| 1. |
- Cho, Chaeyoon, et al.
(author)
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Observation-based estimates of the mass absorption cross-section of black and brown carbon and their contribution to aerosol light absorption in East Asia
- 2019
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 212, s. 65-74
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Journal article (peer-reviewed)abstract
- In this study, we estimated the contribution of black carbon (BC) and brown carbon (BrC) to aerosol light absorption from surface in-situ and aerosol robotic network (AERONET) columnar observations. The mass absorption cross-section (MAC) of BC (MAC(BC)) was estimated to be 6.4 +/- 1.5 m(2) g(-1) at 565 mn from in-situ aerosol measurements at Gosan Climate Observatory (GCO), Korea, in January 2014, which was lower than those observed in polluted urban areas. A BrC MAC of 0.62 +/- 0.06 m(2) g(-1) (565 mn) in our estimate is approximately ten times lower than MACK at 565 nm. The contribution of BC and BrC to the carbonaceous aerosol absorption coefficient at 565 nm from the in-situ measurements was estimated at 88.1 +/- 7.4% and 11.9 +/- 7.4%, respectively at GCO. Similarly, the contribution of BC and BrC to the absorption aerosol optical depth (AAOD) for carbonaceous aerosol (CA), constrained by AERONET observations at 14 sites over East Asia by using different spectral dependences of the absorption (i.e., absorption Angstrom exponent) of BC and BrC, was 84.9 +/- 2.8% and 15.1 +/- 2.8% at 565 nm, respectively. The contribution of BC to CA AAOD was greater in urban sites than in the background areas, whereas the contribution of BrC to CA AAOD was higher in background sites. The overall contribution of BC to CA AAOD decreased by 73%-87% at 365 nm, and increased to 93%-97% at 860 nm. The contribution of BrC to CA AAOD decreased significantly with increasing wavelength from approximately 17% at 365 nm to 4% at 860 nm.
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| 2. |
- Fang, Wenzheng, et al.
(author)
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Combined influences of sources and atmospheric bleaching on light absorption of water-soluble brown carbon aerosols
- 2023
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In: npj Climate and Atmospheric Science. - 2397-3722. ; 6:1
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Journal article (peer-reviewed)abstract
- Light-absorbing Brown Carbon (BrC) aerosols partially offset the overall climate-cooling of aerosols. However, the evolution of BrC light-absorption during atmospheric transport is poorly constrained. Here, we utilize optical properties, ageing-diagnostic delta C-13-BrC and transport time to deduce that the mass absorption cross-section (MACWS-BrC) is decreasing by similar to 50% during long-range oversea transport, resulting in a first-order bleaching rate of 0.24 day(-1) during the 3-day transit from continental East Asia to a south-east Yellow Sea receptor. A modern C-14 signal points to a strong inverse correlation between BrC light-absorption and age of the source material. Combining this with results for South Asia reveals a striking agreement between these two major-emission regions of rapid photobleaching of BrC with a higher intrinsic absorptivity for BrC stemming from biomass burning. The consistency of bleaching parameters constrained independently for the outflows of both East and South Asia indicates that the weakening of BrC light absorption, thus primarily related to photochemical processes rather than sources, is likely a ubiquitous phenomenon.
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| 3. |
- Fang, Wenzheng, et al.
(author)
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Divergent Evolution of Carbonaceous Aerosols during Dispersal of East Asian Haze
- 2017
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Journal article (peer-reviewed)abstract
- Wintertime East Asia is plagued by severe haze episodes, characterized by large contributions of carbonaceous aerosols. However, the sources and atmospheric transformations of these major components are poorly constrained, hindering development of efficient mitigation strategies and detailed modelling of effects. Here we present dual carbon isotope (delta C-13 and Delta C-14) signatures for black carbon (BC), organic carbon (OC) and water-soluble organic carbon (WSOC) aerosols collected in urban (Beijing and BC for Shanghai) and regional receptors (e.g., Korea Climate Observatory at Gosan) during January 2014. Fossil sources (>50%) dominate BC at all sites with most stemming from coal combustion, except for Shanghai, where liquid fossil source is largest. During source-to-receptor transport, the delta C-13 fingerprint becomes enriched for WSOC but depleted for water-insoluble OC (WIOC). This reveals that the atmospheric processing of these two major pools are fundamentally different. The photochemical aging (e.g., photodissociation, photooxidation) during formation and transport can release CO2/CO or short-chain VOCs with lighter carbon, whereas the remaining WSOC becomes increasingly enriched in delta C-13. On the other hand, several processes, e.g., secondary formation, rearrangement reaction in the particle phase, and photooxidation can influence WIOC. Taken together, this study highlights high fossil contributions for all carbonaceous aerosol sub-compartments in East Asia, and suggests different transformation pathways for different classes of carbonaceous aerosols.
