Molecular characterization of free tropospheric aerosol collected at the Pico Mountain Observatory

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Džepina, Katja, Mazzoleni, Claudio, Fialho, Paulo, China, Swarup, Zhang, Bo, Owen, R. Chris, Helmig, D., Hueber, J., Kumar, Sumit, Perlinger, J. A.
• Format: Other/Unknown Material
• Language: English
• Published: 2021
• Subjects: organic aerosol; ultrahigh-resolution FT-ICR MS; electron microscopy; remote marine atmosphere; Pico Mountain Observatory; info:eu-repo/classification/udc/54; North Atlantic
• Online Access: http://repozitorij.ung.si/IzpisGradiva.php?id=6451; https://plus.si.cobiss.net/opac7/bib/59042563?lang=sl

Free tropospheric aerosol was sampled at the Pico Mountain Observatory located at 2225 m above mean sea level on Pico Island of the Azores archipelago in the North Atlantic. The observatory is located ∼ 3900 km east and downwind of North America, which enables studies of free tropospheric air transported over long distances. Aerosol samples collected on filters from June to October 2012 were analyzed to characterize organic carbon, elemental carbon, and inorganic ions. The average ambient concentration of aerosol was 0.9 ± 0.7 µg m−3 . On average, organic aerosol components represent the largest mass fraction of the total measured aerosol (60 ± 51 %), followed by sulfate (23 ± 28 %), nitrate (13 ± 10 %), chloride (2 ± 3 %), and elemental carbon (2 ± 2 %). Water-soluble organic matter (WSOM) extracted from two aerosol samples (9/24 and 9/25) collected consecutively during a pollution event were analyzed using ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Approximately 4000 molecular formulas were assigned to each of the mass spectra in the range of m/z 100–1000. The majority of the assigned molecular formulas had unsaturated structures with CHO and CHNO elemental compositions. FLEXPART retroplume analyses showed the sampled air masses were very aged (average plume age > 12 days). These aged aerosol WSOM compounds had an average O /C ratio of ∼ 0.45, which is relatively low compared to O /C ratios of other aged aerosol. The increase in aerosol loading during the measurement period of 9/24 was linked to biomass burning emissions from North America by FLEXPART retroplume analysis and Moderate Resolution Imaging Spectroradiometer (MODIS) fire counts. This was confirmed with biomass burning markers detected in the WSOM and with the morphology and mixing state of particles as determined by scanning electron microscopy. The presence of markers characteristic of aqueous-phase reactions of phenolic species suggests that the aerosol collected at the Pico ...