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

Garg, S. C.; Chandra, B. P.; Sinha, Vinayak; Sarda‐Estève, Roland; Gros, Valérie; Sinha, Baerbel

doi:10.1021/acs.est.5b03868

Cited by 78 publications

(55 citation statements)

References 80 publications

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“…A near-UV over-or underestimation of the data will substantially affect brown carbon calculations if apportionment algorithms based on the wavelength dependence of absorption are used. More details on the effects of inaccurate å ABS on the BrC / BC apportionment are discussed in Garg et al (2016), Schuster et al (2016a, b), Wang et al (2016), and references therein. A BrC estimation is beyond the scope of this paper.…”

Section: Overestimation Of Near-uv Absorption By Ae Correctionsmentioning

confidence: 99%

“…Assuming a fixed spectral dependence of 1 for BC, several studies have estimated the BrC contribution as a function of å ABS (Favez et al, 2010;Sandradewi et al, 2008). However, given the uncertainties associated with the å ABS of BC, these methods could potentially provide erroneous BrC estimations (Garg et al, 2016;Schuster et al, 2016a, b;Wang et al, 2016).…”

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confidence: 99%

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

et al. 2017

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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 (å ABS ) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct å ABS , 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 å ABS retrieved from offline MWAA measurements.

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Section: Overestimation Of Near-uv Absorption By Ae Correctionsmentioning

confidence: 99%

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confidence: 99%

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

et al. 2017

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“…On the other hand, recently published studies claim that the aerosol spectral dependence is more affected by combustion conditions than the type of fuel being combusted (Garg et al, 2016;Martinsson et al, 2015). Garg et al (2016) found that the gaseous tracer for biomass burning, acetonitrile, correlated well with AAE during smoldering combustion but poorly during flaming combustion, and further that AAE varied greatly throughout combustion of the same fuel type. Calvo et al (2015) measured levoglucosan in a wood stove with controlled combustion and a traditional fireplace; they found elevated concentrations of levoglucosan during the fuel addition followed by a rapid de-crease in concentration in the flaming phase.…”

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confidence: 99%

“…Some studies have found good correlation between levoglucosan and AAE, or calculated BC from wood burning (BC WB ), using the Aethalometer model (Fuller et al, 2014;Herich et al, 2011;Lack et al, 2013). On the other hand, recently published studies claim that the aerosol spectral dependence is more affected by combustion conditions than the type of fuel being combusted (Garg et al, 2016;Martinsson et al, 2015). Garg et al (2016) found that the gaseous tracer for biomass burning, acetonitrile, correlated well with AAE during smoldering combustion but poorly during flaming combustion, and further that AAE varied greatly throughout combustion of the same fuel type.…”

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confidence: 99%

Carbonaceous aerosol source apportionment using the Aethalometer model – evaluation by radiocarbon and levoglucosan analysis at a rural background site in southern Sweden

et al. 2017

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Abstract. With the present demand on fast and inexpensive aerosol source apportionment methods, the Aethalometer model was evaluated for a full seasonal cycle (June 2014-June 2015 at a rural atmospheric measurement station in southern Sweden by using radiocarbon and levoglucosan measurements. By utilizing differences in absorption of UV and IR, the Aethalometer model apportions carbon mass into wood burning (WB) and fossil fuel combustion (FF) aerosol. In this study, a small modification in the model in conjunction with carbon measurements from thermal-optical analysis allowed apportioned non-light-absorbing biogenic aerosol to vary in time. The absorption differences between WB and FF can be quantified by the absorption Ångström exponent (AAE). In this study AAE WB was set to 1.81 and AAE FF to 1.0. Our observations show that the AAE was elevated during winter (1.36 ± 0.07) compared to summer (1.12 ± 0.07). Quantified WB aerosol showed good agreement with levoglucosan concentrations, both in terms of correlation (R 2 = 0.70) and in comparison to reference emission inventories. WB aerosol showed strong seasonal variation with high concentrations during winter (0.65 µg m −3 , 56 % of total carbon) and low concentrations during summer (0.07 µg m −3 , 6 % of total carbon). FF aerosol showed less seasonal dependence; however, black carbon (BC) FF showed clear diurnal patterns corresponding to traffic rush hour peaks. The presumed non-light-absorbing biogenic carbonaceous aerosol concentration was high during summer (1.04 µg m −3 , 72 % of total carbon) and low during winter (0.13 µg m −3 , 8 % of total carbon). Aethalometer model results were further compared to radiocarbon and levoglucosan source apportionment results. The comparison showed good agreement for apportioned mass of WB and biogenic carbonaceous aerosol, but discrepancies were found for FF aerosol mass. The Aethalometer model overestimated FF aerosol mass by a factor of 1.3 compared to radiocarbon and levoglucosan source apportionment. A performed sensitivity analysis suggests that this discrepancy can be explained by interference of non-light-absorbing biogenic carbon during winter. In summary, the Aethalometer model offers a costeffective yet robust high-time-resolution source apportionment at rural background stations compared to a radiocarbon and levoglucosan alternative.

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“…Several studies have used the absorption spectral dependence to apportion the fossil fuel and BB contributions to total absorption (Favez et al, 2010;Massabò et al, 2015;Sandradewi et al, 2008). However, the å abs values do not always reflect the combustion type and using it as a source apportionment parameter could lead to erroneous results (Garg et al, 2016;Lewis et al, 2008;Wang et al, 2016b).…”

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confidence: 99%

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

Saturno¹,

Holanda²,

Pöhlker³

et al. 2017

Preprint

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Abstract. The Amazon rain forest is considered a very sensitive ecosystem that could be significantly affected by a changing climate. It is still one of the few places on Earth where the atmosphere in the continent approaches near-pristine conditions for some periods of the year. The Amazon Tall Tower Observatory (ATTO) has been built in central Amazonia to monitor the atmospheric and forest ecosystem conditions. The atmospheric conditions at the ATTO site oscillate between biogenic and biomass burning (BB) dominated states. By using a comprehensive ground-based aerosol measurement setup, we studied the physical and chemical properties of aerosol particles at the ATTO site. This parameterization of å abs as a function of the BC to OA mass ratio was investigated and was found applicable to tropical forest emissions but further investigation is required, especially by segregating fuel types. Additionally, important enhancements of the BC mass absorption cross-section (α abs ) were found over the measurement period. This enhancement could be linked to heavy coating of the BC aerosol particles. In the future, the BC mixing state should be systematically investigated by using different instrumental approaches.

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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

Cited by 78 publications

References 80 publications

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

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

Carbonaceous aerosol source apportionment using the Aethalometer model – evaluation by radiocarbon and levoglucosan analysis at a rural background site in southern Sweden

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

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