A contribution to subproject GLOREAM
Michael Lüken, John Lewis and William R. Stockwell
Desert Research Institute, Division of Atmospheric Sciences, 2215 Raggio Parkway, Reno, Nevada 89512-1095, United States
Summary
A highly simplified model that couples atmospheric chemistry with a convective boundary layer model was developed to be a theoretical tool to make detailed investigations of the relationship between atmospheric chemistry and boundary layer processes. The model is simple enough so that it can be used to make thousands of simulations and only about 10 minutes of computer time processing is required. Despite its simplicity the model should be able to produce reasonably realistic results. The model calculates the time evolution of the mixing height and the potential temperature of the boundary layer and its affect on the chemistry of a series of first order reactions that proceed from an emission, through an atmospheric concentration and ending in deposition. In future studies the model will be extended to more realistic chemical mechanisms and applied to the analysis of observational data.
Aim of the research
The three dominate factors that affect air quality are emissions, meteorology and atmospheric chemistry. Most chemical transport models (CTMs) incorporate as many physical and chemical processes as possible within constraints imposed by current understanding and by limited computer resources. Analysis of CTM modeling results to determine the effects of each process on air quality may be very difficult. Detailed sensitivity analysis may not be possible because large numbers of CTM simulations will require too many computer resources. In previous GLOREAM reports we have reported on the development of highly complex chemical mechanisms. Here we focus on the development of a tool for sensitivity analysis and data assimilation.
Activities during the year
A box model has been developed that simulates the development of the layer height, the horizontally averaged potential layer temperature, and the temperature jump at the upper layer boundary. The horizontal and vertical air motion, surface pressure, and time dependent surface temperature are calculated according to the parameterizations of Driedonks (1982).
The chemical mechanism consists of a simple scheme of consecutive reactions where E, k1, k2 and d are rate parameters for emission, reaction1 and 2, and deposition, respectively.
Emission → A E
A → B k1
B → C k2
C → Deposition d
An emission and/or an initial concentration of A is assumed. The species A is transformed to B and C in two reactions, and the final product, C, is deposited on the surface. In this model the chemistry is coupled to the meteorology through temperature and mixing height. If the rate parameters are temperature dependent then the temperature is calculated from the potential temperature and height of the mixed layer. The emission is treated as a volume source with a fixed mass flux. Furthermore, the layer height rise causes dilution and deposition. Therefore both the effective rate parameters for the emission of A and the deposition of C depend on the mixing height.
The model is being applied to model field data taken over the Gulf of Mexico. Observations of sea surface temperature and atmospheric temperature were made over a period of 18 hours as the research ship traveled from near New Orleans through the Gulf during the wintertime.
At this location, during this time, the formation of convective boundary layers follows relatively simple physics.
This period is also interesting from a chemical point of view because here nitrogen oxides react to form ammonium nitrate particles. The simple mechanism approximates the mechanism for the formation of ammonium nitrate where [NO]o is the initial concentration, k1[HO2] is the effective first order rate parameter of the first reaction, k2[HO] is the effective first order rate parameter of the second reaction, f is the effective yield of particles for the observed humidity and temperature and d is the deposition rate parameter for ammonium nitrate particles (Stockwell et al., 2000).
Emission → NO [NO]o
NO (+HO2) → NO2 k1[HO2]
NO2 (+HO) → HNO3 → f NH4NO3(s) k2[HO]
NH4NO3(s) → Deposition d
The meteorological boundary conditions have been obtained from measurements made within an 18 hours period. With this highly parameterized model the evolution of nitrate particle formation and deposition over this time period was simulated. The meteorology results are being compared with measurement data while the chemistry simulations can be compared with an analytical solution because of the simplicity of the reaction mechanism.
Principal results
Figure 1 shows a sample simulation with a fixed mixing height and a fixed temperature. The model reached a steady state for the concentrations of A, B and C relatively rapidly and the total deposition increases monotonically with time.
A simulation with chemistry and the convective boundary layer model are shown in Figures 2 and 3. In this simulation the convective boundary layer rises in height from a few hundred meters to about two thousand meters and the mixing layer warms several degrees, Figure 2.
The changes in the meteorology cause significant changes in the chemical concentrations, Figure 3. It is interesting that species A and B reach early peak values while C does not. The final steady state concentration of C is not affected by the height of the boundary layer.
