The Seoul Health and Environment Research Institute issued an ozone advisory for the entire city of Seoul at 2 p.m. on the 27th. This is the first ozone advisory issued in Seoul this year.
An ozone advisory is issued when the hourly average concentration of ozone (O₃) in the air exceeds 0.12 ppm. An ozone warning is issued when it exceeds 0.03 ppm, and a serious ozone warning is issued when it exceeds 0.50 ppm.
Ozone is a secondary pollutant generated from volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the atmosphere through photochemical reactions with solar energy. The research institute noted that "exposure to high concentrations can irritate the respiratory system and eyes, causing inflammation, and in severe cases, respiratory distress may occur."
In response, the city of Seoul operates a comprehensive situation room daily, including weekends and holidays from April 1 to October 31, when ozone levels are expected to rise, preparing for the issuance of advisories.