Air quality comparison · Mongolia, 34 km apart
Nalayh vs Ulan Bator Air quality index (AQI) today
Nalayh has cleaner air than Ulan Bator right now: AQI 25 (Good) against 129 (Unhealthy for sensitive groups).
That puts them in different EPA bands, so the health advice differs today. Over the past 6 days, on modeled daily averages, Nalayh averaged AQI 35 against 130, and it was the cleaner of the two on 6 of those days. Ulan Bator has lost more forest since 2001. Ulan Bator has more tree cover.
Mongolia
AQI 25
Good
Cleaner right now
- PM2.5
- 6 µg/m³
- Main pollutant
- PM2.5
- Source
- Model estimate
- Reading
- Nov 11, 17:00 local
Mongolia
AQI 129
Unhealthy for sensitive groups
Cleaner right now
- PM2.5
- 46.7 µg/m³3.1× WHO guideline
- Main pollutant
- PM2.5
- Source
- Ground station
- Reading
- Nov 12, 22:00 local
Updated . Lower is better on the US EPA index: 0–50 is Good, above 300 is Hazardous. Measured by Airleaf.
Nalayh25Ulan Bator129
Head to head
Nalayh vs Ulan Bator at a glance
Nalayh is ahead on 5 of 6 measures, and Ulan Bator on 1. The better figure in each row is marked.
| Nalayh | Ulan Bator | |
|---|---|---|
| Air quality nowUS AQI. Lower is better. | 25 (better) | 129 |
| PM2.5Fine particles, µg/m³. | 6 (better) | 46.7 |
| Past week's averageUS AQI, 6 days. | 35 (better) | 130 |
| Forest lost since 2001Within 10 km of the center. | 172 ha (better) | 559 ha |
| Tree coverWithin 2 km of the center. | 0.0% | 3.7% (better) |
| Trees still neededTo reach a healthy canopy. | 94.2K (better) | 98.3K |
Air quality today
What is the air like in Nalayh and Ulan Bator right now?
Nalayh has cleaner air than Ulan Bator right now: AQI 25 (Good) against 129 (Unhealthy for sensitive groups). PM2.5 is setting the index in both.
Ulan Bator's PM2.5 is about 3.1× the WHO's 24-hour guideline of 15 µg/m³.
Ulan Bator is read from a nearby ground station and Nalayh is a model estimate, so the two are not quite like for like.
NalayhUlan Bator
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).
Nalayh: Model estimate · no ground station nearby. Data: Open-Meteo / CAMS, US EPA index.
Ulan Bator: Ground station · Bumbugur, 1.8 km away. Data: OpenAQ · AirGradient, Andy.
The past week
Which had cleaner air over the past 6 days?
Over the past 6 days, on modeled daily averages, Nalayh averaged AQI 35 against 130, and it was the cleaner of the two on 6 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
- Nalayh6Ulan Bator0
- Average AQI
- Nalayh35Ulan Bator130
- Worst day, AQI
- Nalayh53Ulan Bator145
The daily numbers (6 days)
| Day | Nalayh | Ulan Bator |
|---|---|---|
| Nov 6 | 27 | 137 |
| Nov 7 | 53 | 103 |
| Nov 8 | 41 | 141 |
| Nov 9 | 28 | 114 |
| Nov 10 | 21 | 145 |
| Nov 11 | 40 | 141 |
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 Nalayh and Ulan Bator today?
Nalayh (AQI 25, Good): Air quality is satisfactory for everyone.
Ulan Bator (AQI 129, Unhealthy for sensitive groups): Sensitive groups should limit long or intense outdoor activity.
Exercise outdoors
- Nalayh
- A good day to be active outside.
- Ulan Bator
- Children, older adults and people with asthma or heart disease should cut down long or hard exercise.
Windows
- Nalayh
- Open them to air the house.
- Ulan Bator
- Close them to keep the outside air out.
Masks
- Nalayh
- Not needed.
- Ulan Bator
- Sensitive groups: an N95 outdoors.
Air purifier
- Nalayh
- Not needed.
- Ulan Bator
- Run one, especially in bedrooms.
