scholarly journals The absorption Angstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization

2020 ◽  
Author(s):  
Xiaolin Zhang ◽  
Mao Mao ◽  
Shihao Tang
Keyword(s):  
Size Distribution ◽  
Volume Fraction ◽  
Optical Parameter ◽  
Brown Carbon ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Highly Sensitive ◽  
Ångström Exponent ◽  
Bc Aerosols ◽  
Ångstrom Exponent

Abstract. Aerosol absorption Angstrom exponent (AAE) is a crucial optical parameter for their apportionment and characterization. Due to considerable inconsistences associated with observations, a numerical research is a powerful means to give better understanding of the AAE of aged BC aerosols. Numerical studies of the AAE of polydisperse BC aggregates with brown coatings using the exact multiple-sphere T-matrix method (MSTM) are performed. The objective of the study is to thoroughly assess the AAE of coated BC influenced by their observation-based detailed microphysics and then provide a new AAE parameterization for application. At odds with our expectations, BC coated by thin brown carbon with more large particles can have an AAE smaller than 1.0, indicating that BC aerosols internally mixing with brown carbon can even show lower AAE than pure BC particles. The AAE of BC with brown coatings is highly sensitive to absorbing volume fraction of coating, coated volume fraction of BC, shell / core ratio, and particle size distribution with a wide variation, whereas the impacts of BC geometry and BC position within coating are trivial. The AAE of BC with brown coatings can be larger than 3.0, if there are more small coated BC particles, heavy coating, or more brown carbon. However, the AAE of BC with non-absorbing coating shows weakly sensitive to particle microphysics with values around 1.0 (i.e., 0.7–1.4), suggesting the substantial role of absorbing volume fraction of coating in the AAE determination. With more realistic BC geometries, our study also indicates that occurrence of brown carbon may be made confidently unless AAE > 1.4. In addition, we present a parameterization of the AAE of coated BC with a size distribution on the basis of numerical results, which can act as a guide for the AAE response to absorbing volume fraction of coating, coated volume fraction of BC, and shell / core ratio. Our findings can improve the understanding and application of the AAE of BC with brown coatings.

scholarly journals The absorption Ångstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization

2020 ◽  
Vol 20 (16) ◽  
pp. 9701-9711 ◽  
Author(s):  
Xiaolin Zhang ◽  
Mao Mao ◽  
Yan Yin ◽  
Shihao Tang
Keyword(s):  
Size Distribution ◽  
Black Carbon ◽  
Volume Fraction ◽  
Optical Parameter ◽  
Brown Carbon ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Ångström Exponent ◽  
Bc Aerosols ◽  
Ångstrom Exponent

Abstract. The aerosol absorption Ångstrom exponent (AAE) is a crucial optical parameter for apportionment and characterization. Due to considerable inconsistences associated with observations, numerical research is a powerful means to give a better understanding of the AAE of aged black carbon (BC) aerosols. Numerical studies of the AAE of polydisperse BC aggregates with brown coatings using the exact multiple-sphere T-matrix method (MSTM) are performed. The objective of the study is to thoroughly assess the AAE of coated BC influenced by their observation-based detailed microphysics and then provide a new AAE parameterization for application. At odds with our expectations, more large-sized BC particles coated by thin brown carbon can have an AAE smaller than 1.0, indicating that BC aerosols internally mixing with brown carbon can even show lower AAE than pure BC particles. The AAE of BC with brown coatings is highly sensitive to the absorbing volume fraction of the coating, coated volume fraction of BC, shell ∕ core ratio, and particle size distribution with a wide variation, whereas the impacts of BC geometry and BC position within the coating are negligible. The AAE of BC with brown coatings can be larger than 3.0 if there are plenty of small-sized coated BC particles, heavy coating, or a large amount of brown carbon. However, the AAE of BC with non-absorbing coating appears to be weakly sensitive to particle microphysics with values around 1.0 (i.e., 0.7–1.4), suggesting the substantial role of the absorbing volume fraction of the coating in AAE determination. With more realistic BC geometries, our study also indicates that the occurrence of brown carbon may not be confidently determined unless AAE > 1.4. The currently popular core–shell Mie model reasonably approximates the AAE of fully coated BC by brown carbon, whereas it underestimates the AAE of partially coated or externally attached BC and underestimates more for a lower coated volume fraction of BC. In addition, we present a parameterization of the AAE of coated BC with a size distribution on the basis of numerical results, which can act as a guide for the AAE response to the absorbing volume fraction of the coating, coated volume fraction of BC, and shell ∕ core ratio. The proposed parameterization of coated BC AAE generates a decent prediction for moderate BC microphysics, whereas caution should be taken in applying it for extreme cases, such as externally attached coated BC morphology. Our findings could improve the understanding and application of the AAE of BC with brown coatings.

