Wildfire Emissions - Source Apportionment and Ageing Effects Analyses via Single-Particle Profiling of Polycyclic Aromatic Hydrocarbons

JOHANNES PASSIG, Ellen-Iva Rosewig, Julian Schade, Mika Ihalainen, Kerneels Jaars, Kajar Köster, Stefan Siebert, Olli Sippula, Markus Somero, Pasi Yli-Pirilä, Pieter G. van Zyl, Annele Virtanen, Ville Vakkari, Andreas Walte, Ralf Zimmermann, Helmholtz Zentrum München and University of Rostock

     Abstract Number: 315
     Working Group: Aerosol Chemistry

Abstract
Open fires emit large amounts of carbon dioxide, reactive trace gases and particulate matter, thus affecting air quality, human health, climate and the earth system (e.g. van der Werf et al., 2017, Yue et al., 2018). Atmospheric ageing and the distribution of these aerosols are complex and highly variable, emphasizing the need for novel source apportionment strategies. In addition, chemical changes of climate- and health-relevant particle components are of particular interest.

A unique method to chemically characterize particles in complex aerosols is single-particle mass spectrometry (SPMS). The method yields the size and a chemical fingerprint from individual particles in real time, providing intriguing insights into the mixing state and distribution of relevant substances in aerosols. Recently, we introduced a new ionization technique to extend the chemical coverage of SPMS to polycyclic aromatic hydrocarbons (PAHs) (Schade et al. 2019).

Here we present results from the first single-particle study on aerosols from smouldering fires of boreal forest floor, savannah wood and savannah grass material as proxies for wildfires in the respective regions. We found that these fires produce distinct PAH patterns that differ from most anthropogenic sources – providing a new route for source apportionment based on PAHs (Passig et al. 2022). The emissions were aged in the atmospheric chamber of the ILMARI facility in Kuopio, Finland. With the real-time capabilities of our technique, we could show that PAHs are rapidly degraded, at least at the particle surface. Furthermore, some PAH signatures were depleted after less than one hour, while other ones emerged with beginning of the photooxidation ageing. The PAH distributions in the particle ensemble suggest an initially high mobility of PAHs between the particle phase and the gas phase. We also discuss correlations between PAHs, oxidation products and the particle’s inorganic particle composition on a single-particle basis.

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[2] Yue, X. et al. (2018), Nat. Commun., 9, 5413.
[3] Schade, J. et al. (2019) Anal. Chem. 91, 15, 10282–10288.
[4] Passig et al. (2022) Atmos. Chem. Phys., 22, 1495–1514.