skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Multiphase Guaiacol Photooxidation: Fenton Reactions, Brown Carbon, and Secondary Organic Aerosol Formation in Suspended Aerosol Particles
Title: Multiphase Guaiacol Photooxidation: Fenton Reactions, Brown Carbon, and Secondary Organic Aerosol Formation in Suspended Aerosol Particles
Guaiacol, present in wood smoke, readily forms secondary organic aerosol (SOA), and, in the aqueous phase, brown carbon (BrC) species. Here, BrC is produced in an illuminated chamber containing guaiacol(g), HOOH(g) as an OH radical source, and either deliquesced salt particles or guaiacol SOA at 50% relative humidity. BrC production slows without an OH source (HOOH), likely due to low levels of radical generation by photosensitization, perhaps involving surface-adsorbed guaiacol and dissolved oxygen. With or without HOOH, BrC mass absorption coefficients at 365 nm generated by the guaiacol + OH reaction reach a maximum at ~6 h of atmospheric OH exposure, after which photobleaching becomes dominant. In the presence of soluble iron but no HOOH, more BrC is produced, likely due to insoluble polymer production observed in previous studies. However, with both soluble iron and HOOH (enabling Fenton chemistry), significantly less SOA and BrC are produced due to very high oxidation rates, and the average SOA carbon oxidation state reaches 2, indicating carboxylate products like oxalate. These results indicate that SOA and BrC formation by guaiacol photooxidation can take place over a wider range of atmospheric conditions than previously thought, and that the effects of iron(II) depend on HOOH. Multiphase guaiacol photooxidation likely makes a significant contribution to producing highly oxidized SOA material in smoke plumes.  more » « less
Award ID(s):
2218491
PAR ID:
10531331
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
American Chemical Society
Date Published:
Journal Name:
ACS ES&T Air
Volume:
1
Issue:
5
ISSN:
2837-1402
Page Range / eLocation ID:
346 to 356
Subject(s) / Keyword(s):
Multiphase, smoke plume, photobrowning, photosensitizer, photobleaching, surface enhanced, Fenton
Format(s):
Medium: X Size: 620 kB Other: PDF/A
Size(s):
620 kB
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, ACS ES&T Air)
    Catechol (1,2-benzenediol), a common phenolic species emitted during biomass burning, is both redox active and metal chelating. When oxidized by OH radicals in the aqueous phase, it rapidly forms brown carbon (BrC). Here, we report chamber studies of the multiphase chemistry of catechol using HOOH as an OH radical source, soluble iron, simulated sunlight, and either deliquesced or solid-phase seed particles. BrC of remarkable similarity (MAC365 = 1.7 ±0.2 m2 g-1, “medium-BrC” category) was produced whenever gas-phase catechol was photolyzed in the chamber, with or without the presence of an OH radical source, soluble iron, or deliquesced aerosol. The speed and quantity of BrC formation varied, however. While BrC production was slower in the absence of an OH radical source, multiple lines of evidence suggest that OH generation via photosensitization by surface-adsorbed catechol can still generate BrC. Fenton chemistry actively occurred in surface-adsorbed water layers even below the seed particle deliquescence point, leading to significant production of gas-phase benzoquinone. Ratios of BrC and secondary organic aerosol (SOA) relative to catechol concentrations were highest in the presence of trace amounts of soluble iron, HOOH, and simulated sunlight, indicating that photo-Fenton chemistry contributed substantially to BrC and SOA formation by catechol. Finally, we observed that BrC and SOA formation by catechol / photo-Fenton chemistry can occur efficiently even at 40% RH. These results are consistent with catechol being a major source of secondary BrC in biomass burning plumes, even at moderate relative humidity. 
    more » « less
  2. ; ; ; (, Atmospheric Chemistry and Physics)
    Abstract. While gas-phase reactions are well established to have significant impacts on the mass concentration, chemical composition, and optical properties of secondary organic aerosol (SOA), the aqueous-phase aging of SOA remains poorly understood. In this study, we performed a series of long-duration photochemical aging experiments to investigate the evolution of the composition and light absorption of the aqueous SOA (aqSOA) from guaiacyl acetone (GA), a semivolatile phenolic carbonyl that is common in biomass burning smoke. The aqSOA was produced from reactions of GA with hydroxyl radical (•OH-aqSOA) or a triplet excited state of organic carbon (3C∗-aqSOA) and was then photoaged in water under conditions that simulate sunlight exposure in northern California for up to 48 h. The effects of increasing aqueous-phase •OH or 3C∗concentration on the photoaging of the aqSOA were also studied. High-resolution aerosol mass spectrometry (HR-AMS) and UV–Vis spectroscopy were utilized to characterize the composition and the light absorptivity of the aqSOA and to track their changes during aging. Compared to •OH-aqSOA, the 3C∗-aqSOA is produced more rapidly and shows less oxidation, a greater abundance of oligomers, and higher light absorption. Prolonged photoaging promotes fragmentation and the formation of more volatile and less light-absorbing products. More than half of the initial aqSOA mass is lost, and substantial photobleaching occurs after 10.5 h of prolonged aging under simulated sunlight illumination for 3C∗-aqSOA and 48 h for •OH-aqSOA. By performing positive matrix factorization (PMF) analysis of the combined HR-AMS and UV–Vis spectral data, we resolved three generations of aqSOA with distinctly different chemical and optical properties. The first-generation aqSOA shows significant oligomer formation and enhanced light absorption at 340–400 nm.The second-generation aqSOA is enriched in functionalized GA species and has the highest mass absorption coefficients in 300–500 nm, while the third-generation aqSOA contains more fragmented products and is the least light absorbing. These results suggest that intermediately aged phenolic aqSOA is more light absorbing than other generations, and that the light absorptivity of phenolic aqSOA results from a competition between brown carbon (BrC) formation and photobleaching, which is dependent on aging time. Although photoaging generally increases the oxidation of aqSOA, a slightly decreased O/C of the •OH-aqSOA is observed after 48 h of prolonged photoaging with additional •OH exposure. This is likely due to greater fragmentation and evaporation of highly oxidized compounds.Increased oxidant concentration accelerates the transformation of aqSOA and promotes the decay of BrC chromophores, leading to faster mass reduction and photobleaching. In addition, compared with •OH, photoaging by3C∗ produces more low-volatility functionalized products, which counterbalances part of the aqSOA mass loss due to fragmentation and evaporation. 
