Abstract
We present Daysmoke, an empirical-statistical plume rise and dispersion model for simulating smoke from prescribed burns. Prescribed fires are characterized by complex plume structure including multiple-core updrafts which makes modeling with simple plume models difficult. Daysmoke accounts for plume structure in a three-dimensional veering/sheering atmospheric environment, multiple-core updrafts, and detrainment of particulate matter. The number of empirical coefficients appearing in the model theory is reduced through a sensitivity analysis with the Fourier Amplitude Sensitivity Test (FAST). Daysmoke simulations for “bent-over” plumes compare closely with Briggs theory although the two-thirds law is not explicit in Daysmoke. However, the solutions for the “highly-tilted” plume characterized by weak buoyancy, low initial vertical velocity, and large initial plume diameter depart considerably from Briggs theory. Results from a study of weak plumes from prescribed burns at Fort Benning GA showed simulated ground-level PM2.5 comparing favorably with observations taken within the first eight kilometers of eleven prescribed burns. Daysmoke placed plume tops near the lower end of the range of observed plume tops for six prescribed burns. Daysmoke provides the levels and amounts of smoke injected into regional scale air quality models. Results from CMAQ with and without an adaptive grid are presented.
Highlights
The forests of the southern United States comprise one of the most productive forested areas in the UnitedStates
If the convective smoke plume is strong, most of the smoke may be ejected into the free atmosphere far above the top of the mixed layer with little or no smoke remaining to be dispersed within the mixed layer
From photogrammetric analysis of video footage of smoke plumes from burning sugar cane, reference [27] determined that a rising smoke plume could be described by a train of rising turrets of heated air that sweep out a three-dimensional volume defined by plume boundaries on expanding through entrainment of surrounding air through the sides and bottoms as they ascend (Figure 3)
Summary
The forests of the southern United States (the 13 States roughly south of the Ohio River and from Texas to the Atlantic Coast) comprise one of the most productive forested areas in the United. Six million acres (2.4 million ha) of forest and agricultural land are burned each year in the southern United States to accomplish a number of land management objectives [3]. Smoke from these burns poses a threat—either as a nuisance, visibility, or transportation hazard [4,5], and/or as a health hazard [6]. Simulate hundreds of prescribed burns daily in the southern United States, much simpler modeling approaches would be required to make available plume rise data for operational air quality models such as CMAQ [16], its adaptive grid version [20] or WRF-Chem [21] for predicting air quality and assessing pollution control strategy development, exposure, impacts of regional climate change, and etc. Results from validation studies for simulating weak plumes and applications to regional scale air quality modeling follow
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