Light Absorbing Properties of Primary and Secondary Brown Carbon in a Tropical Urban Environment

Kasthuriarachchi, Nethmi; Rivellini, Laura-Hélèna; Adam, Max G.; Lee, Alex K. Y.

doi:10.1021/acs.est.0c02414

Cited by 41 publications

(24 citation statements)

References 96 publications

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“…One possible explanation is that 20 secondary BrC formation occurred, perhaps through aqueous-phase chemistry during transport (Hems et al, 2021), for RF05_1 and RF05_2, which were sampled in or close to the MBL with higher RHs. Saleh et al (2013) reported that secondary BrC can be more absorbing than primary BrC at short visible wavelengths; however, to the best of our knowledge, such high MAC for secondary BrC have not been documented (Kasthuriarachchi et al, 2020).…”

mentioning

confidence: 85%

Light Absorption by Brown Carbon over the South-East Atlantic Ocean

Zhang

Segal-Rozenhaimer

Che

et al. 2022

Preprint

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Abstract. Biomass burning emissions often contain brown carbon (BrC), which represents a large family of light-absorbing organics that is chemically complex and therefore difficult to estimate their absorption of incoming solar radiation, resulting in large uncertainties in the estimation of the global direct radiative effect of aerosols. Here we investigate the contribution of BrC to the total light absorption of biomass burning aerosols over the South-East Atlantic Ocean with different optical models utilizing a suite of airborne measurements from the ORACLES 2018 campaign by introducing an effective refractive index of black carbon (BC), meBC = neBC+ikeBC, that accounts for all possible absorbing components at 660 nm wavelength to facilitate the attribution of absorption at shorter wavelengths. Most values of the imaginary part of the refractive index, keBC, were larger than those commonly used for BC from biomass burning emissions, suggesting contributions from absorbers beyond BC at 660 nm. The TEM-EDX single particle analysis further suggests that these long-wavelength absorbers might include iron oxides, as iron is found to be present only when large values of keBC are derived. Using this effective BC refractive index, we find that the contribution of BrC to the total absorption at 470 nm (RBrC,470) ranges from ~5–15 %, with the organic aerosol mass absorption coefficient (MACOA,470) at this wavelength ranging from 0.25 ± 0.34 m2 g−1 to 0.43 ± 0.12 m2 g−1. The core-shell model yielded much higher estimates of MACOA,470 and RBrC,470 than homogeneous mixing models, underscoring the importance of model treatment. Another key finding was that estimates of the BrC contribution at 470 nm from the commonly used AAE (absorption Ångström exponent) attribution method (< 5 %) are much lower than the BrC contribution estimates (RBrC,470) using our new methodology that accounts for contributions from both BrC and non-carbonaceous, long-wavelength absorbers, such as magnetite. Thus, it is recommended that application of any optical properties-based attribution method use absorption coefficients at the longest possible wavelength to minimize the influence of BrC at the long wavelength and to account for potential contributions from other absorbing materials.

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confidence: 85%

Light Absorption by Brown Carbon over the South-East Atlantic Ocean

Zhang

Segal-Rozenhaimer

Che

et al. 2022

Preprint

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“…2.1.3). This enabled us to use the AE33 data quantitatively with no need to assume a range of possible calibration values (Kasthuriarachchi et al, 2020). Specifically, we use Eq.…”

Section: Macbc and Lensing Effectmentioning

confidence: 99%

Source-specific light absorption by carbonaceous components in the complex aerosol matrix from yearly filter-based measurements

