Grantee Research Project Results
Final Report: Development and Application of an Air Quality Modeling System with Integrated Meteorology, Chemistry, and Emissions
EPA Grant Number: R825388Title: Development and Application of an Air Quality Modeling System with Integrated Meteorology, Chemistry, and Emissions
Investigators: Xiu, Aijun , Mathur, Rohit , Hanna, Adel , Coats, Carlie J.
Institution: MCNC / North Carolina Supercomputing Center
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999
Project Amount: $372,830
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Air , Safer Chemicals
Objective:
The overall goal of this project was to develop a computationally efficient, fully-integrated, physically and numerically consistent atmospheric dynamics and chemistry modeling system, that could be used to study the distribution, production, accumulation, and deposition of atmospheric pollutants on regional scales. The specific objectives of this research were to: (1) incorporate atmospheric pollutant transport/transformation/ deposition calculations into a state-of-the-science meteorological model; (2) reduce uncertainty, redundancy, and inconsistency arising from separation of the three main interrelated components (meteorology, emissions, chemistry); (3) maintain flexibility and modularity to facilitate incorporation of alternate/improved process and numerical representations; (4) apply the integrated air quality modeling system to several field studies and compare and evaluate model performance with measurements made during the field programs, and conduct detailed analysis of model results; and (5) use the integrated model as a platform to assess feedbacks between meteorology and chemistry through incorporating a methodology for the radiative feedback of atmospheric aerosols and evaluate the effect of this feedback on meteorology and air quality.
Summary/Accomplishments (Outputs/Outcomes):
In this project we have developed, tested, and applied a modular, physically and numerically consistent, fully integrated regional-scale atmospheric dynamics and chemistry modeling system. The modeling system is based on further development and refinement of three existing models: the MM5 meteorological model, the Multiscale Air Quality Simulation Platform (MAQSIP) atmospheric chemistry/transport model, and the Sparse Matrix Operator Kernel Emissions (SMOKE) modeling system. In developing the integrated model, we have further developed the MM5 modules to represent transport, chemistry, and deposition of various chemical species (gas and aerosol) such that the dynamics and chemistry related model calculations are fully synchronized. The integration of the dynamics and chemistry calculations in a consistent modeling framework also enables the investigation of the potential effects and feedbacks of radiatively important trace species. A variety of test cases involving both tracer transport and detailed treatment of tropospheric chemical pathways have been conducted. We also compared the differences in the online and offline mode of the chemistry calculations. The integrated model has been applied over the eastern United States. Using the integrated modeling system as a platform we incorporated the direct radiative effect of aerosol loading and evaluated how the aerosol feedback changes the meteorology and air quality.
To facilitate the coupling of meteorological and chemical tracer transport and chemistry calculations in the integrated model, a Meteorology CouPLing module (MCPL) that fits directly into MM5 has been developed (Coats, et al., 1998). MCPL is designed for extremely easy insertion into the MM5 source code and is callable at a variety of times scales from the MM5 advection-step frequency on up (Coats, et al., 1998). MCPL is principally controlled by environmental variables and by ASCII tables and can be configured to write data either to buffered files (for on-line integrated chemistry calculations), PVM-based communications channels (for peer-to-peer coupling with other models), or to files on disk (for off-line calculations). Figure 1 illustrates the entire modeling system with the model components and the connections between them. Note that by using MCPL to couple the meteorology model and the chemistry/transport model (CTM) together rather than putting the CTM code directly into the meteorology model, we are able to easily incorporate changes in the meteorology model and/or CTM without disturbing other components. For example, when MM5 code is updated we do not need to change literally anything in CTM and vise versa. This design also facilitates the use of the system both in the online and offline mode.
Figure 1. The schematic diagram of the integrated modeling system.
One of the advantages of the integrated modeling system is that it provides a platform for investigating the radiative feedbacks of aerosols that is not possible using the "offline" approach. To estimate the optical and radiative characteristics of aerosols in the integrated model, we have used the CCM2 radiation scheme in MM5 (Grell, et al., 1994) for radiation calculations. In the CCM2 radiation scheme, the solar spectrum is divided into 18 discrete spectral intervals and the δ-Eddington approximation is used to calculate solar absorption. The -Eddington approximation allows for gaseous absorption by O3, CO2, O2, and H2O and scattering and absorption of cloud water droplet. The optical properties of the cloud droplets are represented in terms of liquid water path, effective radius, and fractional cloud coverage. We included into MM5 the radiative forcing of aerosols simulated by MAQSIP by applying the Mie approximation to calculate aerosol scattering and extinction efficiencies using effective radius and refractive index. Optical properties of aerosols (single scattering albedo, asymmetry parameter, and optical depth) are calculated using extinction, scattering and absorption cross-sections, and aerosol effective radius and number concentration. Then the optical properties of aerosols are included in the d-Eddington approximation for shortwave radiation calculation.
