Investigating the short-term effects of particulate matter (PM) chemical components on mortality and the potential modifying effect of extreme temperature: A time-series analysis in London

TL;DR

This study investigates how specific particulate matter components affect mortality in London and how extreme temperatures modify these effects, highlighting the importance of source-specific pollution control and temperature considerations.

Contribution

It provides a detailed analysis of the short-term health impacts of individual PM chemical components and their interactions with extreme temperature events in an urban setting.

Findings

All PM components were positively associated with mortality, especially respiratory deaths.

Heat waves amplified respiratory mortality risks from PM exposure.

Secondary oxidation products like MO-OOA showed consistent harmful effects.

Abstract

Particulate matter (PM) is linked to adverse health outcomes, yet the roles of specific PM components and their modification by extreme temperature remain unclear. We examined short-term associations between ten PM chemical components and daily mortality in Greater London (2015-2018). PM components include inorganic aerosols (black carbon from wood burning (BCwb) and traffic exhaust (BCtr), SO4, NO3, and NH4) and organic aerosols (hydrocarbon-like organic aerosol (HOA), biomass burning OA (BBOA), cooking-like OA (COA), more and less oxidized oxygenated OA (MO-OOA and LO-OOA)). We applied quasi-Poisson generalized additive models and weighted quantile sum (WQS) regression to estimate single-pollutant, multi-pollutant, and mixture effects, respectively, and included interaction terms to test effect modification by heat waves and cold spells. All ten components showed positive associations with all-cause mortality in single-pollutant models with stronger estimated risks for respiratory mortality, particularly for NH4, NO3, SO4. In mixture analyses, the WQS index was significantly associated with all-cause mortality (RR = 1.015, 95% CI: 1.006-1.024 per 25th-percentile increase) and showed a marginally significance with respiratory mortality (RR = 1.018, 95% CI: 0.994-1.042). MO-OOA and COA contributed most to all-cause mortality, while BBOA and BC Wood dominated respiratory effects. Heat waves consistently amplified respiratory risks in both single-pollutant and mixture models with little evidence for cardiovascular mortality. Overall, MO-OOA demonstrated harmful associations across outcomes, suggesting potential toxicity link to secondary atmospheric oxidation processes. These findings support source-specific control strategies and highlight the importance of accounting for extreme temperature in air pollution mitigation policies.