Korea Air Quality Now

PM10, PM2.5 and yellow dust are not the same thing

PM10 counts every particle up to 10 micrometres across — the PM2.5 inside it included — but what pushes it up is the coarse material: road and construction dust, plus the spring yellow dust (hwangsa) blown east from arid regions of Mongolia and northern China. PM2.5 is the fine fraction, produced mostly by burning something — traffic, heating and industry, near and far.

Because PM10 already contains PM2.5 it is never the lower of the two, but the two do not rise and fall together. On a dusty spring day PM10 spikes while PM2.5 stays moderate: grit on the cars, a scratchy throat, a beige sky. On a still, cold winter day the sky looks ordinary while PM2.5 quietly climbs, because nothing is blowing it away. When the two disagree, read both.

Why your app and this page disagree

• An index is not a concentration. Most international apps display an AQI, a converted index number; for PM10 and PM2.5 this page shows micrograms per cubic metre, the raw measurement. "AQI 80" and "80 µg/m³" are not the same quantity.
• Korea runs an index too. The Comprehensive Air-quality Index (CAI) folds six pollutants into a 0–500 score — good 0 to 50, moderate 51 to 100, unhealthy 101 to 250, very unhealthy above that. It is the big number on AirKorea screens and street display boards, so check the unit label before reading any figure as micrograms.
• An average is not an hour. National standards are written as 24-hour or annual averages, while a live station reading is one hour in one place, so a single high hour is not a breached standard.
• Countries draw the lines differently. One measurement can be labelled with one word under the Korean grading and another under a US or European scale.
• Stations are local. A monitor beside a major intersection reads differently from one in a park a kilometre away, so if your district looks alarming, check a neighbouring one.

When it gets bad, and what to do with the day

The difficult stretch runs roughly from late autumn into spring, when cold, windless weather lets pollution settle over the peninsula; summer rain and sea breezes scrub it out again. On bad days schools cut outdoor activities and the government can trigger emergency measures.

As a visitor, treat a poor reading as a reason to reorder the day rather than abandon it. Swap the mountain hike for a museum, a covered market or a jjimjilbang, and save the summit for the day after rain — the cleanest air you will see.

Masks, eyes, and who should take it seriously

• The KF number is a filtration rating. It describes how much fine particulate the material is certified to capture, but fit decides the result — gaps at the nose and cheeks matter more than the printed number.
• Eyes suffer first. Dusty days sting; glasses beat contact lenses, and eye drops are sold in every pharmacy and convenience store.
• Exertion multiplies exposure. Running or climbing moves far more air through your lungs, so a bad-air day is the one to take easy.
• Some people should take it seriously — anyone with asthma or another respiratory or heart condition, young children and older travellers.

These readings are public monitoring data for general information, not medical advice. If you have a respiratory or cardiac condition, follow your own doctor's plan.

Frequently asked questions

Is Korea's air quality actually dangerous on a short trip?
For a healthy visitor staying a week or two, poor-air days are mostly an inconvenience — a scratchy throat and a hazy view — rather than a serious hazard. The sensible response is to shift strenuous outdoor plans to a clearer day and wear a mask when the reading is bad.

The forecast says bad but the reading right now looks fine — which do I follow?
Both, for different jobs. A forecast grade is a prediction for the day as a whole, issued before it starts; the figure here is what one station is measuring at this minute. Use the forecast the night before to plan the shape of the day, and the live reading to decide whether to walk the last two subway stops.

Where can I buy a mask in Korea?
Convenience stores, pharmacies and supermarkets all sell KF-rated masks individually and in multipacks, so there is no need to bring them from home. Saying "KF94" is understood everywhere.

Is KF94 the same as N95?
They are near equivalents from two certification systems: KF94 is the Korean grade for material that filters at least 94 per cent of the test particles, N95 the American grade at 95 per cent. KF80, sold beside it, is the lighter everyday option most people wear on an ordinary hazy day.