Moschos¹,

Gysel²,

Modini³

et al. 2020

Preprint

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Abstract. Understanding the sources of light-absorbing organic (brown) carbon (BrC) and its interaction with black carbon (BC) and other non-refractory particulate matter (NR-PM) fractions is important for reducing uncertainties in the aerosol direct radiative forcing. In this study, we combine multiple filter-based techniques to achieve long-term, spectrally-resolved, source- and species-specific atmospheric absorption closure. We determine the total aerosol absorption at seven wavelengths based on the Aethalometer attenuation measurements, calibrated with the multi-wavelength absorption analyzer. We measure the spectrally-resolved imaginary part of the refractive index, k, for methanol extracts and determine the source-specific k for organic aerosol (OA) fractions using positive matrix factorization. The average k at 370 nm is found to be 0.06 for fresh biomass smoke, 0.03 for winter-oxygenated OA, and 0.006 for other less absorbing OA, which translates to corresponding mass absorption efficiencies (MAE) in dilute bulk solutions of 1.4, 0.7 and 0.13 m2 g−1. We apply Mie calculations to estimate the contributions of these fractions to total aerosol absorption. While enhanced absorption in the near-UV has been traditionally attributed to primary biomass smoke, here we show that anthropogenic oxygenated OA may be as important for BrC absorption during winter, especially at an urban background site. We demonstrate the absence of tar-balls in residential biomass burning particles of this study, and attribute the totality of the NR-PM absorption at shorter wavelengths to methanol-extractable BrC. As for BC, we show that the mass absorption cross-section (MAC) of this fraction is independent of its source, while we observe evidence for a lensing effect associated with the presence of NR-PM components. We find that bare BC has a MAC of 6.3 m2 g−1 at 660 nm and an absorption Ångström exponent (AAE) of 0.93 ± 0.16, while in the presence of coatings its absorption is enhanced by a factor of ~1.4. This falls within the global average enhancement factor of 1.5 ± 0.3 from filter-based techniques. Based on Mie-calculations of closure between observed and predicted total light absorption, we provide the first experimental evidence for a suppression of the lensing effect by BrC. The total absorption suppression remains modest, ~10–20 % at 370 nm, and is restricted to shorter wavelengths where BrC absorption is significant. Our long-term observations at locations representative of European urban background and rural Alpine sites show that extractable particulate BrC accounts for ~30 % of the absorption in the near-UV range (370 nm) on a yearly basis. However, if lensing suppression occurred due to internal mixing of BC and BrC as apparently the case for many samples in our study, then the additional absorption by BrC (vs transparent OA) would be partially compensated by a concurrent BC lensing factor reduction, which manifests as lower than expected total aerosol AAE values. Overall, when integrated with the solar spectrum at 300–900 nm, bare BC is found to contribute around two thirds of the solar radiation absorption by total carbonaceous aerosols, amplified by the lensing effect (with an interquartile range, IQR, of 8–27 %), while the IQR of yearly average contributions by particulate BrC is 6–13 % (13–20 % at the rural site during winter).

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“…They scatter and absorb solar radiation, resulting in a reduced visibility of the atmosphere, and are a culprit in the formation of haze weather. This has become an important driving factor affecting radiative forcing and disturbing regional climate change [7,8]. There are many kinds of photooxidation products of aromatics, among which some oxygen-containing and nitrogencontaining organic products have a strong toxicity, such as epoxy carbonyl compounds, which could attack human gene tissue and have a strong carcinogenicity [9], as well as nitroaromatic compounds (NAC), which have mutagenicity and carcinogenicity [10,11], compounds, which could attack human gene tissue and have a strong carcinogenicity [9], as well as nitroaromatic compounds (NAC), which have mutagenicity and carcinogenicity [10,11], and seriously endanger human health and have thus attracted extensive attention.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Studies on the Reaction Mechanism and Kinetics of Ethylbenzene-OH Adduct with O2 and NO2

et al. 2021

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The OH-initiated reaction of ethylbenzene results in major OH addition, and the formed ethylbenzene-OH adducts subsequently react with O2 and NO2, which determine the components of the oxidation products. In this study, nine possible reaction paths of the most stable ethylbenzene-OH adduct, EB-Ortho (2-ethyl-hydroxycyclohexadienyl radical intermediate), with O2 and NO2 were studied using density functional theory and conventional transition state theory. The calculated results showed that ethyl-phenol formed via hydrogen abstraction was the major product of the EB-Ortho reaction with O2 under atmospheric conditions. Peroxy radicals generated from O2 added to EB-Ortho could subsequently react with NO and O2 to produce 5-ethyl-6-oxo-2,4-hexadienal, furan, and ethyl-glyoxal, respectively. However, nitro-ethylbenzene formed from NO2 addition to EB-Ortho was the predominant product of the EB-Ortho reaction with NO2 at room temperature. The total calculated rate constant of the EB-Ortho reaction with O2 and NO2 was 9.57 × 10−16 and 1.78 × 10−11 cm3 molecule−1 s−1, respectively, approximately equivalent to the experimental rate constants of toluene-OH adduct reactions with O2 and NO2. This study might provide a useful theoretical basis for interpreting the oxygen-containing and nitrogen-containing organics in anthropogenic secondary organic aerosol particles.

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Light Absorbing Properties of Primary and Secondary Brown Carbon in a Tropical Urban Environment

Cited by 41 publications

References 96 publications

Light Absorption by Brown Carbon over the South-East Atlantic Ocean

Light Absorption by Brown Carbon over the South-East Atlantic Ocean

Source-specific light absorption by carbonaceous components in the complex aerosol matrix from yearly filter-based measurements

Theoretical Studies on the Reaction Mechanism and Kinetics of Ethylbenzene-OH Adduct with O2 and NO2

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