Natural and anthropogenic aerosols affect global climate and ecosystems, and pose the greatest environmental risk to human health. Key components for biological effects are soot, metals and polycyclic aromatic hydrocarbons (PAHs). Some of these components can be detected on a single-particle basis and in real time using single-particle mass spectrometry (SPMS) [1]. However, chemical speciation and particle classification in conventional SPMS is limited by fragmentation, sensitivity and matrix effects. To overcome these limitations, we have developed laser ionization schemes that exploit resonances between the incident laser light and particle-bound molecules and atoms.
For the detection and speciation of PAHs, we combine Resonance-Enhanced Multiphoton Ionization (REMPI) of aromatic molecules with Laser Desorption/Ionization (LDI) of refractory compounds [2]. This technique provides detailed PAH mass spectra along with the particles’ inorganic composition, allowing unprecedented insight into the sources, mixing state and degradation of PAHs in aerosols [3].
In addition, we introduced resonant LDI in SPMS, substantially improving the sensitivity and selectivity for transition metals [4]. The two resonance techniques can be easily combined for PAHs and iron, a key micronutrient for marine life and a particular health-relevant aerosol compound. This will facilitate new studies on aerosol transport of Fe and improved health risk assessment by combined detection of Fe and PAHs.
Here we present results from the application of both techniques in laboratory and field experiments. We show single-particle PAH distributions in ambient air and find signatures for different sources, from traffic emissions and residential to biomass burning and individual ship plumes [3,5]. The combined single-particle information from PAHs and inorganics enables novel source apportionment schemes and allows a deep insight into complex and heavily mixed aerosols. We also present the concept of using PAHs as a molecular sensor of aerosol ageing effects, for example to track the ageing of wildfire emissions [6].
Literature:
[1] J. Passig and R. Zimmermann, 2021 Wiley‐VCH, ISBN: 9783527335107
[2] J. Schade et al., Anal. Chem. 2019, 91, 15, 10282–10288.
[3] J. Passig et al. Atmos. Chem. Phys. 2022, 22, 1495–1514.
[4] J. Passig, et al., Atmos. Chem. Phys. 2020, 20, 7139–7152.
[5] L. Anders et al. Environ. Sci.: Atmos. 2023,3, 1134-1144.
[6] E.-I. Rosewig et al., under preparation, 2024