0 10 20 30 40
Deposition
0.0 0.5 1.0 1.5 2.0 2.5
Concentration
0 5000 10000 15000 20000 25000
Time [A]
[B]
[C]
Deposition
Figure 1. Plot of calculated concentrations of box model without meteorology.
0 500 1000 1500 2000
Mixing Height (m)
294 295 296 297 298 299
Potential Temperature (K)
0 5000 10000 15000 20000 25000
Time
PT
Figure 2. Plot of calculated potential temperature and mixing height for typical simulations with a rising convective mixing height.
0.0 2.5 5.0 7.5 10.0 12.5
Deposition
0.0 0.5 1.0 1.5 2.0
Concentration
0 5000 10000 15000 20000 25000
Time
Deposition
[C]
[B]
[A]
Figure 3. Plot of calculated concentrations for typical simulations with a rising convective mixing height.
Main conclusions
This simple model has been developed for the purpose of testing new methods of sensitivity analysis, including adjoint and inverse methods. Although it does not include detailed chemistry and physics it appears to make reasonable simulations of particle formation and the convective boundary layer. The system is low-order with 7 variables (3 meteorological and 4 chemical). The system is nonlinear and this leads to complex behavior that is nontrivial. The model’s simplicity allows it to make several thousand simulations within a short period of time.
Aim for the coming year
The convective boundary layer model will be used for the development of new methods of adjoint and inverse methods. Furthermore we plan to develop the model to include the Regional Atmospheric Chemistry Mechanism (RACM, Stockwell et al., 1997). To improve the treatment of aerosol formation, we will investigate incorporating the SCAPE aerosol mode within the model. The full model will be used to investigate the effects of ammonia, NOx and volatile organic compound (VOC) limitations on particle formation under the influence of a rising mixing height and an increasing atmospheric temperature.
Acknowledgements
Support for this research was provided by the National Aeronautics and Space Administration, the National Atmospheric and Oceanic Administration, the Idaho Department of Health and Welfare, Division of Environmental Quality and PG&E Generating Company.
References
Driedonks, A.G.M.; Sensitivity analysis of the equations for a convective mixed layer, Boundary-Layer Meteorol. 22 (1982) 475-480.
Stockwell, W.R., F. Kirchner, M. Kuhn and S. Seefeld; A new mechanism for regional atmospheric chemistry modeling, J. Geophys. Res. 102 (1997) 25847-25879.
Stockwell, W.R., J.G. Watson, N.F. Robinson, W. Steiner and W.W. Sylte; The ammonium nitrate particle equivalent of NOx emissions for continental wintertime conditions, Atmos. Environ. 34 (2000) 4711-4717.
GLOREAM Resulting Publication List – William R. Stockwell
Stockwell, W.R., J. G. Watson, N.F. Robinson, W. Steiner and W.W. Sylte; The Ammonium Nitrate Particle Equivalent of NOx Emissions for Continental Wintertime Conditions, Atmos. Environ. 34 (2000) 4711-4717.
Steinbrecher, R., M. Klauer, K. Hauff, W.R. Stockwell, W. Jaeschke, T. Dietrich and F. Herbert; Biogenic and Anthropogenic Fluxes of Non-Methane-Hydrocarbons Over an Urban-Impacted Forest, Frankfurter Stadtwald, Germany, Atmos. Environ. 34 (2000) 3779-3788.
Fuentes, J.D., M. Lerdau, R. Atkinson, D. Baldocchi, J.W. Botteneheim, P.Ciccioli, B.Lamb, C.Geron, L. Gu1, A.Guenther, T.D. Sharkey and W.R. Stockwell; Biogenic Hydrocarbons in the Atmospheric Boundary Layer: A Review, Bull. Amer. Meteor. Soc. 81 (2000) 1537-1575.
Grell, G.A., S. Emeis, W.R. Stockwell, T. Schoenemeyer, R. Forkel, J. Michalakes, R. Knoche and W. Seidl;
Application of a Multiscale, Coupled MM5/Chemistry Model to the Complex Terrain of the VOTALP Valley Campaign, Atmos. Environ. 34 (2000) 1435-1453.
Klemm, O., W.R. Stockwell, H. Schlager and M. Krautstrunk; NOx or VOC Limitation in East German Ozone Plumes?, J. Atmos. Chem. 35 (2000) 1-18.