Daytime atmospheric chemistry of key compounds provoked by nighttime atmospheric chemistry (DARK KNIGHT).
Final Report Abstract
Volatile organic compounds (VOC) are emitted into the atmosphere and have been shown to contribute to secondary organic aerosol (SOA) formation, which has a strong influence on earth’s radiation budget, climate and local air quality. Biogenic sources make up the major fraction of total VOC on a global scale, but in a local context, anthropogenic volatile organic compounds (AVOC’s) can dominate the SOA formation. The atmospheric removal of VOC’s is driven by OH oxidation, ozonolysis and NO3-radical oxidation. During day time, NO3-radicals are photolysed rapidly, but during nighttime they might be the most important oxidant for VOC oxidation. As many studies focus on the most important processes during daytime, there is strong variation in reported SOA formation rate from VOC’s via NO3-radicals. The present study focuses on the different SOA yields from biogenic and anthropogenic sources during night and daytime chemistry and their interconnection. In a series of chamber experiments it has been shown, that the continuous injection of a prereacted NO3-radicals into a chamber containing the VOC precursor yields in better reproducible SOA yields compared to the injection of the VOC precursor into a chamber containing nitrate radicals. As a result, the SOA yields of several antropogenic and biogenic VOC’s were investigated under variation of the relative humidity (RH) condition. The NO 3-radical initiated oxidation of investigated monoterpenes led to comparable SOA yields. In contrast, the nighttime processing of β-caryophyllene showed increased SOA yields with higher RH. In contrast, the NO3-radical oxidation of AVOC’s did not result in observable SOA formation under the chosen oxidation conditions, which were chosen to match atmospherically relevant conditions. As a result, the OH-radical oxidation of NO3-radical oxidation products was studies for these compounds to better understand the interconnection between the different oxidation regimes and their effects on SOA formation. Furthermore, a dedicated series of chamber experiment were performed to disentangle the processes that could contribute to evaporation of SOA mass upon switching between the investigated oxidation regimes. To evaluate the role of photolysis, the OH-radical precursor was not introduced to the chamber setup in a set of experiments. Consequently, a group of compounds could be identified that were only present during OH oxidation of oxidated VOC’s (OVOC’s) from NO3-radical oxidation. Another group of compounds was only observed in experiments without any OH source, which are most likely formed by photolysis of OVOC’s. Finally, the SOA yield of pinonaldehyde and myrtenal, two α-pinene oxidation products were studies with the developed protocols. It could be shown, that the NO3-radical oxidation of OH- initiated OVOC’s resulted in a sharp increase of SOA mass, potentially by organonitrate formation, opposed to much lower SOA yields by NO3-radical initiated oxidation.
Publications
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Importance of the interconnection of the day- and night-chemistry of α-pinene-experiments in the ACD-C aerosol simulation chamber. International Aerosol Conference 2022, 03 – 09 September 2022, Athens, Greece
Kołodziejczyk, Agata; Mutzel, Anke; Herrmann, Hartmut & Poulain, Laurent
