Abstract. To better understand the effects of wildfires on air quality andclimate, it is important to assess the occurrence of chromophoric compoundsin smoke and characterize their optical properties. This study explores themolecular composition of light-absorbing organic aerosol, or brown carbon(BrC), sampled at the Missoula Fire Sciences laboratory as a part of theFIREX Fall 2016 lab intensive. A total of 12 biomass fuels from different planttypes were tested, including gymnosperm (coniferous) and angiosperm(flowering) plants and different ecosystem components such as duff, litter,and canopy. Emitted biomass burning organic aerosol (BBOA) particles werecollected onto Teflon filters and analyzed offline using high-performanceliquid chromatography coupled to a photodiode array spectrophotometer and a high-resolution mass spectrometer(HPLC–PDA–HRMS). Separated BrC chromophores were classified by theirretention times, absorption spectra, integrated absorbance in the near-UVand visible spectral range (300–700 nm), and chemical formulas from theaccurate m∕z measurements. BrC chromophores were grouped into the followingclasses and subclasses: lignin-derived products, which include lignin pyrolysisproducts; distillation products, which include coumarins and flavonoids;nitroaromatics; and polycyclic aromatic hydrocarbons (PAHs). The observedclasses and subclasses were common across most fuel types, although specific BrCchromophores varied based on plant type (gymnosperm or angiosperm) andecosystem component(s) burned. To study the stability of the observed BrCcompounds with respect to photodegradation, BBOA particle samples wereirradiated directly on filters with near UV (300–400 nm) radiation, followedby extraction and HPLC–PDA–HRMS analysis. Lifetimes of individual BrCchromophores depended on the fuel type and the corresponding combustioncondition. Lignin-derived and flavonoid classes of BrC generally hadthe longest lifetimes with respect to UV photodegradation. Moreover,lifetimes for the same type of BrC chromophores varied depending on biomassfuel and combustion conditions. While individual BrC chromophoresdisappeared on a timescale of several days, the overall light absorption bythe sample persisted longer, presumably because the condensed-phasephotochemical processes converted one set of chromophores into anotherwithout complete photobleaching or from undetected BrC chromophores thatphotobleached more slowly. To model the effect of BrC on climate, it isimportant to understand the change in the overall absorption coefficientwith time. We measured the equivalent atmospheric lifetimes of the overallBrC absorption coefficient, which ranged from 10 to 41 d, with subalpinefir having the shortest lifetime and conifer canopies, i.e., juniper, havingthe longest lifetime. BrC emitted from biomass fuel loads encompassingmultiple ecosystem components (litter, shrub, canopy) had absorptionlifetimes on the lower end of the range. These results indicate thatphotobleaching of BBOA by condensed-phase photochemistry isrelatively slow. Competing chemical aging mechanisms, such as heterogeneousoxidation by OH, may be more important for controlling the rate of BrCphotobleaching in BBOA.
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Photosensitized Reactions of a Phenolic Carbonyl from Wood Combustion in the Aqueous Phase—Chemical Evolution and Light Absorption Properties of AqSOA
Guaiacyl acetone (GA) is a phenolic carbonyl emitted in significant quantities by wood combustion that undergoes rapid aqueous-phase oxidation to produce aqueous secondary organic aerosol (aqSOA). We investigate the photosensitized oxidation of GA by an organic triplet excited state (3C*) and the formation and aging of the resulting aqSOA in wood smoke-influenced fog/cloud water. The chemical transformations of the aqSOA were characterized in situ using a high-resolution time-of-flight aerosol mass spectrometer. Additionally, aqSOA samples collected over different time periods were analyzed using high-performance liquid chromatography coupled with a photodiode array detector and a high-resolution Orbitrap mass spectrometer (HPLC-PDA-HRMS) to provide details on the molecular composition and optical properties of brown carbon (BrC) chromophores. Our results show efficient formation of aqSOA from GA, with an average mass yield around 80%. The composition and BrC properties of the aqSOA changed significantly over the course of reaction. Three generations of aqSOA products were identified via Positive Matrix Factorization analysis of the AMS data. Oligomerization and functionalization dominated the production of the first-generation aqSOA, whereas fragmentation and ring-opening reactions controlled the formation of more oxidized second- and third-generation products. Significant formation of BrC was observed in the early stages of the photoreaction, while organic acids were produced throughout the experiment. High-molecular-weight molecules (m/z > 180) with high aromaticity were identified via HPLC-PDA-HRMS and were found to account for a majority of the UV-vis absorption of the aqSOA.
