Radon (222Rn) is the leading environmental cause of lung cancer among nonsmokers. Additionally, schools are critical exposure environments because children spend over 2,000 hours annually in school settings and are more vulnerable than adults. Although various mitigation systems are increasingly being installed in Korean schools, quantitative comparisons of their performance under a unified protocol have been lacking. This study evaluated four types of mitigation systems installed across 19 schools nationwide: active soil depressurization (ASD), ceiling-type (CT), window-type (WT), and floor-standing (FS) mechanical ventilators. Furthermore, three complementary methods were used: long-term alpha-track monitoring (approximately 90 days, two seasons) and short-term continuous monitoring with FRD-400 detectors (three rounds) in all 19 schools. A controlled sealed-condition evaluation during winter break was also conducted in a subset of eight schools (15 measurement points). Indoor radon concentrations were significantly higher in the second half of the year (155.7 ± 169.2 Bq/m3) than in the first half (82.1 ± 48.2 Bq/m3), corresponding to an approximately 1.9- fold seasonal increase (p < 0.01). Daytime concentrations were on average 57% lower than nighttime concentrations under natural ventilation conditions, but remained above the recommended limit (148 Bq/m3) in high-concentration schools. Mean reduction efficiencies were 74.9% for ASD, 55.4% for CT, 40.4% for WT, and 41.4% for FS. While ASD maintained on-condition concentrations below the recommended limit across the entire off-condition range (33.5~611.5 Bq/m3), on-condition concentrations under the three mechanical ventilation systems consistently remained above the recommended limit when off-condition concentrations exceeded approximately 400 Bq/ m3. These findings are consistent with the high-concentration range identified in the U.S. EPA school radon guideline (EPA, 1994), where ventilation alone is insufficient to maintain concentrations below the recommended limit. The results also provide the first quantitative observations of this concentration-dependent limit from Korean school classrooms, offering quantitative grounds for concentration-dependent selection of mitigation systems.

Abstract
1. 서 론
2. 연구 방법
    2.1 연구대상 및 측정 지점 선정
    2.2 측정 방법
    2.3 저감효율 산정
    2.4 자료 분석
3. 연구결과 및 고찰
    3.1 학교별 라돈 배경 농도 (장기측정 결과)
    3.2 단기측정에 의한 시간대별 라돈 농도 변동
    3.3 자연환기에 의한 라돈 저감 효과
    3.4 라돈 저감장치의 정량적 효용성 평가(통제 조건)
    3.5 라돈 농도 수준에 따른 저감장치의 적용 한계와 관리 시사점
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