Feasibility of Photosensitized Reactions with Secondary Organic Aerosol Particles in the Presence of Volatile Organic Compounds

Malecha, Kurtis T.; Nizkorodov, Sergey A.

doi:10.1021/acs.jpca.7b04066

Cited by 22 publications

(30 citation statements)

References 38 publications

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“…First, different matrices could quench the electronic excitation in the chromophores to a different extent. Another possibility is that photodegradation of BrC chromophores could be not due to direct photolysis but rather occurring through condensed-phase photosensitized reactions (Malecha and Nizkorodov, 2017;Monge et al, 2012), in which case the rate of decomposition would depend on concentration of photosensitizers in the samples as well as viscosity of the material (Hinks et al, 2016;Kaur et al, 2019). Lastly, other absorbing species, such as black carbon, could be shielding BrC chromophores from irradiation, altering the amount of radiation absorbed by BrC chromophores.…”

Section: Aging By Condensed-phase Photochemistrymentioning

confidence: 99%

“…Using infrared spectroscopy they observed the emergence of carboxylic acid, aldehyde, and ketone functionalities during photolysis. Miller and Olejnik (2001) irradiated aqueous solutions of PAH mixtures with UVC lamps. They found that the photodegradation of benzo[a]pyrene and chrysene proceeds more rapidly at acidic pH values and proposed a mechanism based on their findings.…”

Section: Introductionmentioning

confidence: 99%

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Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

et al. 2020

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Abstract. To better understand the effects of wildfires on air quality and climate, it is important to assess the occurrence of chromophoric compounds in smoke and characterize their optical properties. This study explores the molecular composition of light-absorbing organic aerosol, or brown carbon (BrC), sampled at the Missoula Fire Sciences laboratory as a part of the FIREX Fall 2016 lab intensive. A total of 12 biomass fuels from different plant types 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 were collected onto Teflon filters and analyzed offline using high-performance liquid chromatography coupled to a photodiode array spectrophotometer and a high-resolution mass spectrometer (HPLC–PDA–HRMS). Separated BrC chromophores were classified by their retention times, absorption spectra, integrated absorbance in the near-UV and visible spectral range (300–700 nm), and chemical formulas from the accurate m∕z measurements. BrC chromophores were grouped into the following classes and subclasses: lignin-derived products, which include lignin pyrolysis products; distillation products, which include coumarins and flavonoids; nitroaromatics; and polycyclic aromatic hydrocarbons (PAHs). The observed classes and subclasses were common across most fuel types, although specific BrC chromophores varied based on plant type (gymnosperm or angiosperm) and ecosystem component(s) burned. To study the stability of the observed BrC compounds with respect to photodegradation, BBOA particle samples were irradiated directly on filters with near UV (300–400 nm) radiation, followed by extraction and HPLC–PDA–HRMS analysis. Lifetimes of individual BrC chromophores depended on the fuel type and the corresponding combustion condition. Lignin-derived and flavonoid classes of BrC generally had the longest lifetimes with respect to UV photodegradation. Moreover, lifetimes for the same type of BrC chromophores varied depending on biomass fuel and combustion conditions. While individual BrC chromophores disappeared on a timescale of several days, the overall light absorption by the sample persisted longer, presumably because the condensed-phase photochemical processes converted one set of chromophores into another without complete photobleaching or from undetected BrC chromophores that photobleached more slowly. To model the effect of BrC on climate, it is important to understand the change in the overall absorption coefficient with time. We measured the equivalent atmospheric lifetimes of the overall BrC absorption coefficient, which ranged from 10 to 41 d, with subalpine fir having the shortest lifetime and conifer canopies, i.e., juniper, having the longest lifetime. BrC emitted from biomass fuel loads encompassing multiple ecosystem components (litter, shrub, canopy) had absorption lifetimes on the lower end of the range. These results indicate that photobleaching of BBOA by condensed-phase photochemistry is relatively slow. Competing chemical aging mechanisms, such as heterogeneous oxidation by OH, may be more important for controlling the rate of BrC photobleaching in BBOA.

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Section: Aging By Condensed-phase Photochemistrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

et al. 2020

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“…Another possibility is that photodegradation of BrC chromophores could be not direct but rather occurring through condensed-phase photosensitized reactions (Malecha and Nizkorodov, 2017;Monge et al, 2012), in which case the rate of decomposition would depend on concentration of photosensitizers in the samples as well as viscosity of the material (Hinks et al, 2016;Kaur et al, 2019). Lastly, other absorbing species, such as black carbon could be shielding BrC chromophores from irradiation, altering the amount of radiation absorbed by BrC chromophores.…”

