Project at a Glance

Title: Evaluation of ozone and HNO3 vapor distribution and ozone effects on conifer forests in the Lake Tahoe Basin and eastern Sierra Nevada.

Principal Investigator / Author(s): Bytnerowicz, Andrzej; Arbaugh, Michael; Padgett, Pamela

Contractor: USDA Forest Service

Contract Number: 01-334

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts, Impacts, Lake Tahoe Study


Two-week average concentrations of ambient ozone (O3), nitric acid vapor (HNO3), and ammonia (NH3) were measured during the 2002 smog season in selected areas of the Sierra Nevada, California (i.e., Lake Tahoe Basin, San Joaquin River Drainage, portions of the eastern and southern Sierra Nevada). In the Lake Tahoe area, local generation of photochemical smog appears to be the main cause of increased O3 and HNO3 concentrations within the Basin. High O3 concentrations were present along the San Joaquin River Drainage and southern Sierra Nevada throughout the summer. Ozone levels were also elevated in the eastern Sierra Nevada, although they were lower than in the San Joaquin River Drainage. The transport of nitrogen oxides, carbon monoxide, and volatile organic compound emissions generated by the McNalley fire, is postulated to have contributed to the very high O3 concentrations that occurred in August. In the San Joaquin River Drainage, ambient concentrations of HNO3 and NH3 were highest near the San Joaquin Valley and decreased gradually toward the east. In addition, an evaluation of O3 injury symptoms was conducted on ponderosa pines in the Lake Tahoe Basin and along the San Joaquin River Drainage. At 25-sites in the Lake Tahoe Basin, 23 percent of the trees evaluated had symptoms of foliar O3 injury, but only slight injury to the pines occurred in this area. Ozone injury was, on average, only slight along the San Joaquin River Drainage.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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