Against everywhere else
How do Nalayh and Ulan Bator compare with the rest of the world?
Right now Nalayh's air is cleaner than 84% of the 5,420 places Airleaf tracks, and Ulan Bator's is cleaner than 14%. Within Mongolia, that is 25% and 0% of its 5 measured places.
Cleaner air than…
- Nalayh
- Beats 84%
- Ulan Bator
- Beats 14%
More tree cover than…
- Nalayh
- Beats 0%
- Ulan Bator
- Beats 7%
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, Nalayh or Ulan Bator?
Ulan Bator has lost more: about 559 ha of forest within 10 km of its center from 2001 to 2025, against 172 ha around Nalayh. under 1 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: 2001, with 92 ha lost.
Worst year: 2008, with 177 ha lost.
| Nalayh | Ulan Bator | |
|---|---|---|
| Forest lost since 2001Cleared, burned or logged. | 172 ha (better) | 559 ha |
| Share of its forestOf what it had in 2000. | 69% | 23% (better) |
| Cleared for goodTurned into farms, mines or towns. | under 1 ha | under 1 ha (better) |
| Recent trend2021–2025 against the five years before. | Too little to call | Too little to call |
| Main known cause | Wildfires (91%) | Wildfires (97%) |
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.
Nalayh
2017: satellite photo from June 2017 of a 5 × 5 km area in the city center.
Ulan Bator
2017: satellite photo from June 2017 of a 5 × 5 km area in the city center.
Trees
Which has more trees, Nalayh or Ulan Bator?
Ulan Bator has more tree cover: 3.7% of the land within 2 km of its center against 0.0% around Nalayh, or about 11,624 trees against 0.
The dark mark is each place's canopy target: 30% of the land, raised where air quality is poor.
| Nalayh | Ulan Bator | |
|---|---|---|
| Trees standingEstimated from the canopy area. | 0 | 11.6K (better) |
| Trees still neededTo reach the target. Fewer is better. | 94.2K (better) | 98.3K |
| CO₂ absorbed each yearBy the trees already standing. | 0 kg | 256K 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
Nalayh vs Ulan Bator: your questions answered
Is Nalayh cleaner than Ulan Bator?
On air quality, yes, right now: Nalayh reads AQI 25 against 129, a gap of 104 points on the US EPA index. This is a live reading rather than an annual average, so it can reverse within a day. Over the past 6 days, on modeled daily averages, Nalayh averaged AQI 35 against 130, and it was the cleaner of the two on 6 of those days.
Is it safe to exercise outdoors in Nalayh and Ulan Bator today?
In Nalayh, at AQI 25: Air quality is satisfactory for everyone. In Ulan Bator, at AQI 129: Sensitive groups should limit long or intense outdoor activity.
Which has lost more forest, Nalayh or Ulan Bator?
Ulan Bator has lost more: about 559 ha of forest within 10 km of its center from 2001 to 2025, against 172 ha around Nalayh. under 1 ha of that was cleared for good, for farms, mines or towns.
Which has more trees, Nalayh or Ulan Bator?
Ulan Bator has more tree cover: 3.7% of the land within 2 km of its center against 0.0% around Nalayh, or about 11,624 trees against 0. Both figures describe the same-sized circle of ground around each center, not the whole municipality.
How many more trees do Nalayh and Ulan Bator need?
Nalayh needs about 94,248 more to reach its canopy target of 30%, and Ulan Bator about 98,332 to reach 35%. The target starts at 30% of the land and rises where air quality is poor.
Why can two places 34 km apart read differently?
Air changes over short distances with traffic, industry, wind and hills, and each reading comes from the nearest ground stations or, where there are none, from a regional model. A gap of a few points between neighbors is within normal variation, while a gap that crosses an EPA band is worth noticing.
Are Nalayh and Ulan Bator 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. Ulan Bator is read from a nearby ground station and Nalayh is a model estimate, so the two are not quite like for like. Nothing is adjusted for population, city limits or climate.
How often does the Nalayh vs Ulan Bator 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 (Sep 15, 2026 and Sep 15, 2026), and the forest figures are published yearly.
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