ABSTRACT

Radon (Rn) is a natural and toxic radioactive gas that accumulates indoors, mainly in low-ventilated underground floors and basements. Several factors make prediction of indoor Rn exposure in enclosed spaces challenging. In this study, we investigated the influence of soil, geology, topography, atmospheric variables, radiation, urbanization, community economic well-being, and monthly and yearly variations on indoor Rn concentrations. We analyzed 7,515 monthly indoor Rn measurements in 623 zip codes from two U.S. States (Michigan and Minnesota) during 2005–2018 using a random forest model. Using Shapley Additive exPlanations (SHAP) values we investigated the contribution of each factor using variable importance and partial dependence plots. Factors that predict indoor Rn differed between states, with topographical, geological and soil composition being most influential. Cross-validated Pearson correlation between predictions and measurements was 0.68 (RMSE = 47.8 Bq/m³) in Minnesota, and 0.67 (RMSE = 52.5 Bq/m³) in Michigan. Our results underline the importance of soil structure for radon exposure, presumably due to strapped Rn in soil. The differences across states also suggest that Rn studies performing model development should consider geographical variables, along with other factors. As indoor Rn levels are multifactorial, an understanding of the factors that influence its emanation and build up indoors will help better assess spatial and temporal variations, which will be useful to improve prevention and mitigation control strategies.

Implications: Radon exposure has become a year-round problem as people spend most of their time indoors. In North America, radon exposure is increasing over time and awareness related to its health effects remains low in the general population. Several factors make prediction of indoor radon exposure in enclosed spaces challenging. In this study, we used random forest to investigate the influence of factors on indoor radon in the Midwest United States. We found that topography, geology, and soil composition were the most influential factors on indoor radon levels. These results will help better assess spatial and temporal variations, which will further help better prevention and mitigation control strategies.

摘要

氡 (Rn) 是一种天然有毒放射性气体，主要在室内积聚，主要存在于通风不良的地下地板和地下室。有几个因素使得在封闭空间内预测室内 Rn 暴露具有挑战性。在这项研究中，我们调查了土壤、地质、地形、大气变量、辐射、城市化、社区经济福祉以及室内 Rn 浓度的月度和年度变化的影响。我们使用随机森林模型分析了 2005-2018 年美国两个州（密歇根州和明尼苏达州）623 个邮政编码中 7,515 次每月室内 Rn 测量值。使用 Shapley Additive exPlanations (SHAP) 值，我们使用变量重要性和部分依赖图研究了每个因素的贡献。预测室内 Rn 的因素因州而异，包括地形、地质和土壤成分影响最大。预测和测量之间的交叉验证 Pearson 相关性为 0.68（RMSE = 47.8 Bq/m³ ) 在明尼苏达州，在密歇根州为0.67 (RMSE = 52.5 Bq/m ³ )。我们的结果强调了土壤结构对氡暴露的重要性，大概是由于土壤中的束缚 Rn。各州之间的差异还表明，进行模型开发的 Rn 研究应考虑地理变量以及其他因素。由于室内 Rn 水平是多因素的，了解影响其在室内散发和积聚的因素将有助于更好地评估时空变化，这将有助于改进预防和缓解控制策略。

影响：由于人们大部分时间都在室内度过，氡暴露已成为一个全年的问题。在北美，氡暴露随着时间的推移而增加，一般人群对其健康影响的认识仍然很低。有几个因素使得在封闭空间内预测室内氡暴露具有挑战性。在这项研究中，我们使用随机森林来调查因素对美国中西部室内氡的影响。我们发现地形、地质和土壤成分是对室内氡水平影响最大的因素。这些结果将有助于更好地评估时空变化，这将进一步有助于更好地预防和缓解控制策略。