Air quality grades and what to do

A number on its own does not tell you whether today is a good day to go out. Here is the Korean grade scale and what each level actually means.

PM10 and PM2.5 — what is the difference?

The number is the diameter of the particle. PM10 means particles up to 10 microns across; PM2.5 means 2.5 microns or smaller. A human hair is roughly 70 microns wide, so PM2.5 is less than a thirtieth of that.

The smaller the particle, the deeper it travels. Most PM10 is caught in the nose and airways, but PM2.5 reaches the alveoli and can cross into the bloodstream. That is why the same number is more serious for PM2.5, and why its thresholds are set at about half those of PM10.

This is also why MiseGauge shows both values side by side. Watch only one and you will miss the days when the other is the problem.

Grade scale (Korean Ministry of Environment)

Grade	PM10	PM2.5
Good	0 – 30 µg/m³	0 – 15 µg/m³
Moderate	31 – 80	16 – 35
Unhealthy	81 – 150	36 – 75
Very unhealthy	151 and above	76 and above

The World Health Organization is stricter. Its 24-hour guideline for PM2.5 is 15 µg/m³ — exactly the ceiling of Korea's "Good" band.

What to do at each level

Good

• A good moment to air the place out. Open the windows.
• No restrictions on exercising outdoors.

Moderate

• Go about your day as usual.
• If you have asthma or allergies, ease off on long, hard exercise outside.

Unhealthy

• Children, older adults, and anyone with a respiratory or heart condition should cut back on time outdoors.
• Wear a certified filtering mask (KF80 or better) when you go out.
• Keep the windows shut; if you must air the place out, do it briefly when levels dip.

Very unhealthy

• Avoid going out; make only the trips you have to.
• Wear a KF94 mask, and wash your hands and face when you get home.
• Run an air purifier and keep indoor humidity around 40–60%.

How to read the station data

Why you need more than one nearby station

Korea has roughly 670 monitoring stations. Even inside one district, a roadside station and a residential one can read very differently, and stations regularly go quiet for maintenance or network faults. If a site shows you only the single closest station, those are the days you learn nothing.

So MiseGauge lists the ten nearest stations in order and lets you swipe between them. If the first has no reading, look at the second.

Types of monitoring network

• Urban air — ordinary air in residential and commercial areas. Closest to what you actually breathe day to day.
• Roadside air — right beside a road. Tends to read higher because of vehicle exhaust.
• Suburban air — background levels on the edge of the city.

That is why each card names its network. A roadside station reading high does not mean the whole neighbourhood is bad — it may just be that spot.

When you see "--"

During maintenance, calibration, or a network fault, AirKorea sends no value at all. Rather than invent a number, we show it as unavailable. Swipe to the next station.

How often it updates

Air quality readings refresh near the top of each hour — the time shown on each card. Current weather updates around half past each hour, and the short-range forecast is issued eight times a day (02, 05, 08, 11, 14, 17, 20 and 23 Korean time).