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month aggregation proposed in the staff paper. Thus the staff recommendations to use only 12 daylight hours and only three summer months will tend to miss ozone effects during biologically important times of day and months of growing season in many sections of the country. The AOT60 for the Look Rock, TN site for 2001-2003 (calculated using all hours of day and aggregated over the period April 1 through October 30) from McLaughlin et al., 2007a,b are presented below in Table l along with my calculations of the 12-hr W 126 aggregated over the maximum three contiguous sununer months in each year (which is the way I'm guessing staff intends this metric to be calculated), Additional rows show the effect on the W 126 of considering a longer 5-month growing season., or of considering ozone for 24 hours a day. If either longer growing seasons or more hours per day were considered, the seasonal W 126 exposure could increase from 50% to 100% at this remote, southern, high elevation forest site. Table 1. Seasonal Ozone Metrics for Look Rock, TN, 2001-2003 2001 2002 2003 AOT60, 24 hr, 7 month N1cLau hlin et al., 2007a,b 11.5 m h 24.0 m h 11.7 m h W 126, 12-hr, 3 max Conti uous summer months 20.0 m h 36.9 m h 17.9 m h W126, 12-hr, 5 month 4/15-9/15 rowin season 29.9 m h 50.5 m h 28.3 m h W 126, 24-hr, 3 max Conti uous summer months 37.9 m h 69.2 m h 35.0 m h Note that the average 12-hr, 3-month W 126 for the yeazs 2001 & 2003 was about 19 ppm h. This is 10% lower than the level (21 ppm h) that staff had recommended as an upper bound for a seasonal W 126 secondary standard. But McLaughlin et al. (2007a) estimate forest growth reductions of 33% for the 2001 & 2003 ozone seasons (compazed to "control" conditions of no exposures > 60 ppb). So the staff-recommended upper range for a secondary standard (which has already been rejected in 1997 for not being sufficiently more protective than 0.084 primary standard) would allow more than a 33% reduction in tree growth (and associated reductions in soil moisture and stream flow). Note also that the higher ozone year of 2002, for which an additiona148% growth reduction is estimated, had a 3-month W 126 (or 7-month AOT60) that was about 50% higher than the 3-yeaz 2001-2003 average. Thus':if multi-year averaging is employed to promote a more "stable" standard (as opposed to more stable ecological health), the level of the standazd should be reduced by at least 1/3 to assure that the intended threshold is not exceeded in individual years. As indicated in pre-meeting comments below: staff recommendations for a seasonal cumulative W 126 secondary standard faze well justified, and the lower end of the proposed range (7.5 ppm h) is appropriate. The upper :end of the proposed range (21 ppm h) is not protective and should be lowered. Consideration s}iould also be given to inclusion of more hours/day and longer growing seasons, with a lazge downwazd adjustment to the level if multi-yeaz averaging is used. References McLaughlin, S. B., M. Nosal, S. D. VJullschleger and G. Sun (2007a) Interactive effects of ozone and climate on tree growth and water use in a southern Appalachian forest in the USA, New Phyiologist 174: 109-124. httu://www.blackwell-svnerav.com/doi/odi%10.llll/i.1469-8137.2007.02018.x .._ ~ f~.. C-23