Review of the Air Quality Criteria Document for Particulate Matter

illustrated using a figure from Kelsall et al (1997) for multiple pollutants for Philadelphia (1974-1988). The inclusion of these figures will help to illustrate the challenge faced in “teasing out”air pollution impacts from other factors that influence mortality (and morbidity) from respiratoryand cardiovascular disease.The above discussion would lay the general groundwork for the section on analy5ticaland statistical considerations. In this reviewer's opinion, the most significant advances since the1996 CD are derived from the NMMAP study. This study benefited from the use of a commondatabase and a common analytical methodology as well as increased statistical power related toanalysis of data from 88 cities over a relatively long time period (1987 – 1994). A briefdiscussion of the analytical methodology used in conducting the NMMAP study and relatedstudies would be helpful to the general reader who is not an expert in epidemiology.The balance in the chapter could be improved by giving more attention to issues ofstatistical certainty/uncertainty. The authors have tended to call attention to statisticallysignificant results while tending to avoid calling attention to the lack of statistical significance inother studies. The authors need to do everything possible to ensure that all studies are reviewedand reported in an even-handed manner. If certain studies are given “special weight,” the basisfor doing so should be clearly articulated.The present draft does not adequately treat the issue of co-pollutants and conveys a viewthat the authors are zealous in putting PM center stage and pushing other pollutants into thebackground. For each study, the CD should clearly state whether the analytical methodologyconsidered only some indicator of PM or also considered co-pollutants. For each of the variousendpoints, tables should be created that would include more detailed information from thestudies that considered co-pollutants. This would include presentation of the relative risks for theother pollutants when they were determined.The present draft does not adequately treat the issue of heterogeneity of effects estimates,especially as reported in the NMMAP study. While it is correct to say that the basis for city tocity differences in effects estimates is unknown, more attention should be given to elaborating onpotential explanations for the differences. This would include the possibility that the differencesare real and the levels of PM 10 present in certain cities did not yield statistically significanteffects estimates for PM 10 for the period studied (1987-1994).CHAPTER 6 - EPIDEMIOLOGY – SPECIFIC COMMENTSPage 6-3, line 18: "Confounding and Effect Modification." This section addresses a veryimportant point when it notes that "the health outcomes attributed to particles are not veryspecific." Indeed, the modifier “very” could be dropped to make the statement more accurate. Itwould be helpful to the reader to illustrate the extent to which the majority of the typical healthoutcomes are attributable to other factors. Indeed, the terms – confounders and effects modifiers– do not adequately relate the extent to which the health outcomes are attributable to factorothers than the identified modifiers and effects modifiers.Page 6-5, lines 28-30 and page 6-6, lines 1-2: It would be useful to add a paragraph or two hereplacing the pollutant increments in perspective. For example, for most of the U.S. increments of50 :g/m 3 for PM 10 or 25 :g/m 3 for PM 2.5 are not at all representative. The use of theseincrements tend to present an exaggerated view of PM effects. I suspect that is why theNMMAPS authors elected to normalize their results to 10 :gm 3 of PM 10 .Pages 6-6 and 6-7: The approach used through the document of discussing the 1996 CDfindings and then the post 1996 CD finding is confusing. I would prefer to see all of theevidence "weighed" to reach a current conclusion. The integrated finding could then becompared to the 1996 CD findings.Table 6-1. The table should be expanded to include information on the effects estimators forpollutants other than PM when the individual study has evaluated other pollutants.Alternatively, this could be done in a separate table for those studies which have looked atA - 58