摘要：Lepeule et al. (2012) associated reduced PM2.5(particulate matter ≤ 2.5 μm in aero-dynamic diameter) with decreased mortality over almost four decades. Because the sulfate/PM2.5ratio dropped among six localities but the PM2.5mortality coefficient did not "substantially" increase, the authors concluded that sulfate must be "about as toxic" as average PM2.5. In a two-pollutant world, perhaps. When a single source emits several PM2.5 species, and a specific species is emitted from several sources, chemical-specific associations might not reflect inherent toxicity but rather status as a marker of harmful coemissions (Grahame and Hidy 2007; Mostofsky et al. 2012). Furthermore, because total PM2.5is often associated with adverse health out-comes, association of a constituent represent-ing a large portion of total mass (e.g., sulfate) may occur unrelated to any inherent toxicity (Mostofsky et al. 2012).
