Indoor radon exposure and ventilation-driven mitigation in a high-rise residential unit using source-term-informed monitored-zone assessment.

Increasing airtightness in high-rise residential buildings can enhance indoor radon accumulation when persistent indoor source terms are combined with limited air exchange. This study evaluated indoor radon accumulation and ventilation-driven reduction in four monitored zones of one newly constructed high-rise residential unit using multi-point detector measurements during actual energy-recovery ventilator (ERV) operation at nominal settings of 0.3, 0.5, and 0.7 h-1, complemented by chamber-derived surface-associated radon source information and zone-specific air volumes. Paired pre-ERV concentrations ranged from 496 to 1010 Bq m-3. The combined mean detector-level reductions were 79.2%, 81.5%, and 84.0% at the three nominal settings, respectively. Relative to the 0.3 h-1 tests, the 0.5 h-1 tests had higher mean reductions and fewer residual detector locations above 148 Bq m-3, whereas the 0.7 h-1 tests had the highest combined mean reduction and shortest average response time. Multi-point measurements showed an 18.6% corner-to-center difference under closed-door conditions, indicating spatial non-uniformity within the monitored unit. The first-order mass-balance calculation was retained only as a descriptive setting-level consistency check (combined-mean RMSE 4.37 percentage points; MAE 3.11 percentage points). Effective in situ ACH was not independently verified, and each room-level condition was tested once; therefore, between-setting differences are interpreted within the tested campaign rather than as isolated causal effects of ventilation rate.