scientific and technical analysis provided, and how effectively policy-relevant questions were addressed.

The draft NARSTO assessment consists of a comprehensive review of the science pertaining to PM and an executive summary intended to synthesize the scientific information for a decision-maker audience. Within the body of the assessment are technical chapters addressing formation and transport of PM, emission inventories, measurement techniques, ambient PM concentrations, source apportionment and air quality-models, health effects, and visibility. Some analysis of the technical information is provided via recommendations for future research needs and “conceptual descriptions” of the factors that affect observed ambient PM concentrations in nine regions in North America. The executive summary of the assessment contains a summary of the information presented in the body of the document and responses to eight policy questions, which are used to synthesize the atmospheric-science information necessary for implementing ambient PM standards. The assessment cochairs informed the committee that the executive summary will be published with the full document and also separately in English, Spanish, and French. Here, the committee summarizes the highest-priority recommendations for the chapters of the draft assessment and its executive summary.

COMMENTS ON THE CHAPTERS OF THE DRAFT NARSTO ASSESSMENT

The committee commends NARSTO for undertaking this assessment, particularly in light of the challenge it posed. The committee finds that the draft NARSTO PM assessment is a good representation of the state of atmospheric science, has an appropriate level of detail in most chapters, and provides the best currently available information on the formation and distribution of PM for North America. In particular, the draft clearly identifies the widespread existence and variable nature of the PM problem in different regions of North America. The draft provides an unmatched compilation of chemical measurements of both inorganic and organic fractions of PM, with preliminary indications of the sources and fates of the components. A comprehensive discussion of computational models shows how the weight of evidence defines a clear path for linking emission sources with air-quality outcomes. The committee finds the descriptions of PM characteristics and source contributions in nine regions to constitute an original scientific contribution and to provide information of great use to decision-makers. With suitable revisions, the document will be useful to the air-quality management community, to atmospheric-science researchers, and potentially to researchers in related fields. Indeed, the committee is unaware of any other assessments of the atmospheric science of PM that are this comprehensive; this NARSTO assessment is potentially of great use.

The draft assessment in its current form needs substantial improvements to meet its goal of providing useful information in a way that is accessible to decision-makers, especially in terms of consistently presenting a framework for informing airborne-PM management and stating clearly the policy implications of scientific findings. The committee’s highest-priority recommendations for improving the main body of the assessment follow. Additional comments are provided in the chapters of the present report and its Attachment B.



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