COUPLING MICRO AND MESO SCALE MODELS FOR DETERMINING FLOW AND DISPERSION OF POLLUTANTS IN URBAN ENVIRONMENT

Name: Igor Richa Menegatti
Type: MSc dissertation
Publication date: 10/01/2020
Advisor:

Namesort descending Role
Neyval Costa Reis Jr. Advisor *

Examining board:

Namesort descending Role
Elisa Valentim Goulart Co advisor *
Jane Meri Santos Internal Examiner *
Neyval Costa Reis Jr. Advisor *

Summary: Currently, the use of photochemical mesoscale models has become significantly important for air quality management in urban regions due to its great potential to produce information regarding air pollutants and meteorology. Mesoscale models, such as WRF-CHEM and CMAQ, can predict dispersion of pollutants in large areas urban areas, with resolution in order of 1 km to 10 km. However, these models are not able to accurately reproduce the airflow and dispersion of pollutants inside the urban canopy, since they are unable to model in detail the characteristics of flow and dispersion in dimensions below its resolution. On the other hand, microscale ComputationalFluid Dynamics (CFD) models can account for the effects of complex building arrays, as well as the dispersion of contaminants from different sources due to its fine resolution. In this sense, the use of mesoscale models coupled with microscale CFD models may provide sufficient level of detail for critical areas of interest, while mesoscale models can provide the flow and dispersion patterns over a large urban region. In this work, WRF and CMAQ modeling systems are off-line coupled with a microscale CFD model. A densely populated neighborhood of 6 km² in the Metropolitan Region of Vitória is studied. WRF and CMAQ data outputs are used as transient boundary conditions for the CFD simulation. A 3D domain with approximately 2x107 tetrahedral elements, representing the study region, is used to solve the conservation equations of mass, momentum and chemical species in the microscale simulation. Data from an air quality monitoring station is used validate the simulated concentration fields. In general, it is possible to conclude that the microscale model results show a considerable improvement in the street level concentration predictions compared to mesoscale data. The results reproduce trends and peaks that are observed on the input data, with statistical indicators of the coupled CFD/WRF model significantly better than CMAQ, demonstrating the CFD modelling robustness. However, it is important to note that the accuracy of the emission inventory and mesoscale prediction have an important impact on the results.

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