scholarly journals Photophoretic spectroscopy in atmospheric chemistry – high sensitivity measurements of light absorption by a single particle

2020 ◽  
Author(s):  
Nir Bluvshtein ◽  
Ulrich K. Krieger ◽  
Thomas Peter
Keyword(s):  
Atmospheric Chemistry ◽  
Single Particle ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Experimental System ◽  
High Sensitivity ◽  
Atmospheric Conditions ◽  
Brown Carbon ◽  
Radiative Balance ◽  
Low Sensitivity

Abstract. Light absorbing organic atmospheric particles, termed brown carbon, undergo chemical and photochemical aging processes during their lifetime in the atmosphere. The role these particles play in the global radiative balance and in the climate system is still uncertain. To better quantify their radiative forcing due to aerosol-radiation interactions, we need to improve process level understanding of aging processes, which lead to either "browning" or "bleaching" of organic aerosols. Currently available laboratory techniques aim to simulate atmospheric aerosol aging and measure the evolving light absorption, but suffer from low sensitivity and precision. This study describes the use of electrodynamic balance photophoretic spectroscopy (EDB-PPS) for high sensitivity and high precision measurements of light absorption by a single particle. We demonstrate the retrieval of time-evolving imaginary part of the refractive index for a single levitated particle in the range of 10−4 to 10−5 with uncertainties of less than 25 % and 60 %, respectively. The experimental system is housed within an environmental chamber, in which aging processes can be simulated in realistic atmospheric conditions and lifetime of days to weeks. This high level of sensitivity enables future studies to explore the major processes responsible for formation and degradation of brown carbon aerosols.

scholarly journals Photophoretic spectroscopy in atmospheric chemistry – high-sensitivity measurements of light absorption by a single particle

2020 ◽  
Vol 13 (6) ◽  
pp. 3191-3203
Author(s):  
Nir Bluvshtein ◽  
Ulrich K. Krieger ◽  
Thomas Peter
Keyword(s):  
Atmospheric Chemistry ◽  
Single Particle ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Experimental System ◽  
High Sensitivity ◽  
Atmospheric Conditions ◽  
Brown Carbon ◽  
Radiative Balance ◽  
Low Sensitivity

Abstract. Light-absorbing organic atmospheric particles, termed brown carbon, undergo chemical and photochemical aging processes during their lifetime in the atmosphere. The role these particles play in the global radiative balance and in the climate system is still uncertain. To better quantify their radiative forcing due to aerosol–radiation interactions, we need to improve process-level understanding of aging processes, which lead to either “browning” or “bleaching” of organic aerosols. Currently available laboratory techniques aim to simulate atmospheric aerosol aging and measure the evolving light absorption, but they suffer from low sensitivity and precision. This study describes the use of electrodynamic balance photophoretic spectroscopy (EDB-PPS) for high-sensitivity and high-precision measurements of light absorption by a single particle. We demonstrate the retrieval of the time-evolving imaginary part of the refractive index for a single levitated particle in the range of 10−4 to 10−5 with uncertainties of less than 25 % and 60 %, respectively. The experimental system is housed within an environmental chamber, in which aging processes can be simulated in realistic atmospheric conditions and lifetimes of days to weeks. This high level of sensitivity enables future studies to explore the major processes responsible for formation and degradation of brown carbon aerosols.

Photophoresis used for measurements of light absorption by a single particle

2020 ◽  
Author(s):  
Nir Bluvshtein ◽  
Ulrich Krieger
Keyword(s):  
Refractive Index ◽  
Momentum Transfer ◽  
Electric Fields ◽  
Atmospheric Chemistry ◽  
Single Particle ◽  
Light Absorption ◽  
Complex Refractive Index ◽  
Organic Aerosols ◽  
Ionization Mass ◽  
Brown Carbon

