Online monitoring of the particle size-dependent reaction of citric acid with boronic acid in aerosols

Reactions occurring within organic aerosols are a crucial factor influencing both environmental systems and industrial processes. The composition of the atmosphere is heavily impacted by aerosol composition, which in turn is a critical factor in our ability to accurately predict global climate change. To calculate the aerosol budget, a deeper understanding of the reactions within aerosol particles and their influence on particle growth is essential. Specifically, the interactions between aerosols and climate parameters, such as cloud formation and radiation balance, are of paramount importance. Analysing these processes enhances our comprehension of aerosols' effects on climate, enabling more precise integration into climate models.

                In industrial processes that rely on multiphase reactions with aerosol particles, reaction rates are theoretically dependent on particle size (Petters, 2022). This understanding is vital for optimizing processes in the chemical, pharmaceutical, and environmental engineering sectors, as it directly impacts the efficiency and safety of industrial applications. To simulate these reactions and measure product formation, we coupled the developed Chemical Ionization Orbitrap inlet (CI Orbitrap) by Riva et al. (2019) with an aerosol inlet consisting of a flow-through heating cartridge and a gas cooling unit. This setup enables the analysis of aerosol particles through thermal evaporation, combining the high mass resolving power of the Orbitrap (R ≥ 140,000 at m/z 200) with the selectivity and sensitivity to oxidized compounds of chemical ionization mass spectrometry (NO3-CIMS). An activated charcoal denuder removes the gas phase of the sample aerosol before thermal evaporation, preventing sampling artifacts and ensuring high time-resolved measurements (Riva, 2019).

                We observed the size dependent reaction of citric acid with 99% ¹¹B-boronic acid, resulting in a condensation product. The equilibrium reaction shows an exchange of boron isotopes, resulting in an increased ¹⁰B percentage in the product molecule.

This work is supported by the Deutsche Forschungsgemeinschaft (DFG) under project number 416710328.

• S. Petters (2022) Res. Lett 49.
• Riva, M. Ehn M., D. Li, S. Tomaz, F. Bourgain, S. Perrier, C. George. (2019) Ana. Chem. 91, 9419-9423.