Limitation of the Use of the Absorption Angstrom Exponent for Source Apportionment of Equivalent Black Carbon: a Case Study from the North West Indo-Gangetic Plain

2015 ◽  
Vol 50 (2) ◽  
pp. 814-824 ◽  
Author(s):  
Saryu Garg ◽  
Boggarapu Praphulla Chandra ◽  
Vinayak Sinha ◽  
Roland Sarda-Esteve ◽  
Valerie Gros ◽  
...  
Keyword(s):  
Black Carbon ◽  
Source Apportionment ◽  
Gangetic Plain ◽  
North West ◽  
Angstrom Exponent ◽  
The North ◽  
Ångström Exponent ◽  
Indo Gangetic Plain ◽  
Ångstrom Exponent

scholarly journals High aerosol loading over mega city Delhi in the western Indo-Gangetic plain : Optical characteristics

MAUSAM ◽  
2021 ◽  
Vol 67 (3) ◽  
pp. 609-618
Author(s):  
S. D. ATTRI ◽  
V. K. SONI ◽  
S. TIWARI ◽  
A. K. SRIVASTAVA ◽  
SHANI TIWARI ◽  
...  
Keyword(s):  
North India ◽  
Winter Period ◽  
Gangetic Plain ◽  
Large Variability ◽  
Angstrom Exponent ◽  
Aerosol Loading ◽  
Post Monsoon ◽  
Ångström Exponent ◽  
Indo Gangetic Plain ◽  
Ångstrom Exponent

Measurements of aerosol optical properties were carried out at an urban mega city Delhi, which is situated in the western Indo-Gangetic Plain (IGP) region in north India using an automatic sun/sky radiometer during 2006-2008. The present study revealed high aerosol loading over the station, which could be due to its topography surrounded by different natural and anthropogenic emission sources, and may have major implications towards health, air quality and climate system. Results show a large variability in AOD during the study period, with nearly equal values during winter (0.67 ± 0.06) and summer (0.71 ± 0.11). The Ångström exponent (AE) values were found to be relatively higher during winter (1.19 ± 0.07, suggests dominance of fine-mode aerosols) and lower during summer (0.74±0.06, suggests dominance of coarse-mode aerosols). A slight decrease in single scattering albedo (SSA) was observed during the study period, with a mean value of ~0.9. SSA was found to be about 0.93 during post-monsoon and 0.96 during the winter period whereas during summer and monsoon, SSA was about 0.95. The estimated monthly absorption Ångström exponent (AAE) values over the station varied from 0.11 to 1.87, which were found to be less than 1.0 by ~55% time (mostly during winter and monsoon), and greater than 1.0 by ~45% time (mostly during summer and post-monsoon).

scholarly journals Aerosol optical properties at Lampedusa (Central Mediterranean). 1. Influence of transport and identification of different aerosol types

2006 ◽  
Vol 6 (3) ◽  
pp. 697-713 ◽  
Author(s):  
G. Pace ◽  
A. di Sarra ◽  
D. Meloni ◽  
S. Piacentino ◽  
P. Chamard
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Central Mediterranean ◽  
Desert Dust ◽  
Central Eastern Europe ◽  
Angstrom Exponent ◽  
The North ◽  
Ångström Exponent ◽  
Summer Maximum ◽  
Ångstrom Exponent

