Review of the Air Quality Criteria Document for Particulate Matter

Chapter 5: Human Exposure to Particulate and its Constituents IntroductionThis chapter has now been substantially improved and the authors should be commended fortheir efforts. A comprehensive review of the most recent exposure studies has been included inthis chapter. My remaining criticism for this chapter is that although it presented a verycomprehensive review of personal and indoor particle studies, it failed to critically synthesizethis information. What are the most important conclusions that this chapter should highlight? Inmy opinion the following points need to be clearly made:a) Personal exposures are associated with both indoor as well as outdoor sources; b) the personalexposure/outdoor concentration ratios present substantial intra- and inter-personal variability; c)Although we originally thought that this variability was mainly due to the presence of personaland micro-environmental sources, the results from recent exposure studies suggest that it is thevarying impact of the outdoor particles on indoor environments that is mainly responsible for theobserved intra- and inter- variability in personal exposure/outdoor concentration ratios and; d) Itappears that home characteristics may be the most important factor that affects the relationshipbetween the average population exposures and ambient concentrations. Air exchange rate seemsto be an important home characteristic surrogate that can explain a large fraction of the observedinter- and intra-personal variability.These findings explain why longitudinal studies (many repeated measurements per person)provide stronger correlations between personal exposure and outdoor concentrations than crosssectionalstudies (few repeated measurements per individual). Since home characteristics is themost important factor affecting personal exposures then one would expect that correlationsbetween average population exposures and outdoor concentrations will vary by season andgeography. To test this hypothesis, Janssen et al. 2001 (Environmental Health Perspectives, inpress) examined the relationship between Hospital admissions (for cardiovascular andrespiratory diseases) in a large number of US cities (NMMAPS study) and found that central airconditioning use explains a large fraction of the variability among cities.Also one important issue that should be stressed in this chapter is that multi-pollutant personalexposure studies have suggested that ambient concentrations of gaseous co-pollutants aresurrogates of personal exposures to particles rather than confounders (Sarnat et al. 2001,Environmental Health Perspectives, in press).However, because the authors have provided a reasonable and objective interpretation of thefindings of the existing exposure studies, it will not be difficult to fix this chapter. This can beeasily done by revising the summary section and by providing some critical discussionsthroughout the chapter.Throughout the chapter the authors discuss the distinction between outdoor and indoor sources.Although I agree with their approach and that this should be presented, I disagree with theirdecision to make this the central issue of the chapter. I think there is some exaggeration here.Finally, the discussion on the exposure error is an important one, but I think it needs to beconcise and straightforward. Many people do not have the background to understand thisdiscussion which is very important.Specific minor comments:Page 5-2, lines 1 and 14-15; need editing.Page 5-14, line 5; P and k are also function of home characteristics, not only particle size and airexchange rate. Same comment for Fint, see page 5-16, line 4.A - 55