Winter and Summer Differences in Oxylipin Responses to Ambient Particles: Roles of Sizes and Constituents

Ambient fine particulate matter (PM2.5) has been associated with increased mortality risk, but whether it is more harmful on colder or warmer days is unclear. Here, we investigate seasonal variations in PM2.5 mass, sizes, constituents, and their association with oxylipin changes in humans. In a panel study of 123 adults in Beijing, we measured 27 PM2.5 metrics and five circulating lipoxygenase-derived oxylipins (i.e., leukotriene B4 [LTB4], 5-, 8-, 12-, and 15-hydroxyeicosatetraenoic acid [HETE]) across winter and summer. PM2.5 exposure was associated with peak oxylipin increases at lag 0–1 days. Across particle size fractions and constituents, oxylipin increases ranged from 3.3% to 114.2%, with the most robust associations for ultrafine particles, accumulation mode particles, organic carbon, and chloride. Furthermore, an exposure-response relationship between UFP and oxylipins was observed only in summer. An IQR increase in UFP was associated with oxylipin changes of 12.9–97.7% in summer and −7.7 to 18.8% in winter. Conversely, oxylipin increases associated with accumulation mode particles and organic carbon were greater in winter. These findings suggest that the sizes and constituents of PM2.5 may partially explain the seasonal difference in the health effect of PM2.5 exposure, helping identify components associated with stronger biomarker responses in specific seasons.