Modeling Approach
The objective of this study is to determine the potential for actions at the local governmental level in the Shenandoah Valley to improve its air quality. We use a state-of-the-art, three-dimensional chemical transport model known as the Community Multiscale Air Quality model (CMAQ) version 4.6 over the southeastern US to determine the sensitivity of predicted pollutant concentrations to changes in emissions. We obtained model inputs--emissions, meteorology, initial conditions, and boundary conditions--from the Visbility Improvement State and Tribal Association of the Southeast (VISTAS) regional planning organization. Based on climatological analysis by the University of Virginia, we selected five week-long modeling periods, intended to be representative of the year's meteorology. We installed and ran the model on Virginia Tech's supercomputer System X.
First, we must distinguish between air pollution generated from local emissions versus air pollution coming from regions outside the Shenandoah Valley. In the first scenario we set all anthropogenic emissions within the valley to zero and will model predicted concentrations stemming from regionally transported pollution. Then, we quantify the sensitivity of O3 and PM to locally implemented air quality management strategies, such as idle reduction rules, school bus retrofitting, and public awareness campaigns. In collaboration with SHENAIR participants, we develop alternative emissions inventories that account for such changes and test the air quality model with them. We also consider policies whose main goal is to reduce emissions of greenhouse gases and whose secondary effects may include improvements in air quality. Based on these results, the local governments can gauge the impact of air management policies they might implement. The scenarios are listed in the table below.
| Name | Description |
|---|---|
| Base case | Best estimate of actual conditions in 2002, the most recent year for which all input data are available. |
| Zero case | All anthropogenic (man-made) emissions in the Shenadoah Valley have been "turned off," or set to zero. Emissions from biogenic sources, i.e. trees and crops, remain. |
| Local government reductions case (LRC) | Emissions within the valley are adjusted assuming that 9 strategies to reduce air pollution have been implemented. |
| Greenhouse gas reductions case (GHG) | Emissions within the valley are adjusted assuming that 10 strategies to reduce emissions of greenhouse gases have been implemented. |
By comparing results from each of the last three cases to the base case, i.e. by subtracting the base case predicted concentrations from those in each of the other scenarios, we can assess what the influence of each case might be.