<p>The contribution of light absorption by brown carbon aerosols to the Earth’s energy balance still poses a significant uncertainty in our understanding of climate forcing. As a result, one of the main open questions regarding organic aerosols in atmospheric chemistry is related to the formation and degradation of light-absorbing compounds during aging processes. Towards this goal, we explore the use of photophoresis for high sensitivity measurements of light absorption by a single levitated particle in an experimental setup that facilitates realistic atmospheric gas concentrations and aging time.</p><p>Photophoresis occurs when the surface of an illuminated, light-absorbing particle is unevenly heated relative to its surroundings. The temperature difference between the illuminated and the ‘dark’ side of the particle results in an uneven momentum transfer from colliding gas-phase molecules. This leads to a net photophoretic force, acting on the particle in the direction of the momentum transfer gradient. The photophoretic force is related to the complex refractive index of the particle and to its size parameter through the distribution of internal electric fields. As such, it may lead to a net force away from (positive) or towards (negative) the light source.</p><p>Using this phenomenon, we were able to retrieve the imaginary part of the complex refractive index (k) of a single particle levitated in an electrodynamic balance (EDB) at 473 nm wavelength. Extremely low values of k from 10<sup>-4</sup> to 10<sup>-5</sup> were successfully retrieved with uncertainty of less than 35% during a photo-bleaching experiment of a slightly absorbing organic particle used as a model for atmospheric brown carbon.    </p><p>An advantage of the EDB is that heterogeneous chemistry and photochemistry experiments are performed on a single particle that is levitated for days and weeks allowing for realistic atmospheric gas concentrations and aging times. In such experiments, measurements of the particle’s light absorption properties using photophoresis would add valuable information on the evolution of light absorption by the aging of organic aerosols.</p><p>A future study will implement this approach in an EDB-MS system where the EDB will be coupled with a soft ionization mass spectrometer. This will allow the identification of the molecular species responsible for light absorption as it evolves.  </p>

scholarly journals Chemical characteristics of brown carbon in atmospheric particles at a suburban site near Guangzhou, China

2018 ◽  
Vol 18 (22) ◽  
pp. 16409-16418 ◽  
Author(s):  
Yi Ming Qin ◽  
Hao Bo Tan ◽  
Yong Jie Li ◽  
Zhu Jie Li ◽  
Misha I. Schurman ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Absorption Coefficient ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Chemical Characterization ◽  
Organic Aerosol ◽  
Atmospheric Particles ◽  
Chemical Characteristics ◽  
Brown Carbon ◽  
Suburban Site

Abstract. Light-absorbing organic carbon (or brown carbon, BrC) in atmospheric particles has received much attention for its potential role in global radiative forcing. While a number of field measurement campaigns have differentiated light absorption by black carbon (BC) and BrC, the chemical characteristics of BrC are not well understood. In this study, we present co-located real-time light absorption and chemical composition measurements of atmospheric particles to explore the relationship between the chemical and optical characteristics of BrC at a suburban site downwind of Guangzhou, China, from November to December 2014. BrC and BC contributions to light absorption were estimated using measurements from a seven-wavelength aethalometer, while the chemical composition of non-refractory PM1 was measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Using the absorption Ångström exponent (AAE) method, we estimated that BrC contributed 23.6 % to the total aerosol absorption at 370 nm, 18.1 % at 470 nm, 10.7 % at 520 nm, 10.7 % at 590 nm, and 10.5 % at 660 nm. Biomass burning organic aerosol (BBOA) has the highest mass absorption coefficient among sources of organic aerosols. Its contribution to total brown carbon absorption coefficient decreased but that of low-volatility oxygenated organic aerosol (LVOOA) increased with increasing wavelength, suggesting the need for wavelength-dependent light absorption analysis for BrC in association with its chemical makeup. Clear correlations of N-containing ion fragments with absorption coefficient were observed. These correlations also depended on their degrees of unsaturation/cyclization and oxygenation. While the current study relates light absorption by BrC to ion fragments, more detailed chemical characterization is warranted to constrain this relationship.

Light absorption properties, chromophore composition and sources of brown carbon aerosol in Xi’an, Northwest China

2020 ◽  
Author(s):  
Ru-Jin Huang ◽  
Wei Yuan ◽  
Lu Yang ◽  
Jie Guo ◽  
Jing Duan ◽  
...  
Keyword(s):  
Light Absorption ◽  
Coal Combustion ◽  
Radiative Forcing ◽  
Northwest China ◽  
Absorption Efficiency ◽  
Vehicular Emissions ◽  
Absorption Properties ◽  
Seasonal Differences ◽  
Brown Carbon ◽  
The Impact

