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Distribution of Ozone, Ozone Precursors and Gaseous Components of Atmospheric Nitrogen Deposition in the Lake Tahoe Basin

A. Bytnerowicz^1*, S. Ahuja², J. Burley³, R. Cisneros², M. Fenn¹, A. Gertler⁴, M. McDaniel⁴, L. Nanus⁵, K. Orr3, H. Preisler¹, T. Procter², C. Ross¹, D. Schweizer² and B. Zielinska⁴

In the 2010-2012 study, we will characterize ozone (O₃), precursors of O₃ formation, and gaseous pollutants that are important contributors to atmospheric nitrogen (N) deposition in the Lake Tahoe Basin (California & Nevada). We will use passive samplers for monitoring of O₃, nitric oxide (NO), nitrogen dioxide (NO₂), ammonia (NH₃), nitric acid (HNO₃) and volatile organic compounds (VOCs) on a network of 32 sites inside and outside of the Basin. Using statistical and geostatistical models we will create distribution maps of the measured compounds for the entire Basin. On a subset of 10 monitoring sites, we will also measure real-time O₃ concentrations with active UV absorption monitors to evaluate diurnal changes of the pollutant, calibrate passive O₃ samplers, and use that data for evaluation of the exceedances of O₃ air pollution standards in the Basin. At the same sites we will also measure N deposition with ion exchange resin (IER) collectors placed in forest clearings (bulk precipitation) and under tree canopies (throughfall). In these bulk and throughfall samples from the IER collectors we will measure the stable isotope composition (¹⁵N and ¹⁸O) of NO₃ and from passive sampler extracts of NH₃ (¹⁵N) to evaluate the origin of N deposition in the Basin. Results of this study will help to evaluate the present and future potential of O₃ formation as well as the biological/ecological effects of N air pollutants and the resulting N deposition in the Lake Tahoe Basin. These results will also help to develop science-based management strategies aimed at improving air quality and ecological sustainability of the Basin. Establishment of monitoring sites has been accomplished and the study is progressing according as planned. First results on air quality measurements will be presented.

¹USDA Forest Service, Pacific Southwest Research Station, Riverside, CA, , 951-680-1562;
²USDA Forest Service, Region 5, CA;
³Desert Research Institute, Reno, NV;
⁴St. Mary's College, Moraga, CA;
⁵San Francisco State University, San Francisco