0-Spatial distributions of indoor radon exposures- from city to regional levels

¹ Department of Building and Environment, School of Environment and Architecture, University of Science and Technology for Shanghai, Shanghai, China.
² Department of Social Epidemiology, School of Public Health, Kyoto University, Kyoto, Japan.
³ Tianjin Key Laboratory of Indoor Air Environmental Quality Control, School of Environmental Engineering and Science, Tianjin University, Tianjin, China.

Abstract

This study investigates the spatial and vertical distribution patterns of indoor radon (Rn- 222) in China’s Yangtze River Delta (YRD) region by integrating field measurements, meta- analysis, and spatial modeling. Field monitoring across ten campus buildings revealed a general decline in radon concentration with increasing floor height, from 55.1 Bq/m³ on ground floors to 21.9 Bq/m³ on the ninth floor. However, a distinct bimodal concentration profile was observed between the fourth and eighth floors, suggesting the involvement of non-gravitational transport mechanisms. Meta-analysis of 3,800 georeferenced samples from 41 cities demonstrated a pronounced west-to-east spatial gradient, with concentrations ranging from 90.1 Bq/m³ in Anhui to 14.8 Bq/m³ in Shanghai. This gradient was associated with synergistic influences from geological background, industrial emissions (e.g., +1.2 Bq/m³ per 1000 tons of particulate emissions), and climatic factors (e.g., -32.94 Bq/m³ per °C increase in temperature). A key finding is the establishment of a dual-mechanism model: in cities with low background concentrations, radon levels increased by 1.56 Bq/m³ per meter of building height, implicating construction materials as a major source; conversely, in high-concentration cities, building parameters exhibited negligible effects, with geological background controlling exposure. Low-rise structures (<15 m) in areas with high soil radon potential (>6,000 Bq/m³) exhibited concentrations 40% higher than those in taller buildings. These findings highlight limitations in current radon standards, which largely overlook vertical heterogeneity and regional mechanistic differences. We propose height-differentiated ventilation protocols, geology-informed building codes, and targeted industrial emission controls to mitigate region-specific exposure risks.