Special Session on Optical Properties of Atmospheric Aerosol ― Observation, Measurement Techniques and Model Analysis for Improving the Accuracy of Aerosol Light Absorption Determinations in Polluted Sites (III)

Stefania Gilardoni This email address is being protected from spambots. You need JavaScript enabled to view it.1, Paola Massoli2, Angela Marinoni3, Claudio Mazzoleni4, Andrew Freedman2, Giovanni Lonati5, Silvana De Iuliis6, Vorne Gianelle7

1 Institute of Polar Sciences, CNR-ISP, 40129 Bologna, Italy
2 Aerodyne Research Inc., Billerica, MA 01821, USA
3 Institute of Atmospheric Sciences and Climate, CNR-ISAC, 40129 Bologna, Italy
4 Department of Physics and Atmospheric Sciences Program, Michigan Technological University, Houghton, MI 49931, USA
5 Department of Civil and Environmental Engineering, Politecnico di Milano, 20133 Milan, Italy
6 Institute of Condensed Matter Chemistry and Technologies for Energy, CNR-ICMATE, 53 - 20125 Milano, Italy
7 Agenzia Regionale per Protezione dell’Ambiente, Via Juvara, Milan, Italy 

Now at Green Energy Consumers Alliance, Boston, MA 02130, USA

Received: March 2, 2020
Revised: September 21, 2020
Accepted: September 29, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.4209/aaqr.2020.03.0085  

Cite this article:

Gilardoni, S., Massoli, P., Marinoni, A., Mazzoleni, C., Freedman, A., Lonati, G., De Iuliis, S. and Gianelle, V. (2020). Spatial and Temporal Variability of Carbonaceous Aerosol Absorption in the Po Valley. Aerosol Air Qual. Res. 20: 2624–2639. https://doi.org/10.4209/aaqr.2020.03.0085


  • We report aerosol light absorption coefficients at two sites in the Po valley, Italy.
  • Limited variability of Elemental Carbon Mass Absorption Cross section is observed.
  • Wood combustion and secondary organic aerosol contribute to brown carbon (BrC).
  • Water-soluble BrC absorption is only 50% of methanol-soluble BrC.


Knowledge gaps in the optical properties of carbonaceous aerosols account for a significant fraction of the uncertainty of aerosol - light interactions in climate models. Both black carbon (BC) and brown carbon (BrC) can display a range of optical properties in ambient aerosol due to different sources and chemical transformation pathways. This study investigates the optical absorption properties of BC and BrC at an urban and a rural site in the Po Valley (Italy), a known European pollution hot spot. We observed spatial and seasonal variability of aerosol absorption coefficients, with the highest values measured in winter at the urban site of Milan (12 Mm–1 on average) and the lowest values in summer at the rural site of Motta Visconti (3 Mm–1 on average). The average aerosol Absorption Ångström Exponent (AAE) measured during the two experiments across the 370–880 nm wavelength range was 1.1 and 1.2 at the urban and the rural site, respectively. The observed AAE values in winter (the average AAE during the two winter campaigns was 1.2) are consistent with the contribution of wood burning BrC, as confirmed by macro-tracer analysis. The BC mass absorption cross section (MACBC) did not show a specific seasonal or spatial variability across the two sites and maintained an average value of 10 ± 5 m2 g–1 at 880 nm. The optical properties of BrC, investigated off-line after extraction of organic aerosol (OA) indicate that wood burning was the dominant BrC source in winter, while secondary organic aerosol (SOA) from other anthropogenic emissions was the main source of BrC in summer.

Keywords: Black carbon; Brown carbon; Optical properties; Mass absorption cross section; Climate change.

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