Jason Ching

Using CMAQ for Exposure Modeling and Characterizing the Subgrid Variability for Exposure Estimates

Abstract Atmospheric processes and the associated transport and dispersion of atmospheric pollutants are known to be highly variable in time and space. Current air-quality models that characterize atmospheric chemistry effects, for example, the Community Multiscale Air Quality model (CMAQ), provide volume-averaged concentration values for each grid cell in the modeling domain given the stated conditions. Given the assumptions made and the limited set of processes included in any model’s implementation, there are many sources of “unresolved” subgrid variability. This raises the question of the importance of the unresolved subgrid variations on exposure assessment results if such models were to be used to assess air toxics exposure. In this study, the Hazardous Air Pollutant Exposure Model (HAPEM) is applied to estimate benzene and formaldehyde inhalation exposure using ambient annually averaged concentrations predicted by CMAQ to investigate how within-grid variability can affect exposure estimates. An urb...

Air Quality Modeling of Hazardous Pollutants: Current Status and Future Directions

Abstract The current requirements and status of air quality modeling of hazardous pollutants are reviewed. Many applications require the ability to predict the local impacts from industrial sources or large roadways as needed for community health characterization and evaluating environmental justice concerns. Such local-scale modeling assessments can be performed by using Gaussian dispersion models. However, these models have a limited ability to handle chemical transformations. A new generation of Eulerian grid-based models is now capable of comprehensively treating transport and chemical transformations of air toxics. However, they typically have coarse spatial resolution, and their computational requirements increase dramatically with finer spatial resolution. The authors present and discuss possible advanced approaches that can combine the grid-based models with local-scale information.

Development and Implementation of the EPA’s Models-3 Initial Operating Version: Community Multi-Scale Air Quality (CMAQ) Model

For the last fifteen years, the Office of Research and Development (ORD) of the U. S. Environmental Protection Agency (EPA) has been developing three-dimensional Eulerian based air quality models (AQMs) to study air quality problems, such as urban and regional tropospheric ozone and regional acid deposition. These AQMs simulate comprehensively atmospheric processes such as chemical transformations, transports, and removal of pollutants and their precursors. Model application experience with second generation air quality modeling systems has revealed several shortcomings such as slow execution speed, difficulty in implementing improved science algorithms in the model, and complexity in data exchange among system submodels. Byun et al. (1995) listed some of the shortcomings of the present AQM modeling systems in detail.

Interpretive analysis of observed and modeled mesoscale ozone photochemistry in areas with numerous point sources

Abstract The Regional Acid Deposition Model (RADM) has been applied to several of the field experiments that were part of the Acid Model Operational and Diagnostic Evaluation Study (AcidMODES) to assess the models ability to simulate photochemical production of ozone in regions dominated by point source emissions. The comparison of model simulations at different grid resolutions suggests that increased resolution improves the simulation of ozone photochemistry in such regions. Further analysis of NO x and NO x concentrations and photochemical production rates of ozone, however, show that the models response to large point source emissions is very unsystematic both spatially and temporally. This is due to the models inability to simulate realistically the small-scale (subgrid) gradients in precursor concentrations in and around large point source plumes. Because of the inherently nonlinear nature of ozone photochemistry with respect to concentrations of NO x and VOC, ozone formation rates in model grid cells depend enormously on grid resolution, dispersion rates (primarily wind speed and mixed layer height), chemical background (VOCs and radicals) and NO x emission rates. Thus, the notion that increased grid resolution leads to better simulations of ozone photochemistry is not necessarily true. This analysis points to the needed to incorporate some kind of subgrid parameterization of plume photochemistry into mesoscale Eulerian grid models.

AcidMODES: a major field study to evaluate regional-scale air pollution models

Regional scale, Eulerian framework air quality simulation models are currently being evaluated using pollutant and meteorological measurements from special surface networks and airborne p1atforms. An evaluation protocol for such models using this data base has been developed and adopted by the National Acid Precipitation Assessment Program; it includes Operational and Diagnostic components. This paper focuses on the diagnostic evaluation of the Regional Acid Deposition Model (RADM) , using aircraft measurements from the Acid Model Operational Diagnostic Evaluation Study (AcidMODES) program under sponsorship of the United States Environmental Protection Agency (USEPA) . RADMs ability to resolve horizontal patterns and gradients as well as the vertical structure of primary and secondary acidic pollutant species in the mixed layer over the major source region for sulfur and nitrogen emissions is an essential diagnostic test and is demonstrated. The potential roles of remote sensing in the evaluation of regional models are suggested.