<p>The impact of brown carbon aerosol (BrC) on the Earth’s radiative forcing balance has been widely recognized but remains uncertain, mainly because the relationships among BrC sources, chromophores, and optical properties of aerosol are poorly understood (Feng et al., 2013; Laskin et al., 2015). In this work, the light absorption properties and chromophore composition of BrC were investigated for samples collected in Xi’an, Northwest China from 2015 to 2016. Both absorption Ångström exponent and mass absorption efficiency show distinct seasonal differences, which could be attributed to the differences in sources and chromophore composition of BrC. Three groups of light-absorbing organics were found to be important BrC chromophores, including those show multiple absorption peaks at wavelength > 350 nm (12 polycyclic aromatic hydrocarbons and their derivatives) and those show single absorption peak at wavelength < 350 nm (10 nitrophenols and nitrosalicylic acids and 3 methoxyphenols). These measured BrC chromophores show distinct seasonal differences and contribute on average about 1.1% and 3.3% of light absorption of methanol-soluble BrC at 365 nm in summer and winter, respectively, about 7 and 5 times higher than the corresponding mass fractions in total organic carbon. The sources of BrC were resolved by positive matrix factorization (PMF) using these chromophores instead of commonly used non-light absorbing organic markers as model inputs. Our results show that in spring vehicular emissions and secondary formation are major sources of BrC (~70%), in fall coal combustion and vehicular emissions are major sources (~70%), in winter biomass burning and coal combustion become major sources (~80%), while in summer secondary BrC dominates (~60%).</p><p> </p><p>References:</p><p>Feng, Y., V. Ramanathan, and V. R. Kotamarthi: Brown carbon: A significant atmospheric absorber of solar radiation?, Atmos. Chem. Phys., 13, 8607-8621, doi:10.5194/acp-13-8607-2013, 2013.</p><p>Laskin, A., J. Laskin, and S. A. Nizkorodov: Chemistry of atmospheric brown carbon, Chem. Rev., 115, 4335-4382, doi:10.1021/cr5006167, 2015.</p>

scholarly journals Light absorption of brown carbon aerosol in the PRD region of China

2016 ◽  
Vol 16 (3) ◽  
pp. 1433-1443 ◽  
Author(s):  
J.-F. Yuan ◽  
X.-F. Huang ◽  
L.-M. Cao ◽  
J. Cui ◽  
Q. Zhu ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Measurement Data ◽  
Theoretical Assumption ◽  
Ambient Aerosols ◽  
Brown Carbon ◽  
Mass Spectrometers ◽  
Rural Environments ◽  
The Pearl River

Abstract. The strong spectral dependence of light absorption of brown carbon (BrC) aerosol is regarded to influence aerosol's radiative forcing significantly. The Absorption Angstrom Exponent (AAE) method has been widely used in previous studies to attribute light absorption of BrC at shorter wavelengths for ambient aerosols, with a theoretical assumption that the AAE of "pure" black carbon (BC) aerosol equals to 1.0. In this study, the AAE method was applied to both urban and rural environments in the Pearl River Delta (PRD) region of China, with an improvement of constraining the realistic AAE of "pure" BC through statistical analysis of on-line measurement data. A three-wavelength photo-acoustic soot spectrometer (PASS-3) and aerosol mass spectrometers (AMS) were used to explore the relationship between the measured AAE and the relative abundance of organic aerosol to BC. The regression and extrapolation analysis revealed that more realistic AAE values for "pure" BC aerosol (AAEBC) were 0.86, 0.82, and 1.02 between 405 and 781 nm, and 0.70, 0.71, and 0.86 between 532 and 781 nm, in the campaigns of urbanwinter, urbanfall, and ruralfall, respectively. Roadway tunnel experiments were conducted and the results further confirmed the representativeness of the obtained AAEBC values for the urban environment. Finally, the average light absorption contributions of BrC (± relative uncertainties) at 405 nm were quantified to be 11.7 % (±5 %), 6.3 % (±4 %), and 12.1 % (±7 %) in the campaigns of urbanwinter, urbanfall, and ruralfall, respectively, and those at 532 nm were 10.0 % (±2 %), 4.1 % (±3 %), and 5.5 % (±5 %), respectively. The relatively higher BrC absorption contribution at 405 nm in the ruralfall campaign could be reasonably attributed to the biomass burning events nearby, which was then directly supported by the biomass burning simulation experiments performed in this study. This paper indicates that the BrC contribution to total aerosol light absorption at shorter wavelengths is not negligible in the highly urbanized and industrialized PRD region.

scholarly journals Measurement Report: Optical properties and sources of water-soluble brown carbon in Tianjin, North China: insights from organic molecular compositions

2022 ◽  
Author(s):  
Junjun Deng ◽  
Hao Ma ◽  
Xinfeng Wang ◽  
Shujun Zhong ◽  
Zhimin Zhang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Light Absorption ◽  
Radiative Forcing ◽  
North China ◽  
Water Soluble ◽  
Formation Mechanisms ◽  
Chemical Compositions ◽  
Brown Carbon ◽  
Near Ultraviolet