scholarly journals Measurements of optical properties of atmospheric aerosols in Northern Finland

2005 ◽  
Vol 5 (6) ◽  
pp. 11703-11728 ◽  
Author(s):  
V. Aaltonen ◽  
H. Lihavainen ◽  
V.-M. Kerminen ◽  
M. Komppula ◽  
J. Hatakka ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Seasonal Pattern ◽  
Late Summer ◽  
Aerosol Optical Properties ◽  
Air Masses ◽  
Angstrom Exponent ◽  
Northern Border ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Three years of continuous measurements of aerosol optical properties and simultaneous aerosol number size distribution measurements at Pallas GAW station, a remote subarctic site in the northern border of the boreal forest zone, have been analysed. The scattering coefficient at 550 nm varied from 0.2 to 94.4 Mm−1 with an average of 7.1±8.6 Mm−1. Both the scattering and backscattering coefficients had a clear seasonal cycle with an autumn minimum and a 4–5 times higher summer maximum. The scattering was dominated by submicron aerosols and especially so during late summer and autumn. The Ångström exponent had a clear seasonal pattern with maximum values in late summer and minimum values during wintertime. The highest hemispheric backscattering fraction values were observed in autumn, indicating clean air with few scattering particles and a particle size distribution strongly dominated by ultrafine particles. To analyse the influence of air mass origin on the aerosol optical properties a trajectory climatology was applied to the Pallas aerosol data. The most polluted trajectory patterns represented air masses from the Kola Peninsula, Scandinavia and Russia as well as long-range transport from Britain and Eastern Europe. These air masses had the largest average scattering and backscattering coefficients for all seasons. Higher than average values of the Ångström exponent were also observed in connection with transport from these areas.

scholarly journals Estimating cloud condensation nuclei number concentrations using aerosol optical properties: role of particle number size distribution and parameterization

2019 ◽  
Vol 19 (24) ◽  
pp. 15483-15502 ◽  
Author(s):  
Yicheng Shen ◽  
Aki Virkkula ◽  
Aijun Ding ◽  
Krista Luoma ◽  
Helmi Keskinen ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Cloud Condensation Nuclei ◽  
Size Distributions ◽  
Condensation Nuclei ◽  
Aerosol Optical Properties ◽  
Average Bias ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. The concentration of cloud condensation nuclei (CCN) is an essential parameter affecting aerosol–cloud interactions within warm clouds. Long-term CCN number concentration (NCCN) data are scarce; there are a lot more data on aerosol optical properties (AOPs). It is therefore valuable to derive parameterizations for estimating NCCN from AOP measurements. Such parameterizations have already been made, and in the present work a new parameterization is presented. The relationships between NCCN, AOPs, and size distributions were investigated based on in situ measurement data from six stations in very different environments around the world. The relationships were used for deriving a parameterization that depends on the scattering Ångström exponent (SAE), backscatter fraction (BSF), and total scattering coefficient (σsp) of PM10 particles. The analysis first showed that the dependence of NCCN on supersaturation (SS) can be described by a logarithmic fit in the range SS <1.1 %, without any theoretical reasoning. The relationship between NCCN and AOPs was parameterized as NCCN≈((286±46)SAE ln(SS/(0.093±0.006))(BSF − BSFmin) + (5.2±3.3))σsp, where BSFmin is the minimum BSF, in practice the 1st percentile of BSF data at a site to be analyzed. At the lowest supersaturations of each site (SS ≈0.1 %), the average bias, defined as the ratio of the AOP-derived and measured NCCN, varied from ∼0.7 to ∼1.9 at most sites except at a Himalayan site where the bias was >4. At SS >0.4 % the average bias ranged from ∼0.7 to ∼1.3 at most sites. For the marine-aerosol-dominated site Ascension Island the bias was higher, ∼1.4–1.9. In other words, at SS >0.4 % NCCN was estimated with an average uncertainty of approximately 30 % by using nephelometer data. The biases were mainly due to the biases in the parameterization related to the scattering Ångström exponent (SAE). The squared correlation coefficients between the AOP-derived and measured NCCN varied from ∼0.5 to ∼0.8. To study the physical explanation of the relationships between NCCN and AOPs, lognormal unimodal particle size distributions were generated and NCCN and AOPs were calculated. The simulation showed that the relationships of NCCN and AOPs are affected by the geometric mean diameter and width of the size distribution and the activation diameter. The relationships of NCCN and AOPs were similar to those of the observed ones.