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| 4. |
- Fang, Wenzheng, et al.
(author)
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Dual-Isotope Constraints on Seasonally Resolved Source Fingerprinting of Black Carbon Aerosols in Sites of the Four Emission Hot Spot Regions of China
- 2018
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In: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 123:20, s. 11735-11747
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Journal article (peer-reviewed)abstract
- Despite much recent efforts, the emission sources of black carbon (BC) aerosols. central input to understanding and predicting environmental and climate impact. remain highly uncertain. Here we present observational delta C-13/Delta C-14-based constraints on the sources of BC aerosols over the four seasons in each of the four key hot spot emission regions of China: Beijing-Tianjin-Hebei (BTH-Wuqing; where Wuqing is the sampling location), Yangtze River Delta (YRD-Haining), Pearl River Delta (PRD-Zhongshan), and Sichuan Basin (SC-Deyang). Overall, BC loadings were highest in winter, yet elevated loadings were also observed in other seasons, for example, spring at SC-Deyang and fall at PRD-Zhongshan. Annually, the dominant BC sources were coal (50 +/- 20%) for BTH-Wuqing, liquid fossil for YRD-Haining (46 +/- 8%) and PRD-Zhongshan (48 +/- 18%), whereas liquid fossil (42 +/- 17%) and biomass burning (41 +/- 14%) equally affected SC-Deyang. There is also different but distinct seasonalities in BC sources for the different sites. As an example, for BTH-Wuqing coal burning increased from summer to winter, while summer and spring BTH-Wuqing were more influenced by liquid fossil. In contrast, for YRD-Haining, the relative importance of emission sources was more constant over the year. These quantitative observational constraints on source-seasonality of BC aerosols in receptor sites located in China's four key economic zones highlight that regulatory control on BC aerosol emissions from different fuels should consider both seasonal and regional variations. Our results also suggest that models on estimates of BC-induced climate and air quality should consider variations over both regional and seasonal scales.
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| 5. |
- Sun, Ruirui, et al.
(author)
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Experimental and theoretical study on the dissociative photoionization of methyl methacrylate
- 2017
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:23
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Journal article (peer-reviewed)abstract
- The photoionization of methyl methacrylate and dissociation of its cation have been investigated by tunable vacuum ultraviolet synchrotron radiation coupled with time-of-flight mass spectrometer in the photon energy region of 9.0-15.5 eV. The ionization energy of methyl methacrylate and the appearance energies (AEs) for major fragments, C5H7O2+, C5H6O+, C4H5O2+,C4H5O+, C3H3O+ (C4H7+), C3H5+, C3H4+, C2H3O2+, and CH3+ are determined to be 9.76, 10.30, 10.66, 10.51, 11.17, 10.51, 10.74, 12.88, 12.73, 12.52, and 12.82 eV, respectively, by measurement of the photoionization efficiency curves. Possible formation pathways of the major fragments are proposed based on comparison of experimental AEs and energies predicted by ab initio G3B3 calculations. Transition states and intermediates involved in the dissociation channels are also located. The majority of the proposed channels occur through isomerization prior to dissociation. Hydrogen shift and ring closing/opening are found to be the dominant processes during photofragmentaion of methyl methacrylate.
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| 6. |
- Yu, Kuangyou, et al.
(author)
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Characterizing and sourcing ambient PM2.5 over key emission regions in China III : Carbon isotope based source apportionment of black carbon
- 2018
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 177, s. 12-17
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Journal article (peer-reviewed)abstract
- Regional haze over China has severe implications for air quality and regional climate. To effectively combat these effects the high uncertainties regarding the emissions from different sources needs to be reduced. In this paper, which is the third in a series on the sources of PM2.5 in pollution hotspot regions of China, we focus on the sources of black carbon aerosols (BC), using carbon isotope signatures. Four-season samples were collected at two key locations: Beijing-Tianjin-Hebei (BTH, part of Northern China plain), and the Pearl River Delta (PAD). We find that that fossil fuel combustion was the predominant source of BC in both BTH and PRD regions, accounting for 75 +/- 5%. However, the contributions of what fossil fuel components were dominating differed significantly between BTH and PRD, and varied dramatically with seasons. Coal combustion is overall the all-important BC source in BTH, accounting for 46 +/- 12% of the BC in BTH, with the maximum value (62%) found in winter. In contrast for the PAD region, liquid fossil fuel combustion (e.g., oil, diesel, and gasoline) is the dominant source of BC, with an annual mean value of 41 +/- 15% and the maximum value of 55% found in winter. Region- and season-specific source apportionments are recommended to both accurately assess the climate impact of carbonaceous aerosol emissions and to effectively mitigate deteriorating air quality caused by carbonaceous aerosols.
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