Abstract
Abstract. The molecular characteristics of aerosol organic matter (OM) determines to a large extent its impacts on the atmospheric radiative budget and ecosystem function in terrestrial and aquatic environments, yet the OM molecular details of aerosols from different sources are not well established. Aerosol particulate samples with North American-influenced, North African-influenced, and marine (minimal recent continental influence) air mass back trajectories were collected as part of the 2011 trans-North Atlantic US GEOTRACES cruise and analyzed for their water soluble OM (WSOM) molecular characteristics using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Principal component analysis (PCA) separated the samples into five groups defined by distinct molecular formula characteristics. An abundance of nitrogen containing compounds with molecular formulas consistent with amino acid derivatives defined the two samples comprising the primary marine group (henceforth referred to as Primary Marine), which suggest a primary marine biological source to their WSOM in spite of their North American-influenced air mass trajectories. A second group of samples (aged marine, henceforth referred to as Aged Marine) with marine air mass trajectories was characterized by an abundance of low O / C (0.15–0.45) sulfur containing compounds consistent with organosulfate compounds formed via secondary aging reactions in the atmosphere. Several samples having North American-influenced air mass trajectories formed another group again characterized by organosulfate and nitrooxyorganosulfate type compounds with higher O / C ratios (0.5–1.0) than the Aged Marine samples reflecting the combustion influence from the North American continent. All the samples with North African-influenced air mass trajectories were grouped together in the PCA and were characterized by a lack of heteroatom (N, S, P) containing molecular formulas covering a wide O / C range (0.15–0.90) reflecting the desert source of this WSOM. The two marine groups showed molecular formulas that, on average, had higher H / C ratios and lower O / C ratios and modified aromaticity indices than the two continentally influenced groups, which suggests that these properties are characteristic of marine vs. continental aerosol WSOM. The final sample group, the mixed source samples (henceforth referred to as Mixed Source), showed intermediate molecular characteristics, which suggests no dominant continental or marine source. The source-specific OM details described here will aid efforts to link aerosol OM source with molecular characteristics and impacts in the environment.
Highlights
IntroductionNatural and anthropogenic atmospheric aerosols play significant roles in important environmental processes impacting climate via direct and indirect effects on the Earth’s radiative balance (e.g., Charlson et al, 1992; Ramanathan et al, 2001; Hansen et al, 2005; Booth et al, 2012), human health via reduction in air quality due to increased atmospheric loadings of particles and pollutant compounds (e.g., Davidson et al, 2005; Brook, 2008), and biogeochemical cycles and ecosystem function via the atmospheric delivery of nutrients (e.g., Duce and Tindale, 1991; Prospero et al, 1996; Duarte et al, 2006; Baker et al, 2010), organic matter (e.g., Wozniak et al, 2011, 2013), and pollutants (e.g., Driscoll et al, 2001; Rhind, 2009)
Principal component analysis (PCA) enabled the distinction of three types of marine aerosols defined by the degree to which they have been processed post-emission and their dilution with continental aerosol water soluble OM (WSOM) (Primary Marine, Aged Marine, and Mixed Source) and identified two samples with North American back trajectories as having primary marine sourced aerosol WSOM
The PCA and FTICR MS results demonstrate that for samples collected over the ocean, aerosol WSOM having marine sources has lower O / C and higher H / C ratios than continentally influenced WSOM, properties that derive from the characteristics of sea surface dissolved OM (DOM) and the bubble bursting process that emits that DOM as marine aerosols
Summary
Natural and anthropogenic atmospheric aerosols play significant roles in important environmental processes impacting climate via direct and indirect effects on the Earth’s radiative balance (e.g., Charlson et al, 1992; Ramanathan et al, 2001; Hansen et al, 2005; Booth et al, 2012), human health via reduction in air quality due to increased atmospheric loadings of particles and pollutant compounds (e.g., Davidson et al, 2005; Brook, 2008), and biogeochemical cycles and ecosystem function via the atmospheric delivery of nutrients (e.g., Duce and Tindale, 1991; Prospero et al, 1996; Duarte et al, 2006; Baker et al, 2010), organic matter (e.g., Wozniak et al, 2011, 2013), and pollutants (e.g., Driscoll et al, 2001; Rhind, 2009). Aerosol OM can absorb (or scatter) light contributing a warming (or cooling) effect to the atmospheric radiative budget via the direct effect (e.g., Ramanathan et al, 2001; Hansen et al, 2005) or act as condensation nuclei contributing to the growth of clouds impacting climate via the indirect effect (e.g., Ramanathan et al, 2001) Much of this OM is transported and deposited to terrestrial and aquatic systems where it has been implicated as an important OM source to riverine export (Likens et al, 1984; Velinsky et al, 1986; Wozniak et al, 2011) and as a complexing agent facilitating the delivery of soluble, bioavailable Fe to the ocean (Paris and Desboeufs, 2013; Wozniak et al, 2013)
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