Abstract
Organic aerosols (OA) are universally regarded as an important component of the atmosphere that have far-ranging impacts on climate forcing and human health. Many of these impacts are related to OA molecular characteristics. Despite the acknowledged importance, current uncertainties related to the source apportionment of molecular properties and environmental impacts make it difficult to confidently predict the net impacts of OA. Here we evaluate the specific molecular compounds as well as bulk structural properties of total suspended particulates in ambient OA collected from key emission sources (marine, biomass burning, and urban) using ultrahigh resolution mass spectrometry (UHR-MS) and proton nuclear magnetic resonance spectroscopy (1H NMR). UHR-MS and 1H NMR show that OA within each source is structurally diverse, and the molecular characteristics are described in detail. Principal component analysis (PCA) revealed that (1) aromatic nitrogen species are distinguishing components for these biomass burning aerosols; (2) these urban aerosols are distinguished by having formulas with high O/C ratios and lesser aromatic and condensed aromatic formulas; and (3) these marine aerosols are distinguished by lipid-like compounds of likely marine biological origin. This study provides a unique qualitative approach for enhancing the chemical characterization of OA necessary for molecular source apportionment.
Highlights
TSP loadings were highest for the biomass burning samples (73.2 μgm3 ) followed by the urban (47.1 μgm3 ) and mixed source (24.1 μgm3 ) samples
The marine samples show total carbon (TC) loadings (0.5 μgm3 ) one order of magnitude lower than the mixed source (5.7 μgm3 ) and urban (6.3 μgm3 ) samples and two orders of magnitude lower than the biomass burning samples (24.8 μgm3 ) as one would expect for samples collected over the middle of the ocean far from major terrestrial and anthropogenic sources
The carbon backbones of these molecules are more aliphatic and less diverse than terrestrial Organic aerosol (OA), and the Organic matter (OM) is overall less oxidized
Summary
Organic aerosol (OA) compounds, once emitted into the atmosphere as primary OA or formed in situ as secondary OA (SOA) from gas-phase precursors, can undergo a myriad of atmospheric reactions forming new compounds that have different chemical structures and associated physical properties. The composition and relative concentrations of OA are expected to vary spatially and temporally due to differences in emission inputs and in the extent to which OA are transformed in the atmosphere by secondary aging processes [1]. The molecular composition of OA resulting from these emissions and aging processes will, in part, determine its impacts on e.g., aerosol hygroscopicity [3,4], light absorption [5], and biogeochemical cycling upon deposition [6,7].
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