Hybrid multiple-site mass closure and source apportionment of PM2.5 and aerosol acidity at major cities in the Po Valley

• Published in: The Science of the total environment Vol. 704; p. 135287
• Main Authors: Masiol, Mauro, Squizzato, Stefania, Formenton, Gianni, Khan, Md Badiuzzaman, Hopke, Philip K., Nenes, Athanasios, Pandis, Spyros N., Tositti, Laura, Benetello, Francesca, Visin, Flavia, Pavoni, Bruno
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.02.2020
• Subjects: Atmospheric aerosol; Chemical speciation; North Italy; PMF; Water content; PMF; pH; Atmospheric aerosol; Chemical speciation; North Italy; Water content
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.135287

[Display omitted] •The addition of aerosol water content returns reasonable mass closures.•Six common PM2.5 sources are present over 5 cities in the lower end of Po Valley.•Aerosol is acidic/moderately acidic throughout the year with lower pH in summer.•Sulfate and fossil fuel lower pH; nitrate and biomass burning increase pH.•Secondary sources and pH increase when air masses pass Central/Eastern Europe. This study investigates the major chemical components, particle-bound water content, acidity (pH), and major potential sources of PM2.5 in major cities (Belluno, Conegliano, Vicenza, Mestre, Padua, and Rovigo) in the eastern end of the Po Valley. The measured PM2.5 mass was reconstructed using a multiple-site hybrid chemical mass closure approach that also accounts for aerosol inorganic water content (AWC) estimated by the ISORROPIA-II model. Annually, organic matter accounted for 31–45% of the PM2.5 at all sites, followed by nitrate (10–19%), crustal material (10–14%), sulfate (8–10%), ammonium (5–9%), elemental carbon (4–7%), other inorganic ions (3–4%), and trace elements (0.2–0.3%). Water represented 7–10% of measured PM2.5. The ambient aerosol pH varied from 1.5 to 4.5 with lower values in summer (average in all sites 2.2 ± 0.3) and higher in winter (3.9 ± 0.3). Six major PM2.5 sources were quantitatively identified with multiple-site positive matrix factorization: secondary sulfate (34% of PM2.5), secondary nitrate (30%), biomass burning (17%), traffic (11%), re-suspended dust (5%), and fossil fuel combustion (3%). Biomass burning accounted for ~90% of total PAHs. Inorganic aerosol acidity was driven primarily by secondary sulfate, fossil fuel combustion (decreasing pH), secondary nitrate, and biomass burning (increasing pH). Secondary nitrate was the primary driver of the inorganic AWC variability. A concentration-weighted trajectory (multiple-site) analysis was used to identify potential source areas for the various factors and modeled aerosol acidity. Eastern and Central Europe were the main source areas of secondary species. Less acidic aerosol was associated with air masses originating from Northern Europe owing to the elevated presence of the nitrate factor. More acidic particles were observed for air masses traversing the Po Valley and the Mediterranean, possibly due to the higher contributions of fossil fuel combustion factor and the loss of nitric acid due to its interaction with coarse sea-salt particles.