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

Bernardoni, V.; Ferrero, Luca; Bolzacchini, Ezio; Forello, Alice Corina; Gregorič, Asta; Massabò, Dario; Močnik, Griša; Prati, P.; Rigler, Martin; Santagostini, Luca; Soldan, Francesca; Valentini, S.; Valli, G.; Vecchi, R.

doi:10.5194/amt-14-2919-2021

Cited by 30 publications

(32 citation statements)

References 58 publications

(100 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the aforementioned techniques have so far proved difficult to deploy in a field setting, thus limiting their broader use in international measurement networks. Filter-based instruments (either on-line or off-line) rely on the sampling of aerosol particles collected in a filter matrix and on the measurement of the resulting change in light intensity with a photometer, either in the transmittance (Hansen et al, 1984;Bond et al, 1999;Drinovec et al, 2015) or in both transmittance and reflectance (Petzold and Schönlinner, 2004). This method is affected by artefacts resulting mainly from the effects that the filter has on the measurements.…”

Section: Introductionmentioning

confidence: 99%

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

Yus-Díez¹,

Bernardoni

Močnik³

et al. 2021

Atmos. Meas. Tech.

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Introductionmentioning

confidence: 99%

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

Yus-Díez¹,

Bernardoni

Močnik³

et al. 2021

Atmos. Meas. Tech.

Self Cite

View full text Add to dashboard Cite

show abstract

“…We believe that the absorption enhancement reported by the aethalometer is an artefact arising from keeping the C value fixed. Under this assumption, it is possible to calculate new values of C (Bernardoni et al, 2021) as a function of SSA using the mean babs value of the PTAAM and PAX as a reference (Bernardoni et al, 2021): S4. The error bars correspond to one standard deviation of the mean (k=1; 68 % confidence interval; n=100-160).…”

Section: Resultsmentioning

confidence: 99%

Response of black carbon and aerosol absorption measuring instruments to laboratory-generated soot coated with controlled amounts of secondary organic matter

Kalbermatter

Močnik²,

Drinovec

et al. 2021

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. We report on an inter-comparison of black carbon and aerosol absorption measuring instruments with laboratory-generated soot particles coated with controlled amounts of secondary organic matter (SOM). The aerosol generation setup consisted of a miniCAST 5201 Type BC burner for the generation of soot particles and a new automated oxidation flow reactor based on the micro smog chamber (MSC) for the generation of SOM from the ozonolysis of α-pinene. A series of test aerosols were generated with elemental to total carbon (EC/TC) mass fraction ranging from about 90 % down to 10 % and single scattering albedo (SSA) from almost 0 to about 0.7. A dual-spot aethalometer AE33, a photoacoustic extinctiometer (PAX, 870 nm), a multi-angle absorption photometer (MAAP), a prototype photoacoustic instrument and two prototype photo-thermal interferometers (PTAAM-2λ and MSPTI) were exposed to the test aerosols in parallel. Significant deviations in the response of the instruments were observed depending on the amount of secondary organic coating. We believe that the setup and methodology described in this study can easily be standardized and provide a straightforward and reproducible procedure for the inter-comparison and characterisation of both filter-based and in situ BC-measuring instruments based on realistic test aerosols.

show abstract

“…The AE31 and the PSAP have a similar measurement principle (Bond et al, 1999). Before σ abs can be determined by using different correction algorithms, the instruments measure the attenuation coefficient (σ ATN ), which is the attenuation of light through the sample collected on the filter.…”

Section: Absorption Measurementsmentioning

confidence: 99%

“…2). In this study the PSAP data were corrected with two algorithms: one described by Bond et al (1999) and later specified by Ogren (2010), which is hereafter referred to as B1999, and the other determined by Virkkula et al (2005) and later corrected by Virkkula (2010), which is hereafter referred to as V2010. The algorithms of Müller et al (2014) and Li et al (2020) were not applied.…”

Section: Psap Correction Algorithmsmentioning

confidence: 99%

“…Therefore, the instruments report a lower σ abs for loaded filters compared to pristine filter measurements. Several studies have developed algorithms to overcome this problem that has been observed with different instruments (Arnott et al, 2005;Bond et al, 1999;Collaud Coen et al, 2010;Li et al, 2020;Müller et al, 2014;Ogren, 2010;Schmid et al, 2006;Weingartner et al, 2003;Virkkula et al, 2005Virkkula et al, , 2007Virkkula, 2010). In general, after correcting the data for the multiple-scattering and loading effects, the absorption instruments agree rather well with the reference measurements (Drinovec et al, 2015;Hyvärinen et al, 2013;Park et al, 2010;Segura et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site

et al. 2021

View full text Add to dashboard Cite

Abstract. We present a comparison between three absorption photometers that measured the absorption coefficient (σabs) of ambient aerosol particles in 2012–2017 at SMEAR II (Station for Measuring Ecosystem–Atmosphere Relations II), a measurement station located in a boreal forest in southern Finland. The comparison included an Aethalometer (AE31), a multi-angle absorption photometer (MAAP), and a particle soot absorption photometer (PSAP). These optical instruments measured particles collected on a filter, which is a source of systematic errors, since in addition to the particles, the filter fibers also interact with light. To overcome this problem, several algorithms have been suggested to correct the AE31 and PSAP measurements. The aim of this study was to research how the different correction algorithms affected the derived optical properties. We applied the different correction algorithms to the AE31 and PSAP data and compared the results against the reference measurements conducted by the MAAP. The comparison between the MAAP and AE31 resulted in a multiple-scattering correction factor (Cref) that is used in AE31 correction algorithms to compensate for the light scattering by filter fibers. Cref varies between different environments, and our results are applicable to a boreal environment. We observed a clear seasonal cycle in Cref, which was probably due to variations in aerosol optical properties, such as the backscatter fraction and single-scattering albedo, and also due to variations in the relative humidity (RH). The results showed that the filter-based absorption photometers seemed to be rather sensitive to the RH even if the RH was kept below the recommended value of 40 %. The instruments correlated well (R≈0.98), but the slopes of the regression lines varied between the instruments and correction algorithms: compared to the MAAP, the AE31 underestimated σabs only slightly (the slopes varied between 0.96–1.00) and the PSAP overestimated σabs only a little (the slopes varied between 1.01–1.04 for a recommended filter transmittance >0.7). The instruments and correction algorithms had a notable influence on the absorption Ångström exponent: the median absorption Ångström exponent varied between 0.93–1.54 for the different algorithms and instruments.

show abstract

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

Cited by 30 publications

References 58 publications

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

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

Response of black carbon and aerosol absorption measuring instruments to laboratory-generated soot coated with controlled amounts of secondary organic matter

Effects of different correction algorithms on absorption coefficient – a comparison of three optical absorption photometers at a boreal forest site

Contact Info

Product

Resources

About