J Am Soc Mass Spectrom
January 2025
While gas chromatography mass spectrometry (GC-MS) has long been used to identify compounds in complex mixtures, this process is often subjective and time-consuming and leaves a large fraction of seemingly good-quality spectra unidentified. In this work, we describe a set of new mass spectral library-based methods to assist compound identification in complex mixtures. These methods employ mass spectral uniqueness and compound ubiquity of library entries alongside noise reduction and automated comparison of retention indices to library compounds.
View Article and Find Full Text PDFPhenolic compounds, which are significant emissions from biomass burning (BB), undergo rapid photochemical reactions in both gas and aqueous phases to form secondary organic aerosol, namely, gasSOA and aqSOA, respectively. The formation of gasSOA and aqSOA involves different reaction mechanisms, leading to different product distributions. In this study, we investigate the gaseous and aqueous reactions of guaiacol-a representative BB phenol-to elucidate the compositional differences between phenolic aqSOA and gasSOA.
View Article and Find Full Text PDFUrbanization and fires perturb the quantities and composition of fine organic aerosol in the central Amazon, with ramifications for radiative forcing and public health. These disturbances include not only direct emissions of particulates and secondary organic aerosol (SOA) precursors but also changes in the pathways through which biogenic precursors form SOA. The composition of ambient organic aerosol is complex and incompletely characterized, encompassing millions of potential structures relatively few of which have been synthesized and characterized.
View Article and Find Full Text PDFBiomass burning is the largest combustion-related source of volatile organic compounds (VOCs) to the atmosphere. We describe the development of a state-of-the-science model to simulate the photochemical formation of secondary organic aerosol (SOA) from biomass-burning emissions observed in dry (RH <20%) environmental chamber experiments. The modeling is supported by (i) new oxidation chamber measurements, (ii) detailed concurrent measurements of SOA precursors in biomass-burning emissions, and (iii) development of SOA parameters for heterocyclic and oxygenated aromatic compounds based on historical chamber experiments.
View Article and Find Full Text PDFAcid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), key isoprene oxidation products, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur compounds. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. In this article, we demonstrate that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate concentration ratio (IEPOX/Sulf), as determined by laboratory measurements.
View Article and Find Full Text PDFOne of the least understood aspects in atmospheric chemistry is how urban emissions influence the formation of natural organic aerosols, which affect Earth's energy budget. The Amazon rainforest, during its wet season, is one of the few remaining places on Earth where atmospheric chemistry transitions between preindustrial and urban-influenced conditions. Here, we integrate insights from several laboratory measurements and simulate the formation of secondary organic aerosols (SOA) in the Amazon using a high-resolution chemical transport model.
View Article and Find Full Text PDFEnviron Sci Process Impacts
November 2018
Organosulfates are formed in the atmosphere from reactions between reactive organic compounds (such as oxidation products of isoprene) and acidic sulfate aerosol. Here we investigated speciated organosulfates in an area typically downwind of the city of Manaus situated in the Amazon forest in Brazil during "GoAmazon2014/5" in both the wet season (February-March) and dry season (August-October). We observe products consistent with the reaction of isoprene photooxidation products and sulfate aerosols, leading to formation of several types of isoprene-derived organosulfates, which contribute 3% up to 42% of total sulfate aerosol measured by aerosol mass spectrometry.
View Article and Find Full Text PDFProc Natl Acad Sci U S A
February 2018
Environ Sci Technol
September 2016
Exchange of atmospheric organic compounds between gas and particle phases is important in the production and chemistry of particle-phase mass but is poorly understood due to a lack of simultaneous measurements in both phases of individual compounds. Measurements of particle- and gas-phase organic compounds are reported here for the southeastern United States and central Amazonia. Polyols formed from isoprene oxidation contribute 8% and 15% on average to particle-phase organic mass at these sites but are also observed to have substantial gas-phase concentrations contrary to many models that treat these compounds as nonvolatile.
View Article and Find Full Text PDFThe effects of structure, NOx conditions, relative humidity, and aerosol acidity on the chemical composition of secondary organic aerosol (SOA) are reported for the photooxidation of three C12 alkanes: n-dodecane, cyclododecane, and hexylcyclohexane. Acidity was modified through seed particle composition: NaCl, (NH4)2SO4, and (NH4)2SO4 + H2SO4. Off-line analysis of SOA was carried out by solvent extraction and gas chromatography-mass spectrometry (GC/MS) and direct analysis in real-time mass spectrometry.
View Article and Find Full Text PDFOrganic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs).
View Article and Find Full Text PDFThe extended photooxidation of and secondary organic aerosol (SOA) formation from dodecane (C(12)H(26)) under low-NO(x) conditions, such that RO(2) + HO(2) chemistry dominates the fate of the peroxy radicals, is studied in the Caltech Environmental Chamber based on simultaneous gas and particle-phase measurements. A mechanism simulation indicates that greater than 67% of the initial carbon ends up as fourth and higher generation products after 10 h of reaction, and simulated trends for seven species are supported by gas-phase measurements. A characteristic set of hydroperoxide gas-phase products are formed under these low-NO(x) conditions.
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