Quantitative Uncertainty Of Chemical Plume Transport In Low Wind Speeds Using Measured Field Data And Stochastic Modeling PDF Download

The Field Research Division of the Air Resources Laboratory of the National Oceanic and Atmospheric Administration, in collaboration with the Laboratory for Atmospheric Research at Washington State University, conducted a series of tracer field experiments at the Idaho National Laboratory. The emphasis of these tracer experiments was plume dispersion in low wind speed conditions. Four tests were conducted during the daytime in unstable conditions in July and August of 2016. Four additional tests were conducted in October at nighttime in the very stable boundary layer. The field study was designated Project Sagebrush Phase 2 (PSB2), the second in a series that began with PSB1 in October, 2013. Each experimental period consisted of a continuous 2.5 h SF6 point source tracer release from 1.5 m agl with consecutive 10 min average bag sampling over the last 2 h of the tracer release period. Sampling resources were limited. The main motivation was to provide good resolution of the plume at a minimum of three downwind distances and allow for some vertical sampling when possible. Bag sampling was done across 210o of arc at 100, 200, and 400 m downwind at 6o spacing. The daytime tests also included sampling along 90o of arc at 800 m and one mobile tower up to 25 m agl. The nighttime tests did not use the 800 m arc but deployed samplers on the mobile tower as well as four additional fixed towers. The bag sampling was complemented by four fast response tracer analyzers and an extensive suite of meteorological measurements of wind, turbulence, and temperature in the horizontal and vertical. This PSB2 study provides a dataset with a unique combination of higher resolution (10 min) time-averaged bag sampling, fast response tracer sampling, and extensive meteorological measurements for examining plume dispersion in low wind conditions in an open terrain setting. This is particularly the case for analyzing plume structure and dispersion in the very stable boundary layer. Wind directions were such that not all of the eight tests (Intensive Observation Periods) were successful due to the 210o arc limitation. Daytime IOPs 1 and 2 and nighttime IOPs 5 and 7 were largely successful with relatively minimal plume truncation (edge effects) with respect to the sampling arcs. These should provide good cases for testing plume models and IOPs 5 and 7 are particularly interesting for what they indicate about horizontal dispersion in the very stable boundary layer. IOPs 3 and 8 were more qualified successes. IOPs 4 and 6 had severe edge effects although some useful data can probably be gleaned from them. A key result from PSB2 regards the uncertainty in tracer measurements. It was found that measurement uncertainty related to plume stochastic factors increases with decreasing downwind distance from the source and is about twice as large in the very stable boundary layer as it is during the daytime. This result has implications on how to account for uncertainties in mean concentration and the probability distribution of concentration in plume dispersion models. [doi:10.7289/V5/TM-OAR-ARL-275 (https://doi.org/10.7289/V5/TM-OAR-ARL-275)]