Effects of air pollution and meteorological factors on hematological exacerbation phenotypes in patients presenting to the emergency department with COPD exacerbation.

To evaluate the short-term effects and lagged temporal patterns of air pollutants and meteorological factors on hematological exacerbation phenotypes in patients presenting to the emergency department with chronic obstructive pulmonary disease (COPD) exacerbation. Patients who presented to a tertiary emergency department with COPD exacerbation between April 2022 and April 2023 were retrospectively reviewed. Exacerbations were classified as eosinophilic, neutrophilic, or mixed-type based on admission complete blood counts. Daily air pollutant concentrations (PM₁₀, PM₂.₅, SO₂, NO₂, CO, O₃) and meteorological parameters were obtained from official monitoring stations. Day-level associations between environmental variables and phenotype-specific daily exacerbation counts were analyzed using quasi-Poisson distributed lag non-linear models (DLNM) and a time-stratified case-crossover design (lag 0-3 days). Of all exacerbations (n = 354), 65.8% were neutrophilic, 20.3% mixed-type, and 13.8% eosinophilic. The neutrophilic phenotype was associated with the most severe clinical presentation. No significant environmental association was identified for the overall COPD exacerbation count. In the eosinophilic phenotype, same-day exposure to CO and SO₂ was associated with increased exacerbation risk (RR = 1.39, 95% CI: 1.06-1.82 and RR = 1.21, 95% CI: 1.03-1.43, respectively). In the mixed-type phenotype, higher humidity was positively associated with exacerbation counts, whereas lower wind speed was associated with decreased counts. In the neutrophilic phenotype, an inverse association with O₃ observed in the DLNM was not confirmed in the case-crossover analysis. COPD exacerbations do not appear homogeneous with respect to environmental triggers; the eosinophilic phenotype showed clearer associations with gaseous pollutants, whereas the mixed-type phenotype showed associations with meteorological conditions. The absence of associations in the overall population supports the value of phenotype-based environmental risk assessment. These findings may contribute to the development of phenotype-oriented environmental warning strategies in COPD management.