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Mr. Rich Poirot Post-meeting comments on Chapters 7 & 8 of the January, 2007 OAQPS Ozone Staff Paper R. Poirot, VT DEC, March 19, 2007 My written comments prepared prior to the 3/5/07 Ozone Review Panel Teleconference on EPA's Final Ozone Staff Paper are pasted below. More recently, two important new papers by Sandy McLaughlin and others on environmental effects of ozone were published in the latest issue (Apri12007) of New Phytologist. Clearly EPA staff can't continually revise completed Criteria Documents and Staff Papers as each new publication appears in the literature, but I would like to especially recommend these papers for staff consideration as they work with the Administrator to develop final proposals on revised (primary and) secondary standards for ozone. I`ll also try to use some of these recent results to illustrate and emphasize several points raised in eazlier CASAC ozone panel comments on the Staff Paper. The first of these papers (McLaughlin et al., 2007a) shows current (2001-03) ozone levels causing 30 to 50% reductions in tree growth in mature trees in the southern Appalachian forests, while the second (McLaughlin et al., 2007b) shows how ozone induced reductions in the efficiency of water use by mature forest trees can lead to substantial reductions in soil moisture content (causing further indirect stress effects on under-story vegetation) and ultimately leading to reduced stream flow, especially under late season drought conditions, which are otherwise projected to become more common and/or severe in the future. This is the first demonstration Pve seen that ozone effects on terrestrial ecosystems can lead directly to additional adverse effects on aquatic ecosystems. Thus the environmental effects of ozone at current levels of exposure are more intensive and extensive than we a~td staff had previously considered. Ozone utduced reductions in tree growth were noted in 9 of 10 tree species evaluated, with estimated seasonal growth reductions in the southern Appalachian study region of33% during average ozone years (2001 and 2003), with further growth reductions of an additional 48% in a bad ozone year (2002) iit that region. These large growth reductions were attributed not only to alterations in photosynthetic rates and carbon allocation but also to increased levels of water stress. The less efficient water usage by mature forest trees is attributed to reduced stomata( control, leading to increased water loss and increased ozone uptake, through increases in both daytime and nighttime stomata( conductance. Thus ozone exposures are increasingly relevant over more horns per day; ozone damage at one point in time predisposes trees to additional damage later in the growing season; and the effects on mature trees, as well as reductions in water availability for other components of forested terrestrial and aquatic ecosystems, are compounded over the entire growing season. This evidence of increasing cumulative seasonal damage clearly illustrates why the current, short-tens secondary standard needs to be revised to reflect longer-term seasonal effects. It can be noted that the cumulative ozone exposure metric employed in these studies, AOT60 (sum over the growing season of ozone in excess of 60 ppb), is similar to and well correlated with both the seasonal SUM06 attd W 126. However, the researchers in this case calculated their indices using alt 24 hours of the day and over substantially longer growing seasons than the 12-hr, 3- G .. ~ 1 C-22