Temperature dependent formation of HOM from BVOCs and AVOCs

Air pollution and climate change represent serious threats to human wellbeing and ecosystems. Unfortunately, several aspects related to this topic are still poorly understood. Regarding climate change, especially the role of aerosols currently comprises the highest uncertainty amongst all known atmospheric processes. The proposed work targets the understanding of the formation process of highly oxygenated multifunctional organic compounds (HOM) from organic substances which are emitted from biogenic and anthropogenic sources. HOM influence particle formation and growth and thus impact the climatically highly relevant cloud condensation nuclei. The aim of the work is to quantify the temperature dependent HOM formation, for the most abundant anthropogenic and biogenic VOCs. Further physico-chemical properties of HOM are investigated by means of quantum chemical calculations. This allows determining the contribution of HOM to new particle formation and particle growth. The project is based on data conducted under well-defined laboratory conditions. The findings of the experiments will be converted to a software code describing HOM formation and its properties. This code is then implemented to aerosol dynamics and chemical transport models allowing to assess the impact of HOM on new particle formation and growth in measurement chambers and in the field. This forms the basis for a final goal which is to develop parameterisations that represent HOM formation in a simplified way in large scale models applied to forecast our daily weather or future climate. Several innovative, unique aspects regarding the computer models combined with the network of excellent experimental, computational and theoretic scientists characterize this project.

Temperature dependent formation of highly oxygenated organic molecules from volatile organic compounds and its atmospheric relevance Poor air quality and related adverse health effects, according to WHO, represents the single largest environmental risk of premature death. Various metrics to quantify the hazard, including particulate matter (PM), particle surface or oxidative potential (OP) of the aerosol, are under discussion. Secondary organic aerosols (SOA) which forms upon the oxidation of volatile organic compounds in the atmosphere contributes to the burden of ambient air pollution. In Europe, it even dominates the OP of the airborne particles, making it a significant threat to health and causing costs of roughly 500 billion per year. However, the formation SOA under atmospheric conditions, yet, is still poorly understood. In the present project, we aim to bridge from present-day description of SOA formation, which is mainly empirically based, towards a more mechanistic understanding. Therefore, a method was developed which serves to predict the formation of low volatile organic species from parent VOC via a process called autoxidation chemistry. The latter allows molecules, after a single oxidation step, to transform to (highly) oxygenated organic molecules via intra-molecular hydrogen abstraction and O2 addition. The transformation alters the physical properties allowing the gas phase products to partition to the particle phase and, accordingly, increase the amount of ambient aerosol load. In particular, a method to set up the autoxidation chemistry equations for any VOC system was developed. Additionally, the structures for the products formed in the chemistry are predicted enabling to assess their physicochemical properties. The resulting computer model allows to study SOA formation under realistic conditions. The newly developed method was applied to benzene and toluene, two molecules typically related to anthropogenic activity. In this project, we were able to reproduce the observed distribution of gas phase chemical products and SOA mass formation in chamber settings, respectively. For both, benzene and toluene, the condensation flux is dominated by the species formed by autoxidation highlighting the relevance of the process. Further, we conducted atmospheric simulations to show the contribution to the organic aerosol formed. The present work forms the starting point for more mechanistic description of SOA formation for any VOC species. Eventually, the mechanisms developed that way will be reduced to parameter-representations allowing them to be included into large-scale models such as climate- or earth system models. This will enable better climate as well as air quality predictions, respectively.