This study analyzed the causes of indoor radon in school classrooms in Chungcheongbuk-do, South Korea, and evaluated the reduction efficiency of various air purification devices. From January to September 2021, indoor radon concentrations were continuously measured for approximately eight days at 30 schools located in 10 administrative districts. The results were interpreted in conjunction with soil radon concentrations and the geological characteristics of each region. The mean indoor radon concentration of the 30 schools in summer was 88.2 ± 42.2 Bq/m3, with a maximum of 201.1 Bq/m3 at Goesan B and a minimum of 29.4 Bq/m3 at Jecheon B. Three schools (Goesan B, Goesan C, and Danyang B) exceeded the management standard of 148 Bq/m3. Time-of-day analysis showed that radon concentrations were relatively low during occupied daytime hours (08:00~17:00) and increased again during nighttime hours (18:00~07:00). On weekends, when natural ventilation was minimal, radon accumulated continuously, resulting in initial Monday morning concentrations approximately twice those of other weekdays. The mean radon reduction efficiency of mechanical ventilators was 22.5%, and floor-type ventilators (mean 20.1%) were more effective than ceilingtype ventilators (mean 15.3%). When the same mechanical ventilators were operated alone, the mean CO2 reduction efficiency across 23 schools was 17.3% (range 1.5~33.1%). Soil radon concentrations averaged 23,844 Bq/m3 across 10 regions and were highest in areas where the parent rock was metamorphic or acidic igneous rock (Goesan, Yeongdong, and Chungju). Although based on a single school, the high reduction efficiency observed with a soil depressurization system (ASD, 65.7%) suggests that, for classrooms with chronically high radon driven primarily by soil gas intrusion, ASD may be considered a priority option. Meanwhile, mechanical ventilation can be applied to classrooms that exceed the standard but cannot be managed through natural ventilation alone. The results provide quantitative evidence to support regionspecific radon management strategies for schools in Chungcheongbuk-do.

Abstract
1. 서 론
2. 연구 방법
    2.1 연구대상 및 기간
    2.2 측정 및 분석방법
3. 연구결과 및 고찰
    3.1 학교별 실내 라돈 농도
    3.2 계절별 실내 라돈 농도
    3.3 고농도 라돈 교실에 대한 발생요인 및 원인분석
    3.4 시간대별 실내 라돈 농도
    3.5 요일별 실내 라돈 농도
    3.6 공기정화장치 가동여부에 따른 실내 라돈 농도
    3.7 토양 중 라돈 측정 결과
4. 결 론
References
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• 김재필(전남대학교 지질환경과학과, (재)FITI시험연구원) | Jae-Pil Kim (Department of Geological and Environmental Sciences, Chonnam National University, FITI Testing & Research Institute) Corresponding author