Measurements of Stable Carbon Isotopes in Volatile Organic Compounds in the Outflow of Megacities. This proposal is a contribution to the HALO missions EMeRGe-EU and EMeRGe-ASIA.

• Applicant: Dr. Marc Krebsbach
• Subject Area: Atmospheric Science
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 316505256

The impact of volatile organic compounds (VOC) on air quality and on human health at the local or regional scale is directly evident by the detrimental effects on our environment. Even more important is the critical role that VOC play in the chemistry of the atmosphere. The formation of many important secondary pollutants, such as ozone, peroxides, aldehydes, and peroxyacyl nitrates and secondary organic particulate matter depends critically on the availability of VOC as their precursors. We propose to measure isotopic signatures and concentrations of specific VOC in the emission plumes and outflow of certain major population centres (MPCs) over Europe and Asia by deploying the whole air sampler MIRAH during the HALO missions EMeRGe-EU and EMeRGe-Asia. The whole air samples will be analysed in the laboratory by a gas chromatograph combustion isotope ratio mass spectrometer system. Isotope ratios in VOC are useful tracers to investigate reactions that are not directly accessible to current measurement techniques. Transport and mixing processes in the atmosphere can thus be visualised and valuable information on the dominant processes these compounds are involved in is thus provided. We already demonstrated in the recent HALO missions TACTS/ESMVal and both OMO missions that the proposed methodology is a sensitive tool for source apportionment of VOC, to infer transport pathways and their impact on the VOC distribution, to estimate the degree of mixing and to differentiate between impacts of mixing and chemical processes, as well as to study their atmospheric processing and the residence times of specific VOC. The value of these results will even be enhanced by the comparison with the results of 3-dimensional chemistry transport models. The following scientific objectives envisaged of this proposal and following the overall objectives of EMeRGe-EU and EMeRGe-ASIA are: (1) measure the composition of pollution plumes leaving Europe and Asia and determine the contribution of specific VOC to the atmospheric composition; (2) determinate the long-distance air pollution transport and infer the impact of transport processes on the distribution of VOC; (3) identify possible differences in transport and transformation associated with particular and unique features of European and Asian MPCs; (4) measure both precursor and oxidation products to get information on oxidation pathways; (5) estimate the age of air masses traced at different stages of pollution plumes and therewith (6) contrast photochemical aging versus transport and mixing; (7) identify oxidation products and reaction intermediates from VOC degradation; (8) combine the information of isotope ratios with specific regional meteorology for the assignment of sources; (9) stimulate modelling studies by providing the gathered data for chemistry transport model simulations, since almost no data of the isotopic composition of specific VOC in the probed atmospheric region are available so far.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1294: Atmospheric and Earth System Research with the "High Altitude and Long Range Research Aircraft" (HALO)
• Co-Investigator: Professor Dr. Ralf Koppmann