Abstract. Brown carbon (BrC) aerosols exert vital impacts on climate change and atmospheric photochemistry due to their light absorption in the wavelength range from near-ultraviolet (UV) to visible light. However, the optical properties and formation mechanisms of ambient BrC remain poorly understood, limiting the estimation of their radiative forcing. In the present study, fine aerosols (PM2.5) were collected during 2016–2017 on a day/night basis over urban Tianjin, a megacity in North China, to obtain seasonal and diurnal patterns of atmospheric water-soluble BrC. There were obvious seasonal but no evident diurnal variations in light absorption properties of BrC. In winter, BrC showed much stronger light absorbing ability since mass absorption efficiency at 365 nm (MAE365) (1.54 ± 0.33 m2 g−1), which was 1.8 times larger than that (0.84 ± 0.22 m2 g−1) in summer. Direct radiative effects by BrC absorption relative to black carbon in the UV range were 54.3 ± 16.9 % and 44.6 ± 13.9 %, respectively. In addition, five fluorescent components in BrC, including three humic-like fluorophores and two protein-like fluorophores were identified with excitation-emission matrix fluorescence spectrometry and parallel factor (PARAFAC) analysis. The lowly-oxygenated components contributed more to winter and nighttime samples, while more-oxygenated components increased in summer and daytime samples. The higher humification index (HIX) together with lower biological index (BIX) and fluorescence index (FI) suggest that the chemical compositions of BrC were associated with a high aromaticity degree in summer and daytime due to photobleaching. Fluorescent properties indicate that wintertime BrC were predominantly affected by primary emissions and fresh secondary organic aerosol (SOA), while summer ones were more influenced by aging processes. Results of source apportionments using organic molecular compositions of the same set of aerosols reveal that fossil fuel combustion and aging processes, primary bioaerosol emission, biomass burning, and biogenic and anthropogenic SOA formation were the main sources of BrC. Biomass burning contributed much larger to BrC in winter and at nighttime, while biogenic SOA contributed more in summer and at daytime. Especially, our study highlights that primary bioaerosol emission is an important source of BrC in urban Tianjin in summer.

High light absorption and radiative forcing contributions of primary brown carbon and black carbon to urban aerosol

2021 ◽  
Vol 90 ◽  
pp. 159-164
Author(s):  
Chong-Shu Zhu ◽  
Yao Qu ◽  
Yue Zhou ◽  
Hong Huang ◽  
Hui-Kun Liu ◽  
...  
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Radiative Forcing ◽  
High Light ◽  
Urban Aerosol ◽  
Brown Carbon

scholarly journals Chemical characteristics of brown carbon in atmospheric particles at a suburban site near Guangzhou, China

2018 ◽  
Author(s):  
Yi Ming Qin ◽  
Hao Bo Tan ◽  
Yong Jie Li ◽  
Zhu Jie Li ◽  
Misha I. Schurman ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Absorption Coefficient ◽  
Light Absorption ◽  
Radiative Forcing ◽  
Chemical Characterization ◽  
Organic Aerosol ◽  
Atmospheric Particles ◽  
Chemical Characteristics ◽  
Brown Carbon ◽  
Suburban Site

Abstract. Light-absorbing organic carbon (or brown carbon, BrC) in atmospheric particles has received much attention for its potential role in global radiative forcing. While a number of field measurement campaigns have differentiated light absorption by black carbon (BC) and BrC, the chemical characteristics of BrC are not well understood. In this study, we present co-located real-time light absorption and chemical composition measurements of atmospheric particles to explore the relationship between the chemical and optical characteristics of BrC at a suburban site downwind of Guangzhou, China from November to December 2014. BrC and BC contributions to light absorption were estimated using measurements from a seven-wavelength aethalometer, while the chemical composition of non-refractory PM1 was measured with a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Using the Absorption Angstrom Exponent (AAE) method, we estimated that BrC contributed 23.6 % to the total aerosol absorption at 370 nm, 18.1 % at 470 nm, 10.7 % at 520 nm, 10.7 % at 590 nm, and 10.5 % at 660 nm. Biomass burning organic aerosol (BBOA) has the highest mass absorption coefficient among sources of organic aerosols. Its contribution to total brown carbon absorption coefficient decreased but that of low-volatility oxygenated organic aerosol (LVOOA) increased with increasing wavelength, suggesting the need for wavelength-dependent light absorption analysis for BrC in association with its chemical makeup. Clear correlations of N-containing ion fragments with absorption coefficient were observed. These correlations also depended on their degrees of unsaturation/cyclization and oxygenation. While the current study relates light absorption by BrC to ion fragments, more detailed chemical characterization is warranted to constrain this relationship.

scholarly journals Atmospheric evolution of molecular-weight-separated brown carbon from biomass burning

