Investigating Meteorological Impacts on Ozone Levels in the Lake Tahoe Basin

Ozone levels in the Lake Tahoe Basin are close to violating federal and California air quality standards and are trending upward. Previous studies have indicated that local generation of ozone in the basin is likely to be more important than the long-range transport from out-of-basin sources. However, until recently very little was known about the Lake Tahoe Basin's spatial and temporal distribution of ozone, as well as how the large scale or local effects of meteorology impact this distribution.

In order to develop a better understanding of the factors affecting ozone levels in the basin, a comprehensive field study was performed in the summer of 2010. The study characterized the spatial and temporal distribution of ozone concentrations using passive samplers (34 sites) and continuous analyzers (10 sites) in and around the basin. In addition to the air quality measurements, meteorological data was obtained through the National Weather Service's National Centers for environmental Prediction (NCEP) and NOAA's Air Resources Laboratory (ARL). Archived wind data for the summer was collected at three hour increments from the North American Mesoscale (NAM) 12 km meteorological model from the ARL. Along with using North American Regional Reanalysis data, synoptic meteorological regimes (which categorize periods of high and low pressure systems) were developed to classify the periods of high and low ozone concentrations. Transport was also assessed using the Hysplit trajectory model. Preliminary analysis of this data indicates that these large-scale regimes have little impact on the observed ozone concentrations and the distribution of ozone in and around the basin, further supporting the conclusion that the ozone air quality issues in the Tahoe Basin are primarily due to local sources.