Radon and Thoron Concentrations in Dwellings of Kanpur City, Uttar Pradesh: Assessment, Influencing Factors and Radiological Significance Author Radon; Thoron; ^222Rn; ^220Rn; Indoor air; Dwellings; Kanpur; Uttar Pradesh; SSNTD; CR-39; Radiation exposure; Radon progeny; Thoron progeny; Effective dose; Ventilation. Radon (^222Rn) and thoron (^220Rn) are naturally occurring radioactive noble gases generated in the uranium-238 and thorium-232 decay series, respectively. Because both gases can accumulate indoors, their short-lived radioactive progeny may contribute appreciably to radiation exposure of occupants. The present research paper reviews and evaluates the available evidence concerning indoor radon and thoron concentrations in residential dwellings of Kanpur City, Uttar Pradesh, with particular emphasis on measured radon concentrations, building characteristics, ventilation, floor level, dwelling type, equilibrium factors, and associated radiation-dose considerations. An important earlier investigation involving 120 dwellings in Kanpur reported mean radon concentrations of approximately 40 ± 10 Bq m^-3 in living rooms, 46 ± 6 Bq m^-3 in bedrooms, and 70 ± 5 Bq m^-3 in kitchens. The corresponding geometric means were approximately 25.3, 36.2 and 40 Bq m^-3, respectively. The study also reported an average radon equilibrium factor of 0.38 ± 0.26 and an estimated annual effective dose equivalent of approximately 1.0 mSv y^-1 for living-room exposure. Poorly ventilated dwellings showed substantially greater radon concentrations than well-ventilated dwellings, demonstrating the importance of indoor air exchange. Although thoron is increasingly recognized as an important component of indoor natural radiation exposure, the published Kanpur-specific study cited here primarily quantified ^222Rn rather than providing a complete modern ^220Rn dataset. Therefore, thoron values reported for Central Uttar Pradesh should not be incorrectly presented as direct Kanpur measurements. The available regional evidence nevertheless establishes the scientific importance of simultaneous radon–thoron monitoring in Uttar Pradesh. Contemporary international guidance recommends that residential radon concentrations be kept as low as reasonably achievable, with WHO proposing a reference level of 100 Bq m^-3 where feasible and indicating that the selected national reference level should not exceed 300 Bq m^-3 when 100 Bq m^-3 cannot reasonably be achieved. The present review demonstrates that the historical Kanpur radon measurements were below these reference values, while still indicating measurable exposure and considerable variation between rooms and building conditions. A systematic city-wide survey using radon–thoron discriminating passive detectors, seasonal measurements and detailed building questionnaires would provide an updated exposure map for Kanpur. STEMMA International Research Journal 2026-06-30 Text application/pdf 10.65919/stemma.2026.v2i3001 en