Seoul saw its first ozone advisory of the year take effect Thursday in southwestern parts of the city.
The advisory was issued at 3 p.m. in the city's seven southwestern districts, including Dongjak, Guro and Yangcheon Ward.
The ozone advisory is issued when ozone concentration levels reach an hourly average of 0.12 parts per million (ppm).
The average in the southwestern districts stood at 0.121 ppm at 3 p.m., according to the city.
Ozone exposure can lead to respiratory diseases, especially among the elderly and children, and people are advised to stay indoors when an ozone advisory is in place. (Yonhap)