Review of the Air Quality Criteria Document for Particulate Matter

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Wexler, A.S., Lurmann, F.W. and Seinfeld, J.H. Modeling urban and regional aerosols: I. Modeldevelopment. Atmos. Environ., 28, 531-546, 1994.Chapter 5 - General:1. The chapter on exposures is a vast improvement over the previous version.2. The chapter provides a reasonable summary of all recent studies on exposure, andinterpretative analyses of previous work.3. Unfortunately in the attempt to be current, the authors have forgotten to put some majorconcepts and results into a historical context. Some of the recent studies look as if they arepresenting the first set of results on a particular issue. They clearly build upon previousresearch. This should be acknowledged by referring to previous criteria document (AQCD,1996) for further information on specific concepts.4. There is still an over-emphasis on correlations. I have stated before, an “association(correlation) makes the poison” is not a valid concept. Every particle that deposits in the lungbecomes part of a dose delivered to the individual. Although the variability is very relevant toresults obtained in many epidemiological studies that support PM health effects, no one has yetshown that a constant or “quasi-constant” baseline level of PM from indoor or personal sourcesis irrelevant in causing health effects. This point is mentioned in the integration chapter (9), butnot in chapter 5. The variable portion may provide the final stress to individuals who has hadsustained contact and deposition of particles from all sources. So, both E ag and E ig may havepartial influence on the ultimate dose affecting an individual at risk for one or more diseaseendpoints, especially potential acute effects.5. The chapter needs another E descriptor, E ov-rxn-iv or E (ioRn) . This is PM exposure derived fromoutdoor vapor (ov) reacting (rxn) with indoor vapors (iv). This is a source that could also varywith outdoor PM when the (ov) is ozone.6. The range and distribution of many variables that affect PM penetration and deposition arenicely presented in the discussion. However, these are never integrated and placed into a finalcontext for the uncertainties about the conclusions. The entire discussion is still attempting tosteer us to a mean value for exposure used in epidemiological studies, a point that is wellestablished. Unfortunately, the current approach ignores the distributional aspects of exposure tooutdoor and other sources. It precludes further efforts in the staff paper to mention theuncertainties about the dose of specific agents or the entire mixture of PM from indoor andoutdoor air, which could be relevant to acute or chronic outcomes. It precludes any discussion inthe staff paper on the variety of exposures and sources, which may cause health effects. I do notbelieve the major ion contributing to the mean PM (e.g., SO 4-2) is necessarily the chemical ofconcern. It may be an indicator, but we still need to define what it is an indicator of -- ambientPM 2.5 mass or toxic sub-fractions.7. Last conclusion is a working hypothesis, but it is not the sole reason for understandingexposure. We need to eventually determine which dose or doses contribute to acute or chroniceffects. The statement needs to be modified accordingly.Detailed Comments:P. 5.6, Table 5.1 Very good summary.P. 5.7, Line 6 We have no definitive “outer limit” it is still a guess, and/or convenientlocation on the person. It is usually found somewhere within the personalenvelop for inhalation.P. 5.8, Line 21 Integral referenced to, NRC 1991. It was published previously by Lioy,A - 37
1990. Reference Lioy, P.J. “The Analysis of Total Human Exposure forExposure Assessment: Multi-Discipline Science for Examining HumanContact with Contaminants“ Environmental Science & Technology, 24,938-945, 1990.P. 5.11 Good summary of published activity pattern data.P. 5.13 to 5.14, 5.3.2.2.2 Very simple explanation of mass balance model. Authors need toremind readers that all variables have ranges, and in some casesmay change in value by a factor of 5 to 10. Therefore, sensitivityand uncertainty analysis are necessary when attempting to explainresults.5.3.2.3 The equation is a linear simplification of exposure and ignores possiblesynergisms. The authors need to provide qualifiers here!5.3.2.3.1 Need to state that equilibrium is a simplification of indoor systems that areoccupied by residents. Thus, equilibrium may only represent a “virtual”set of individuals or populations at potential risk. The alpha in Equation5-9 can, and will, vary based upon lifestyle, meteorology, etc.Also, need qualifiers because of personal activities, housingcharacteristics, and particle size and composition.P. 5.19 Very good introduction, and Table 5.4 is well done. There are others, butmost are still work in progress (e.g., RIOPA study by Weisel et al; COPDby Koutrakis, et al.). Table 5.5 good summary table.P. 5.30 Mage – Qualify to “average person” in PTEAM.P. 5.31 to 5.35 The net result is that there are many different types of correlations and youcan get many different results. Conclusion, we still need and more workon which variable(s) is (are) needed to represent personal ambientexposure. This is essential for assessing which compounds and whichexposures cause the observed effects.P. 5.37, Lines 9-10 A low correlation doesn’t mean much, r 2 < 0.05!P. 5.39, Lines 29-30 Is “tracked” the right term? This only explains 25% of variability.P. 5.41 Subjects in Baltimore were very sedentary!! Could these individuals bedescribed as stationary personal monitors?P. 5.41 Sulfate is an indicator of ammonium sulfate, and not even the dominantacid species (sulfuric acid, ammonia bisulfate). In areas where there arelarge organic, or nitrate loadings, the SO 4-2ion may not be an indicator ofthose portions of the mass. I think SO 4-2is an indicator of the variabilityof aged secondary aerosol in the fine fraction.P. 5.41, Lines 26-27 Confusing. SO 4-2is a strong indicator of neutralized sulfur particulateexposure, where there are no indoor sources. In contrast, PM 2.5 has manysources besides SO 4-2.P. 5.43, Lines 6-8 Is this the appropriate way to interpret these data?A - 38
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