Abstract. Aerosol optical depth and Ångström exponent were obtained from multi filter rotating shadowband radiometer (MFRSR) observations carried out at the island of Lampedusa, in the Central Mediterranean, in the period July 2001–September 2003. The average aerosol optical depth at 495.7 nm, τ, is 0.24±0.14; the average Ångström exponent, α, is 0.86±0.63. The observed values of τ range from 0.03 to 1.13, and the values of α vary from −0.32 to 2.05, indicating a large variability in aerosol content and size. In cloud-free conditions, 36% of the airmasses come from Africa, 25% from Central-Eastern Europe, and 19% from Western France, Spain and the North Atlantic. In summer, 42% of the airmasses is of African origin. In almost all cases African aerosols display high values of τ and low values of α, typical of Saharan dust (average values of τ and α are 0.36 and 0.42, respectively). Particles originating from Central-Eastern Europe show relatively large average values of τ and α (0.23 and 1.5, respectively), while particles from Western France, Spain and the North Atlantic show the lowest average values of τ (0.15), and relatively small values of α (0.92). Intermediate values of α are often connected with relatively fast changes of the airmass originating sector, suggesting the contemporary presence of different types of particles in the air column. Clean marine conditions are rare at Lampedusa, and are generally associated with subsidence of the airmasses reaching the island. Average values of τ and α for clean marine conditions are 0.11 and 0.86, respectively. The largest values of α (about 2) were observed in August 2003, when large scale forest fires in Southern Europe produced consistent amounts of fine combustion particles, that were transported to the Central Mediterranean by a persistent high pressure system over Central Europe. Smoke particles in some cases mix with desert dust, producing intermediate values of α. The seasonal distribution of the meteorological patterns over the Mediterranean, the efficiency of the aerosol production mechanisms, and the variability of the particles' residence time produce a distinct seasonal cycle of aerosol optical depths and Ångström exponent values. Particles originating from all sectors show a summer maximum in aerosol optical depth. The summer increase in optical depth for European aerosols is linked with an increment in the values of α, that indicates an enhancement in the number of fine particles. The summer maximum of τ for African particles is associated with a weak reduction in the Ångström exponent, suggesting an increase in the total number of particles and a relatively more intense transport of large particles. The observations were classified according to the aerosol optical properties, and two main classes have been identified: desert dust and biomass burning/urban-industrial aerosols. Values of τ and α averaged over the whole observing period are 0.37 and 0.15 for desert dust, and 0.27 and 1.77 for urban-industrial/biomass burning aerosols.

scholarly journals The Ångström Exponent and Single-Scattering Albedo of Black Carbon: Effects of Different Coating Materials

Atmosphere ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1103
Author(s):  
Jie Luo ◽  
Yongming Zhang ◽  
Qixing Zhang
Keyword(s):  
Black Carbon ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Optical Measurements ◽  
Coating Materials ◽  
Total Size ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Mixing States ◽  
Ångstrom Exponent

In this work, the absorption Ångström exponent (AAE), extinction Ångström exponent (EAE), and single-scattering albedo (SSA) of black carbon (BC) with different coating materials are numerically investigated. BC with different coating materials can provide explanations for the small AAE, small EAE, and large AAE observed in the atmosphere, which is difficult to be explained by bare BC aggregate models. The addition of organic carbon (OC) does not necessarily increase AAE due to the transformation of BC morphologies and the existence of non-absorbing OC. The addition of coating materials does also not necessarily decrease EAE. While the addition of coating materials can increase the total size of BC-containing particles, the effective refractive index can be modified by introducing the coating materials, so increases the EAE. We found that it is not possible to differentiate between thinly- and heavily-coated BC based on EAE or AAE alone. On the other hand, SSA is much less sensitive to the size and can provide much more information for distinguishing heavily-coated BC from thinly-coated BC. For BC with different coating materials and mixing states, AAE, EAE, and SSA show rather different sensitivities to particle size and composition ratios, and their spectral-dependences also exhibit distinct differences. Different AAE and EAE trends with BC/OC ratio were also found for BC with different coating materials and mixing states. Furthermore, we also found empirical fittings for AAE, EAE, SSA, and optical cross-sections, which may be useful for retrieving the size information based on the optical measurements.

scholarly journals Black Carbon physical and optical properties across northern India during pre-monsoon and monsoon seasons

2019 ◽  
Author(s):  
James Brooks ◽  
Dantong Liu ◽  
James D. Allan ◽  
Paul I. Williams ◽  
Jim Haywood ◽  
...  
Keyword(s):  
Physical Properties ◽  
Black Carbon ◽  
Mixing State ◽  
Atmospheric Measurements ◽  
Core Diameter ◽  
Gangetic Plain ◽  
North West ◽  
North East ◽  
Northern India ◽  
Indo Gangetic Plain

Abstract. Black carbon (BC) is known to have major impacts on both climate and human health, so is therefore of global importance, particularly so in regions close to large populations that have strong sources. The physical properties and mixing state of black carbon containing particles are important determinants in these effects but information is often lacking, particularly in some of the most important regions of the globe. Detailed analysis into the vertical and horizontal BC optical and physical properties across northern India has been carried out using airborne in-situ measurements. The size-resolved mixing state of BC-containing particles was characterised using a single particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11th and 12th June) and monsoon (30th June to 11th July) seasons of 2016. Over the Indo-Gangetic Plain, BC mass concentrations were greater (1.95 µg/m3) compared to north-west India (1.50 µg/m3) and north-east India (0.70 µg/m3) during the pre-monsoon. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter 

scholarly journals Absorption Angstrom Exponent in AERONET and related data as an indicator of aerosol composition

