PM_2.5 and its chemical components interact with hypoxia to increase the risk of hospitalization for peripheral arterial disease

This study investigated the combined effects of fine particulate matter (PM_2.5) exposure and ambient oxygen (O₂) availability on peripheral artery disease (PAD) hospitalizations in Gansu Province, China, from 2018 to 2022 (N = 38,514). A time-series case-crossover design with conditional logistic regression assessed short-term exposure to daily PM_2.5 and its major chemical components (black carbon [BC], organic carbon [OC], sulfate [SO₄ ^2-], nitrate [NO₃ ^-], ammonium [NH₄ ⁺], and chloride [Cl^-]). Atmospheric O₂ levels were estimated based on altitude, temperature, and humidity. Short-term exposure to PM_2.5 was associated with an increased risk of PAD hospitalization, notably at lag 1 (odds ratio [OR] = 1.003; 95% confidence interval [CI]: 1.002-1.004). Carbonaceous pollutants exhibited delayed effects, with peak associations at lag 6 for BC (OR = 1.069; 95% CI: 1.035-1.105) and OC (OR = 1.028; 95% CI: 1.011-1.050), per 1 μg/m³ increase. Secondary inorganic aerosols showed acute effects at lag 1: Cl^- (OR = 1.107; 95% CI: 1.063-1.150), NH₄ ⁺ (OR = 1.040; 95% CI: 1.022-1.060), SO₄ ^2- (OR = 1.025; 95% CI: 1.015-1.036), and NO₃ ^- (OR = 1.030; 95% CI: 1.018-1.042), per 1 μg/m³ increase. Nonlinear exposure-response curves revealed a stronger PAD risk under lower O₂ conditions (<18%). The PM_2.5-related risk was amplified in high-altitude residents (>1500 m), older adults (>60 years), females, emergency admissions, and during the cold season. These findings suggest that ambient PM_2.5 and lower O₂ levels interact synergistically to elevate PAD hospitalization risk, emphasizing the urgent need for region-specific air quality controls and targeted health protection strategies.