Joint effects of temperature and humidity with PM_2.5 on COPD

Particulate matter less than 2.5 microns in aerodynamic diameter (PM_2.5) is a significant air pollutant known to adversely affect respiratory health and increase the incidence of chronic obstructive pulmonary disease (COPD). Furthermore, climate change exacerbates these impacts, as extreme temperatures and relative humidity (RH) levels can intensify the effects of PM_2.5. This study aims to examine the joint effects of PM_2.5, temperature, and RH on the risk of COPD.

A case-control study was conducted among 1,828 participants from 2017 to 2022 (995 COPD patients and 833 controls). The radial basis function interpolation was utilized to estimate participants' individual mean and differences in PM_2.5, temperature, and RH in 1-day, 7-day, and 1-month periods. Logistic regression models examined the associations of environmental exposures with the risk of COPD adjusting for confounders. Joint effects of PM_2.5 by quartiles of temperature and RH were also examined.

We observed that a 1 µg/m³ increase in PM_2.5 7-day and 1-month mean was associated with a 1.05-fold and 1.06-fold increase in OR of COPD (p < 0.05). For temperature and RH, we observed U-shaped effects on OR for COPD with optimal temperatures identified as 21.2 °C, 23.8 °C, and 23.8 °C for 1-day, 7-day, and 1-month mean temperature, respectively, and optimal RH levels identified as 73.8%, 76.7%, and 75.4% for 1-day, 7-day, and 1-month mean RH, respectively (p < 0.05). The joint effect models show that high temperatures (> 23.5 °C) and both extremely low (69.3%) and high (80.9%) RH levels generally exacerbate the effects of PM_2.5 on OR for COPD, especially over longer exposure durations.

The joint effects of PM_2.5, temperature, and RH on the risk of COPD underscore the importance of air pollution control and comprehensive research to mitigate COPD risk in the context of climate change.