A cyclist bikes across Anyang Stream in Seoul, Sept. 3. Yonhap

Ozone-alert days in Seoul have totaled 31 so far this year, a sharp rise from just three for all of 2015, the city government said Wednesday, advising citizens to take precautions against adverse respiratory and other health effects.

The number of alerts issued in the city also jumped to 109 this year through August from just four in 2015, the city government said. Multiple alerts can be issued in one day because the city issues such advisories in five separate regions.

The yearly average ozone concentration level also rose to 0.037 parts per million (ppm) this year from 0.024 ppm in 2015. It marked the highest average ozone concentration level this year since record-keeping began in 2000, recording an average of 0.044 ppm during the high-concentration period between May and August.

The city said it expects to see days with high levels of ozone concentration levels continue even after this month, adding it plans to speedily inform people of the air quality through various mediums, including the city's air quality notification service.

"Due to the recent record-breaking heat wave, September could also experience high ozone concentration levels from the strong sunlight and high temperatures," a Seoul city official said, warning the public to take special care of their health. (Yonhap)