Review of the Air Quality Criteria Document for Particulate Matter

substantial uncertainty in the organic carbon measurements. I do not remember whether thisissue was addressed in this chapter. If not, this is an important topic that should be discussedextensively. These inherent organic carbon measurement uncertainties may make it moredifficult to reach particle mass closure.This chapter would be better if the discussion about carbon was a little more concise. Incontrast, the discussion on the elemental analysis, pages 77-80 is only rudimentary. If theauthors do not want to give many details about the methods, this is fine, but at least they shoulddiscuss the advantages and shortcomings of these methods. A more critical discussion isappropriate because elemental tracers are of paramount importance to source apportionmentstudies. The problem (which is good news from the health effects perspective) is that traceelement concentrations have decreased and XRF may not be the most adequate method, althoughis the most practical one. Reading this section one cannot find a take-home message about thestate-of-science in this area.Below are some minor specific comments:Section 2.2.1.5; It may be worthwhile to report some results from the compliance network. Iknow OAQPS has results from the FRM audits. I think it is important to mention somethingabout the precision of the FRM sampler under real ambient conditions as operated throughoutthe country by different states.Page 2-64, lines 7-8; I am not sure if this statement is correct.Page 2-73, line 10; Particle/particle interactions also are very important. For example, thereaction between ammonium nitrate and sulfuric acid or other acid sulfate particles can result inthe formation of nitric acid vapor that can be lost from the filter. Of course, it is notthermodynamically possible that ammonium nitrate coexists with acid sulfates in theatmosphere. However, during the collection of a multi-hour sample, e.g. 24 hours, thesecompounds can be present in the atmosphere at different times and thus can be collected on thesame collection mediumSection 2.2.5; There was in inter-comparison study of continuous methods supported by CARBin Bakersfield. Some of the findings from this study should be presented here, since this is oneof the most comprehensive continuous particle methods inter-comparison studies.Page 2-91, line 22-until the end of the sections; Too many details are presented here and I do notunderstand the point being made.Page 2-94; A section on continuous sulfate measurements should be included. Discuss the oldFID method and the new Fluorescence method which will be used by most of the supersites (byAllen et al, Harvard University).Page 2-97; The discussions on data quality is very superficial and incomplete. I suggest to fix itor drop it.Page 2-102, lines 24-26; Need to eliminate. The authors have been made a big deal of thisthroughout the chapter.Page 2-105, lines 4-5; This sentence does not mean anything, therefore I suggest to eliminate it.Chapter 3: Concentration, Sources, and Emissions of Atmospheric Particulate MatterThe revised chapter has been considerably improved. The authors considered most of ourprevious comments. They have used more recent information and have expanded the scope ofA - 53