: about 158 ha of forest within 10 km of its center from 2001 to 2025, against 64 ha around Siem Reap. 147 ha of that was cleared for good, for farms, mines or towns.
Measured within 10 km of each center, from the yearly satellite maps of forest loss: a wider circle than the one for tree cover, because forest is usually lost at a city's edges.
Worst year: 2015, with 31 ha lost.
Worst year: 2024, with 19 ha lost.
| Phnom Penh | Siem Reap | |
|---|---|---|
| Forest lost since 2001Cleared, burned or logged. | 158 ha | 64 ha (better) |
| Share of its forestOf what it had in 2000. | 13% | 2.5% (better) |
| Cleared for goodTurned into farms, mines or towns. | 147 ha | 25 ha (better) |
| Recent trend2021–2025 against the five years before. | Too little to call | Too little to call |
| Main known cause | Farms, pasture and plantations (49%) | Wildfires (35%) |
Satellite timelapses
Watch both change, year by year
A clear satellite photo a year of the land around each city. Press play, turn on the forest cleared since the first year, or drag the before and after.
Phnom Penh
2017: satellite photo from April 2017 of a 5 × 5 km area in the city center.
Siem Reap
2017: satellite photo from February 2017 of a 5 × 5 km area in the city center.
Trees
Which has more trees, Phnom Penh or Siem Reap?
Siem Reap has more tree cover: 31.6% of the land within 2 km of its center against 7.0% around Phnom Penh, or about 99,274 trees against 21,661.
The dark mark is each place's canopy target: 30% of the land, raised where air quality is poor.
| Phnom Penh | Siem Reap | |
|---|---|---|
| Trees standingEstimated from the canopy area. | 21.7K | 99.3K (better) |
| Trees still neededTo reach the target. Fewer is better. | 71.2K | 0 (better) |
| CO₂ absorbed each yearBy the trees already standing. | 477K kg | 2.2M kg (better) |
Tree cover on the satellite image
The same 2 km radius around each center, with the tree cover the satellite found marked on it.
Reading these numbers
How this comparison is made
Air quality index
The US EPA index, computed from current pollutant concentrations: ground stations where a place has them nearby, and the CAMS atmospheric model everywhere else. It moves hour to hour, so it is a snapshot rather than a verdict on either place. The guideline marks are from the WHO's 2021 air quality guidelines.
Trees and forest
Tree cover is the share of ground under canopy within 2 km of each center, read from Sentinel-2 satellite imagery at 10 m detail. It measures that circle, not the whole municipality, which is what makes the two comparable. Forest loss comes from the University of Maryland's Global Forest Change maps.
More on the method on the About Airleaf page.
Frequently asked
Phnom Penh vs Siem Reap: your questions answered
Is Phnom Penh cleaner than Siem Reap?
On air quality, yes, right now: Phnom Penh reads AQI 28 against 47, a gap of 19 points on the US EPA index. This is a live reading rather than an annual average, so it can reverse within a day. But over the past 7 days, on modeled daily averages, Siem Reap averaged AQI 30 against 52, and it was the cleaner of the two on 7 of those days.
Is it safe to exercise outdoors in Phnom Penh and Siem Reap today?
The advice is the same for both today. Air quality is satisfactory for everyone. Phnom Penh reads AQI 28 and Siem Reap reads AQI 47.
Which has lost more forest, Phnom Penh or Siem Reap?
Phnom Penh has lost more: about 158 ha of forest within 10 km of its center from 2001 to 2025, against 64 ha around Siem Reap. 147 ha of that was cleared for good, for farms, mines or towns.
Which has more trees, Phnom Penh or Siem Reap?
Siem Reap has more tree cover: 31.6% of the land within 2 km of its center against 7.0% around Phnom Penh, or about 99,274 trees against 21,661. Both figures describe the same-sized circle of ground around each center, not the whole municipality.
How many more trees do Phnom Penh and Siem Reap need?
Phnom Penh needs about 71,173 more to reach its canopy target of 30%, and Siem Reap about 0 to reach 30%. The target starts at 30% of the land and rises where air quality is poor.
Are Phnom Penh and Siem Reap measured the same way?
The method is the same: the US EPA index for air, and Sentinel-2 satellite imagery at 10 m detail over an identical radius for trees. Both readings come from nearby ground stations. Nothing is adjusted for population, city limits or climate.
How often does the Phnom Penh vs Siem Reap comparison update?
The air readings refresh about once an hour, and each reading's local time is shown at the top of the page. Tree cover comes from the latest clear satellite image of each area (Jun 18, 2026 and Jul 21, 2026), and the forest figures are published yearly.
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