Evaluation of Wind Fields Used in Grand Canyon Visibility Transport Commission Analyses

Abstract

The Grand Canyon Visibility Transport Commission (GCVTC) was established by the U.S. Congress to assess the potential impacts of projected growth on atmospheric visibility at Grand Canyon National Park and to make recommendations to the U.S. Environmental Protection Agency on what measures could be taken to avoid such adverse impacts. A critical input to the assessment tool used by the commission was three-dimensional modelderived wind fields used to transport the emissions. This paper describes the evaluation of the wind fields used at various stages in the assessment. Wind fields evaluated included those obtained from the Colorado State University Regional Atmospheric Modeling System (RAMS), the National Meteorological Center's Nested Grid Model (NGM), and the National Oceanic and Atmospheric Administration's Atmospheric Transport and Dispersion (ATAD) trajectory model. The model-derived wind fields were evaluated at multiple vertical levels at several locations in the southwestern United States by determining IMPLICATIONS Model winds used for the Grand Canyon Visibility Transport Commission assessment were not in good agreement with measured winds. The poor performance of the wind field models adds significant uncertainty to the quantification of source-receptor relationships used in the GCVTC assessment. Until wind fields are improved, considerable caution must be used when considering the results of air quality models in the highly complex terrain of the southwestern United States. differences between model predicted winds and winds that were measured using radiosonde and radar wind profiler data. Model-derived winds were also evaluated by determining the percent of time that they were within acceptable differences from measured winds.All models had difficulties, generally meeting the acceptable criteria for less than 50% of the predictions. The RAMS model had a persistent bias toward southwesterly winds at the expense of other directions, especially failing to represent channeling by north-south mountain ranges in the lower levels. The NGM model exhibited a substantial bias in the summer months by extending northwesterly winds in the eastern Pacific Ocean well inland, in contrast to the observed southwesterlies at inland locations. The simpler ATAD trajectory model performed somewhat better than the other models, probably because of its use of more upper air sites. The results of the evaluation indicated that these wind fields could not be used to reliably predict source-receptor impacts on a particular day; thus, seasonally averaged impacts were used in the GCVTC assessment.

Summer time haze characteristics of the urban atmosphere of Gwangju and the rural atmosphere of Anmyon, Korea

“…Atmospheric aerosol particles affect the visibility impairment directly by both scattering and absorbing the solar radiation especially at the wavelength of visual range. Visibility monitoring studies have been carried out at natural air basins, marine backgrounds, natural parks, urban areas, and industrial complexes over the past decades (Friedlander 1977;Dzubay et al 1982;Vinzani and Lamb 1985;Mathai et al 1990;Mazurek and Cass 1991;Baik et al 1996;Tanner and Schorran 1995;Barthelmie and Pryor 1998;Tsai and Cheng 1999;Chan et al 1999;Hand et al 2000;Green et al 2000). The atmosphere is never hazefree, and the gases and particles constituting the hazeforming aerosols are emitted from the majority of human and industrial activities.…”

Directional Biases in Back Trajectories Caused by Model and Input Data

“…For example, in a tracer study at Grand Canyon National Park, the simplest back trajectory model performed slightly better than two prognostic mesoscale models. 4 Also, more sophisticated models and data are more expensive in terms of complexity, time, effort, and computer resources. If simpler models produce similar results, then their ease of use and lower cost may justify their continued use.…”

Multilinear Model for Spatial Pattern Analysis of the Measurement of Haze and Visual Effects Project

“…However, there were few sites north of this release point to examine flow in that direction. More detailed analysis of the flow patterns particularly for the summer period have been made (3,6) as well as an analysis of the ability of numerical wind models based on the existing meteorological database to model the flow. These result suggest the difficulty in using the data to provide accurate estimates of flow patterns or supporting information such as air parcel back trajectories.…”