Variability in Daytime Stability Class Designation Under Partly Foggy Conditions in a Monitoring Study
Abstract
A monitoring study conducted in August of 2004 along the Northern California coast (Wofford et al. 2005) provided an opportunity to compare two different methods for determining daytime stability classes for modeling. The ‘conventional’ method utilized field notes to determine foggy periods and assigned these hours D stability. The remaining daytime hours were assigned Pasquill-Gifford stabilities in accordance with procedures that rely on estimating the sun angle and satisfying the requirement of no more than one stability class change per hour (Johnson et al. 1999). The ‘solar radiation’ method utilized solar radiation measurements and wind speed to determine daytime hour stability (U.S. EPA 2000). Both the conventional and solar radiation methods gave similar results. The differences in stability class were well within U.S. EPA guidelines. The resulting differences in flux calculations over daytime flux intervals averaged 9.3 percent (± 11.1 standard deviation).