Chemical characterization of free tropospheric aerosols in the North Atlantic measured at the Pico Mountain observatory during summer of 2012
Free tropospheric aerosol was sampled at the Pico Mountain Observatory located at 2225 m a.s.l. on Pico Island in the Azores archipelago in the North Atlantic. The observatory is ~3900 km east and downwind of North America (38°28'15''N; 28°24'14''W) and thus enables sampling of free tropospheric air transported over long distances mainly from North America, and is rarely affected by local emissions. Currently, little is known about the nature of aged aerosol motivating new measurements at the Observatory. This work enabled for the first time a detailed chemical characterization of the free tropospheric, aged aerosols intercepted at the Observatory, as well as its comparison with collocated measurements of optical and physical properties. Samples of fine particles (PM2.5) were collected during summer 2012 on quartz filters using high-volume samplers and analyzed for organic and elemental carbon (OC and EC, respectively), water-soluble organic carbon (WSOC) and inorganic ion species. Special attention was given to aerosol samples collected on September 24 and 25 and its WSOC composition was analyzed using ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Approx. 4000 formulas were assigned to each of the mass spectra in the range of m/z 100-900. The majority of assigned molecular formulas have CHO and CHNO elemental composition (~ 2/3 and 1/3, respectively), while sulfur containing species with CHOS and CHNOS elemental composition represent a very small number fraction. Surprisingly, this highly processed aerosol has a fairly low O/C ratio of 0.45. Most of the assigned formula species have aliphatic and olefinic structures, as indicated by the aromaticity index and double bond equivalents of the detected species. The detailed chemical characterization of samples analyzed with FT-ICR MS, including its elemental composition, elemental ratios (O:C, H:C and OM:OC), and their carbon oxidation state will be presented. Chemical characterization of the observed aerosols is compared to the collocated measurements of gases, particle size and optical properties, meteorological parameters and it is critically compared to the other characterizations found in the current literature. Finally, we compare our results to the physical properties of collected aerosols as observed by electron microscopy.
Fall Meeting 2013
Dzepina, K.; China, Swarup; Kumar, S.; Mazzoleni, Claudio; Dziobak, M. P.; Fialho, Paulo; Hueber, Jacques; Helmig, D.; Owen, R. C.; Kramer, L.; Olsen, S.; and Mazzoleni, Lynn, "Chemical characterization of free tropospheric aerosols in the North Atlantic measured at the Pico Mountain observatory during summer of 2012" (2013). Department of Chemistry Publications. 35.