Today over half of the world's population resides in urban areas, almost 10% live in megacities. About 67% of these megacities are located at the coast and even more have coastal influence. Even though megacities and their specific problems have attracted a lot of research in recent years, the additional challenges of coastal megacities have been largely ignored.

The atmospheric flow around coastal megacities is complicated by urban heat island effects and topographic flows and sea breezes. The emissions of gases and seasalt particles from the coastal zone have the potential to modify the atmosphere over the megacity affecting air quality and weather. The interaction of urban atmospheric emissions and seasalt can affect regional climate via changes in cloud condensation nuclei number and size distribution. These links between marine and urban emissions may therefore result in fundamentally different atmospheric chemistry than that arising from emissions from inland urban areas. These interactions have the potential to significantly reduce urban air quality in areas already subject to poor air quality and associated health risks, exacerbating impacts from other global change pressures such as climate change.

This project will use an established regional three-dimensional model (WRF/CHEM) to investigate the consequences for atmospheric chemistry of the unique factors at play in coastal megacities, including halogen chemistry. Furthermore, the effects of special topography as well as features such as coastal fog will be studied and the deposition of nutrients such as nitrogen, and contaminants such as trace metals from the megacity in the adjacent coastal waters will be quantified to provide quantitative input to facilitate the assessment of megacities on the coastal ocean.

The specific overarching scientific questions to be addressed in this project are:
• How do air-sea interactions (such as trace gas emissions and seasalt aerosol formation) within the coastal zone affect air pollution within megacities? The scale of emissions and the key role of halogens in ozone cycling mean that these regions may have a unique chemical environment.
• How do the interactions of large urban emissions and the marine boundary layer affect regional oxidation capacity and climate?

This project will focus on a small selection of coastal megacities (such as Los Angeles, USA; Lima, Peru; or the Pearl River Delta in China) based on their regional and global significance as well as their specific topographic features.

This project is suitable for a student with a strong interest and ideally experience in atmospheric science and numerical modelling with a BSc or preferably MSc in Meteorology, Atmospheric Sciences, Environmental Sciences, Physics, Mathematics, Chemistry or similar. The student will receive training in WRF-specific modelling and will acquire transferable skills, such as project planning, data analysis, effective collaboration, scientific writing, and oral communication, while participating in research of global significance.
 

von Glasow, R. et al. (2012), Megacities and large urban agglomerations in the Coastal Zone, Ambio, in press, DOI 10.1007/s13280-012-0343-9