scholarly journals Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: A multi-instrumental approach

2021 ◽  
Author(s):  
Jesús Yus-Díez ◽  
Vera Bernardoni ◽  
Griša Močnik ◽  
Andrés Alastuey ◽  
Davide Ciniglia ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Multiple Scattering ◽  
Correction Factor ◽  
Wavelength Dependence ◽  
Cross Sensitivity ◽  
Coated Glass ◽  
Mountain Station ◽  
Scattering Correction ◽  
Absorption Measurements

Abstract. Accurate measurements of light absorption by aerosolized particles, especially black carbon (BC), are of utter importance since BC represents the second most important climate-warming agent after carbon dioxide (CO2). Reducing the uncertainties related to the absorption measurement techniques will improve the global estimation of BC concentration and the radiative effects of light absorbing aerosols. Currently, one of the most widely used instruments for BC and absorption measurements is the dual-spot aethalometer, AE33, which derives the absorption coefficients of aerosol particles at 7 different wavelengths from the measurements of optical attenuation through a filter where particles are continuously collected. An accurate determination of the absorption coefficient relies on the quantification of non-linear processes related to the collection of sample on the filter. The multiple-scattering correction factor (C(λ)), which depends on the filter tape used and on the optical properties of the collected particles, is the parameter with the greatest uncertainty.An in-depth analysis of the AE33 multiple-scattering correction factor and its wavelength dependence for different filter tapes, i.e. the old most referenced known as TFE-coated glass and the current most widely used M8060, has been carried out by comparing the AE33 attenuation measurements with the absorption measurements from different filter-based techniques. Online co-located multi-angle absorption photometer (MAAP) measurements and offline PP_UniMI polar photometer measurements were used with this aim. We used data from three different measurement stations in North-East of Spain: an urban background station (Barcelona; BCN), a regional background station (Montseny; MSY) and a mountain-top station (Montsec d'Ares; MSA). The median C values (at 637 nm) measured at the three stations ranged between 2.29 (at BCN and MSY; lowest 5th percentile of 1.97 and highest 95th percentile of 2.68) and 2.51 (at MSA; lowest 5th percentile of 2.06 and highest 95th percentile of 3.06). The C factor was wavelength-dependent only at the mountain-top station, whereas at the urban and regional stations no statistically significant difference was found at the 7 different AE33 wavelengths. The wavelength-dependence of C at the mountain station was in part driven by the predominant effect of dust particles during Saharan dust outbreaks at this station. At the mountain station, neglecting the wavelength dependence of the C factor led to an underestimation of the Absorption Ångström Exponent (AAE) of 12 %. The analysis of the cross-sensitivity to scattering for different filter tapes revealed a large increase of the C factor at the three stations when the single scattering albedo (SSA) of the collected particles was above 0.90–0.95, with up to a 3-fold increase above the average values. The result of the cross-sensitivity to scattering displayed a fitted constant multiple scattering parameter, Cf, of 2.21 and 1.96 and a cross-sensitivity factor, ms, of 0.8 % and 1.7 % for MSY and MSA stations, respectively, for the TFE-coated glass filter tape. For the M8060 filter tape, Cf of 2.50, 1.96, 1.82 and a ms of 0.7 %, 1.5 %, 2.7 %, for BCN, MSY and MSA stations, respectively, were obtained. Differences in the absorption coefficient determined from AE33 measurements at BCN, MSY and MSA of around a 35–40 % can be expected when using the site-dependent C determined experimentally instead of the nominal C value.

scholarly journals Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: a multi-instrumental approach

2021 ◽  
Vol 14 (10) ◽  
pp. 6335-6355
Author(s):  
Jesús Yus-Díez ◽  
Vera Bernardoni ◽  
Griša Močnik ◽  
Andrés Alastuey ◽  
Davide Ciniglia ◽  
...  
Keyword(s):  
Multiple Scattering ◽  
Correction Factor ◽  
Aerosol Particles ◽  
Wavelength Dependence ◽  
Absorption Coefficients ◽  
Scattering Parameter ◽  
Cross Sensitivity ◽  
Scattering Correction ◽  
C Value ◽  
Factor C

