A Stratified Meta-analysis of Source-specific Particulate Matter and its Health Effects

Earlier epidemiological studies have consistently found that airborne particulate matter less than or equal to 10 µm in diameter (PM10) can affect people’s health in many ways, such as cardiopulmonary diseases and related premature deaths. In recent years, studies are increasingly addressing the sources of particles as a factor that plays an important role in the health effects. For instance, some argued that particles from different sources are not equally toxic to the exposed population, but some of them such as particles from combustion-related sources may pose a greater health risk. Given this evidence, it is not appropriate to assume that every pollution abatement strategy has the same health impact per unit change in the mass concentrations. However, currently the source-specific PM10 health risks are not yet sufficiently understood due to the difficulty in source apportionment. To explore the source-specific PM10 health risk quantitatively based on earlier epidemiological evidence, this study conducted a stratified meta-analysis by grouping similar time-series studies and pooling their estimates of the association between short-term exposure to PM10 and mortality. The sources of particles are classified into three categories: mobile, industrial and crustal. Separate meta-analyses were conducted within each source group. The pooled estimates were: a 10 µg/m3 increase in PM10 from mobile sources were associated with a 1.22% increase in daily mortality, whereas an equivalent increase in PM10 from industrial and crustal sources were associated with 0.58% and 0.55% increases in daily mortality, respectively. The results of this study suggest that particles from mobile sources may pose the greatest health risk, but particles from industrial and crustal sources are not ruled out either. Given this, PM10 regulation strategies should not only focus on a national ambient standard, but also particle sources, particularly traffic-related sources.