2019 ◽  
Vol 19 (11) ◽  
pp. 7319-7334 ◽  
Author(s):  
Jenny P. S. Wong ◽  
Maria Tsagkaraki ◽  
Irini Tsiodra ◽  
Nikolaos Mihalopoulos ◽  
Kalliopi Violaki ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Biomass Burning ◽  
Light Absorption ◽  
Laboratory Experiments ◽  
Atmospheric Transport ◽  
Water Soluble ◽  
Brown Carbon ◽  
Atmospheric Lifetime ◽  
Radiative Balance ◽  
Considerable Uncertainty

Abstract. Biomass burning is a major source of atmospheric brown carbon (BrC), and through its absorption of UV/VIS radiation, it can play an important role in the planetary radiative balance and atmospheric photochemistry. The considerable uncertainty of BrC impacts is associated with its poorly constrained sources, transformations, and atmospheric lifetime. Here we report laboratory experiments that examined changes in the optical properties of the water-soluble (WS) BrC fraction of laboratory-generated biomass burning particles from hardwood pyrolysis. Effects of direct UVB photolysis and OH oxidation in the aqueous phase on molecular-weight-separated BrC were studied. Results indicated that the majority of low-molecular-weight (MW) BrC (<400 Da) was rapidly photobleached by both direct photolysis and OH oxidation on an atmospheric timescale of approximately 1 h. High MW BrC (≥400 Da) underwent initial photoenhancement up to ∼15 h, followed by slow photobleaching over ∼10 h. The laboratory experiments were supported by observations from ambient BrC samples that were collected during the fire seasons in Greece. These samples, containing freshly emitted to aged biomass burning aerosol, were analyzed for both water- and methanol-soluble BrC. Consistent with the laboratory experiments, high-MW BrC dominated the total light absorption at 365 nm for both methanol and water-soluble fractions of ambient samples with atmospheric transport times of 1 to 68 h. These ambient observations indicate that overall, biomass burning BrC across all molecular weights has an atmospheric lifetime of 15 to 28 h, consistent with estimates from previous field studies – although the BrC associated with the high-MW fraction remains relatively stable and is responsible for light absorption properties of BrC throughout most of its atmospheric lifetime. For ambient samples of aged (>10 h) biomass burning emissions, poor linear correlations were found between light absorptivity and levoglucosan, consistent with other studies suggesting a short atmospheric lifetime for levoglucosan. However, a much stronger correlation between light absorptivity and total hydrous sugars was observed, suggesting that they may serve as more robust tracers for aged biomass burning emissions. Overall, the results from this study suggest that robust model estimates of BrC radiative impacts require consideration of the atmospheric aging of BrC and the stability of high-MW BrC.

scholarly journals Sources and light absorption of water-soluble brown carbon aerosols in the outflow from northern China

2013 ◽  
Vol 13 (7) ◽  
pp. 19625-19648 ◽  
Author(s):  
E. N. Kirillova ◽  
A. Andersson ◽  
J. Han ◽  
M. Lee ◽  
Ö. Gustafsson
Keyword(s):  
Light Absorption ◽  
Radiative Forcing ◽  
Climate Models ◽  
Large Fraction ◽  
Regional Climate ◽  
Northern China ◽  
Water Soluble ◽  
Cloud Formation ◽  
Carbonaceous Aerosols ◽  
Brown Carbon

Abstract. High loadings of anthropogenic carbonaceous aerosols in Chinese air influence the air quality for over 1 billion people and impact the regional climate. A large fraction (17–80%) of this aerosol carbon is water soluble, promoting cloud formation and thus climate cooling. Recent findings, however, suggest that water-soluble carbonaceous aerosols also absorb sunlight, bringing additional direct and indirect climate warming effects, yet the extent and nature of light absorption by this water-soluble brown carbon (WS-BrC) and its relation to sources is poorly understood. Here, we combine source estimates constrained by dual-carbon-isotope with light absorption measurements of WS-BrC for a March 2011 campaign at the Korea Climate Observatory at Gosan (KCOG), a receptor station in SE Yellow Sea for the outflow from N. China. The mass absorption cross-section (MAC) of WS-BrC for air masses from N. China were in general higher (0.8–1.1 m2 g−1), than from other source regions (0.3–0.8 m2 g−1). We estimate that this effect corresponds to 13–49% of the radiative forcing caused by light absorption by black carbon. Radiocarbon constraints show that the WS-BrC in Chinese outflow had significantly higher amounts of fossil sources (30–50%) compared to previous findings in S. Asia, N. America and Europe. Stable carbon (δ13C) measurements indicated influence of aging during air mass transport. These results indicate the importance of incorporating WS-BrC in climate models and the need to constrain climate effects by emission source sector.

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