Environment ministry reports drop in ozone alerts despite summer heat

The environment ministry said Tuesday that ozone alerts were issued on 48 days between May and August, the second-lowest figure recorded since 2016, even as temperatures remained high.

The National Institute of Environmental Research attributed the decline to unfavorable weather conditions for ozone formation. Increased rainfall and reduced sunlight created an atmosphere less conducive to the photochemical reactions that generate ground-level ozone.

Warning days have fallen from 61 in 2024 to 54 in 2025 before reaching this year's low. The previous record low occurred in 2020, when prolonged monsoon rains limited alerts to 40 days over the same four-month period.

August saw the most dramatic improvement, with only 10 days of warnings issued nationwide. This marks a 27 percent drop compared to the 10-year average of 13.7 days for the month, and a decrease from the 21 alert days recorded in August 2024.

Regionally, the southern area experienced the largest reduction, falling 17.5 percent to 17 days from a 10-year average of 20.6 days. The capital region recorded 27 alert days, while the central and southeastern areas saw 16 and 23 days respectively. All regions posted declines ranging from 9.1 to 17.5 percent against their decadal averages.

Analysis revealed that total solar radiation and the number of rainy days were the primary factors influencing ozone levels. In the Gwangyang Bay area of the south, increased wind speeds and cloud cover from May to July further hindered ozone accumulation.

The national average concentration of nitrogen dioxide, a key ozone precursor, stood at 0.0077 parts per million from May through August, approximately 36 percent lower than the average recorded over the past decade.

Sung Ji-won, head of the Air Quality Research Department at the National Institute of Environmental Research, emphasized that high temperatures do not automatically lead to more ozone warnings. "This year's case shows that high temperatures do not necessarily lead to an increase in ozone advisories, as ozone is the result of complex interactions between meteorological conditions, emissions of precursors, and photochemical reactions in the atmosphere," Sung said. He added that the institute will analyze the specific causes of the sharp decline in the southern region to serve as scientific grounds for future customized ozone management policies.

The institute plans to conduct further analysis combining weather data, pollutant concentrations, and industrial emission conditions to pinpoint the specific causes of the regional decreases and establish tailored management measures.