MOSAIK-2: Model-based urban planning and application in climate change: Urban Air Quality Module

Air pollution and heat stress are the two most important environmental issues for people living in cities, leading to an increased burden of disease and ultimately premature death. The World Health Organization (WHO) estimates that air pollution alone is responsible for seven million premature deaths worldwide each year. Air quality policy framework and consequent mitigation strategies play a vital role in improving air quality of urban areas. Hence, assessment of the current local air pollution mitigation measures is one of the central applications of PALM-4U, which receives a large amount of scientific and political attention.

Chemistry modeling is in many aspects more complex than urban meteorology modeling, as the chemistry depends on more variables (including highly fluctuating emission forcing in space and time) and processes. Evaluation is also more challenging, as chemistry processes are less well understood than physical fundamentals (that is, the skill of meteorological models is better than for chemistry). Relevant air pollutants are nitrogen oxides (NOx), ozone (O3), anthropogenic and biogenic organic compounds, as well as aerosols, which are complex mixtures of coarse (< 10 μm), fine (< 2.5 μm) and ultrafine (< 0.1 μm) primary and secondary particulate matters. Aerosol composition (e.g.
black carbon) and water uptake are the key variables for future investigations into the urban radiation budget and cloud/rain formation.