аЯрЁБс>ўџ 13ўџџџ0џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџьЅСY ПbjbjѓWѓW ‘=‘=х0џџџџџџ]||||ЬЬЬ8H TЩ Жt(œœœœлллŽ       $ єsОД ЬлзлллД ||œœ;tлZ|8œЬœŽ рј||||лŽ  n ДЬŽ œh аYе@пП5р† ADMS – Atmospheric Dispersion Modelling System Notes for presentation at the US-EPA’s 7th Conference of Air Quality Modelling David J. Carruthers Washington June 2000 Slides 1-7 . A description of ADMS is given on the US-EPA website at http:/www.epa.gov/scram001/7thconf/information/adms.pdf, and at  HYPERLINK http://www.cerc.co.uk http://www.cerc.co.uk 2. Flat terrain validation (slide 8). Hanna et al compared the predictions of ISC3, ADMS and AERMOD with field data from Kincaid, Indianaolis and Lovett power plants, and from the OPTEX and Duke Forest field tests. The difference between the two tables mainly results from a change in roughness for the calculations for Duke Forest (from 0.85m to 0.05m). Note that best use of ADMS would employ variable roughness. The results show that over flat terrain ADMS and AERMOD have quite similar performance from a statistical viewpoint; both have much better performance than ISC3. 3. Power Station comparison (slide 8). Despite similar statistical performance ADMS and AERMOD can produce markedly different predictions of concentration for specific cases. 4. Building effects slides (10-12). A detailed note contrasting the ADMS buiding note with PRIME is available at  HYPERLINK http://www.cerc.co.uk http://www.cerc.co.uk. There are many similar features in the two models the main difference being in the main wake where ADMS employs a velocity field based on wall wake theory (Counihan, Hunt and Jackson (1974), J.Fluid Mech,Vol 64, p529-563), whereas PRIME uses empirically based streamline slopes. Since PRIME was developed after ADMS it is surprising that there is no reference to ADMS in the PRIME documentation. Both models have been validated against a number of (mainly different) datasets. The full reference to the data shown in the presentation is Carruthers, McKeown, Hall and Porter (1999), Validation of ADMS against wind tunnel data of dispersion from chemical warehouse fires, Atmospheric Environment vol 33, 1937-1954. 5. Complex Terrain (slides 13-17). The ADMS model is based on the FLOWSTAR model for flow over complex terrain (see e.g. Carruthers, Hunt and Weng 1988: In Computer Technique in Environmental Studies (Editor) P.Zanetti p481-472 Springer Verlag). This model is quasi-linear and has been found through validation with field and wind tunnel data to predict the flow well over slopes of up to 1/2 (upstream and 1/3 (wake), except where there is flow around the hill in very stable flow where alternative algorithms are employed. Slides 14 and 15 show terrain amplification factors for neutral flow. Slide 14 shows ‘maximum concentration’ and ‘distance to maximum’ ratios for a 50m stack. ADMS, as expected, shows elevated concentrations for upwind sources (when streamline convergence brings the plume closer to the hill surface), and for downwind sources (wake effect) . AERMOD shows a different (unphysical) behaviour with elevated concentration values for releases from near the hill summit. Slide 15 shows vertical cross- sections. In this case an approximate comparison can be made with the US-EPA wind tunnel data of Lawson, Snyder and Thompson (1989) (Atmospheric Environment vol 23, 321-331). ADMS shows a similar pattern to the data whilst AERMOD does not, again showing elevated concentrations for stacks close to the hill top. In very stable flows (slide 16), when plume impaction may occur, maximum values would be expected to occur for upstream sources – consistent with ADMS, however at variance with AERMOD, which again shows very elevated values for stacks close to the hill summit. Slide 17 shows an example of concentrations due to emissions form a cement works in complex terrain in NW England. Whereas the ADMS results are consistent with the measurements taken on site, the tendency for AERMOD to imply flow around the main hill (in the SE corner) rather than over this hill is inconsistent with observations and with estimates of flow patterns based on the Froude number, which do not suggest flow around the hills at the plume height. 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