Rate of atmospheric brown carbon whitening governed by environmental conditions

Schnitzler, Elijah G.; Gerrebos, Nealan G. A.; Carter, Therese S.; Huang, Yuanzhou; Heald, Colette L.; Bertram, Allan K.; Abbatt, Jonathan P. D.

doi:10.1073/pnas.2205610119

Cited by 42 publications

(76 citation statements)

References 72 publications

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“…Light-absorbing organic aerosol, or brown carbon (BrC), impacts climate directly by scattering and absorbing sunlight , and indirectly by influencing cloud formation and properties. , Together, these effects are predicted to result in a significant overall warming effect for BrC, , but there are uncertainties regarding both the direct and indirect radiative effects. − Primary BrC, including nitrophenols emitted from biomass burning, − may react with light or oxidants and ultimately whiten during its atmospheric lifetime. − Initially nonabsorbing emissions may react to give secondary BrC, − potentially counteracting the whitening of primary BrC to some extent. − If primary BrC from a particular source were not highly absorbing or if it were to whiten rapidly, the warming effect of BrC would be lessened. Furthermore, if BrC were to become more hygroscopic during its atmospheric lifetime, generally consistent with oxidation, the cooling effect of enhanced cloud activation would be increased.…”

Section: Introductionmentioning

confidence: 99%

Hygroscopicity of Secondary Brown Carbon Aerosol from Aqueous Photo-Oxidation of Phenolic Precursors

Betz

Calvert

Al-Mashala

et al. 2022

ACS Earth Space Chem.

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To understand the impact of light-absorbing organic aerosol, also called brown carbon (BrC), it is necessary to determine the extent to which the direct effect through aerosol− radiation interactions and the indirect effect through aerosol−cloud interactions change during its atmospheric residence time. Toward addressing this need, the light absorption and water uptake of secondary BrC aerosol produced from phenolic compounds, abundant biomass burning emissions, were measured. Phenol, catechol, and pyrogallol were selected to form a homologous series, varying in the number of hydroxyl substituents, and they were exposed to aqueous hydroxyl radical in a photoreactor, leading to the formation of secondary BrC. The absorptivity of the BrC was monitored by UV−vis spectroscopy; the hygroscopicity was determined using a hygroscopic tandem differential mobility analyzer. The absorptivity of the secondary BrC increased within 8 h of photo-oxidation and then began decreasing. After 24 h of photooxidation, at an atmospherically relevant OH exposure of 2.2 × 10 −10 mol s L −1 , the hygroscopicity parameters for BrC from phenol, catechol, and pyrogallol were similar, i.e., 0.13 ± 0.02, 0.10 ± 0.02, and 0.13 ± 0.02, respectively, so BrC from phenolic compounds exhibits similar water uptake regardless of the functionalization of the precursor. After 36 and 48 h of continued photo-oxidation, during which the product mixture exhibited further whitening, the hygroscopicity parameter of secondary BrC from catechol did not change. These observations suggest that the changes in absorptivity (related to the direct effect) of secondary BrC produced from phenolic precursors are greater than the changes in hygroscopicity (related to the indirect effect) upon atmospheric aging.

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Section: Introductionmentioning

confidence: 99%

Hygroscopicity of Secondary Brown Carbon Aerosol from Aqueous Photo-Oxidation of Phenolic Precursors

Betz

Calvert

Al-Mashala

et al. 2022

ACS Earth Space Chem.

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“…The viscosity of BB-POA from the pyrolysis of pine wood has been studied previously and was found to depend strongly on relative humidity (RH) and temperature. 56 Similarly, the diffusion rates of organic molecules in BB-POA, which are inversely related to particle viscosity, were also found to depend on RH. 57 In contrast to BB-POA, much less is known about the viscosity of BB-SOA.…”

Section: Introductionmentioning

confidence: 86%

“…81-83 Schnitzler et al (2022) showed that the whitening of BB-POA depends on the viscosity of the BB-POA, with whitening rates strongly decreasing with increasing particle viscosity. 56 The strong contrast in viscosity between BB-POA and phenolic BB-SOA (Fig. 3) could have considerable implications for the whitening rates of BB-POA in the atmosphere.…”

Section: Soa Type O/cmentioning

confidence: 99%

“…their direct climate effects. 14,15,56 While transported in the atmosphere, BB-POA can undergo various aging processes, such as heterogeneous oxidation reactions that can impact the chemical composition of the brown carbon. 80 Ozonolysis of BB-POA causes a decrease in the absorbance of brown carbon (i.e., whitening) of the BB-POA, thus changing the particle's radiative properties from a warming to a cooling climate effect.…”