Abstract. Providing reliable observations of aerosol particles' absorption properties at spatial and temporal resolutions suited to climate models is of utter importance to better understand the effects that atmospheric particles have on climate. Nowadays, one of the instruments most widely used in international monitoring networks for in situ surface measurements of light absorption properties of atmospheric aerosol particles is the multi-wavelength dual-spot Aethalometer, AE33. The AE33 derives the absorption coefficients of aerosol particles at seven different wavelengths from the measurements of the optical attenuation of light through a filter where particles are continuously collected. An accurate determination of the absorption coefficients from the AE33 instrument relies on the quantification of the non-linear processes related to the sample collection on the filter. The multiple-scattering correction factor (C), which depends on the filter tape used and on the optical properties of the collected particles, is the parameter with both the greatest uncertainty and the greatest impact on the absorption coefficients derived from the AE33 measurements. Here we present an in-depth analysis of the AE33 multiple-scattering correction factor C and its wavelength dependence for two different and widely used filter tapes, namely the old, and most referenced, TFE-coated glass, or M8020, filter tape and the currently, and most widely used, M8060 filter tape. For performing this analysis, we compared the attenuation measurements from AE33 with the absorption coefficients measured with different filter-based techniques. On-line co-located multi-angle absorption photometer (MAAP) measurements and off-line PP_UniMI polar photometer measurements were employed as reference absorption measurements for this work. To this aim, we used data from three different measurement stations located in the north-east of Spain, namely an urban background station (Barcelona, BCN), a regional background station (Montseny, MSY) and a mountaintop station (Montsec d'Ares, MSA). The median C values (at 637 nm) measured at the three stations ranged between 2.29 (at BCN and MSY, lowest 5th percentile of 1.97 and highest 95th percentile of 2.68) and 2.51 (at MSA, lowest 5th percentile of 2.06 and highest 95th percentile of 3.06). The analysis of the cross-sensitivity to scattering, for the two filter tapes considered here, revealed a large increase in the C factor when the single-scattering albedo (SSA) of the collected particles was above a given threshold, up to a 3-fold increase above the average C values. The SSA threshold appeared to be site dependent and ranged between 0.90 to 0.95 for the stations considered in the study. The results of the cross-sensitivity to scattering displayed a fitted constant multiple-scattering parameter, Cf, of 2.21 and 1.96, and a cross-sensitivity factor, ms, of 1.8 % and 3.4 % for the MSY and MSA stations, respectively, for the TFE-coated glass filter tape. For the M8060 filter tape, Cf values of 2.50, 1.96 and 1.82 and ms values of 1.6 %, 3.0 % and 4.9 % for the BCN, MSY and MSA stations, respectively, were obtained. SSA variations also influenced the spectral dependence of C, which showed an increase with wavelength when SSA was above the site-dependent threshold. Below the SSA threshold, no statistically significant dependence of C on the wavelength was observed. For the measurement stations considered here, the wavelength dependence of C was to some extent driven by the presence of dust particles during Saharan dust outbreaks that had the potential to increase the SSA above the average values. At the mountaintop station, an omission of the wavelength dependence of the C factor led to an underestimation of the absorption Ångström exponent (AAE) by up to 12 %. Differences in the absorption coefficient determined from AE33 measurements at BCN, MSY and MSA of around 35 %–40 % can be expected when using the site-dependent experimentally obtained C value instead of the nominal C value. Due to the fundamental role that the SSA of the particles collected on the filter tape has in the multiple-scattering parameter C, we present a methodology that allows the recognition of the conditions upon which the use of a constant and wavelength-independent C is feasible.

scholarly journals Multiple scattering correction factor estimation for aethalometer aerosol absorption coefficient measurement

2018 ◽  
Vol 53 (2) ◽  
pp. 160-171 ◽  
Author(s):  
Ji-Hyoung Kim ◽  
Sang-Woo Kim ◽  
John A. Ogren ◽  
Patrick J. Sheridan ◽  
Soon-Chang Yoon ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Multiple Scattering ◽  
Correction Factor ◽  
Aerosol Absorption ◽  
Scattering Correction ◽  
Coefficient Measurement ◽  
Factor Estimation

scholarly journals Multiple-scattering correction factor of quartz filters and the effect of filtering particles mixed in water: implications for analyses of light absorption in snow samples

