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

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.