STATUS OF THE PROGRAM

Funding has limited the number of different exposure atmospheres to less than the 10-12 originally envisioned. Multi-concentration exposure-response studies of diesel exhaust, hardwood smoke, gasoline exhaust, and simulated “downwind” coal combustion emissions were completed – in that order. Papers in peer-reviewed journals describing the exposures and results have been published, although two papers from the coal study are still in press as of early June 2011. Citations for the papers can be found in the NERC publication list under Center News.

As described in the 2010 Annual Report (see Center News), current effort is directed toward conducting an integrated analysis of the combined results from the four studies. At present, it is anticipated that the program will conclude with the publication of those results. Two approaches are being used to summarize the results. There will be one or more papers comparing the results of the different exposures on an atmosphere (study)-by-atmosphere basis and commenting on the advantages and disadvantages of the general research strategy undertaken by NERC. There will also be two or more papers describing associations between exposure components and significant biological responses across the combined database (i.e., regardless of the source of exposure). The latter evaluation is underway using a combination of multiple additive regression trees (MART) software to rank the impacts of individual physical-chemical exposure species and classes on significant responses, followed by single regression analyses of the few top-ranked exposure variables vs. responses to test confidence that the exposure components most highly ranked by MART were indeed the most likely putative causal agents. As is true in the real world, of course, the exposure components so identified were the strongest drivers of response as present in complex mixtures; it is not assured that the responses would be duplicated by exposure to one or more of the top-ranked components in the absence of the rest of the mixtures.

It is anticipated that the NERC program could be completed as described above by the end of CY 2011, although appearance of the final papers in print may extend into 2012. A logical extension of the NERC strategy would be to conduct follow-on, limited-scope studies to validate the causality of the top-ranked components identified by MART analysis. At this time, it is not envisioned that such studies will be conducted under the NERC program per se and further funding for NERC is not being actively sought for that purpose. Related research is being, and undoubtedly will continue to be, conducted under other programs at LRRI and other laboratories. Regardless of its final results, the NERC program has served well as a stimulus to a shift of air quality health research from its historic single-pollutant, single-source focus to a more realistic multi-pollutant focus.