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McLaughlin, S. B., S. D. Wullschleger, G. Sun and M. Nosal (20076) Interactive effects of ozone and climate on water use, soil moisture content and streamflow in a southern Appalachian forest in the USA, New Phytolagist 174: 125--136. http:!! www.blackwel l-synerey.com/doi/pdfi l 0- I ] 11!j.1469-8137 ?007.0 1970.x Pre-meeting comments on Chapters 7 & 8 of the January, 2007 OAQPS Ozone Staff Paper R. Poirot, VT DEC, March 2, 2007 In the July 06 Second Drafr Ozone Staff Paper, staff had proposed a secondary standard that differed substantially from the primary standard in averaging time, level and form. They recommended a seasonal index - SUM06 or W 126 -limited to the 12 "daylight hours" accumulated over the three-month summer "growing season", within a range of 15 to 25 ppm-hrs for the SUM06, or a "comparable" range for the W 126 metric (although there was some uncertainty in the calculation of an "equivalent W 126", since some of the W 126 values in that staffpaper had been incorrectly calculated). CASAC review comments (10/24/06) strongly supported the staff recommendations for a seasonal secondary standard that should be accumulated over at least the 12 daylight hours and at least the 3 maximum summer months. CASAC recommended that the range for a SUM06 indicator be lowered from the proposed I S to 25 ppm-hrs to a more protective range of 10 to 20 ppm-hrs, and also advised that the W 126, with no lower threshold, was conceptually preferable to the SUM06, and that a W 126 range that was approximately equivalent to this SUM06 range would be preferable. The current (January 07) Staff Paper revisions are directly responsive to most of the CASAC recommendations, providing an improved technical justification for a separate secondary standard, adding a more thorough analysis & discussion of uncertainties, and also in advocating the W 126 as a preferable metric to the SUM06. Staff also concurred with CASAC suggestions to reduce the lower end of the range to a W 126 of 7 ppm-hrs (estimated to be equivalent to a SUM06 at 10 ppm-hrs), but retained their original upper range of 21 ppm-hrs (a W 126 level estimated to be equivalent to a SUM06 at 25 ppm-hrs -the same level staff had proposed in the 1997 review). Overall, I think chapters 7 and 8 are much improved, although I would have preferred to see a lower, more protective upper end of the proposed range, closer to what CASAC recommended in the last review. There are still likely to be significant adverse environmental effects at a seasonal W 1261eve1 of 21 ppm-hrs, especially if the form of the standard is expressed as a 3-year average -thus allowing W 1261evels substantially greater than 21 ppm-hrs in individual years. One potential problem with the currently proposed upper end of the level is that, if combined with a revised primary standard at (or below) the upper end of the proposed range of .070 ppm 4cn highest 8-hour average, there are likely to be no locations where the secondary standard would be exceeded if the primary standard was not also exceeded (for example no points to the lower right of the intersecting 0.07 ppm 8-hr max and the 21 ppm-hrs W 126 lines in Figure 7-1 on page 7-19 of the staff paper or in Figures 7B-] or 7B-2 of the Appendices). Although it should be C-24