Air quality is a separate planning check from temperature or rain. Korea Environment Corporation's AirKorea service publishes current regional and station-level information for PM2.5, PM10 and ozone, along with forecasts and active warning information.

For PM2.5, the English current-air-quality page uses these public categories: Good 0–15 µg/m³, Moderate 16–35, Unhealthy 36–75 and Very Unhealthy 76 or higher. Do not confuse a forecast category with a real-time station reading; check both when the day's plan is sensitive to conditions.

AirKorea also publishes today/tomorrow/next-day forecasts and a warning page covering PM10, PM2.5, ozone and yellow-dust alerts. A high-pollution day can be local even when another region is fine, so check the region where you will actually spend time.

A practical routine for hiking, cycling, long park days or coastal activity is to check the forecast the evening before, check again in the morning, and recheck shortly before departure. Children, older travelers and people with respiratory or cardiovascular conditions may need a more cautious plan; follow individual medical advice rather than treating this guide as a health prescription.

Air quality can change during the day, so this page does not claim that a particular month is always safe or always poor.