Abstract. 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 Fe signatures for many more aerosol particles compared to the more common ArF-excimer laser line of 193.3 nm. Moreover, resonant ionization of iron appeared to be less dependent on the particle matrix than conventional non-resonant LDI, allowing a more universal and secure detection of Fe. 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.
Supplementary material to "Resonance-Enhanced Detection of Metals in Aerosols using Single Particle Mass Spectrometry"
