Issues Related to On/Offline Meteorological and Atmospheric Chemistry Model Coupling
The online approach consists of the coupled treatment of chemical parameters, simultaneously with the meteorological parameters, in a single integrated modeling system that is referred to as chemical weather modeling. This approach offers the possibility to simulate the links and feedbacks between atmospheric processes that are traditionally neglected in air quality models. Both meteorological and chemical components are expected to benefit from this approach. Both approaches have advantages and disadvantages that make their use appropriate for different applications. This study discusses and evaluates the performance of the online Integrated Community Limited Area Modeling System (RAMS/ICLAMS) and the offline model, Comprehensive Air Quality Model with Extensions (CAMx), for a month long retrospective summertime text period, over Europe and the Greater Mediterranean Area (GMR). The implementation of the same chemical mechanisms, meteorological fields, emissions, initial and boundary conditions makes it easier to compare the results from the two models. However, there are some differences in the physical parameterizations utilized in the two models that are expected to result in differences between them. The feedback mechanisms are not activated in order to evaluate the performance of the two models regarding the advantages that the online approach offers (same projection, no interpolation in time and space, explicit calculation of the meteorological components, availability of the meteorological fields at each time step etc.). Results showed that the online approach gave better results regarding ground 1 h ozone and 24 h sulfate aerosol concentrations improving the main statistical parameters by roughly 20 % and increased correlation from 0.51 to 0.70. The differences may be mainly the outcome of the utilization of different methods for the calculation of the photolysis rates and the interpolation of the meteorological data for use in the offline model.
KeywordsSulfate Aerosol Photolysis Rate Online Approach Meteorological Dataset Actinic Flux
This work was supported by EUROCONTROL Research Studentship Agreement no CO6/22048ST and FP6 project CIRCE contract no 036961.
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