Indoor Air Quality in Climbing Gyms: Multi-Zone Assessment of Particulate Matter, CO2 Accumulation, and User Perception

Indoor climbing gyms are high-occupancy settings, yet integrated indoor air quality (IAQ) studies that analyze objective exposure and occupant perception remain scarce. The novelty consists of combining user perception with multi-zone, high-resolution IAQ measurements. We investigated a climbing gym in Romania to (i) quantify particulate matter (PM1, PM2.5, PM10) and carbon dioxide (CO2), (ii) compare natural and mechanical ventilation under real operating conditions with per capita normalization, (iii) relate exposure to occupancy and user perception, and (iv) coupling continuous optical monitoring with 24 h gravimetric and morphological/chemical analyses (scanning electron microscopy, confocal microscopy, X-ray fluorescence, and inductively coupled plasma mass spectrometry). The gravimetric 24 h reference measurements (EN 12341:2014) showed that daily means for PM2.5 and PM10 were 1.9–2.0× and 2.3–2.8× higher than the WHO guideline values, which confirms persistent daily particulate loads. Mechanical ventilation reduced coarse PM and CO2, but absolute PM remained elevated and fine fractions persisted. CO2 revealed a near-uniform vertical mixing, confirming dilution but indicating that CO2 is not a surrogate for particulate exposure. Survey responses from occupants revealed a gap between perception and reality: most of the users rated IAQ as good despite high PM. This study is among the few integrations of perception of IAQ for climbing gyms and the first comprehensive assessment in Romania, providing evidence-based recommendations on ventilation and filtration upgrades, chalk use management, and dust-reservoir control, thus creating sparkling interest for IAQ researchers, building services engineers, sports facilities operators, and policymakers.