Abstract
BACKGROUND: Tropospheric ozone (O₃) is a secondary air pollutant associated with respiratory morbidity. Lleida is an inland Mediterranean city with a continentalized climate, frequent winter thermal inversions and hot, dry summers, where ozone episodes and high humidity often co-occur under stagnant atmospheric conditions. This study explores the association between air pollutants, weather variables, and respiratory emergency admissions in Lleida, Spain. METHODS: We conducted a time-series analysis using distributed lag non-linear models (DLNM) on hospital emergency room admissions for acute respiratory conditions in Lleida (2010-2019). Data on weather (temperature, humidity, solar radiation) and air pollution (O₃, NO₂, PM10, SO₂) were obtained from local monitoring stations. The primary outcome was the daily number of admissions for respiratory conditions (ICD-10 codes J09-J18, J20-J22, J44.1, J45.9). RESULTS: A total of 19,428 respiratory admissions were recorded. High O₃ concentrations and elevated relative humidity were significantly associated with increased admissions, even after adjusting for temperature and solar radiation. The strongest effects were observed with delayed lags (up to 21 days). NO₂, PM10, CO and SO₂ levels did not show a significant association. CONCLUSIONS: Our findings support a significant and independent association between elevated ozone concentrations, high humidity, and respiratory emergencies. These results highlight the need for public health strategies and policy interventions focused on environmental risk forecasting and air quality management, particularly in vulnerable inland Mediterranean regions.