2019 ◽  
Vol 12 (11) ◽  
pp. 5913-5925
Author(s):  
Jonas Svensson ◽  
Johan Ström ◽  
Aki Virkkula
Keyword(s):  
Multiple Scattering ◽  
Correction Factor ◽  
Measurement Techniques ◽  
Ultrasonic Bath ◽  
Mass Absorption ◽  
Finnish Lapland ◽  
Soot Aerosol ◽  
Scattering Correction ◽  
Water Filters ◽  
Snow Samples

Abstract. The deposition of light-absorbing aerosol (LAA) onto snow initiates processes that lead to increased snowmelt. Measurements of LAA, such as black carbon (BC) and mineral dust, have been observed globally to darken snow. Several measurement techniques of LAA in snow collect the particulates on filters for analysis. Here we investigate micro-quartz filters' optical response to BC experiments in which the particles are initially suspended in air or in a liquid. With particle soot absorption photometers (PSAPs) we observed a 20 % scattering enhancement for quartz filters compared to the standard PSAP Pallflex filters. The multiple-scattering correction factor (Cref) of the quartz filters for airborne soot aerosol is estimated to be ∼3.4. In the next stage correction factors were determined for BC particles mixed in water and also for BC particles both mixed in water and further treated in an ultrasonic bath. Comparison of BC collected from airborne particles with BC mixed in water filters indicated a higher mass absorption cross section by approximately a factor of 2 for the liquid-based filters, which is probably due to the BC particles penetrating deeper in the filter matrix. The ultrasonic bath increased absorption still further, roughly by a factor of 1.5, compared to only mixing in water. Application of the correction functions to earlier published field data from the Himalaya and Finnish Lapland yielded mass absorption coefficient (MAC) values of ∼7–10 m2 g−1 at λ=550 nm, which is in the range of the published MAC of airborne BC aerosol.

scholarly journals Aethalometer multiple scattering correction C<sub>ref</sub> for mineral dust aerosols

2017 ◽  
Author(s):  
Claudia Di Biagio ◽  
Paola Formenti ◽  
Mathieu Cazaunau ◽  
Edouard Pangui ◽  
Nicholas Marchand ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Multiple Scattering ◽  
Mineral Dust ◽  
Single Scattering ◽  
Ambient Aerosols ◽  
Dust Aerosols ◽  
Scattering Coefficients ◽  
Scattering Correction ◽  
The Difference ◽  
Mineral Dust Aerosols

Abstract. In this study we provide a first estimate of the aethalometer multiple scattering correction Cref for mineral dust aerosols. The Cref at 450 and 660 nm was obtained from the direct comparison of aethalometer data (Magee Sci. AE31) with the absorption coefficient calculated as the difference between the extinction and scattering coefficients measured by a CAPS PMex and a nephelometer at 450 nm and the absorption coefficient from a MAAP (Multi-Angle Absorption Photometer) at 660 nm. Measurements were performed on seven dust aerosol samples generated in the laboratory by the mechanical shaking of natural parent soils issued from different source regions worldwide. The single scattering albedo (SSA) at 450 and 660 nm and the size distribution of the aerosols were also measured. Cref for mineral dust varies between 1.81 and 2.56 for a SSA of 0.85–0.96 at 450 nm and between 1.75 and 2.28 for a SSA of 0.98–0.99 at 660 nm. The calculated mean Cref for dust is 2.09 (± 0.22) at 450 nm and 1.92 (± 0.17) at 660 nm. With this new Cref the dust absorption coefficient by aethalometer is about 2 % (450 nm) and 11 % (660 nm) higher than that obtained by using Cref = 2.14, usually assumed in the literature. This difference induces up to 3 % change in the dust SSA. The Cref seems independent of the particle fine and coarse size fractions, and so the obtained Cref can be applied to dust both close to sources and following transport. Additional experiments performed with pure kaolinite mineral and polluted ambient aerosols indicate a Cref of 2.49 (± 0.02) and 2.32 (± 0.01) at 450 and 660 nm (SSA = 0.96–0.97) for kaolinite, and a Cref of 2.32 (± 0.36) at 450 nm and 2.32 (± 0.35) at 660 nm for pollution aerosols (SSA = 0.62–0.87 at 450 nm and 0.42–0.76 at 660 nm).

