Fine particle components and health—a systematic review and meta-analysis of epidemiological time series studies of daily mortality and hospital admissions

Short-term exposure to fine particle mass (pm) has been associated with adverse health effects, but little is known about the relative toxicity of particle components. we conducted a systematic review to quantify the associations between particle components and daily mortality and hospital admissions. medline, embase and web of knowledge were searched for time series studies of sulphate (so42−), nitrate (no3−), elemental and organic carbon (ec and oc), particle number concentrations (pnc) and metals indexed to october 2013. a multi-stage sifting process identified eligible studies and effect estimates for meta-analysis. so42−, no3−, ec and oc were positively associated with increased all-cause, cardiovascular and respiratory mortality, with the strongest associations observed for carbon: 1.30% (95% ci: 0.17%, 2.43%) increase in all-cause mortality per 1 μg/m3. for pnc, the majority of associations were positive with confidence intervals that overlapped 0%. for metals, there were insufficient estimates for meta-analysis. there are important gaps in our knowledge of the health effects associated with short-term exposure to particle components, and the literature also lacks sufficient geographical coverage and analyses of cause-specific outcomes. the available evidence suggests, however, that both ec and secondary inorganic aerosols are associated with adverse health effects.