Variation of Absorption Ångström Exponent in Aerosols From Different Emission Sources

A. Helin, A. Virkkula, J. Backman, L. Pirjola, O. Sippula, P. Aakko-Saksa, S. Väätäinen, F. Mylläri, A. Järvinen, M. Bloss, M. Aurela, G. Jakobi, P. Karjalainen, R. Zimmermann, J. Jokiniemi, S. Saarikoski, J. Tissari, T. Rönkkö, J. V. Niemi, H. Timonen

Research output: Contribution to journalArticleScientificpeer-review

44 Citations (Scopus)
33 Downloads (Pure)


The absorption Ångström exponent (AAE) describes the spectral dependence of light absorption by aerosols. AAE is typically used to differentiate between different aerosol types for example., black carbon, brown carbon, and dust particles. In this study, the variation of AAE was investigated mainly in fresh aerosol emissions from different fuel and combustion types, including emissions from ships, buses, coal-fired power plants, and residential wood burning. The results were assembled to provide a compendium of AAE values from different emission sources. A dual-spot aethalometer (AE33) was used in all measurements to obtain the light absorption coefficients at seven wavelengths (370–950 nm). AAE470/950 varied greatly between the different emission sources, ranging from −0.2 ± 0.7 to 3.0 ± 0.8. The correlation between the AAE470/950 and AAE370-950 results was good (R2 = 0.95) and the mean bias error between these was 0.02. In the ship engine exhaust emissions, the highest AAE470/950 values (up to 2.0 ± 0.1) were observed when high sulfur content heavy fuel oil was used, whereas low sulfur content fuels had the lowest AAE470/950 (0.9–1.1). In the diesel bus exhaust emissions, AAE470/950 increased in the order of acceleration (0.8 ± 0.1), deceleration (1.1 ± 0.1), and steady driving (1.2 ± 0.1). In the coal-fired power plant emissions, the variation of AAE470/950 was substantial (from −0.1 ± 2.1 to 0.9 ± 1.6) due to the differences in the fuels and flue gas cleaning conditions. Fresh wood-burning derived aerosols had AAE470/950 from 1.1 ± 0.1 (modern masonry heater) to 1.4 ± 0.1 (pellet boiler), lower than typically associated with wood burning, while the burn cycle phase affected AAE variation.

Original languageEnglish
Article numbere2020JD034094
Number of pages21
JournalJournal of Geophysical Research: Atmospheres
Issue number10
Publication statusPublished - 2021
Publication typeA1 Journal article-refereed


  • absorption Ångström exponent
  • aethalometer, black carbon, emissions
  • source apportionment

Publication forum classification

  • Publication forum level 2

ASJC Scopus subject areas

  • Atmospheric Science
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


Dive into the research topics of 'Variation of Absorption Ångström Exponent in Aerosols From Different Emission Sources'. Together they form a unique fingerprint.

Cite this