Chemical transport models |
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Authors: | Dragutin T Mihailovic Kiran Alapaty Zorica Podrascanin |
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Institution: | (1) Faculty of Agriculture, University of Novi Sad, Trg Dositeja Obradovica 8, 21000 Novi Sad, Serbia;(2) U.S. Department of Energy, 1000 Independence Ave. SW, Washington, DC 20585-1290, USA;(3) ACIMSI-University Center for Meteorology and Environmental Modelling, University of Novi Sad, Trg Dositeja Obradovica 3, 21000 Novi Sad, Serbia |
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Abstract: | Background, aim, and scope Improving the parameterization of processes in the atmospheric boundary layer (ABL) and surface layer, in air quality and
chemical transport models. To do so, an asymmetrical, convective, non-local scheme, with varying upward mixing rates is combined
with the non-local, turbulent, kinetic energy scheme for vertical diffusion (COM). For designing it, a function depending
on the dimensionless height to the power four in the ABL is suggested, which is empirically derived. Also, we suggested a
new method for calculating the in-canopy resistance for dry deposition over a vegetated surface.
Materials and methods The upward mixing rate forming the surface layer is parameterized using the sensible heat flux and the friction and convective
velocities. Upward mixing rates varying with height are scaled with an amount of turbulent kinetic energy in layer, while
the downward mixing rates are derived from mass conservation. The vertical eddy diffusivity is parameterized using the mean
turbulent velocity scale that is obtained by the vertical integration within the ABL. In-canopy resistance is calculated by
integration of inverse turbulent transfer coefficient inside the canopy from the effective ground roughness length to the
canopy source height and, further, from its the canopy height.
Results This combination of schemes provides a less rapid mass transport out of surface layer into other layers, during convective
and non-convective periods, than other local and non-local schemes parameterizing mixing processes in the ABL. The suggested
method for calculating the in-canopy resistance for calculating the dry deposition over a vegetated surface differs remarkably
from the commonly used one, particularly over forest vegetation.
Discussion In this paper, we studied the performance of a non-local, turbulent, kinetic energy scheme for vertical diffusion combined
with a non-local, convective mixing scheme with varying upward mixing in the atmospheric boundary layer (COM) and its impact
on the concentration of pollutants calculated with chemical and air-quality models. In addition, this scheme was also compared
with a commonly used, local, eddy-diffusivity scheme. Simulated concentrations of NO2 by the COM scheme and new parameterization of the in-canopy resistance are closer to the observations when compared to those
obtained from using the local eddy-diffusivity scheme.
Conclusions Concentrations calculated with the COM scheme and new parameterization of in-canopy resistance, are in general higher and
closer to the observations than those obtained by the local, eddy-diffusivity scheme (on the order of 15–22%).
Recommendations and perspectives To examine the performance of the scheme, simulated and measured concentrations of a pollutant (NO2) were compared for the years 1999 and 2002. The comparison was made for the entire domain used in simulations performed by
the chemical European Monitoring and Evaluation Program Unified model (version UNI-ACID, rv2.0) where schemes were incorporated. |
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Keywords: | Asymmetrical mixing Atmospheric chemistry Convective boundary layer Dry deposition Environmental modeling Non-local convective mixing scheme Turbulent kinetic energy diffusivity scheme Vertical mixing |
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