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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 05 Apr 2019

Submitted as: research article | 05 Apr 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

The impact of biomass burning and aqueous-phase processing on air quality: a multi-year source apportionment study in the Po Valley, Italy

Marco Paglione1, Stefania Gilardoni1, Matteo Rinaldi1, Stefano Decesari1, Nicola Zanca1,a, Silvia Sandrini1, Lara Giulianelli1, Dimitri Bacco2, Silvia Ferrari2, Vanes Poluzzi2, Fabiana Scotto2, Arianna Trentini2, Laurent Poulain3, Hartmut Herrmann3, Alfred Wiedensohler3, Francesco Canonaco4, André S. H. Prévôt4, Paola Massoli5,6, Claudio Carbone7, Maria Cristina Facchini1, and Sandro Fuzzi1 Marco Paglione et al.
  • 1Italian National Research Council – Institute of Atmospheric Sciences and Climate (CNR-ISAC), Bologna, 40129 Italy
  • 2Regional Agency for prevention, environment and energy (ARPAE) of Emilia-Romagna, Bologna, Italy
  • 3Leibniz-Institut für Troposphärenforschung (TROPOS), Leipzig, 04318, Germany
  • 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen PSI 5232, Switzerland
  • 5Aerodyne Research, Inc. Billerica, MA, USA
  • 6MultiSensor Scientific, Inc., Greentown Labs, Sommerville, MA, USA
  • 7Proambiente S.c.r.l., CNR Research Area, Bologna, Italy
  • anow at: Department of Chemistry and Institute for Atmospheric and Earth System Research (INAR), University of Helsinki, FI-00014, Finland

Abstract. The Po Valley (Italy) is a well-known air quality hotspot characterized by Particulate Matter (PM) levels well above the limit set by the European Air Quality Directive and by the World Health Organization, especially during the colder season. In the framework of the Emilia-Romagna regional project SUPERSITO, the southern Po Valley submicron aerosol chemical composition was characterized by means of High-Resolution Aerosol Mass Spectroscopy (HR-AMS) with the specific aim of organic aerosol (OA) characterization and source apportionment. Eight intensive observation periods (IOPs) were carried out over four years (from 2011 to 2014) at two different sites (Bologna, BO, urban background and San Pietro Capofiume, SPC, rural background), to characterize the spatial variability and seasonality of the OA sources, with a special focus on the cold season.

On the multi-year basis of the study, the AMS observations show that OA accounts for an average 45 ± 8 % (ranging 33–58 %) and 46 ± 7 % (ranging 36–50 %) of the total non-refractory submicron particle mass (PM1-NR) at the urban and at the rural site, respectively. Primary organic aerosol (POA) comprises biomass burning (23 ± 13 % of OA) and fossil fuel (12 ± 7 %) contributions with a marked seasonality in concentration. As expected, the biomass burning contribution to POA is more significant at the rural site (urban/rural concentrations ratio of 0.67), but it is also an important source of POA at the urban site during the cold season, with contributions ranging from 14 to 38 % of the total OA mass.

Secondary organic aerosol (SOA) contribute to OA mass to a much larger extent than POA at both sites throughout the year (69 ± 16 % and 83 ± 16 % at urban and rural, respectively), with important implications for public health. Within the secondary fraction of OA, the measurements highlight the importance of biomass burning ageing products during the cold season, even at the urban background site. This biomass burning SOA fraction represents 14–44 % of the total OA mass in the cold season, indicating that in this region a major contribution of combustion sources to PM mass is mediated by environmental conditions and atmospheric reactivity.

Among the environmental factors controlling the formation of SOA in the Po Valley, the availability of liquid water in the aerosol was shown to play a key role in the cold season. We estimate that organic fraction originating from aqueous reactions of biomass burning products (bb-aqSOA) represents 21 % (14–28 %) and 25 % (14–35 %) of the total OA mass and 44 % (32–56 %) and 61 % (21–100 %) of the SOA mass at the urban and rural sites, respectively.

Marco Paglione et al.
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Marco Paglione et al.
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Short summary
Our multi-year observational study regarding Organic Aerosol (OA) in Po Valley, indicates that more than half of the OA is of secondary origin (SOA) through all the year and at both urban and rural sites. Within the SOA, the measurements show the importance of biomass burning (BB) aging products during cold seasons and indicate aqueous-phase processing of BB emissions as a fundamental driver of SOA formation in wintertime with important consequences on air quality policy also at the global level.
Our multi-year observational study regarding Organic Aerosol (OA) in Po Valley, indicates that...