Observation of Speciated Peroxy Radicals in the Urban forest and Comparison Exercise (SPRUCE)

• Applicant: Maria Dolores Andrés Hernández, Ph.D.
• Subject Area: Atmospheric Science
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501368835

Peroxy radicals are short lived species involved in most of the oxidation processes in the atmosphere leading to the generation of longer lived and chemically or toxicologically important pollutants, such as ozone. Particularly in areas affected by complex emission sources, peroxy radical measurement methods of sufficient accuracy, reproducibility and sensitivity are required for understanding chemical transformations of urban pollution. In that respect, comparison exercises of state-of-the-art instruments in reactor chambers enable their characterisation under controlled conditions and improve the confidence in the measurement of peroxy radicals. An overarching aim of SPRUCE is to deliver an improved understanding of the role of the peroxy radicals in atmospheric chemical transformations resulting from the interaction between urban anthropogenic and rural biogenic emissions. Within the proposed work, the PeRCEAS instrument (Peroxy Radical Chemical Enhancement and Absorption Spectrometer) developed at the Institute of Environmental Physics of the University of Bremen will participate in the measurement campaign of the international project ACROSS (Atmospheric ChemistRy Of the Suburban forest) to study the pollution outflow from Paris over a forested area, and in the international comparison exercise of ROxCOMP22 for scientific instruments measuring atmospheric peroxy radicals. These two campaigns address two main aspects of SPRUCE by providing a unique opportunity for a) the measurement of peroxy radicals in the specific environment of interest in conjunction with an extensive suite of observations of essential importance for the interpretation of the radical chemistry, and b) the assessment of the data quality and performance of PeRCEAS, in particular exploring the sensitivity and efficiency for radical speciation under controlled conditions. A focus of the study will be on the investigation of oxidation reactions and ozone yields in air masses with different anthropogenic/biogenic signatures in relation to the amount and composition of peroxy radicals. Steady state and numerical calculations will be constrained with the observations of precursor species to estimate peroxy radical budgets. The comparison with the PeRCEAS measurements will be used for testing the current understanding of oxidation mechanisms in urban plumes mixed with biogenic emissions. The analysis of the resultant comprehensive data set is anticipated to test the current knowledge of the chemical transformation of megacities outflows during atmospheric transport.

• DFG Programme: Research Grants