Air Quality Guidelines Global Update 2005 - World Health ...

10. Particulate matter
Jonathan M. Samet, Michael Brauer, Richard Schlesinger
Introduction
Since the second edition of Air quality guidelines for Europe was issued in 2000
(1), there has been an explosive growth in research relevant to the health effects
of airborne PM. The evidence comes from a variety of research disciplines, including
epidemiology, toxicology, exposure assessment and atmospheric sciences.
The evidence obtained has deepened understanding of the risks posed to
human health and to ecosystems by airborne particles, and also provided insights
into the complexity of airborne particles and their myriad sources, along with the
attendant implications for control. The scientific foundation for proposing air
quality guidelines is far more substantial than in the past; the voluminous scope
of available evidence, however, poses a challenge in developing guidelines, as the
amount of evidence for a number of adverse health effects is now increasingly
sufficient for this purpose but not easily summarized, either quantitatively or
qualitatively. For some of the health outcomes, including increased risk of mortality
on a short-term basis, dose–response relationships have been demonstrated
at concentrations extending, at the lowest levels, well into the ranges measured at
present in many cities in both developed and developing countries. The consequent
inability to identify levels below which adverse effects are not anticipated
implies that any standard may leave some residual risk unless concentrations are
reduced to background levels.
A systematic review of this new evidence is beyond the scope of this chapter,
which draws extensively from recent comprehensive syntheses and from the
meta-analyses of time series studies carried out by Anderson et al. for WHO (2).
The full suite of evidence on PM was assembled by the US Environmental Protection
Agency (USEPA) in its 2004 document Air quality criteria for particulate
matter (3). The related document, Review of the national ambient air quality
standards for particulate matter: policy assessment of scientific and technical
information (4), provides a distillation of the findings of the criteria document
and policy implications. In 1998, the US National Research Council established
its Committee on Research Priorities for Airborne Particulate Matter, which was
charged with setting out an agenda for PM research and then tracking progress
on this agenda (5). In its fourth and final report, the Committee gauged progress
on its research agenda, based on a process involving expert judgement and a systematic
review. It also highlighted uncertainties in the evidence available on PM,
across its framework that begins with sources of PM and ends with adverse effects
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