scholarly journals Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data

2017 ◽  
Vol 10 (8) ◽  
pp. 2837-2850 ◽  
Author(s):  
Jorge Saturno ◽  
Christopher Pöhlker ◽  
Dario Massabò ◽  
Joel Brito ◽  
Samara Carbone ◽  
...  
Keyword(s):  
Wavelength Dependence ◽  
Absorption Coefficients ◽  
Multiple Wavelength ◽  
Filter Loading ◽  
Multi Wavelength ◽  
Online Measurements ◽  
Loading Effects ◽  
Wavelength Absorption ◽  
Absorption Photometer ◽  
Absorption Measurements

Abstract. Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to seven-wavelength Aethalometer data, using multi-angle absorption photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to five-wavelength offline absorption measurements obtained with a multi-wavelength absorbance analyzer (MWAA), which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June–September 2014). The mean absorption coefficient (at 637 nm) during this period was 1.8 ± 2.1 Mm−1, with a maximum of 15.9 Mm−1. Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Ångström exponent (åABS) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct åABS, which is commonly implemented in brown carbon contribution calculations. Additionally, we found that the wavelength dependence of uncompensated Aethalometer attenuation data significantly correlates with the åABS retrieved from offline MWAA measurements.

scholarly journals Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data

2016 ◽  
Author(s):  
Jorge Saturno ◽  
Christopher Pöhlker ◽  
Dario Massabò ◽  
Joel Brito ◽  
Samara Carbone ◽  
...  
Keyword(s):  
Absorption Coefficients ◽  
Multiple Wavelength ◽  
Filter Loading ◽  
Multi Wavelength ◽  
Online Measurements ◽  
Loading Effects ◽  
Wavelength Absorption ◽  
Absorption Photometer ◽  
Absorption Measurements ◽  
Absorption Technique

Abstract. Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to 7-wavelength Aethalometer data, using Multi-Angle Absorption Photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to 5-wavelength offline absorption measurements obtained with a Multi-Wavelength Absorbance Analyzer (MWAA), which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June–September 2014). The mean absorption coefficient (at 637 nm) during this period was 1.8 ± 2.1 Mm−1, with a maximum of 15.9 Mm−1. Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Ångström exponent (AAE) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct AAE, which is commonly implemented in brown carbon contribution calculations. We found that a "hybrid" algorithm was more appropriate to achieve optimal correlations with the MAAP absorption coefficients and with the AAE retrieved from offline MWAA measurements.

scholarly journals Minimizing light absorption measurement artifacts of the Aethalometer: evaluation of five correction algorithms

2009 ◽  
Vol 2 (4) ◽  
pp. 1725-1770 ◽  
Author(s):  
M. Collaud Coen ◽  
E. Weingartner ◽  
A. Apituley ◽  
D. Ceburnis ◽  
H. Flentje ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Light Absorption ◽  
Wavelength Dependence ◽  
Radiation Budget ◽  
Absorption Coefficients ◽  
Light Absorption Coefficient ◽  
Correction Scheme ◽  
Multi Wavelength ◽  
Measurement Artifacts ◽  
Absorption Photometer

Abstract. The aerosol light absorption coefficient is an essential parameter involved in atmospheric radiation budget calculations. The Aethalometer (AE) has the great advantage of measuring the aerosol light absorption coefficient at several wavelengths, but the derived absorption coefficients are systematically too high when compared to reference methods. Up to now, four different correction algorithms of the AE absorption coefficients have been proposed by several authors. A new correction scheme based on these previously published methods has been developed, which accounts for the optical properties of the aerosol particles embedded in the filter. All the corrections have been tested on six datasets representing different aerosol types and loadings and include multi-wavelength AE and white-light AE. All the corrections have also been evaluated through comparison with a Multi-Angle Absorption Photometer (MAAP) for four datasets lasting between 6 months and five years. The modification of the wavelength dependence by the different corrections is analyzed in detail. The performances and the limits of all AE corrections are determined and recommendations are given.

scholarly journals Determination and analysis of in situ spectral aerosol optical properties by a multi-instrumental approach

