A person walks by a notice announcing the issuance of an ozone alert in Seoul in this June 16, 2018 file photo. Yonhap

The first ozone alert of the year was issued in most parts of Seoul and Incheon on Friday, municipal authorities said.

The alert was issued between 1 p.m. and 2 p.m. for western and southeastern Seoul and southeastern Incheon, as ozone concentration levels there exceeded the threshold of 0.120 parts per million, or ppm, they said.

Ozone is a secondary pollutant produced by photochemical reactions among solar energy and volatile organic compounds and nitrogen oxides in the atmosphere.

High concentrations of ozone can cause inflammation of respiratory organs and eyes. In severe cases, it can even lead to breathing problems.

The authorities advised patients with respiratory diseases, the elderly and children to refrain from going outside. (Yonhap)