Measurements of Ammonia at Blodgett Forest

Ammonia is a reactive trace gas that is emitted in large quantities by animal agriculture and other sources in California, which subsequently forms aerosol particulate matter, potentially affecting visibility, climate, and human health. We performed initial measurements of NH₃ at the Blodgett Forest Research Station (BFRS) during a 3 week study in June, 2006. The site is used for ongoing air quality research and is a relatively low-background site in the foothills of the Sierra Nevada. Measured NH₃ mixing ratios were quite low (< 1 to ~ 2 ppb), contrasting with typical conditions in many parts of the Central Valley. Eddy covariance measurements showed NH₃ fluxes that scaled with measured NH₃ mixing ratio and calculated aerodynamic deposition velocity, suggesting dry deposition is a significant loss mechanism for atmospheric NH₃ at BFRS. A simple model of NH₃ transport to the site supports the hypothesis that NH₃ is transported from the Valley to BFRS, but deposits on vegetation during the summer. Further work is necessary to determine whether the results obtained in this study can be generalized to other seasons.