Section: Soa Type O/cmentioning

confidence: 99%

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Secondary Organic Aerosol from Biomass Burning Phenolics Could Increase Brown Carbon Lifetimes, Seed Ice Clouds, and Transport Pollutants

Kiland

Mahrt

Peng

et al. 2023

Preprint

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Biomass burning events emit large amounts of phenolic compounds, which are oxidized in the atmosphere and form secondary organic aerosol (SOA). Using the poke-flow technique, we measured room-temperature and relative humidity (RH)-dependent viscosities of SOA generated by the oxidation of three biomass burning phenolic compounds: catechol, guaiacol, and syringol. All systems had viscosity < 3 × 10³ Pa s at RH ⪆ 40% and > 2 × 10⁸ Pa s at RH ⪅ 3%. At RH values of 0-10%, the viscosities of these SOA were at least 2 orders of magnitude higher than the viscosity of primary organic aerosol (POA) from biomass burning. These results suggest that mixing biomass burning SOA and POA may extend the lifetime of the brown carbon in the atmosphere. Based on an extrapolation of our results to tropospheric temperature and RH values, phenolic SOA is in a glassy state (𝜂 > 10¹² Pa s) above ∼6 km in the troposphere, potentially acting as heterogeneous ice nuclei in clouds, thereby influencing climate. Furthermore, the mixing time of organic molecules in a 200 nm phenolic SOA particle exceeds 1 h above 3 km in the troposphere, which has implications for the long-range transport of pollutants.

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“…7,8 Compounds that strongly absorb visible radiation are constituents of brown carbon (BrC), 9,10 which contributes a warming effect on climate, the magnitude of which remains uncertain. 11,12 These compounds can be emitted into the atmosphere directly from the source (i.e., primary) or form downwind from the source (i.e., secondary), 13,14 as a result of reactions involving light or oxidants, including OH and NO 3 radicals. 15,16 Constituents of BrC can undergo functionalization or oligomerization that may give more-absorbing products, causing absorption enhancement, or fragmentation that may give less-absorbing products, causing whitening.…”

Section: ■ Introductionmentioning

confidence: 99%

Light Absorption by Cinnamaldehyde Constituents of Biomass Burning Organic Aerosol Modeled Using Time-Dependent Density Functional Theory

Calvert

Schnitzler

2023

ACS Earth Space Chem.

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Organic aerosol emitted from biomass burning absorbs visible radiation. However, the impact of this light absorption on the overall climate effects of atmospheric aerosol is not well known, partly due to variability in particle composition and absorptivity. Cinnamaldehydes, which consist of an aromatic ring with an unsaturated aldehyde substituent, are an important class of chromophores in light-absorbing organic aerosol, or brown carbon. Here, light absorption by a homologous series of three cinnamaldehydescoumaraldehyde, coniferaldehyde, and sinapaldehydeis modeled with time-dependent density functional theory (TD-DFT) calculations, in the gas and aqueous phases. Based on a survey of hydration and acid dissociation equilibria, the neutral aldehyde is expected to be the predominant form of each species in the atmospheric aqueous phase. These species have complicated conformational landscapes compared to many other brown carbon constituents, like rigid polycyclic aromatic hydrocarbons. For coumaraldehyde, coniferaldehyde, and sinapaldehyde, a total of 8, 26, and 18 conformers were located, respectively. For each species, most of the total population is accounted for by the four most-populated conformers. The relative contributions of the conformers to the total light absorption of the respective species are dictated more by differences in the relative free energies than by differences in the molar absorption coefficients. As the functionalization increases, the absorption is red-shifted. The peaks predicted in water agree well with experimental spectra of coniferaldehyde and sinapaldehyde. No conformers have vertical transitions in the visible spectral range, so absorption above 380 nm is due to the shoulders of transitions of major conformers at ultraviolet wavelengths. These results demonstrate the importance of exploring potential energy landscapes, determining conformer stability and absorptivity, to predict the light absorption of chromophores in brown carbon.

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Rate of atmospheric brown carbon whitening governed by environmental conditions

Cited by 42 publications

References 72 publications

Hygroscopicity of Secondary Brown Carbon Aerosol from Aqueous Photo-Oxidation of Phenolic Precursors

Hygroscopicity of Secondary Brown Carbon Aerosol from Aqueous Photo-Oxidation of Phenolic Precursors

Secondary Organic Aerosol from Biomass Burning Phenolics Could Increase Brown Carbon Lifetimes, Seed Ice Clouds, and Transport Pollutants

Light Absorption by Cinnamaldehyde Constituents of Biomass Burning Organic Aerosol Modeled Using Time-Dependent Density Functional Theory

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