Project at a Glance
Project Status: complete
Title: Sampling and analysis for the Lake Tahoe atmospheric deposition study.
Principal Investigator / Author(s): Chow, Judith
Contractor: Desert Research Institute
Contract Number: 01-351
Research Program Area: Atmospheric Processes
Topic Areas: Field Studies, Lake Tahoe Study, Monitoring
The Lake Tahoe Atmospheric Deposition Study (LTADS) is a multi-agency sampling effort to improve the quality of the Lake Tahoe by identifying and quantifying the sources that contribute to its decrease in clarity. Improved estimates of atmospheric deposition are needed for input into water quality models that will be used to develop Total Maximum Daily Loads required under the federal Clean Water Act.
The initial study design is described in a draft workplan for the LTADS dated June 10, 2002. To avoid problems associated with episodic sampling contributed from specific sources, the California Air Resources Board (CARB) developed a particulate monitoring program for LTADS using Two Week Samplers (TWS) and Airmetrics MiniVol samplers. TWS provide two week integrated samples of ammonia (NH3), nitric acid (HNO3), total suspended particles (TSP), PM10, and PM2.5 (particles with aerodynamic diameters less than 10 and 2.5 micrometers [µm], respectively) at “cornerstone” sites for one year. MiniVol samplers were used to collect TSP at various remote/satellite sites. Collected TSP, PM10, and PM2.5 samples were gravimetrically analyzed for total mass concentration, followed by chemical speciation.
The site locations for the TWS and MiniVol samplers are shown in Figure 1-1 and summarized in Table 1-1. A total of five sites were instrumented with the TWS samplers and twelve sites were instrumented with MiniVol samplers. The TWS site at Big Hill (BH), located southwest of the Lake Tahoe Air Basin, was selected as an indicator site of potential pollutant transport. The remaining TWS sites, Lake Forest (LF), Thunderbird Lodge (TB), South Lake Tahoe (SOLA), and South Lake Tahoe - Sandy Way (SW), were located around the lake and within the Tahoe Basin. Development of site selections and sampling logistics were described in the CARB report (California Environmental Protection Agency, 2005).
In general, SOLA was a shoreline site in South Lake Tahoe proximate to Highway 50. When off-shore winds were in effect, SOLA was substantially affected by emissions from Highway 50 and the surrounding urban regions of South Lake Tahoe. SW was an urban site situated within the urban region south of Highway 50 and roughly 200 meters away from SOLA. When the winds were on-shore, SW was affected by emissions from Highway 50, and when the winds were off-shore, SW was affected by composite emissions of urban South Lake Tahoe. LF was a shoreline site in the northwest Tahoe basin, a short distance from Tahoe City and proximate to Highway 89. When the wind was off-shore, LF was affected by highway emissions, but when the wind was on-shore, LF was affected by lake-wide emissions. Prevailing regional flow is from the southwest and tends to deliver local emissions from South Lake Tahoe across the lake toward the north and northwest. Southwest regional flow may also carry local emissions from LF east towards mid-lake and TB.
For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893
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