The average ozone concentration level in South Korea hit a record high in May.

According to data from the Ministry of Environment on Wednesday, the average ozone concentration level stood at zero-point-051 parts per million(ppm) last month, the highest since such data was first compiled in 2001.

Reflecting the record-high concentration levels, nationwide ozone warnings were issued for 18 days last month, 10 days more than the previous year.

The ministry attributed the record to increased solar radiation and a decline in rainfall and relative humidity.

The government will strengthen related measures and inspect businesses that emit large amounts of air pollutants which contribute to rising ozone levels.

An ozone warning is issued when the average ozone concentration level per hour stands at zero-point-12 ppm or higher.