The Ministry of Environment forecast that this year, an ozone warning would be issued around mid- or late May, a little earlier compared to past year, due to weather conditions, such as unusually high temperatures, that easily raise the ozone concentration. Last year, the first ozone warning was issued for the metropolitan area in June.

Large cities have increasing number of ozone warnings coupled with ozone warning days as the ozone concentration level more frequently goes up above 0.12 ppm per hour. Particularly, last year, the metropolitan area experienced 100 ozone warnings amounting for 64 percent of the entire number of ozone warnings.

The number of ozone warning days and ozone warnings decreased in 2001 and 2002 thanks to the bad weather conditions of typhoons and the rainy season and special measures taken in preparation for the 2002 World Cup. However, the number again started to increase after 2003 and jumped in 2004 due to two severe heat waves. The scorching heat waves occurred for most of the cities as well as the metropolitan area, so that even Daejeon city, South Kyeongsang and Gangwon provinces were under the ozone warning.

In order to prevent any damage from bad ozone in summer, the Ministry of Environment supports to extend the ozone warning system, find best cases of the system and hold seminars on the implementation of extended ozone warning system.

The ozone warning system was first initiated in July, 1995 for Seoul. Once an ozone warning is issued, the city majors and local governors in charge of giving an order of an ozone warning directly announce current conditions for the senior and children in schools, hospitals, etc. through wired phones and faxes, and for ordinary citizens through TVs, radios, the Internet and electronic boards.