2014 ◽  
Vol 7 (8) ◽  
pp. 2373-2387 ◽  
Author(s):  
S. Segura ◽  
V. Estellés ◽  
G. Titos ◽  
H. Lyamani ◽  
M. P. Utrillas ◽  
...  
Keyword(s):  
Optical Properties ◽  
Wavelength Dependence ◽  
Single Scattering ◽  
Aerosol Optical Properties ◽  
Absorption Coefficients ◽  
Instrumental Approach ◽  
Loading Effects ◽  
Absorption Photometer ◽  
Integrating Nephelometer

Abstract. Continuous in situ measurements of aerosol optical properties were conducted from 29 June to 29 July 2012 in Granada (Spain) with a seven-wavelength Aethalometer, a Multi-Angle Absorption Photometer, and a three-wavelength integrating nephelometer. The aim of this work is to describe a methodology to obtain the absorption coefficients (babs) for the different Aethalometer wavelengths. In this way, data have been compensated using algorithms which best estimate the compensation factors needed. Two empirical factors are used to infer the absorption coefficients from the Aethalometer measurements: C – the parameter describing the enhancement of absorption by particles in the filter matrix due to multiple scattering of light in the filter matrix – and f, the parameter compensating for non-linear loading effects in the filter matrix. Spectral dependence of f found in this study is not very strong. Values for the campaign lie in the range from 1.15 at 370 nm to 1.11 at 950 nm. Wavelength dependence in C proves to be more important, and also more difficult to calculate. The values obtained span from 3.42 at 370 nm to 4.59 at 950 nm. Furthermore, the temporal evolution of the Ångström exponent of absorption (αabs) and the single-scattering albedo (ω0) is presented. On average αabs is around 1.1 ± 0.3, and ω0 is 0.78 ± 0.08 and 0.74 ± 0.09 at 370 and 950 nm, respectively. These are typical values for sites with a predominance of absorbing particles, and the urban measurement site in this study is such. The babs average values are of 16 ± 10 Mm−1 (at 370 nm) and 5 ± 3 Mm−1 (at 950 nm), respectively. Finally, differences between workdays and Sundays have been further analysed, obtaining higher babs and lower ω0 during the workdays than on Sundays as a consequence of the diesel traffic influence.

scholarly journals Minimizing light absorption measurement artifacts of the Aethalometer: evaluation of five correction algorithms

2010 ◽  
Vol 3 (2) ◽  
pp. 457-474 ◽  
Author(s):  
M. Collaud Coen ◽  
E. Weingartner ◽  
A. Apituley ◽  
D. Ceburnis ◽  
R. Fierz-Schmidhauser ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Light Absorption ◽  
Wavelength Dependence ◽  
Radiation Budget ◽  
Absorption Coefficients ◽  
Light Absorption Coefficient ◽  
Correction Scheme ◽  
Multi Wavelength ◽  
Measurement Artifacts ◽  
Absorption Photometer

Abstract. The aerosol light absorption coefficient is an essential parameter involved in atmospheric radiation budget calculations. The Aethalometer (AE) has the great advantage of measuring the aerosol light absorption coefficient at several wavelengths, but the derived absorption coefficients are systematically too high when compared to reference methods. Up to now, four different correction algorithms of the AE absorption coefficients have been proposed by several authors. A new correction scheme based on these previously published methods has been developed, which accounts for the optical properties of the aerosol particles embedded in the filter. All the corrections have been tested on six datasets representing different aerosol types and loadings and include multi-wavelength AE and white-light AE. All the corrections have also been evaluated through comparison with a Multi-Angle Absorption Photometer (MAAP) for four datasets lasting between 6 months and five years. The modification of the wavelength dependence by the different corrections is analyzed in detail. The performances and the limits of all AE corrections are determined and recommendations are given.

scholarly journals Determination and analysis of spectral aerosol optical properties by a multi-instrumental approach

