Air quality comparison · South Korea, 34 km apart
Ulsan vs Yangsan Air quality index (AQI) today
Yangsan has cleaner air than Ulsan right now: AQI 58 (Moderate) against 70 (Moderate).
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, Ulsan averaged AQI 53 against 55, and it was the cleaner of the two on 6 of those days. Ulsan has lost more forest since 2001. Yangsan has more tree cover.
Updated . Lower is better on the US EPA index: 0–50 is Good, above 300 is Hazardous. Measured by Airleaf.
Ulsan70Yangsan58
Head to head
Ulsan vs Yangsan at a glance
Yangsan is ahead on 5 of 6 measures, and Ulsan on 1. The better figure in each row is marked.
| Ulsan | Yangsan | |
|---|---|---|
| Air quality nowUS AQI. Lower is better. | 70 | 58 (better) |
| PM2.5Fine particles, µg/m³. | 19.5 | 13 (better) |
| Past week's averageUS AQI, 7 days. | 53 (better) | 55 |
| Forest lost since 2001Within 10 km of the center. | 1,060 ha | 684 ha (better) |
| Tree coverWithin 2 km of the center. | 17.0% | 42.2% (better) |
| Trees still neededTo reach a healthy canopy. | 38.9K | 0 (better) |
Air quality today
What is the air like in Ulsan and Yangsan right now?
Yangsan has cleaner air than Ulsan right now: AQI 58 (Moderate) against 70 (Moderate). PM2.5 is setting the index in both.
Ulsan's PM2.5 is about 1.3× the WHO's 24-hour guideline of 15 µg/m³.
Both readings come from nearby ground stations.
UlsanYangsan
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).
Ulsan: Ground station · 신정로, 1.5 km away · median of 17 stations. Data: OpenAQ · Korea Air Ministry of Environment, Korea Environment Corporation · AirKorea.
Yangsan: Ground station · 청룡동, 9.2 km away · median of 3 stations. Data: OpenAQ · Korea Air Ministry of Environment, Korea Environment Corporation · AirKorea.
The past week
Which had cleaner air over the past 7 days?
But over the past 7 days, on modeled daily averages, Ulsan averaged AQI 53 against 55, and it was the cleaner of the two on 6 of those days. The two are close enough that the air model behind these daily figures barely separates them, so their lines nearly overlap.
- Cleaner days
- Ulsan6Yangsan1
- Average AQI
- Ulsan53Yangsan55
- Worst day, AQI
- Ulsan70Yangsan72
The daily numbers (7 days)
| Day | Ulsan | Yangsan |
|---|---|---|
| Nov 5 | 50 | 53 |
| Nov 6 | 46 | 49 |
| Nov 7 | 46 | 47 |
| Nov 8 | 57 | 59 |
| Nov 9 | 54 | 55 |
| Nov 10 | 48 | 47 |
| Nov 11 | 70 | 72 |
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 Ulsan and Yangsan today?
Unusually sensitive people should consider limiting long outdoor exertion. Both are in the same EPA band today (Moderate), so the advice is the same.
Exercise outdoors
Fine for most people; unusually sensitive people should take long or hard exercise easier.
Windows
Fine to open; close them if you are sensitive to pollution.
Masks
Not needed for most people.
Air purifier
Worth running if you are sensitive.
Against everywhere else
How do Ulsan and Yangsan compare with the rest of the world?
Right now Ulsan's air is cleaner than 38% of the 5,420 places Airleaf tracks, and Yangsan's is cleaner than 49%. Within South Korea, that is 76% and 96% of its 56 measured places.
Cleaner air than…
- Ulsan
- Beats 38%
- Yangsan
- Beats 49%
More tree cover than…
- Ulsan
- Beats 39%
- Yangsan
- Beats 86%
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, Ulsan or Yangsan?
Ulsan has lost more: about 1,060 ha of forest within 10 km of its center from 2001 to 2025, against 684 ha around Yangsan. 609 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: 2021, with 200 ha lost.
Worst year: 2012, with 90 ha lost.
| Ulsan | Yangsan | |
|---|---|---|
| Forest lost since 2001Cleared, burned or logged. | 1,060 ha | 684 ha (better) |
| Share of its forestOf what it had in 2000. | 8.7% | 3.5% (better) |
| Cleared for goodTurned into farms, mines or towns. | 609 ha | 568 ha (better) |
| Recent trend2021–2025 against the five years before. | Speeding up | Too little to call |
| Main known cause | Towns and roads (56%) | Towns and roads (66%) |
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.
Ulsan
2017: satellite photo from September 2017 of a 5 × 5 km area about 7 km southwest of the city center.
Yangsan
2017: satellite photo from June 2017 of a 5 × 5 km area about 4 km north of the city center.
Trees
Which has more trees, Ulsan or Yangsan?
Yangsan has more tree cover: 42.2% of the land within 2 km of its center against 17.0% around Ulsan, or about 130,719 trees against 50,844.
The dark mark is each place's canopy target: 30% of the land, raised where air quality is poor.
| Ulsan | Yangsan | |
|---|---|---|
| Trees standingEstimated from the canopy area. | 50.8K | 131K (better) |
| Trees still neededTo reach the target. Fewer is better. | 38.9K | 0 (better) |
| CO₂ absorbed each yearBy the trees already standing. | 1.1M kg | 2.9M 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
Ulsan vs Yangsan: your questions answered
Is Yangsan cleaner than Ulsan?
On air quality, yes, right now: Yangsan reads AQI 58 against 70, a gap of 12 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, Ulsan averaged AQI 53 against 55, and it was the cleaner of the two on 6 of those days.
Is it safe to exercise outdoors in Ulsan and Yangsan today?
The advice is the same for both today. Unusually sensitive people should consider limiting long outdoor exertion. Ulsan reads AQI 70 and Yangsan reads AQI 58.
Which has lost more forest, Ulsan or Yangsan?
Ulsan has lost more: about 1,060 ha of forest within 10 km of its center from 2001 to 2025, against 684 ha around Yangsan. 609 ha of that was cleared for good, for farms, mines or towns.
Which has more trees, Ulsan or Yangsan?
Yangsan has more tree cover: 42.2% of the land within 2 km of its center against 17.0% around Ulsan, or about 130,719 trees against 50,844. Both figures describe the same-sized circle of ground around each center, not the whole municipality.
How many more trees do Ulsan and Yangsan need?
Ulsan needs about 38,880 more to reach its canopy target of 30%, and Yangsan about 0 to reach 30%. 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 Ulsan and Yangsan 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 Ulsan vs Yangsan 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 12, 2026 and Sep 12, 2026), and the forest figures are published yearly.
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