Absorption coefficients of a hydrogen plasma for laser radiation

1974 ◽  
Vol 11 (1) ◽  
pp. 111-129 ◽  
Author(s):  
James R. Stallcop
Keyword(s):  
Laser Radiation ◽  
Absorption Coefficient ◽  
Hydrogen Plasma ◽  
Radiation Absorption ◽  
Graphical Form ◽  
Wide Range ◽  
Plasma Absorption ◽  
Common Laboratory ◽  
Absorption Measurements

The formalism for the calculation of the absorption of radiation by a hydrogen plasma at common laboratory conditions is summarized. The hydrogen plasma absorption coefficient for laser radiation has been computed for a wide range of electron densities (1015- 1018 cm-3) and temperatures (10 000–40 000 °K). The results of this computation are presented in a graphical form that permits a determination of the absorption coefficient for the following laser wavelengths: 0.176, 0.325, 0.337, 0.442, 0.488, 0.51, 0.633, 0.694, 1.06, 1.15, 2.36, 3.39, 5.40 and 10.6 Μm. The application of these results and laser radiation absorption measurements to plasma diagnostics is discussed briefly.

scholarly journals Determination of Aethalometer multiple-scattering enhancement parameters and impact on source apportionment during the winter 2017–2018 EMEP/ACTRIS/COLOSSAL campaign in Milan

2020 ◽  
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 ◽  
Attenuation Coefficients ◽  
Aerosol Absorption ◽  
The Difference ◽  
Absorption Photometer

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 the 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 7 wavelengths (λs, where λ = 370, 470, 520, 590, 660, 880, 950 nm). Aerosol absorption coefficient at 637 nm (babs_MAAP) was determined by MAAP measurements. Furthermore, babs was also measured at 4 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 parameters by linear regression of the Aethalometer bATN against the babs measured by PP_UniMI. We found significant filter material, and hence instrumental, dependence of the multiple-scattering enhancement parameter with the difference 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. Opposite, optimised multiple-scattering enhancement parameters led to 5 % agreement among the approaches. Also, the component-apportionment “MWAA model” was applied to the dataset. It resulted 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 %).

scholarly journals Multiple scattering correction factor of quartz filters and the effect of filtering particles mixed in water: implications to analyses of light-absorption in snow samples

2019 ◽  
Author(s):  
Jonas Svensson ◽  
Johan Ström ◽  
Aki Virkkula
Keyword(s):  
Multiple Scattering ◽  
Correction Factor ◽  
Measurement Techniques ◽  
Ultrasonic Bath ◽  
Finnish Lapland ◽  
Soot Aerosol ◽  
Scattering Correction ◽  
Absorbing Aerosols ◽  
Water Filters ◽  
Snow Samples

Abstract. The deposition of light-absorbing aerosols (LAA) onto snow initiates processes that lead to increased snowmelt. Measurements of LAA, such as black carbon (BC) and mineral dust, have been observed globally to darken snow. Several measurement techniques of LAA in snow collects the particulates on filters for analysis. Here we investigate micro-quartz filters optical response to BC experiments where the particles initially are suspended in air or in a liquid. With particle soot absorption photometers (PSAP) we observed a 20 % scattering enhancement for quartz filters compared to the standard PSAP Pallflex filters. The multiple-scattering correction factor (Cref) of the quartz filters for airborne soot aerosol is estimated to ~3.4. In the next stage correction factors were determined for BC particles mixed in water and also for BC particles both mixed in water and further treated in an ultrasonic bath. Comparison of BC collected from airborne particles with BC mixed in water filters indicated approximately a factor of two higher mass absorption cross section for the liquid based filters, probably due to the BC particles penetrating deeper in the filter matrix. The ultrasonic bath increased absorption still further, roughly by a factor of 1.5 compared to only mixing in water. Application of the correction functions to earlier published field data from the Himalaya and Finnish Lapland yielded MAC values of ~7–10 m2 g−1 at λ= 550 nm which is in the range of published MAC of airborne BC aerosol.

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