Air quality comparison · South Korea, 28 km apart
Daejeon vs Sejong Air quality index (AQI) today
Daejeon has cleaner air than Sejong right now: AQI 74 (Moderate) against 105 (Unhealthy for sensitive groups).
That puts them in different EPA bands, so the health advice differs today. Over the past 7 days, on modeled daily averages, both averaged AQI 63. Sejong has lost more forest since 2001. Sejong has more tree cover.
South Korea
AQI 74
Moderate
Cleaner right now
- PM2.5
- 21.5 µg/m³1.4× WHO guideline
- Main pollutant
- PM2.5
- Source
- Ground station
- Reading
- Nov 12, 02:00 local
South Korea
AQI 105
Unhealthy for sensitive groups
Cleaner right now
- PM2.5
- 37 µg/m³2.5× WHO guideline
- Main pollutant
- PM2.5
- Source
- Ground station
- Reading
- Nov 12, 02:00 local
Updated . Lower is better on the US EPA index: 0–50 is Good, above 300 is Hazardous. Measured by Airleaf.
Daejeon74Sejong105
Head to head
Daejeon vs Sejong at a glance
Daejeon is ahead on 4 of 6 measures, and Sejong on 1. The better figure in each row is marked.
| Daejeon | Sejong | |
|---|---|---|
| Air quality nowUS AQI. Lower is better. | 74 (better) | 105 |
| PM2.5Fine particles, µg/m³. | 21.5 (better) | 37 |
| Past week's averageUS AQI, 7 days. | 63 | 63 |
| Forest lost since 2001Within 10 km of the center. | 191 ha (better) | 1,070 ha |
| Tree coverWithin 2 km of the center. | 13.6% | 17.3% (better) |
| Trees still neededTo reach a healthy canopy. | 51.3K (better) | 55.4K |
Air quality today
What is the air like in Daejeon and Sejong right now?
Daejeon has cleaner air than Sejong right now: AQI 74 (Moderate) against 105 (Unhealthy for sensitive groups). PM2.5 is setting the index in both.
Daejeon's PM2.5 is about 1.4× the WHO's 24-hour guideline of 15 µg/m³. Sejong's PM2.5 is about 2.5× the WHO's 24-hour guideline of 15 µg/m³.
Both readings come from nearby ground stations.
DaejeonSejong
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).
Daejeon: Ground station · 둔산동, 600 m away · median of 14 stations. Data: OpenAQ · Korea Air Ministry of Environment, Korea Environment Corporation · AirKorea.
Sejong: Ground station · 조치원읍, 100 m 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?
Over the past 7 days, on modeled daily averages, both averaged AQI 63. The two are close enough that the air model behind these daily figures barely separates them, so their lines nearly overlap.
- Cleaner days
- Daejeon0Sejong0
- Average AQI
- Daejeon63Sejong63
- Worst day, AQI
- Daejeon84Sejong84
The daily numbers (7 days)
| Day | Daejeon | Sejong |
|---|---|---|
| Nov 5 | 66 | 66 |
| Nov 6 | 47 | 47 |
| Nov 7 | 53 | 53 |
| Nov 8 | 66 | 66 |
| Nov 9 | 62 | 62 |
| Nov 10 | 65 | 65 |
| Nov 11 | 84 | 84 |
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 Daejeon and Sejong today?
Daejeon (AQI 74, Moderate): Unusually sensitive people should consider limiting long outdoor exertion.
Sejong (AQI 105, Unhealthy for sensitive groups): Sensitive groups should limit long or intense outdoor activity.
Exercise outdoors
- Daejeon
- Fine for most people; unusually sensitive people should take long or hard exercise easier.
- Sejong
- Children, older adults and people with asthma or heart disease should cut down long or hard exercise.
Windows
- Daejeon
- Fine to open; close them if you are sensitive to pollution.
- Sejong
- Close them to keep the outside air out.
Masks
- Daejeon
- Not needed for most people.
- Sejong
- Sensitive groups: an N95 outdoors.
Air purifier
- Daejeon
- Worth running if you are sensitive.
- Sejong
- Run one, especially in bedrooms.
Against everywhere else
How do Daejeon and Sejong compare with the rest of the world?
Right now Daejeon's air is cleaner than 34% of the 5,420 places Airleaf tracks, and Sejong's is cleaner than 20%. Within South Korea, that is 62% and 9% of its 56 measured places.
Cleaner air than…
- Daejeon
- Beats 34%
- Sejong
- Beats 20%
More tree cover than…
- Daejeon
- Beats 31%
- Sejong
- Beats 40%
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, Daejeon or Sejong?
Sejong has lost more: about 1,070 ha of forest within 10 km of its center from 2001 to 2025, against 191 ha around Daejeon. 432 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: 2020, with 23 ha lost.
Worst year: 2016, with 108 ha lost.
| Daejeon | Sejong | |
|---|---|---|
| Forest lost since 2001Cleared, burned or logged. | 191 ha (better) | 1,070 ha |
| Share of its forestOf what it had in 2000. | 2.2% (better) | 15% |
| Cleared for goodTurned into farms, mines or towns. | 121 ha (better) | 432 ha |
| Recent trend2021–2025 against the five years before. | Too little to call | Holding steady |
| Main known cause | Towns and roads (62%) | Logging (60%) |
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.
Daejeon
2017: satellite photo from June 2017 of a 5 × 5 km area about 7 km northeast of the city center.
Sejong
2017: satellite photo from June 2017 of a 5 × 5 km area about 7 km west of the city center.
Trees
Which has more trees, Daejeon or Sejong?
Sejong has more tree cover: 17.3% of the land within 2 km of its center against 13.6% around Daejeon, or about 54,187 trees against 42,512.
The dark mark is each place's canopy target: 30% of the land, raised where air quality is poor.
| Daejeon | Sejong | |
|---|---|---|
| Trees standingEstimated from the canopy area. | 42.5K | 54.2K (better) |
| Trees still neededTo reach the target. Fewer is better. | 51.3K (better) | 55.4K |
| CO₂ absorbed each yearBy the trees already standing. | 935K kg | 1.2M 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
Daejeon vs Sejong: your questions answered
Is Daejeon cleaner than Sejong?
On air quality, yes, right now: Daejeon reads AQI 74 against 105, a gap of 31 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 7 days, on modeled daily averages, both averaged AQI 63.
Is it safe to exercise outdoors in Daejeon and Sejong today?
In Daejeon, at AQI 74: Unusually sensitive people should consider limiting long outdoor exertion. In Sejong, at AQI 105: Sensitive groups should limit long or intense outdoor activity.
Which has lost more forest, Daejeon or Sejong?
Sejong has lost more: about 1,070 ha of forest within 10 km of its center from 2001 to 2025, against 191 ha around Daejeon. 432 ha of that was cleared for good, for farms, mines or towns.
Which has more trees, Daejeon or Sejong?
Sejong has more tree cover: 17.3% of the land within 2 km of its center against 13.6% around Daejeon, or about 54,187 trees against 42,512. Both figures describe the same-sized circle of ground around each center, not the whole municipality.
How many more trees do Daejeon and Sejong need?
Daejeon needs about 51,265 more to reach its canopy target of 30%, and Sejong about 55,439 to reach 35%. The target starts at 30% of the land and rises where air quality is poor.
Why can two places 28 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 Daejeon and Sejong 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 Daejeon vs Sejong 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 8, 2026 and Sep 23, 2026), and the forest figures are published yearly.
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