2009 ◽  
Vol 9 (5) ◽  
pp. 21785-21817 ◽  
Author(s):  
P. B. Russell ◽  
R. W. Bergstrom ◽  
Y. Shinozuka ◽  
A. D. Clarke ◽  
P. F. DeCarlo ◽  
...  
Keyword(s):  
Black Carbon ◽  
Optical Depth ◽  
Aerosol Layer ◽  
Ozone Monitoring Instrument ◽  
Aerosol Composition ◽  
Cluster Analyses ◽  
Angstrom Exponent ◽  
Near Ultraviolet ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Recent results from diverse air, ground, and laboratory studies using both radiometric and in situ techniques show that the fractions of black carbon, organic matter, and mineral dust in atmospheric aerosols determine the wavelength dependence of absorption (expressed as Absorption Angstrom Exponent, or AAE). Taken together, these results hold promise of improving information on aerosol composition from remote measurements. The purpose of this paper is to show that AAE values for Aerosol Robotic Network (AERONET) retrievals from Sun-sky measurements describing the full aerosol vertical column are also strongly correlated with aerosol composition or type. In particular, we find AAE values near 1 (the theoretical value for black carbon) for AERONET-measured aerosol columns dominated by urban-industrial aerosol, larger AAE values for biomass burning aerosols, and the largest AAE values for Sahara dust aerosols. Ambiguities in aerosol composition or mixtures thereof, resulting from intermediate AAE values, can be reduced via cluster analyses that supplement AAE with other variables, for example Extinction Angstrom Exponent (EAE), which is an indicator of particle size. Together with previous results, these results strengthen prospects for determining aerosol composition from space, for example using the Glory Aerosol Polarimetry Sensor (APS), which promises retrievals of multiwavelength single-scattering albedo (SSA) and aerosol optical depth (and therefore aerosol absorption optical depth (AAOD) and AAE), as well as shape and other aerosol properties. Cluster analyses promise additional information content, for example by using the Ozone Monitoring Instrument (OMI) to add AAOD in the near ultraviolet and CALIPSO aerosol layer heights to reduce height-absorption ambiguity.

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 The absorption Ångström exponent of black carbon: from numerical aspects

2018 ◽  
Vol 18 (9) ◽  
pp. 6259-6273 ◽  
Author(s):  
Chao Liu ◽  
Chul Eddy Chung ◽  
Yan Yin ◽  
Martin Schnaiter
Keyword(s):  
Particle Size ◽  
Refractive Index ◽  
Black Carbon ◽  
Numerical Study ◽  
Geometric Mean ◽  
Optical Parameter ◽  
Angstrom Exponent ◽  
Wide Range ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. The absorption Ångström exponent (AAE) is an important aerosol optical parameter used for aerosol characterization and apportionment studies. The AAE of black carbon (BC) particles is widely accepted to be 1.0, although observational estimates give quite a wide range of 0.6–1.3. With considerable uncertainties related to observations, a numerical study is a powerful method, if not the only one, to provide a better and more accurate understanding on BC AAE. This study calculates BC AAE using realistic particle geometries based on fractal aggregate and an accurate numerical optical model (namely the multiple-sphere T-matrix method), and considers bulk properties of an ensemble of BC particles following lognormal size distributions. At odds with the expectations, BC AAE is not 1.0, even when BC is assumed to have small sizes and a wavelength-independent refractive index. With a wavelength-independent refractive index, the AAE of fresh BC is approximately 1.05 and relatively insensitive to particle size. For BC with geometric mean diameters larger than 0.12 µm, BC AAE becomes smaller when BC particles are aged (compact structures or coated by other non-absorptive materials). For coated BC, we prescribe the coating fraction variation based on a laboratory study, where smaller BC cores are shown to develop larger coating fractions than those of bigger BC cores. For both compact and coated BC, the AAE is highly sensitive to particle size distribution, ranging from approximately 0.8 to even over 1.4 with wavelength-independent refractive index. When the refractive index is allowed to vary with wavelength, a feature with observational backing, the BC AAE may show an even wider range. For different BC morphologies, we derive simple empirical equations on BC AAE based on our numerical results, which can serve as a guide for the response of BC AAE to BC size and refractive index. Due to its complex influences, the effects of BC geometry is better to be discussed at certain BC properties, i.e., known size and refractive index.

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