We applied the integrated model to a domain over the Eastern U.S. employing a 36km resolution grid in horizontal and 21 layers of various thickness between surface and 100 mb in vertical. The episode covers a 10 day period in the summer of 1995, which is July 10 - July 20, 1995. The MM5 was run in a one-way nested mode wherein a coarse domain with horizontal resolution of 108 km was used for providing hourly boundary conditions for the nested fine domain with horizontal resolution of 36 km. The integrated model domain is located within the 36 km MM5 domain; this set-up is essential for specifying meteorological variables at the boundary of the integrated model. Chemistry/transport calculations are coupled with the dynamical calculation at every MM5 time step, i.e., 100 seconds for this case. The CCM2 radiation scheme with or without aerosol feedback is called every hour but can be called more frequently. The analysis focuses on the results from the last 7 days of simulation, which have less influence of the initial conditions. In our current testing and simulations with the integrated model, we use input emissions computed in an offline mode.
Refractive index of aerosols is the particle optical property relative to the atmosphere and is used in the Mie scattering calculations for the radiative properties of aerosols. The refractive index is defined as a complex variable, in which the real part (Rr) and the imaginary part (Ri) of the refractive index represents the scattering and absorbing components, respectively. In the sensitivity tests of the refractive index in the integrated modeling system, we ran the model in four different ways: (1) with no radiative feedback of aerosols; (2) including radiative feedback of aerosols and defining Rr = 1.5 and Ri = 0; (3) with radiative feedback of aerosols and including the effect of aerosol water fraction (WFRAC) on the real part of the refractive index: Rr = 1.5 - 0.27 ? WFRCA and Ri = 0; and (4) with radiative feedback of aerosols and including the effect of aerosol water fraction on both the real and the imaginary part of the refractive index: Rr = 1.5 - 0.27 ?WFRCA and Ri = 0.01.- 0.01?WFRCA. It should be noted that scenarios 2 and 3 represent aerosol effect with no absorption (zero imaginary refractive index).
The comparison of the model results with observations (e.g., the data from IMPROVE observation network) suggests that the model reasonably well captures spatial gradients in concentrations (Figure 2). The case study and sensitivity tests show that the direct radiative effects of aerosols tend to cool the earth/atmosphere system due to the scattering of shortwave radiation (refer to Figure 3), as also shown by previous studies. The use of the integrated meteorology-chemistry model simulates the effect of the aerosol feedback on the planetary boundary layer (PBL) height, which is generally lowered due to reduced surface heat fluxes. Comparisons of spatial distribution of various aerosol loading parameters (mass, size, and number) indicate that the net reduction in shortwave radiation reaching the surface is not only related to the aerosol mass loading, but is also dependent on particle size and number density. Therefore, the aerosol size parameters play an important role in forming the regional feedback pattern.
Figure 2. The comparison of model predicted event average surface fine particle mass versus observations from the IMPROVE network.
Figure 3. Simulated reduction of shortwave radiation reaching the surface due to direct aerosol radiative forcing (scenario 4).
In addition, we compared the "online" and "offline" simulations and found the most differences occurred at times when the planetary boundary layer (PBL) evolves in the morning and collapses in the late afternoon. This is because at those times the integrated model (with the "online" approach) is able to better capture the PBL development (getting PBL height every MM5's advection time step) compared to the "offline" model that interpolates PBL height hourly.
References:
Coats Jr CJ, McHenry JN, Lario-Gibbs A, Peters-Lidard CD. MCPL: a drop-in MM5-V2 module suitable for coupling MM5 to parallel environmental models; with lessons learned for the design of the weather research and forecasting (WRF) model. In: Preprints of the Eighth PSU/NCAR Mesoscale Model Users' Workshop, Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, CO, 1998, pp 117-120.
Grell GA, Dudhia J, Stauffer DR. A description of the fifth-generation Penn State/NCAR mesoscale model (MM5). NCAR Technical Note NCAR/TN-398+STR, 1994.
Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
meteorology, radiative feedback, chemistry, coupled model, tropospheric, aerosol, ozone., RFA, Scientific Discipline, Air, particulate matter, air toxics, Environmental Chemistry, Environmental Monitoring, tropospheric ozone, Engineering, meteorology, air quality models, ambient air, emission-based modeling, ozone, chemical composition, air pollution models, air quality data, atmospheric aerosols, atmospheric aerosol particles, atmospheric chemistry, engineering modelsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.