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Ann Arbor Science/Butterworth Publishers: Woburn, MA, 1984; pp 353-370. Mazurek, M. A. Ph.D. Thesis, University of California, Los Angeles, 1985. Cox, R. E.; Mazurek, M. A.; Simoneit, B. R. T. Nature 1982, 296,848-849. Mazurek. M. A.: Cass. G. R.: Simoneit. B. R. T. Aerosol Sci. -- -~ ---, Technol. 1989,'10, 408-420. U S . Environmental Protection Agency. Fed. Regist. 1971, 36(247), 24888-24890. U S . Environmental Protection Agency. Code of Federal Regulations, Title 40-Protection of Environment, Part 60; Superintendent of Documents: Washington, DC, 1984; pp 436-455. House of Representatives, Committee on Energy and Commerce, Subcommittee on Health and the Environment. Comprehensive Smoking Prevention Education Act.
Hearings, March 5 , l l and 12,1982; Serial No. 97-10f3, pp 421-438. (37) Simoneit, B. R. T.; Chester, R.; Eglinton, G. Nature 1977, 267, 682-685. (38) Simoneit, B. R. T.; Mazurek, M. A. CRC Crit. Rev. Environ. Control 1981, 219-276.
Received for review August 17,1990. Revised manuscript received February 15, 1991. Accepted March 4, 1991. Portions of this paper were presented at the 1989 AAAR Conference in Reno, N V . This work was supported by EPA Grant R-813277-01-0, and by gifts to the Environmental Quality Laboratory. This paper has not been subject to the EPAB peer and policy review, and hence does not necessarily reflect the views of the EPA. Mention of trade names or commercial products does not constitute E P A endorsement or recommendation for use.
Co-Occurrence of Ozone and Acidic Cloudwater in High-Elevation Forests Rlchard J. Vong"%t and Peier Guttorpt Department of Atmospheric Sciences, Oregon State University, Cowallis, Oregon 9 7 3 3 1 and Department of Statistics, University of Washington, GN-22, Seattle, Washington 98 195
A chemical climatology for high-elevation forests was estimated from Ozone and cloudwater acidity d a h collected in the eastern United States. Besides frequent ozone-only and PH-On1y single-pollutant episodes, both simulheous and sequential co-occurrence of ozone and acidic cloudwater were observed a few times each month above cloud base. Co-occurrence was observed more frequently at two southern sites than at two northern sites. This co-occurrente represents a multiple chemical stress whose biological implications can now for the first time be studied in controlled exposures of trees.
Introduction The rates of mortality for red spruce in high-elevation forests of the northeastern United States have increased over the last 30 years (1-3). Although the causes of this decline are still under investigation, ozone and cloudwater acidity are thought to affect spruce adversely and are candidates for causation ( 4 ) . Mechanisms for acid damage to trees include both effects on soil solution chemistry (5) and direct effects on foliage (6-9). Controlled acid exposure studies conducted on conifers usually involve spraying seedlings in open-top chambers with constant pH mists, although one study varied the pH of the mist (10, 11). These controlled exposures have produced somewhat inconsistent results (12). In general, acid mist did not injure red spruce at pH > 3.5 but resulted in some type of visible injury or functional alteration from mists with pH I3.0. Few data exist for mists with pH values between 3.0 and 3.5. Ozone has been shown to injure crops (13)and to affect some tree species (14-1 7). Controlled exposures typically use square-wave patterns for ozone (no peaks); a few recent studies used more realistic exposure scenarios (18). Ozone and acidic cloudwater represent chemical stresses for high-elevation forests that are already subjected to natural competition, biotic stresses, and climate extremes ( 4 ) . Although a single co-occurrence event was observed in Maine (19),t,he dynamics of ozone and acidic cloudwater 'Oregon State University. *University of Washington.
exposures and their co-occurrence have not been identified previously. ~~~~~i~~ that an insultlrepair cycle is involved in pollutant injury to trees(2&22), the temporal characteristics of the ambient exposure regime are importantfor determining the degree of imposed stress. Despite a lack of clearcut laboratory evidence of ozone or acid injury to red spruce, visible decline symptoms are observed a t high elevation in the Appalachian Mountains (3). The exclusion of ambient cloudwater and ozone from mature red spruce reduced these symptoms in one study (A. H. Johnson, personal communication). Therefore, we have asked how the ambient exposure of forests to ozone and acidity differs from controlled exposures.
Experimental Section Ambient ozone and cloudwater were collected over the 1986-1988 growing seasons (April-October) at five sites in the Appalachian Mountains: Whiteface, NY (44'23' N, 73'5' W, 1483-m elevation), Moosilauke, NH (40'1' N, 71'50' W, 1000 m), Shenandoah, VA (37'72' N, 78'20' W, 1000 m), Whitetop, VA (36'39' N, 81'36' W, 1686 m), and Mitchell, NC (35'44' N, 82'17' W, 2006 m). The gases ozone [UV photometric technique (23)1, SO2 [UV fluorescence technique ( 2 4 ) ] ,and H202 [reaction with p-hydroxyphenylacetic acid (25)] were measured (Table I). Cloudwater was collected with a passive string collector (26) and analyzed for solution pH (electrometric technique), aqueous SO:-, and NO< (ion chromatograph). Following quality assurance procedures ensured a t least f15% accuracy and precision (27). Data Analysis Methodology Atmospheric pollution episodes were classified as one of five types (Figure 1)by comparing hourly ambient data to [ozone] I70 ppbv and pH I 3.2, cutoff levels that are stringent enough to be potentially damaging to trees, while accepting enough data for characterization of distributions. We assumed that the movement between the pollution episodes is stochastic so that, given the pollution history up to the present, the conditional probability of going to any other episode depends only on the current episode type (except respites between episodes, which depend on the current and previous episode type). Furthermore, we as-
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Table I Chemical Climate a t High Elevation in the Appalachian Mountains d u r i n g the Growing Seasons of 1986-1988 in Terms of the Mean Concentrations of Os(&, H202(g), and SO&) and Mean Cloudwater S04"(aq), pH, and NO