scholarly journals Extinction-related Angström exponent characterization of submicrometric volume fraction in atmospheric aerosol particles

2019 ◽  
Vol 228 ◽  
pp. 270-280 ◽  
Author(s):  
A. Quirantes ◽  
J.L. Guerrero-Rascado ◽  
D. Pérez-Ramírez ◽  
I. Foyo-Moreno ◽  
P. Ortiz-Amezcua ◽  
...  
Keyword(s):  
Atmospheric Aerosol ◽  
Volume Fraction ◽  
Aerosol Particles ◽  
Angstrom Exponent ◽  
Atmospheric Aerosol Particles ◽  
Ångström Exponent ◽  
Ångstrom Exponent

scholarly journals On the attribution of black and brown carbon light absorption using the Ångström exponent

2013 ◽  
Vol 13 (6) ◽  
pp. 15493-15515 ◽  
Author(s):  
D. A. Lack ◽  
J. M. Langridge
Keyword(s):  
Black Carbon ◽  
Light Absorption ◽  
Absorption Efficiency ◽  
Potential Range ◽  
Brown Carbon ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Absorbing Material ◽  
Visible Wavelengths ◽  
Ångstrom Exponent

Abstract. The absorption Ångström exponent (åAbs) of black carbon (BC), or BC internally mixed with non-absorbing material (BCInt), is often used to differentiate the contribution of black carbon, dust and brown carbon to light absorption at low-visible wavelengths. This attribution method contains assumptions with uncertainties that have not been formally assessed. We show that the potential range of åAbs for BC (or BCInt) in the atmosphere can reasonably lead to +7% to −22% uncertainty in BC (or BCInt) absorption at 404nm derived from measurements made at 658 nm. These uncertainties propagate to errors in the attributed absorption and mass absorption efficiency (MAE) of brown carbon (BrC). For data collected during a biomass-burning event, the mean uncertainty in MAE at 404 nm attributed to BrC using the åAbs method was found to be 34%. In order to yield attributed BrC absorption uncertainties of ±33%, 23% to 41% of total absorption must be sourced from BrC. In light of the potential for introducing significant and poorly constrained errors, we caution against the universal application of the åAbs attribution method.

scholarly journals Impacts of the Variations of Aerosols Components and Relative Humidity on the Visibility and Particles Size Distribution of the Desert Atmosphere

2021 ◽  
pp. 42-65
Author(s):  
S. U. Yerima ◽  
U. Y. Abdulkarim ◽  
B. I. Tijjani ◽  
U. M. Gana ◽  
M. Idris ◽  
...  
Keyword(s):  
Size Distribution ◽  
Hygroscopic Growth ◽  
Angstrom Exponent ◽  
Microphysical Properties ◽  
Coarse Mode ◽  
Ångström Exponent ◽  
Particles Size Distribution ◽  
Fine Mode ◽  
The Mean ◽  
Ångstrom Exponent

