Issue of correcting for intake air pollutants

by Todd Sherwood, USEPA (04. Febr2011)

At the 4th meeting of the DTP subgroup of WLTP, in January 2011, a position from EPA was requested regarding the issue of correcting for intake air pollutants from tailpipe emission results measured during constant volume sample (CVS) testing (please refer to WLTP-DTP-LabProcICE-020). This memorandum states the technical assessment of EPA on the issue.
While the proposal laid out in LabProcICE-020 is technically sound with respect to how to correct exhaust emissions for intake contributions, the real issue for EPA is what happens to those intake air pollutants during the combustion process and post combustion catalytic treatment. This issue is not addressed or even mentioned in LabProcICE-020. Without an in-depth research effort, we do not and cannot know. One could assume that some or all of the intake air CO and HC would be oxidized during combustion. It is not clear what would happen to intake NOx, N2O, or CO2. Note that EPA defines exhaust emissions as "substances emitted to the atmosphere from any opening downstream from the exhaust port of a motor vehicle engine." (see 40 CFR Part 86.082-2)
Therefore, EPA would not allow the procedure as proposed in LabProcICE-020 without first knowing what happens to the intake air criteria pollutants during combustion and as they pass over the 3-way catalyst (assuming that they survive the combustion process). In general, to determine what would happen to the intake air criteria pollutants, one would have to generate synthetic intake air using isotopically labeled compounds and then capture them in the exhaust for batch analysis to determine what percent is recovered. This would not be an easy task by any means.
Lastly, and perhaps most importantly, whatever happens to the intake air pollutants as they partake in the combustion process and post combustion catalytic treatment is part of EPA’s current regulatory standard (i.e., emission limit) setting process. If we were to allow a correction for pollutants in the intake air, EPA would presumably have to lower current US emissions standards/limits to maintain current levels of stringency. Such a needed effort would seem to make the issue of intake air correction moot.
I hope this information is helpful. Feel free to share it with DTP members as you see fit. Please do not hesitate to contact me with questions you might have.
Best regards,
Todd Sherwood
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Todd Sherwood
United States Environmental Protection Agency
2000 Traverwood, Ann Arbor, MI48105, USA

+1.734.214.4405
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