Resonance-enhanced detection of metals in aerosols using single-particle mass spectrometry

• Published in: Atmospheric chemistry and physics Vol. 20; no. 12; pp. 7139 - 7152
• Main Authors: Passig, Johannes, Schade, Julian, Rosewig, Ellen Iva, Irsig, Robert, Kröger-Badge, Thomas, Czech, Hendryk, Sklorz, Martin, Streibel, Thorsten, Li, Lei, Li, Xue, Zhou, Zhen, Fallgren, Henrik, Moldanova, Jana, Zimmermann, Ralf
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 18-06-2020; Copernicus Publications
• Subjects: Ablation; Absorption; Aerosol particles; Aerosols; Anthropogenic factors; Atmospheric particulates; Bioavailability; Carbon; Detection; Dust; Dust storms; Electromagnetic absorption; Excimer lasers; Excimers; Experiments; Heavy metals; Human influences; Hydrocarbons; Ionization; Iron; Iron transport; Krypton fluoride lasers; Laboratories; Lasers; Light absorption; Manganese; Marine environment; Mass spectrometry; Mass spectroscopy; Metals; Micronutrients; Oceans; Organic carbon; Particle mass; Primary production; Resonance; Scientific imaging; Selectivity; Soot; Spectroscopy; Technology application; Wavelength; Wavelengths; Zinc; United States > US; Germany
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-20-7139-2020

We describe resonance effects in laser desorption–ionization (LDI)
of particles that substantially increase the sensitivity and selectivity to
metals in single-particle mass spectrometry (SPMS). Within the proposed
scenario, resonant light absorption by ablated metal atoms increases their
ionization rate within a single laser pulse. By choosing the appropriate
laser wavelength, the key micronutrients Fe, Zn and Mn can be detected on
individual aerosol particles with considerably improved efficiency. These
ionization enhancements for metals apply to natural dust and anthropogenic
aerosols, both important sources of bioavailable metals to marine
environments. Transferring the results into applications, we show that the
spectrum of our KrF-excimer laser is in resonance with a major absorption
line of iron atoms. To estimate the impact of resonant LDI on the metal
detection efficiency in SPMS applications, we performed a field experiment
on ambient air with two alternately firing excimer lasers of different
wavelengths. Herein, resonant LDI with the KrF-excimer laser (248.3 nm)
revealed iron signatures for many more particles of the same aerosol
ensemble compared to the more common ArF-excimer laser line of 193.3 nm
(nonresonant LDI of iron). Many of the particles that showed iron contents
upon resonant LDI were mixtures of sea salt and organic carbon. For
nonresonant ionization, iron was exclusively detected in particles with a
soot contribution. This suggests that resonant LDI allows a more universal
and secure metal detection in SPMS. Moreover, our field study indicates
relevant atmospheric iron transport by mixed organic particles, a pathway
that might be underestimated in SPMS measurements based on nonresonant LDI.
Our findings show a way to improve the detection and source attribution
capabilities of SPMS for particle-bound metals, a health-relevant aerosol
component and an important source of micronutrients to the surface oceans
affecting marine primary productivity.