Review of the Air Quality Criteria Document for Particulate Matter

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The rest of the sections are fine.Overall, I think the different chapter sections should be balanced and use the same approach.Sometimes this chapter reads like a very long summary rather than an integrative synthesis anddefinitely there is very little connective tissue among the different sections. In other words, onecould place each of the sections at the end of the corresponding chapter as a summary. I hopethe executive summary (which I have not seen yet) will provide some real synthesis and adiscussion which expands across disciplines.Roger McClellan, DVMOVERALL COMMENTSThe present draft represents a significant step forward in summarizing the current statusof knowledge on the health effects of ambient particulate matter (PM). However, the presentversion is not an adequate review and synthesis of the information on PM required forestablishing the indicators, level, averaging time and statistical form of National Ambient AirQuality Standards for PM.The document will be improved by using the “source to health responses” paradigmshown in the NAS/NRC PM report as an integrating structure for the Criteria Document.In my opinion, the document tends to overstate positive associations between increasedlevels of ambient PM and increased rates of mortality and morbidity and does not always conveythe high degree of uncertainty in the date. While the NMMAP study represents a substantialadvance in our identification of PM in some locales as having hazardous properties, the highdegree of variability in effects estimates across the U.S. with lack of statistical significance inmany cities suggests caution in interpreting relative risks of less than 1.1 and certainly forrelative risks of less than 1.05. The use of normalized values of 50 :g/m 3 for PM 10 and 25:g/m 3 for PM 2.5 and PM 10-2.5 tend to exaggerate the actual findings. This could be illustrated byconstructing a table presenting the actual estimated relative risk in percentage relative to the 10 thto 90 th percentile (or 25 th to 75 th percentile) range of the PM measurements.The CD needs, in multiple places, to offer an admonishment that the quantitativestatement of effects estimators, while useful for comparing and interpreting data, should not beused to make "body count" estimates or predictions for any city or region and certainly not forthe U.S.CHAPTER 6 - EPIDEMIOLOGY – GENERAL COMMENTSIn general, this chapter provides a comprehensive survey of the epidemiological studiesthat have analyzed for PM associated health effects. However, the chapter can and should beimproved to provide a more balanced presentation of the current information available on thehuman health effects of PM.The chapter could be improved by development of an expanded introduction. Three keyelements of an expanded version would be sections on (a) baseline health statistics, (b) the issueof inter-city and intra-city (temporal) variations in air quality and (c) analytical methods andstatistical considerations. All three of these issues become critical to the conduct andinterpretation of epidemiological studies. The baseline health statistics data are covered in acursory manner in Chapter 9. That information should be presented at the beginning of Chapter6 in an expanded format. To help the reader appreciate inter-city variability in health, adistribution histogram might be developed of the cardiovascular and respiratory death rates forthe 88 cities in the NMMAP study. It would be preferable to show the rates for cardiovascularand respiratory deaths separately, rather than combining them as done in Table 6A. To illustrateintra-city temporal trends, the figure from Kelsall et al (1997) showing mortality data (1974-1988) for Philadelphia should be included.For air quality data, distribution histograms could be developed for PM 10 from theNMMAP study data to illustrate inter-city variability. The intra-city (temporal) trends could beA - 57
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
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Review of the Air Quality Criteria Document for Particulate Matter

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