2014 ◽  
Vol 7 (2) ◽  
pp. 1871-1916
Author(s):  
S. Segura ◽  
V. Estellés ◽  
G. Titos ◽  
H. Lyamani ◽  
M. P. Utrillas ◽  
...  
Keyword(s):  
Optical Properties ◽  
Wavelength Dependence ◽  
Single Scattering ◽  
Aerosol Optical Properties ◽  
Absorption Coefficients ◽  
Instrumental Approach ◽  
Loading Effects ◽  
Absorption Photometer ◽  
Integrating Nephelometer

Abstract. Continuous in-situ measurements of aerosol optical properties where conducted from 20 June to 20 July in Granada (Spain) with a 7-wavelength Aethalometer, a Multi Angle Absorption Photometer, and a 3-wavelength integrating Nephelometer. The aim of this work is to describe a methodology to obtain the absorption coefficients (babs) for the different Aethalometer wavelengths. In this way, data have been compensated using algorithms which best estimate the compensation factors needed. Two empirical factors are used to infer the absorption coefficients from the Aethalometer measurements: C – the parameter describing the enhancement of absorption by particles in the filter matrix due to multiple scattering of light in the filter matrix; and f – the parameter compensating for non-linear loading effects in the filter matrix. Spectral dependence of f found in this study is not very strong. Values for the campaign lie in the range from 1.15 at 370 nm to 1.11 at 950 nm. Wavelength dependence in C proves to be more important, and also more difficult to calculate. The values obtained span from 3.40 at 370 nm to 4.35 at 950 nm. Furthermore, the temporal evolution of the Ångström exponent of absorption (αabs) and the single scattering albedo (ω0), is presented. On average αabs is around 1.1 ± 0.3, and ω0 is 0.78 ± 0.08 and 0.74 ± 0.09 at 370 and 950 nm, respectively. These are typical values for sites with a predominance of absorbing particles, and the urban measurement site in this study is such. The babs average values are of 16 ± 10 Mm−1 (at 370 nm) and 5 ± 3 Mm−1 (at 950 nm), respectively. Finally, differences between working days and Sunday have been further analyzed, obtaining higher babs and lower ω0 during week than on Sundays as a consequence of the influence of diesel traffic.

scholarly journals Measurement report: Determination of Black Carbon concentration in PM<sub>2.5</sub> fraction by Multi-wavelength absorption black carbon instrument (MABI)

2021 ◽  
Author(s):  
Anna Ryś ◽  
Lucyna Samek
Keyword(s):  
Seasonal Variation ◽  
Black Carbon ◽  
Biomass Burning ◽  
Fossil Fuel ◽  
Environmental Sciences ◽  
Absorption Coefficients ◽  
Multi Wavelength ◽  
Wavelength Absorption ◽  
The Mean

Abstract. The evaluation of black carbon (BC) sources is very important, especially in environmental sciences. This study shows how the contributions of biomass burning and fossil fuel/traffic to PM2.5 mass can be assessed. MABI was used for this purpose and gave the possibility to measure the transmission of light at different wavelengths. Absorption coefficients were calculated from measurements data and recalculated for concentrations of eBC. The samples of PM2.5 fraction were collected from February 1, 2020 to March 27, 2021 every third day in Krakow, Poland (50°04' N, 19°54'47" E). The concentrations of equivalent BC (eBC) from fossil fuel/traffic and biomass burning were in the range 0.82–11.64 μg m−3) and 0.007–0.84 μg m−3, respectively. At the same time, PM2.5 concentrations varied from 3.14 to 55.24 μg m−3. It means that about 18 % of PM2.5 mass belongs to eBC and 11.3 % of this value comes from biomass burning. The eBC contribution is the significant part of PM2.5 mass and we observed seasonal variation of the eBC concentration during the year with the peak in winter. The contribution of biomass burning to PM2.5 mass is more stable during the whole year. The eBC concentration during workdays is a bit higher than during weekend days but biomass burning is similar for both days (work and weekend taken as the mean for the whole period).

scholarly journals Deriving brown carbon from multiwavelength absorption measurements: method and application to AERONET and Aethalometer observations