Section: Aging By Condensed-phase Photolysismentioning

confidence: 99%

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

Fleming¹,

Roberts²,

Selimovic³

et al. 2019

Preprint

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Abstract. To better understand the effects of wildfires on air quality and climate, it is important to assess the occurrence of chromophoric compounds in smoke and characterize their optical properties. This study explores the molecular composition of light-absorbing organic aerosol, or brown carbon (BrC), sampled at the Missoula Fire Sciences laboratory as a part of the FIREX Fall 2016 lab intensive. Twelve biomass fuels from different plant types were tested, including gymnosperm (coniferous) and angiosperm (flowering) plants, and different ecosystem components such as duff, litter, and canopy. Emitted particles were collected onto Teflon filters and analyzed offline using high performance liquid chromatography/ photodiode array/high resolution mass spectrometry (HPLC/PDA/HRMS). Separated BrC chromophores were classified by their retention times, absorption spectra, integrated PDA absorbance in the near-UV and visible spectral range (300&#8211;700&#8201;nm), and chemical formulas from the accurate m/z measurements. BrC chromophores were grouped into the following classes and subclasses: lignin-derived, which includes lignin pyrolysis products; distillation products, which include coumarins and flavonoids; nitroaromatics; and polycyclic aromatic hydrocarbons (PAHs). The observed classes/subclasses were common across most fuel types, although specific BrC chromophores varied based on plant type (gymnosperm or angiosperm) and ecosystem component(s) burned. To study the stability of the observed BrC compounds with respect to photodegradation, biomass burning organic aerosol (BBOA) particle samples were irradiated directly on filters with near UV (300&#8211;400&#8201;nm) radiation, followed by extraction and the HPLC/PDA/HRMS analysis. Lifetimes of individual BrC chromophores depended on the fuel type and the corresponding combustion conditions, but lignin-derived and flavonoid classes of BrC generally had the longest lifetimes with respect to UV photodegradation. Moreover, lifetimes for the same type of BrC chromophores varied depending on biomass fuel and combustion conditions. While individual BrC chromophores disappeared on a timescale of several days, the overall light absorption by the sample persisted longer, presumably because the photolysis processes converted one set of chromophores into another without complete photobleaching, or from undetected BrC chromophores that photobleached more slowly. To model the effect of BrC on climate, it is important to understand the change in the absorption coefficient with time. We measured the equivalent atmospheric lifetimes of the overall BrC absorption coefficient which ranged from 10 to 41 days, with subalpine fir having the shortest lifetime, and conifer canopies having the longest. BrC emitted from biomass fuel loads encompassing multiple ecosystem components (litter, shrub, canopy) had absorption lifetimes on the lower end of the range. These results indicate that photobleaching by atmospheric photolysis is relatively slow. Other chemical aging mechanisms, such as heterogeneous oxidation by OH, may be more important for BrC degradation than photolysis for predicting the decay of BBOA BrC absorption in models.

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“…BrC, which is excited by visible and ultraviolet radiation in the sunlight, can act as photosensitizer to facilitate free radical reactions and contribute to photochemical aging of organic aerosol (Smith et al, 2014;Yu et al, 2014). The photosensitized uptake of limonene was also observed for several SOA materials containing a complex mixture of photosensitive organic compounds collected from the chamber (Malecha and Nizkorodov, 2017). When aerosols containing photosensitizers such as IC and HA were exposed to isoprene, limonene, α-pinene, β-pinene and toluene in the presence of UV light, there was significant SOA formation (Palacios et al, 2016).…”

Section: Atmospheric Implicationmentioning

confidence: 93%

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface

Li¹,

Jiang²,

George³

et al. 2019

Preprint

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Abstract. Photosensitizing compounds containing brown carbon can absorb UV light and transfer that energy to low volatile organic compounds at the surface of aqueous particles. To better understand the reactivity and photochemical aging processes of organic coating on the aqueous aerosol surface, we have simulated the photosensitized reaction of organic films made of several long chain fatty acids in a Langmuir trough in the presence or absence of irradiation. Several chemicals (imidazole-2-carboxaldehyde and humic acid), PM2.5 samples collected from the field and secondary organic aerosols samples generated from a simulation chamber were used as photosensitizers to be involved in the photochemistry of the organic films. Stearic acid, elaidic acid, oleic acid and two different phospholipids with the same carbon chain length and different degrees of saturation i.e., 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC) were chosen as the common organic film-forming species in this analysis. The double bond (trans and cis) in unsaturated organic compounds has an effect on the surface area of the organic monolayer. The OA monolayer possessing a cis double bond in an alkyl chain is more expanded than EA monolayers on artificial seawater that contain a photosensitizer. Monitoring the change in the relative area of DOPC monolayers has shown that DOPC does not react with photosensitizers under dark conditions. Instead, the photochemical reaction initiated by the excited photosensitizer and molecular oxygen can generate hydroperoxidation in the DOPC monolayers, accompanied by an increase in the molecular area. The DSPC monolayers did not yield any photochemical oxidized products under the same conditions. The spectra measured with polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) were also consistent with the results of a surface pressure-area isotherm. Here, a reaction mechanism explaining these observations is presented and discussed. The results will contribute to our understanding of the processing of organic aerosol aging that controls the aerosol composition.

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Feasibility of Photosensitized Reactions with Secondary Organic Aerosol Particles in the Presence of Volatile Organic Compounds

Cited by 22 publications

References 38 publications

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

Molecular composition and photochemical lifetimes of brown carbon chromophores in biomass burning organic aerosol

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface

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