![\"Citizens](\"https:\/\/www.europesays.com\/korea\/wp-content\/uploads\/2026\/05\/news-p.v1.20260516.ccdd14c1deda4333a7429e753ad6e2da_P1.png\"\/ "\\"Colorless,")
Citizens wearing masks. Yonhap News<\/p>\nCitizens wearing masks. Yonhap News<\/p>\n
Daytime temperatures across most of Korea will exceed 30 degrees Celsius this weekend, extending early summer heat. Under clear skies and strong ultraviolet rays, high concentrations of ground-level ozone are filling the gap left by receding fine dust, requiring heightened attention to health management.<\/p>\n
According to the Korea Meteorological Administration on Thursday, expected low and high temperatures in major cities are 18 and 31 degrees in Seoul, 16 and 29 degrees in Incheon, 15 and 31 degrees in Daejeon and Gwangju, 13 and 33 degrees in Daegu, 12 and 28 degrees in Ulsan, and 14 and 25 degrees in Busan. On Friday, morning lows will range from 13 to 18 degrees and daytime highs from 25 to 34 degrees, intensifying the heat.<\/p>\n
Heat is not the only concern. As strong sunlight beats down through cloudless skies, surface ozone concentrations are thickening. The National Institute of Environmental Research forecast that ozone concentrations nationwide, except on Jeju Island, would be “bad” or worse on Thursday, with southern Gyeonggi Province expected to soar to “very bad” levels.<\/p>\n
Ozone (O\u2083) is a secondary pollutant formed when air pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) undergo photochemical reactions with strong ultraviolet rays.<\/p>\n
In the stratosphere, 10 to 50 kilometers above the ground, ozone protects ecosystems by blocking ultraviolet rays. In the troposphere, however, repeated exposure causes chest pain, coughing and nausea, and in severe cases worsens bronchitis, heart disease and emphysema. Concentrations rise sharply particularly in the afternoon hours from May through August, when temperatures are high and sunlight is intense.<\/p>\n
This is why declining springtime fine dust offers little reason for complacency. The number of days with ozone advisories was 60 in 2019, 67 in 2021, 62 in 2023 and 60 in 2025, hovering around 60 days a year for more than five years.<\/p>\n
Starting this year, the ozone alert system’s operating period has been expanded from the previous mid-April to mid-October (six months) to April 1 through October 31 (seven months). Analysts say rising temperatures and increased solar radiation driven by climate change are boosting the frequency of high ozone concentrations.<\/p>\n
What makes ozone fundamentally different from fine dust is that masks cannot block it. Because it is a gas rather than a particle, neither ordinary masks nor health masks are effective. The most reliable response is therefore to reduce outdoor activity and stay indoors during peak hours from 2 p.m. to 5 p.m.<\/p>\n
According to the Seoul Metropolitan Government’s air quality information service, residents are advised to adjust their outdoor schedules and plan indoor activities on days with high ozone concentrations. Refueling vehicles in the morning or evening rather than during the sunny daytime helps reduce ozone formation.<\/p>\n
Ozone forecasts are issued in four levels \u2014 good, moderate, bad and very bad \u2014 while alerts are issued in three levels based on hourly average concentrations: advisory (0.12 ppm or higher), warning (0.30 ppm or higher) and serious warning (0.50 ppm or higher). Real-time ozone concentrations can be checked on AirKorea or the Seoul Metropolitan Government’s air quality information website.<\/p>\n","protected":false},"excerpt":{"rendered":"Citizens wearing masks. Yonhap News Daytime temperatures across most of Korea will exceed 30 degrees Celsius this weekend,…\n","protected":false},"author":2,"featured_media":19355,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[13348,13768,13769,8120,13772,13770,13773,13771,112],"class_list":{"0":"post-19354","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-seoul","8":"tag-fine-dust","9":"tag-ground-level-ozone","10":"tag-korea-air-quality","11":"tag-korea-meteorological-administration","12":"tag-national-institute-of-environmental-research","13":"tag-ozone-advisory","14":"tag-ozone-alert-system","15":"tag-photochemical-pollution","16":"tag-seoul"},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/posts\/19354","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/comments?post=19354"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/posts\/19354\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/media\/19355"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/media?parent=19354"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/categories?post=19354"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/korea\/wp-json\/wp\/v2\/tags?post=19354"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}