Single-Particle Distribution and Aging of Organic Compounds in Wildfire Emissions

Johannes Passig, Ellen Iva Rosewig, Aleksandrs Kalamasnikovs, Haseeb Hakkim, Marco Schmidt, Thomas Gröger, Mika Ihalainen, Anni Hartikainen, Markus Somero, Pasi Yli-Pirilä, Olli Sippula, Kerneels Jaars, Pieter Gideon van Zyl, Kajar Köster, Stefan Siebert, Saara Peltokorpi, Angela Buchholz, Liqing Hao, Annele Virtanen, Ville Vakkari, Andreas Walte, RALF ZIMMERMANN, Mass Spectrometry Centre;Rostock University/Helmholtz Munich

     Abstract Number: 271
     Working Group: Aerosol Chemistry

Abstract
Widfires emit large quantities of CO2, reactive trace gases, and particulate matter, which have profound impacts on air quality, human health, and climate (Yue et al., 2018). The atmospheric aging and aerosol distribution of these substances are highly complex and variable. Moreover, the photochemical changes they undergo are of great relevance to climate and human health, as they determine the particle’s optical and radiative effects, cloud condensation activity, and biological effects. A more comprehensive understanding of these effects requires information on the mixing state of the aerosol, i.e. the distribution of the constituents over the particle ensemble.

The advent of resonance-enhanced ionization in single-particle mass spectrometry (Passig et al., 2020 & 2022; Schade et al., 2019) has ushered in a new era of unprecedented access to single-particle chemical distribution information.

We studied particles from the smoke from wildfire simulation burns and the effect of photochemical aging. Typical vegetation from e.g., the boreal forest and the African savannah were used as fuels. For climate- and health-relevant PAHs we found high concentrations of the softwood combustion marker retene in boreal forest burns and its rapid degradation during aging. The toxic, unsubstituted PAHs showed higher stability against photooxidation. Particles with the highest PAH loads were observed in the long-range transported size mode even after prolonged aging, in agreement with a previous ambient air study (Passig et al., 2022). For the water-soluble components, we could show the emission and time-resolved formation of glyoxal/methylglyoxal during photochemical chamber aging. Interestingly, a non-uniform mixing of water-soluble glyoxal/methylglyoxal and non-polar PAH was observed. While the cloud condensation nucleation (CCN) activity of boreal forest emissions was increased by photooxidation, the CCN activity of African fuel emissions was reduced. This counterintuitive result may be explained by the observed sulfatization of potassium chloride to the less hygroscopic potassium sulfate during aging.