    more » « less
  3. ; ; ; ; ; ; ; (, Atmospheric Chemistry and Physics)
    Abstract. Indole (ind) is a nitrogen-containing heterocyclic volatile organic compound commonly emitted from animal husbandry and from different plants like maize with global emissions of 0.1 Tg yr−1. The chemical composition and optical properties of indole secondary organic aerosol (SOA) and brown carbon (BrC) are still not well understood. To address this, environmental chamber experiments were conducted to investigate the oxidation of indole at atmospherically relevant concentrations of selected oxidants (OH radicals and O3) with or without NO2. In the presence of NO2, the SOA yields decreased by more than a factor of 2, but the mass absorption coefficient at 365 nm (MAC365) of ind-SOA was 4.3 ± 0.4 m2 g−1, which was 5 times higher than that in experiments without NO2. In the presence of NO2, C8H6N2O2 (identified as 3-nitroindole) contributed 76 % to all organic compounds detected by a chemical ionization mass spectrometer, contributing ∼ 50 % of the light absorption at 365 nm (Abs365). In the absence of NO2, the dominating chromophore was C8H7O3N, contributing to 20 %–30 % of Abs365. Indole contributes substantially to the formation of secondary BrC and its potential impact on the atmospheric radiative transfer is further enhanced in the presence of NO2, as it significantly increases the specific light absorption of ind-SOA by facilitating the formation of 3-nitroindole. This work provides new insights into an important process of brown carbon formation by interaction of two pollutants, NO2 and indole, mainly emitted by anthropogenic activities. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; (, AAAR 40th Annual Conference)
    Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX) with inorganic sulfate aerosols contributes substantially to formation of secondary organic aerosol (SOA), which constitutes a large mass fraction of atmospheric fine particulate matter (PM2.5). However, atmospheric chemical sinks of freshly generated IEPOX-SOA particles remain unclear. We examined the role of heterogeneous oxidation of freshly-generated IEPOX-SOA particles by gas-phase hydroxyl radical (•OH) under dark conditions as one potential atmospheric sink. After 4 h of gas-phase •OH exposure (~3x108 molecules cm-3), chemical changes in smog chamber-generated IEPOX-SOA particles were assessed by hydrophilic interaction liquid chromatography coupled with electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS). Comparison of molecular-level compositional changes in IEPOX-SOA particles during aging with or without •OH revealed that decomposition of oligomers by heterogeneous •OH oxidation acts as a sink for •OH and maintains a reservoir of low-volatility compounds including monomeric sulfate esters and oligomer fragments. We propose tentative structures and formation mechanisms for previously uncharacterized SOA constituents in PM2.5. Our results suggest that this •OH-driven renewal of low-volatility products may extend atmospheric lifetimes of IEPOX-SOA particles by slowing production of low-molecular weight, high-volatility organic fragments, and likely contributes to large quantities of 2-methyltetrols and methyltetrol sulfates reported in PM2.5. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Environmental Science: Atmospheres)
    Wildfires are an important atmospheric source of primary organic aerosol (POA) and precursors for secondary organic aerosol (SOA) at regional and global scales. However, there are large uncertainties surrounding the emissions and physicochemical processes that control the transformation, evolution, and properties of POA and SOA in large wildfire plumes. We develop a plume version of a kinetic model to simulate the dilution, oxidation chemistry, thermodynamic properties, and microphysics of organic aerosol (OA) in wildfire smoke. The model is applied to study the in-plume OA in four large wildfire smoke plumes intercepted during an aircraft-based field campaign in summer 2018 in the western United States. Based on estimates of dilution and oxidant concentrations before the aircraft first intercepted the plumes, we simulate the OA evolution from very close to the fire to several hours downwind. Our model results and sensitivity simulations suggest that dilution-driven evaporation of POA and simultaneous photochemical production of SOA are likely to explain the observed evolution in OA mass with physical age. The model, however, substantially underestimates the change in the oxygen-to-carbon ratio of the OA compared to measurements. In addition, we show that the rapid chemical transformation within the first hour after emission is driven by higher-than-ambient OH concentrations (3×10 6 -10 7 molecules cm -3 ) and the slower evolution over the next several hours is a result of lower-than-ambient OH concentrations (<10 6 molecules cm -3 ) and depleted SOA precursors. Model predictions indicate that the OA measured several hours downwind of the fire is still dominated by POA but with an SOA fraction that varies between 30% and 56% of the total OA. Semivolatile, heterocyclic, and oxygenated aromatic compounds, in that order, were found to contribute substantially (>90%) to SOA formation. Future work needs to focus on better understanding the dynamic evolution closer to the fire and resolving the rapid change in the oxidation state of OA with physical age. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email