Measurement intensity and regulatory effectiveness in radon governance: A comparative analysis of the United States and Europe.

Measurement intensity, understood as the capacity of a regulatory system to generate exposure-relevant data at scale, is a revealing indicator of how legal frameworks translate scientific knowledge into protective action. Radon is a leading environmental carcinogen, yet the U.S. and Euratom Community legal systems have responded to the same body of scientific evidence through structurally different regulatory architectures. These architectures have produced deep asymmetrical levels of measurement intensity, thereby substantively shaping the foundations upon which mitigation, optimization, and enforcement rest. The present study examines the development of radon governance in the U.S. and Europe through a combined doctrinal, empirical, and regulatory lens. Drawing on U.S. national radon datasets, European Indoor Radon Maps and an analysis of epistemic capacity, it demonstrates that regulatory effectiveness is not strictly correlated with legal stringency. The U.S. federal-state-market architecture, combining non-binding federal guidance with state disclosure rules, transaction-driven testing, and private-market incentives, has generated reported measurement volumes more than one order of magnitude above the currently documented European map-based dataset, together with substantially greater reported mitigation activity. These gross outputs do not, by themselves, establish a net reduction in the number of high-radon dwellings or in population risk, but they demonstrate a markedly greater capacity to generate exposure-relevant information and activate remedial pathways. The Euratom Community has developed a codified framework under Directive, 2013/59, but exhibits structurally lower testing rates, largely because mandatory workplace duties are concentrated within Radon Priority Areas and because comparable mechanisms for embedding household testing in ordinary social and economic routines remain limited. The article concludes that measurement intensity can function as a structural diagnostic of epistemic and remedial capacity, revealing how divergent normative designs generate distinct pathways for converting scientific insight into concrete public-health protection.