Project at a Glance
Title: Chemistry and transport of nitrogen oxides on the western slopes of the Sierra Nevada Mountains: Implications for Lake Tahoe
Principal Investigator / Author(s): Cohen, Ronald C.
Contractor: UC Berkeley
Contract Number: 02-331
Research Program Area: Atmospheric Processes
Topic Areas: Transport
This review describes the current knowledge of the concentrations of nitrogen oxides and their transport up the western slopes of the Sierra Nevada. Most deposition of bioavailable nitrogen from the atmosphere occurs in the form of nitric acid (HNO3), ammonia (NH3), ammonium (NH4+), or nitrate (NO3-). However, many additional nitrogen-containing chemicals are found in the atmosphere and most of them are removed by deposition, although more slowly than HNO3. In relation to nitrogen deposition, the cumulative effects of transport on seasonal and annual timescales need to be considered. Short term studies can be used to identify possible transport patterns or occurrences but long term observations are required for an accurate representation of the overall contribution of transport to the deposition of N within the Tahoe Basin.
Analysis of long term ground level observations suggests that most HNO3 within the urban plume deposits prior to reaching Lake Tahoe, though organic nitrates may persist. Short-term aircraft studies attempting to identify transport pathways for pollutants have occasionally observed higher concentrations of photochemical products lofted above the mixed layer. Downwind of biomass burning episodes, elevated levels of reactive nitrogen in both the gaseous and particulate phase have been observed. If these burning events occur within five hours transit time to the Tahoe Basin, they may be capable of delivering additional nitrogen to the atmosphere above the Lake. More quantitative research is needed to understand the flow dynamics within the Tahoe Basin that would permit better characterization of vertical mixing processes and improve estimates of reactive nitrogen deposition to the lake.
For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893
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