The purpose of the Sierra Cooperative Ozone Impact Assessment Study (SCOIAS) is to document the degree to which sensitive pine species in Sierran forests are exposed to ozone and the amount of injury the exposed trees exhibit. The major cooperators are the U.S. Forest Service (USFS), the California Air Resources Board (ARB) and the University of California, Davis (UCD). This document reports progress made by the UCD cooperators during the third year of the project (June 7, 1992 to October 30, 1993). The major tasks performed were the following: the continued operation of the six sites established in the previous years' efforts, tree water potential measurements, and data quality control, analysis and archiving. The six stations are Mountain Home within the Sequoia, Shaver Lake and Jerseydale in the Sierra, Five-Mile Learning Center in the Stanislaus, Sly Park Learning Center in the Eldorado and White Cloud in the Tahoe National Forests. The ozone monitoring season is the warm part of the year, from about April 15 to October 15, although actual station operating dates depend on accessibility in the spring. At all but one site, the targeted 80% data coverage was attained or exceeded during 1992. At one site, a combination of computer system problems and ozone monitor and temperature sensor malfunctions caused data voids totaling almost 35% of the operational period. However, valid ozone data is available for about 80% of the season at this station. These problems appear to have been solved by mid-season. At three of the sites, data coverage was better than 99%. Measured ozone concentrations were typically highest in the afternoon hours, and tend to increase toward the southern end of the network. Stations located on well defined steep slopes show a very strong diurnal variation in ozone concentration and meteorological conditions. Hourly peak ozone concentrations from June through September were greater than 60 ppbv at all sites nearly every day, in excess of 80 ppbv at most sites more than half the days and in excess of 100 ppbv at least a few days a month at all sites and nearly half the days at the most impacted sites (Mountain Home and Shaver Lake). At several sites, ozone concentrations were frequently high several hours after sunset. At White Cloud, the highest concentrations occurred between 10:00 p.m. and midnight.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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