nerc.ac.uk

Evidence for ambient dark aqueous SOA formation in the Po Valley, Italy

Sullivan, Amy P.; Hodas, Natasha; Turpin, Barbara J.; Skog, Kate; Keutsch, Frank N.; Gilardoni, Stefania; Paglione, Marco; Rinaldi, Matteo; Decesari, Stefano; Facchini, Maria Cristina; Poulain, Laurent; Herrmann, Hartmut; Wiedensohler, Alfred; Nemitz, Eiko; Twigg, Marsailidh M.; Collett Jr, Jeffrey L.. 2016 Evidence for ambient dark aqueous SOA formation in the Po Valley, Italy. Atmospheric Chemistry and Physics, 16 (13). 8095-8108. 10.5194/acp-16-8095-2016

This is the latest version of this item.

Before downloading, please read NORA policies.
[img]
Preview
Text
N513916JA.pdf - Published Version
Available under License Creative Commons Attribution.

Download (1MB) | Preview
[img]
Preview
Text (Supplement)
N513916JAX.pdf - Published Version
Available under License Creative Commons Attribution.

Download (1MB) | Preview

Abstract/Summary

Laboratory experiments suggest that water-soluble products from the gas-phase oxidation of volatile organic compounds can partition into atmospheric waters where they are further oxidized to form low volatility products, providing an alternative route for oxidation in addition to further oxidation in the gas phase. These products can remain in the particle phase after water evaporation, forming what is termed as aqueous secondary organic aerosol (aqSOA). However, few studies have attempted to observe ambient aqSOA. Therefore, a suite of measurements, including near-real-time WSOC (water-soluble organic carbon), inorganic anions/cations, organic acids, and gas-phase glyoxal, were made during the PEGASOS (Pan-European Gas-AeroSOls-climate interaction Study) 2012 campaign in the Po Valley, Italy, to search for evidence of aqSOA. Our analysis focused on four periods: Period A on 19–21 June, Period B on 30 June and 1–2 July, Period C on 3–5 July, and Period D on 6–7 July to represent the first (Period A) and second (Periods B, C, and D) halves of the study. These periods were picked to cover varying levels of WSOC and aerosol liquid water. In addition, back trajectory analysis suggested all sites sampled similar air masses on a given day. The data collected during both periods were divided into times of increasing relative humidity (RH) and decreasing RH, with the aim of diminishing the influence of dilution and mixing on SOA concentrations and other measured variables. Evidence for local aqSOA formation was only observed during Period A. When this occurred, there was a correlation of WSOC with organic aerosol (R2 = 0.84), aerosol liquid water (R2 = 0.65), RH (R2 = 0.39), and aerosol nitrate (R2 = 0.66). Additionally, this was only observed during times of increasing RH, which coincided with dark conditions. Comparisons of WSOC with oxygenated organic aerosol (OOA) factors, determined from application of positive matrix factorization analysis on the aerosol mass spectrometer observations of the submicron non-refractory organic particle composition, suggested that the WSOC differed in the two halves of the study (Period A WSOC vs. OOA-2 R2 = 0.83 and OOA-4 R2 = 0.04, whereas Period C WSOC vs. OOA-2 R2 = 0.03 and OOA-4 R2 = 0.64). OOA-2 had a high O ∕ C (oxygen ∕ carbon) ratio of 0.77, providing evidence that aqueous processing was occurring during Period A. Key factors of local aqSOA production during Period A appear to include air mass stagnation, which allows aqSOA precursors to accumulate in the region; the formation of substantial local particulate nitrate during the overnight hours, which enhances water uptake by the aerosol; and the presence of significant amounts of ammonia, which may contribute to ammonium nitrate formation and subsequent water uptake and/or play a more direct role in the aqSOA chemistry.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.5194/acp-16-8095-2016
CEH Sections: Dise
ISSN: 1680-7316
Additional Information. Not used in RCUK Gateway to Research.: Open Access paper - full text available via Official URL link.
NORA Subject Terms: Atmospheric Sciences
Chemistry
Date made live: 05 Jul 2016 14:26 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/513916

Available Versions of this Item

  • Evidence for ambient dark aqueous SOA formation in the Po Valley, Italy. (deposited 05 Jul 2016 14:26) [Currently Displayed]

Actions (login required)

View Item View Item

Document Downloads

Downloads for past 30 days

Downloads per month over past year

More statistics for this item...