Review of the Air Quality Criteria Document for Particulate Matter

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