2016 ◽  
Vol 16 (19) ◽  
pp. 12733-12752 ◽  
Author(s):  
Xuan Wang ◽  
Colette L. Heald ◽  
Arthur J. Sedlacek ◽  
Suzane S. de Sá ◽  
Scot T. Martin ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Cape Cod ◽  
Ambient Atmosphere ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Multiple Wavelength ◽  
Radiative Impact ◽  
Wavelength Absorption ◽  
Photochemical Aging ◽  
Absorption Measurements

Abstract. The radiative impact of organic aerosols (OA) is a large source of uncertainty in estimating the global direct radiative effect (DRE) of aerosols. This radiative impact includes not only light scattering but also light absorption from a subclass of OA referred to as brown carbon (BrC). However, the absorption properties of BrC are poorly understood, leading to large uncertainties in modeling studies. To obtain observational constraints from measurements, a simple absorption Ångström exponent (AAE) method is often used to separate the contribution of BrC absorption from that of black carbon (BC). However, this attribution method is based on assumptions regarding the spectral dependence of BC that are often violated in the ambient atmosphere. Here we develop a new AAE method which improves upon previous approaches by using the information from the wavelength-dependent measurements themselves and by allowing for an atmospherically relevant range of BC properties, rather than fixing these at a single assumed value. We note that constraints on BC optical properties and mixing state would help further improve this method. We apply this method to multiwavelength absorption aerosol optical depth (AAOD) measurements at AERONET sites worldwide and surface aerosol absorption measurements at multiple ambient sites. We estimate that BrC globally contributes up to 40 % of the seasonally averaged absorption at 440 nm. We find that the mass absorption coefficient of OA (OA-MAC) is positively correlated with the BC ∕ OA mass ratio. Based on the variability in BC properties and BC ∕ OA emission ratio, we estimate a range of 0.05–1.5 m2 g−1 for OA-MAC at 440 nm. Using the combination of AERONET and OMI UV absorption observations we estimate that the AAE388∕440 nm for BrC is generally  ∼ 4 worldwide, with a smaller value in Europe (< 2). Our analyses of observations at two surface sites (Cape Cod, to the southeast of Boston, and the GoAmazon2014/5 T3 site, to the west of Manaus, Brazil) reveal no significant relationship between BrC absorptivity and photochemical aging in urban-influenced conditions. However, the absorption of BrC measured during the biomass burning season near Manaus is found to decrease with photochemical aging with a lifetime of  ∼ 1 day. This lifetime is comparable to previous observations within a biomass burning plume but much slower than estimated from laboratory studies. Given the large uncertainties associated with AERONET retrievals of AAOD, the most challenging aspect of our analysis is that an accurate, globally distributed, multiple-wavelength aerosol absorption measurement dataset is unavailable at present. Thus, achieving a better understanding of the properties, evolution, and impacts of global BrC will rely on the future deployment of accurate multiple-wavelength absorption measurements to which AAE methods, such as the approach developed here, can be applied.

scholarly journals Deriving Brown Carbon from Multi-Wavelength Absorption Measurements: Method and Application to AERONET and Surface Observations

2016 ◽  
Author(s):  
Xuan Wang ◽  
Colette L. Heald ◽  
Arthur J. Sedlacek ◽  
Suzane S. de Sá ◽  
Scot T. Martin ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Cape Cod ◽  
Ambient Atmosphere ◽  
Brown Carbon ◽  
Radiative Impact ◽  
Multi Wavelength ◽  
Modelling Studies ◽  
Wavelength Absorption ◽  
Photochemical Aging ◽  
Absorption Measurements

