To explore the influence and lag effects of different groups of relative humidity, temperature, atmospheric pollutants and their interactions on respiratory disease mortality in a basin city in southwest China under a subtropical humid climate.

Daily meteorological, air pollutant and respiratory-related mortality data of residents in a city in southwest China from 2018 to 2022 were collected, and time-series analysis was carried out using the distributed lag-wise nonlinear model (DLNM) with quasi-Poisson distribution and the generalized additive model (GAM).

A total of 11 779 people died of respiratory diseases in this city. At lag15, when the SO₂ concentration increased by 10 μg/m³, the impact on the respiratory disease mortality of the population was the greatest, with RR=1.055 (95%CI: 0.993-1.120). In the single-factor grouped lag model, in the extremely high-temperature group (≥P₉₅), when the temperature increased by 1 °C, the impact on respiratory disease mortality was the greatest at lag0, which was 1.710(95%CI: 1.209-2.418). In the multi-factor model, when SO₂ and NO₂ were taken as synergistic factors, the impact of relative humidity on respiratory mortality was the greatest at lag18, which was 1.026 (95%CI: 1.000-1.053), and the RR of temperature on mortality was the greatest at lag0, which was 1.024 (95%CI: 1.010-1.038). Interaction analysis showed that there were interactions among relative humidity, temperature and various pollutants, and the mortality risk generated by the interaction between 60%-80% humidity level and SO₂ and NO₂ was the greatest.

Each factor has an independent influence and lag effect on respiratory disease mortality.The interactions between different humidity levels and pollutants have different impacts on respiratory disease mortality and may have synergistic or antagonistic effects. Among them, the mortality risk generated by the interaction between medium humidity level and pollutants is the greatest, while the impact generated by the interaction between high humidity and pollutants is instead reduced.