This paper investigates the Impact of relative humidity, varying the concentrations of water-soluble aerosol particle concentrations (WASO), Mineral Nuclei Mode Aerosols Particle Concentration (MINN), mineral accumulation mode, nonspherical (MIAN) aerosol particles concentrations and Mineral Coarse Mode Aerosols Particle Concentration (MICN) on the visibility and particles size distribution of desert aerosols based on microphysical properties of desert aerosols. The microphysical properties (the extinction coefficients, volume mix ratios, dry mode radii and wet mode radii) were extracted from Optical Properties of Aerosols and Clouds (OPAC 4.0) at eight relative humidities, RHs (00 to 99%) and at the spectral visible range of 0.4-0.8mm, the concentrations were varied to obtain five different models for each above-mentioned component. Regression analysis of some standard equations were used to determine the Angstrom exponent (α), the turbidity coefficient (β), the curvature (α2), humidification factor (), the mean exponent of aerosol growth curve (µ) and the mean exponent of aerosol size distributions (n). The values of angstrom exponent (α) were observed to be less than 1 throughout the five models at all RHs for the four studied components, and this signifies the dominance of coarse mode particles over fine mode particles. But the magnitude of the angstrom exponent (α) fluctuates all through the studied components except for WASO which increased with the increase in RH across the models and this also signifies the dominance of coarse mode particles with some traces of fine mode particles. The investigation also revealed that the curvature (α2) has both monomodal (negative signs) and bimodal (positive signs) types of distributions all through the five models and this also signifies the dominance of coarse mode particles with some traces of fine mode particles across the individual models for all the studied components. it was also found that the visibility decreased with the increase in RH and increased with the increase in wavelength. The investigation further revealed that the turbidity coefficient (β) fluctuates with the increase in RH and the particles concentrations, and this might be due to major coagulation and sedimentation. The analysis further found that there is a direct inverse power relation between the humidification factor and the mean exponent of aerosols size distribution with the mean exponent of aerosols growth curve. It was also found that as the magnitude of µ increased for MIAN, MINN and MICN, the effective hygroscopic growth  decreased. For WASO, it was found that as the magnitude of µ decreased, the effective hygroscopic growth  increased with the increase in particles concentrations and RH. The decreased in the magnitude of µ for WASO might be due to the fact that as we increase the non-hygroscopic particles, we decrease the deliquescence. The mean exponent of aerosol size distribution (n) being less than 3 shows foggy condition of the desert atmosphere the four investigated components and five studied models.

scholarly journals Light absorption of brown carbon in eastern China based on 3-year multi-wavelength aerosol optical property observations at the SORPES station and an improved Absorption Ångstrom exponent segregation method

2018 ◽  
Author(s):  
Jiaping Wang ◽  
Wei Nie ◽  
Yafang Cheng ◽  
Yicheng Shen ◽  
Xuguang Chi ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Light Absorption ◽  
Mie Theory ◽  
Brown Carbon ◽  
Angstrom Exponent ◽  
Lagrangian Modeling ◽  
Ångström Exponent ◽  
Multi Wavelength ◽  
Ångstrom Exponent

Abstract. Brown carbon (BrC), a certain group of organic carbon (OC) with strong absorption from the visible to ultraviolet (UV) wavelengths, makes considerable contribution to light absorption on both global and regional scales. High concentration and proportion of OC has been reported in China, but studies of BrC absorption based on long-term observations are rather limited in this region. In this study, we reported 3-year results of light absorption of BrC based on continuous measurement at the Station for Observation Regional Processes of the Earth System (SORPES) in the Yangtze River Delta, China combined with Mie-theory calculation. Light absorption of BrC was obtained using an improved Absorption Ångstrom exponent (AAE) segregation method to calculate AAE of pure and non-absorbing coated black carbon (BC) at each time step based on Mie-theory simulation and measurement of multi-wavelength aerosol light absorption. By using this improved method, the variation of AAE over time is taken into consideration, making it applicable for long-term analysis. The yearly average light absorption of BrC (babs_BrC) at 370 nm was 4.3 Mm−1 at the SORPES station. The contribution of BrC to total aerosol absorption (PBrC) at 370 nm ranged from 6 % to 18 % (10th and 90th percentiles, respectively), and reached up to ~ 28 % in biomass burning-dominant season and winter. Both babs_BrC and PBrC exhibited clear seasonal cycles with two peaks in later spring/early summer (May–June, babs_BrC ~ 4 Mm−1, PBrC ~ 11 %) and winter (December, babs_BrC ~ 12 Mm−1, PBrC ~ 17 %), respectively. Lagrangian modeling and chemical signature observed at the site suggested that open biomass burning and residential emissions were the dominate sources influencing BrC in the two seasons.

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