Characterization of Urban Grime Photochemistry as Sink or Source for Air Pollutants (GrimePaSS)

• Applicant: Professor Dr. Hartmut Herrmann
• Subject Area: Atmospheric Science
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 415705351

The improvement of urban air quality in Europe is a major concern that strengthens the interest in understanding the most relevant chemical processes and pathways of air pollutants, like nitrogen oxides (NOx), ozone (O3) and several volatile organic compounds (VOCs). Besides gas phase chemistry, also heterogeneous and multiphase reactions when gases interact with urban surfaces (e.g., windows, building walls, rooftops, sidewalks, roads, etc.) are processes which could affect the fate of air pollutants. When such surfaces are exposed to the atmosphere for a certain time, it is known that a so called “urban grime” film consisting of inorganic and organic components will develop. However, the knowledge about the interaction of this new environmental compartment with air pollutants under illumination is still limited to a handful individual studies.The proposed project, therefore, will combine real urban grime sampling with laboratory and modelling studies to characterize the photoreactive behavior of urban grime at impervious surfaces. Small lab scale photoreactor and aerosol chamber experiments will be performed to investigate whether urban grime is potentially acting as a sink or a source for air pollutants. This experimental approach will provide for the first time comprehensive data on the kinetics (uptake coefficients, deposition velocities, etc.) for different air pollutants (e.g., NOx, O3, toluene) and will give insights into reaction mechanisms and potential secondary product formation. The additional analysis of the urban grime chemical composition by CPP-GC-MS and ion chromatography before and after these photoreactivity experiments will extend the results to a multiphase chemical data set which will further be applied in a modelling module. The modelling will finally provide useful insights into the overall lifetimes and fates of air pollutants associated with urban grime.Overall, the proposed project will give for the first time a comprehensive answer to the question how urban grime as a new environmental compartment in urban areas will impact air quality and associated health effects.

• DFG Programme: Research Grants