Stable Carbon Isotope Ratios in Atmospheric VOC during the EMeRGe-EU and ASIA campaigns

VOC (volatile organic compounds) play a critical role in the chemistry of the atmosphere. The formation of many important secondary pollutants in the atmosphere, such as ozone, peroxides, aldehydes, and peroxyacyl nitrates and secondary organic particulate matter depends critically on the availability of VOC as their precursors. Many of them have strong direct adverse effects on our environment. The assessment of the impact of VOC on the atmosphere can be significantly improved by measuring their stable carbon isotope ratios. The isotopic composition of compounds emitted by natural or anthropogenic activities vary for emissions from different sources. In almost all atmospheric processes, e.g. chemical reactions, photolytic processes, transport and dilution, diffusion, and phase transitions, the isotopic ratio in VOC is altered. Studying the isotope ratios of both precursors and products makes it possible to distinguish between freshly emitted VOC and photochemically processed compounds, to increase our knowledge of transport versus chemistry, to study the ultimate fate of oxidation products, and to help assess the impact of emissions, e.g. from large population centres (MPCs), on local, regional and even global pollution.
The automated high volume air sampling system MIRAH has been deployed during several missions with the German High Altitude – Long-range research aircraft (HALO). Here we focus on the campaigns EMeRGe-EU and -ASIA (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales). The objectives were to measure the pollution emitted, transported and transformed from the MPCs London, BeNeLux, Rhine-Ruhr and Po Valley for the European Part. The second part of EMeRGe was conducted from Taiwan with the goal to investigate the pollution outflow from Asian MPCs such as Taipei, Hongkong, Shanghai, Beijing, Manila, Seoul and Tokio. In both parts a key experiment was the identification of the source of the air masses by collecting whole air samples on ground prior and during particular flights in specific metropolitan regions. On 7 flights in Europe and 12 flights in Asia, mostly below 6 km altitude, more than 140 air samples were collected on HALO during each campaign, and additional 46 samples at specific ground sides. The whole air samples were analysed for mixing ratios and stable carbon isotope ratios of selected aldehydes, ketones, alcohols, and aromatics. This allowed investigating air masses of different origin, characteristic, and atmospheric processing. In this presentation we will give an overview of the data and show exemplary results.

This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG Priority Program SPP 1294) under grant-No. KR3861/1-1.