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- Award ID(s):
- 1649212
- NSF-PAR ID:
- 10221757
- Date Published:
- Journal Name:
- Environmental Science & Technology
- ISSN:
- 0013-936X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Isoprene is the most abundant non‐methane volatile organic compound (VOC) emitted globally. Isomeric isoprene hydroxy hydroperoxides (ISOPOOH), key photooxidation products of isoprene, likely comprise the second most abundant class of peroxides in the atmosphere, following hydrogen peroxide. Studies have shown that hydrogen peroxide plays important roles in the formation of inorganic sulfates in cloud water mimics. However, the potential for ISOPOOH to play a role in sulfate formation in wet aerosol oxidation from reduced sulfur species (such as inorganic sulfite) is not well understood. This study systematically investigates the reaction kinetics and products of ISOPOOH reacting with particle phase inorganic sulfite and discusses implications to the sulfate aerosol budget. In order to examine the reaction kinetics of ISOPOOH with aqueous sulfite, ammonium bisulfite particles were injected into the UNC indoor environmental chamber under dark conditions with 70% RH. After the inorganic sulfite concentrations stabilized, selected concentrations of gas‐phase 1,2‐ISOPOOH was injected into the chamber to initiate the multiphase reaction. The gas‐phase ISOPOOH and particle‐phase species were sampled with online instruments, including a chemical ionization mass spectrometer (CIMS), an aerosol chemical speciation monitor (ACSM), and a particle‐into‐liquid sampler (PILS), and also collected by Teflon filters for offline molecular level analyses by an ultra‐performance liquid chromatography coupled to an electrospray ionization high resolution quadrupole time‐of‐flight mass spectrometry (UPLC‐ESI‐HR‐QTOFMS). Results show that a significant amount of inorganic sulfite was converted to inorganic sulfate and organosulfates in the particle phase at relatively fast reaction rates, altering the chemical and physical properties of the particles including phase state, pH, reactivity, and composition. Given the high abundance and water solubility of ISOPOOH in the ambient environment, the multiphase reactions examined in our study indicate significant impacts of ISOPOOH on the atmospheric lifecycle of sulfur and the physicochemical properties of ambient particles.more » « less
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Isoprene is the most abundant non‐methane volatile organic compound (VOC) emitted globally. Isomeric isoprene hydroxy hydroperoxides (ISOPOOH), key photooxidation products of isoprene, likely comprise the second most abundant class of peroxides in the atmosphere, following hydrogen peroxide. Studies have shown that hydrogen peroxide plays important roles in the formation of inorganic sulfates in cloud water mimics. However, the potential for ISOPOOH to play a role in sulfate formation in wet aerosol oxidation from reduced sulfur species (such as inorganic sulfite) is not well understood. This study systematically investigates the reaction kinetics and products of ISOPOOH reacting with particle phase inorganic sulfite and discusses implications to the sulfate aerosol budget. In order to examine the reaction kinetics of ISOPOOH with aqueous sulfite, ammonium bisulfite particles were injected into the UNC indoor environmental chamber under dark conditions with 70% RH. After the inorganic sulfite concentrations stabilized, selected concentrations of gas‐phase 1,2‐ISOPOOH was injected into the chamber to initiate the multiphase reaction. The gas‐phase ISOPOOH and particle‐phase species were sampled with online instruments, including a chemical ionization mass spectrometer (CIMS), an aerosol chemical speciation monitor (ACSM), and a particle‐into‐liquid sampler (PILS), and also collected by Teflon filters for offline molecularlevel analyses by an ultra‐performance liquid chromatography coupled to an electrospray ionization high resolution quadrupole time‐of‐flight mass spectrometry (UPLC‐ESI‐HR‐QTOFMS). Results show that a significant amount of inorganic sulfite was converted to inorganic sulfate and organosulfates in the particle phase at relatively fast reaction rates, altering the chemical and physical properties of the particles including phase state, pH, reactivity, and composition. Given the high abundance and water solubility of ISOPOOH in the ambient environment, the multiphase reactions examined in our study indicate significant impacts of ISOPOOH on the atmospheric lifecycle of sulfur and the physicochemical properties of ambient particles.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.est.0c07581
