Preprints
https://doi.org/10.5194/amt-2023-245
https://doi.org/10.5194/amt-2023-245
06 Dec 2023
 | 06 Dec 2023
Status: this preprint is currently under review for the journal AMT.

Field comparison of dual- and single-spot aethalometers: Equivalent black carbon, light absorption, and Ångström exponent and secondary brown carbon estimations

Liangbin Wu, Cheng Wu, Tao Deng, Dui Wu, Mei Li, Yong Jie Li, and Zhen Zhou

Abstract. Aethalometer is a widely used instrument for black carbon (BC) mass concentration and light absorption coefficient (babs) measurements around the world. However, field intercomparison of the two popular models, dual-spot (AE33) and single-spot (AE31) aethalometers, remain limited; in addition, the difference in secondary brown carbon (BrCsec) light absorption estimation between the two models is largely unknown. We performed full-year collocated AE33 and AE31 measurements in a megacity in southern China – Guangzhou. The babs values agree well between the two aethalometers (R2 > 0.95), with AE33/AE31 slopes ranging from 0.87 to 1.04 for 7 wavelengths. AE33 consistently exhibits lower limits of detection (LOD) than AE31 for time resolutions of 2 to 60 min. The AE33/AE31 slope for equivalent BC (eBC) was 1.2, implying the need for site-specific post-correction. The Ångström exponent (AAE) obtained from different approaches agrees not very well between the two models, with the biggest discrepancy found in AAE880/950. The estimated BrCsec light absorption at 370 nm (babs370_BrCsec) was calculated using the minimum R squared method (MRS) for both Aethalometers. The babs370_BrCsec comparison yields a slope of 0.78 and an R2 of 0.72 between the two models, implying a non-negligible inter-instrument difference. This study highlights the high consistency in babs but less so in AAE between AE31 and AE33, and reveals site-specific correction for eBC estimation and non-negligible difference in BrCsec estimation. The results are valuable for data continuity in long-term aethalometer measurements when transiting from the older (AE31) to the newer (AE33) model, as anticipated in permanent global-climate and air-quality stations.

Liangbin Wu, Cheng Wu, Tao Deng, Dui Wu, Mei Li, Yong Jie Li, and Zhen Zhou

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-245', Anonymous Referee #1, 16 Jan 2024
  • RC2: 'Comment on amt-2023-245', Anonymous Referee #2, 30 Jan 2024
Liangbin Wu, Cheng Wu, Tao Deng, Dui Wu, Mei Li, Yong Jie Li, and Zhen Zhou
Liangbin Wu, Cheng Wu, Tao Deng, Dui Wu, Mei Li, Yong Jie Li, and Zhen Zhou

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Short summary
Field comparison of dual-spot (AE33) and single-spot (AE31) aethalometers by full-year collocated measurements suggests that site-specific correction factors are needed to ensure the data continuity of long-term measurements for AE31-to-AE33 transition in BC monitoring networks.