# Modelling Pollutant Dispersion in Urban Canyons to Enhance Air Quality and Urban Planning
## 5 Conclusions  
This work aims to mitigate the gaps in the literature regarding street ventilation and pollutant dispersion for a large number of cases covering different urban layouts, for Reynolds number values in a realistic range that can typically be found in cities. This comprehensive study has generated valuable insights into the dynamics of airflow within various urban street morphologies, particularly for Reynolds numbers commonly encountered in urban environments. The analysis of streamline patterns resulting from varying aspect ratios and Reynolds numbers can be crucial for identifying critical urban layouts. This work evidenced that narrower streets tend to exhibit inferior ventilation, particularly in the lower vortices formed within these configurations. More specifically, streets characterised by AR > 2.5 are particularly risky due to their tendency to transition into a multi-vortex regime, which can lead to situations where the pollutant dispersion is significantly poorer than expected. This phenomenon contributes to a significant accumulation of pollutants, exacerbating urban air quality issues. Consequently, the implementation of innovative pollution control and dispersion techniques becomes essential in addressing these adverse health effects. Moreover, the application of the findings of this study to a practical case involving five streets in Seville demonstrates the applicability of this research to forecasting pollution scenarios, enabling the identification of locations and periods when the risk level for human health due to pollution exposure is elevated. The findings indicate that streets with minimal variations in the AR exhibit heightened sensitivity to external pollution conditions, as narrower streets can attain a higher level of risk for pedestrians when subjected to equivalent levels of pollutant emissions. This study's contributions to the field of urban environmental planning are invaluable, providing a foundational basis for the creation of sustainable and liveable urban spaces for future generations. This research has not only addressed configurations that promote natural ventilation but has also identified those that necessitate further intervention. This dual focus serves as a pivotal guide for future urban development. By integrating these insights into the urban planning process, cities can be designed to be more resilient against pollution-related health risks, ultimately leading to significant improvements in the quality of life for urban residents. This study also presents opportunities for further exploration. Future research could encompass the characterisation of additional street morphologies, including various roof shapes and asymmetric street canyon configurations. Such expansions would enhance the comprehensiveness of pollution dispersion characterisation in urban settings, thereby improving future urban layouts. Moreover, subsequent investigations could include a broader range of AR values, thereby encompassing morphologies not addressed in this initial study. This could involve examining very low ARs indicative of avenues or open plazas, as well as exceptionally high ARs characteristic of densely populated areas with tall structures. Expanding the scope of research in this manner will significantly enrich our understanding of urban air quality dynamics and inform more effective urban planning strategies. Conceptualisation, F.R.S. and S.A.D. ; methodology, F.R.S., S.A.D., M.G.D. and J.S.R. ; software, F.R.S. ; validation, S.A.D., M.G.D., R.M.P., T.P.A. and J.S.R. ; investigation, S.A.D., F.R.S., M.G.D., T.P.A., R.M.P. and J.S.R. ; data curation, F.R.S. and M.G.D. ; writing--original draft preparation, F.R.S. ; writing--review and editing, M.G.D., R.M.P. and J.S.R. ; visualisation, F.R.S. ; supervision, T.P.A., R.M.P. and M.G.D. ; project administration, J.S.R. ; funding acquisition, S.A.D. All authors have read and agreed to the published version of this manuscript.