Intercomparison and characterization of 23 Aethalometers under laboratory and ambient air conditions: procedures and unit-to-unit variabilities

Abstract

Abstract. Aerosolized black carbon is monitored worldwide to quantify its impact on air quality and climate. Given its importance, measurements of black carbon mass concentrations must be conducted with instruments operating in quality-checked and ensured conditions to generate data which are reliable and comparable temporally and geographically. In this study, we report the results from the largest characterization and intercomparison of filter-based absorption photometers, the Aethalometer model AE33, belonging to several European monitoring networks. Under controlled laboratory conditions, a total of 23 instruments measured mass concentrations of black carbon from three well-characterized aerosol sources: synthetic soot, nigrosin particles, and ambient air from the urban background of Leipzig, Germany. The objective was to investigate the individual performance of the instruments and their comparability; we analyzed the response of the instruments to the different aerosol sources and the impact caused by the use of obsolete filter materials and the application of maintenance activities. Differences in the instrument-to-instrument variabilities from equivalent black carbon (eBC) concentrations reported at 880 nm were determined before maintenance activities (for soot measurements, average deviation from total least square regression was −2.0 % and the range −16 % to 7 %; for nigrosin measurements, average deviation was 0.4 % and the range −15 % to 17 %), and after they were carried out (for soot measurements, average deviation was −1.0 % and the range −14 % to 8 %; for nigrosin measurements, the average deviation was 0.5 % and the range −12 % to 15 %). The deviations are in most of the cases explained by the type of filter material employed by the instruments, the total particle load on the filter, and the flow calibration. The results of this intercomparison activity show that relatively small unit-to-unit variability of AE33-based particle light absorbing measurements is possible with well-maintained instruments. It is crucial to follow the guidelines for maintenance activities and the use of the proper filter tape in the AE33 to ensure high quality and comparable black carbon (BC) measurements among international observational networks.

Performance evaluation of portable dual-spot micro-aethalometers for source identification of Black Carbon aerosols: Application to wildfire smoke and traffic emissions in the Pacific Northwest

“…For the multi-wavelength b abs , the unit-to-unit variability did not show any trend along the spectral light absorption measurements. Yet, large instrumental noise was visible in the b absU V measurements, which is consistent with previous studies on multi-wavelength aethalometers (Cuesta-Mosquera et al, 2021;Müller et al, 2011a).…”

“…We reported the precision of MA300 eBC in terms of unit-to-unit variability as 15%. This value is higher than that reported in the previously studied other aethalometer models: 4.3% for AE31 (Müller et al, 2011a), 0.5% for AE33 (Cuesta-Mosquera et al, 2021). For the multi-wavelength b abs , the unit-to-unit variability did not show any trend along the spectral light absorption measurements.…”

“…Typically, the aethalometer's instrumental noise is defined as the single standard deviation of the eBC mass concentration with particle-free air (Müller et al, 2011a;Cuesta-Mosquera et al, 2021), which has been reported as 0.032 µg m −3 for AE33 (Cuesta-Mosquera et al, 2021). Due to the absence of particle-free measurements in our study, we assume 0.032 µg m −3 as our reference noise levels.…”

“…Dual-spot aethalometers use two deferentially loaded filter spots to estimate real-time light attenuation measurement with respect to a reference (or clean) spot. AE33s have been extensively used in recent field studies around the world (Cuesta-Mosquera et al, 2021;Duc et al, 2020;Goel et al, 2021;Li et al, 2020;Wang et al, 2021) and are considered a referencegrade instrument for accurate and real-time measurement of BC (or equivalent BC) (Bernardoni et al, 2021;Healy et al, 2017;Meena et al, 2021;Rajesh et al, 2021). Data collected from AE33s have also been used to provide insights into aerosol light absorption and to identify BC sources (biomass burning or traffic emission) based on the widely-used two-component aethalometer model (Sandradewi et al, 2008a;Healy et al, 2017;Rajesh et al, 2021).…”

A dual-wavelength photothermal aerosol absorption monitor: design, calibration and performance

“…Standardization, validation and calibration of the aerosol absorption coefficient measurement require well-defined reference samples: particles or absorbing gases (Arnott et al, 2000). The greatest advantage of in situ methods is the ability of calibration with gases (Arnott et al, 2000;Lack et al, 2006Lack et al, , 2012Nakayama et al, 2015;Davies et al, 2018), while filter photometers need to be compared with each other (Müller et al, 2011;Cuesta-Mosquera et al, 2021) or with other reference instruments (Bond et al, 1999;Arnott et al, 2003) using model aerosols: fullerene soot, spark discharge particles, soot generated with controlled gas combustion and dyes, especially nigrosin (Bond et al, 1999;Schnaiter et al, 2006;Müller et al, 2011;Cuesta-Mosquera et al, 2021). The advantage of using gases for calibration is conceptual -gas concentration can be measured with great precision and accuracy, and its absorption cross section is usually well known.…”