A molecular-level approach for characterizing water-insoluble components of ambient organic aerosol particulates using ultrahigh-resolution mass spectrometry

摘要

The chemical composition of organic aerosols in the atmosphere is stronglyinfluenced by human emissions. The effect these have on the environment,human health, and climate change is determined by the molecular nature ofthese chemical species. The complexity of organic aerosol samples limits theability to study the chemical composition, and therefore the associatedproperties and the impacts they have. Many studies have addressed the water-solublefraction of organic aerosols and have had much success in identifyingspecific molecular formulas for thousands of compounds present. However,little attention is given to the water-insoluble portion, which can containmost of the fossil material that is emitted through human activity. Here wecompare the organic aerosols present in water extracts and organic solventextracts (pyridine and acetonitrile) of an ambient aerosol sample collectedin a rural location that is impacted by natural and anthropogenic emissionsources. A semiquantitative method was developed using proton nuclearmagnetic resonance spectroscopy to determine that the amount of organicmatter extracted by pyridine is comparable to that of water. Electrosprayionization Fourier transform ion cyclotron resonance mass spectra show thatpyridine extracts a molecularly unique fraction of organic matter comparedto water or acetonitrile, which extract chemically similar organic mattercomponents. The molecular formulas unique to pyridine were less polar, morealiphatic, and reveal formulas containing sulfur to be an importantcomponent of insoluble aerosol organic matter.