Abstract. The radiative impact of organic aerosols (OA) is a large source of uncertainty in estimating the global direct radiative effect (DRE) of aerosols. This radiative impact includes not only light scattering but also light absorption from a subclass of OA referred to as brown carbon (BrC). However the absorption properties of BrC are poorly understood leading to large uncertainties in modelling studies. To obtain observational constraints from measurements, a simple Absorption Ångström Exponent (AAE) method is often used to separate the contribution of BrC absorption from that of black carbon (BC). However, this attribution method is based on assumptions regarding the spectral dependence of BC that are often violated in the ambient atmosphere. Here we develop a new method that decreases the uncertainties associated with estimating BrC absorption. By applying this method to multi-wavelength absorption aerosol optical depth (AAOD) measurements at AERONET sites worldwide and surface aerosol absorption measurements at multiple ambient sites, we estimate that BrC globally contributes 6–40 % of the absorption at 440 nm. We find that the mass absorption coefficient of OA (OA-MAC) is positively correlated with BC / OA mass ratio. Based on the variability of BC properties and BC / OA emission ratio, we estimate a range of 0.05–1.2 m2/g for OA-MAC at 440 nm. Using the combination of AERONET and OMI UV absorption observations we estimate that the AAE388/440 nm for BrC is generally ~ 4 world-wide, with a smaller value in Europe (< 2). Our analyses of two surface sites (Cape Cod, to the southeast of Boston, and the GoAmazon2014/5 T3 site, to the west of Manaus, Brazil) reveal no significant relationship between BrC absorptivity and photochemical aging in typical urban-influenced conditions. However, the absorption of BrC measured during the biomass burning season near Manaus is found to decrease with photochemical aging with a lifetime of ~ 1 day. This lifetime is comparable to previous observations within a biomass burning plume but much slower than estimated from laboratory studies.

scholarly journals Determination of Aethalometer multiple-scattering enhancement parameters and impact on source apportionment during the winter 2017/18 EMEP/ACTRIS/COLOSSAL campaign in Milan

2021 ◽  
Vol 14 (4) ◽  
pp. 2919-2940
Author(s):  
Vera Bernardoni ◽  
Luca Ferrero ◽  
Ezio Bolzacchini ◽  
Alice Corina Forello ◽  
Asta Gregorič ◽  
...  
Keyword(s):  
Source Apportionment ◽  
Multiple Scattering ◽  
Filter Material ◽  
Wavelength Dependence ◽  
Optical Source ◽  
Aerosol Absorption ◽  
Multi Wavelength ◽  
Wavelength Absorption ◽  
The Difference

Abstract. In the frame of the EMEP/ACTRIS/COLOSSAL campaign in Milan during winter 2018, equivalent black carbon measurements using the Aethalometer 31 (AE31), the Aethalometer 33 (AE33), and a Multi-Angle Absorption Photometer (MAAP) were carried out together with levoglucosan analyses on 12 h resolved PM2.5 samples collected in parallel. From AE31 and AE33 data, the loading-corrected aerosol attenuation coefficients (bATN) were calculated at seven wavelengths (λ, where λ values are 370, 470, 520, 590, 660, 880, and 950 nm). The aerosol absorption coefficient at 637 nm (babs_MAAP) was determined by MAAP measurements. Furthermore, babs was also measured at four wavelengths (405, 532, 635, 780 nm) on the 12 h resolved PM2.5 samples by a polar photometer (PP_UniMI). After comparing PP_UniMI and MAAP results, we exploited PP_UniMI data to evaluate the filter multiple-scattering enhancement parameter at different wavelengths for AE31 and AE33. We obtained instrument- and wavelength-dependent multiple-scattering enhancement parameters by linear regression of the Aethalometer bATN against the babs measured by PP_UniMI. We found significant dependence of the multiple-scattering enhancement parameter on filter material, hence on the instrument, with a difference of up to 30 % between the AE31 and the AE33 tapes. The wavelength dependence and day–night variations were small – the difference between the smallest and largest value was up to 6 %. Data from the different instruments were used as input to the so-called “Aethalometer model” for optical source apportionment, and instrument dependence of the results was investigated. Inconsistencies among the source apportionment were found fixing the AE31 and AE33 multiple-scattering enhancement parameters to their usual values. In contrast, optimised multiple-scattering enhancement parameters led to a 5 % agreement among the approaches. Also, the component apportionment “MWAA model” (Multi-Wavelength Absorption Analyzer model) was applied to the dataset. It was less sensitive to the instrument and the number of wavelengths, whereas significant differences in the determination of the absorption Ångström exponent for brown carbon were found (up to 22 %).

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