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Preprints
https://doi.org/10.5194/acp-2020-887
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-887
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  05 Nov 2020

05 Nov 2020

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This preprint is currently under review for the journal ACP.

Aircraft measurements of aerosol and trace gas chemistry in the Eastern North Atlantic

Maria A. Zawadowicz1, Kaitlyn Suski1,c, Jiumeng Liu1,b, Mikhail Pekour1, Jerome Fast1, Fan Mei1, Arthur Sedlacek2, Stephen Springston2, Yang Wang3,a, Rahul A. Zaveri1, Robert Wood4, Jian Wang3, and John E. Shilling1 Maria A. Zawadowicz et al.
  • 1Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, 99352, USA
  • 2Environmental & Climate Sciences Department, Brookhaven National Laboratory, Upton, NY 11973, USA
  • 3Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, Saint Louis, MO, 63130, USA
  • 4Department of Atmospheric Science, University of Washington, Seattle, WA, 98195, USA
  • anow at: Department of Civil, Architectural and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO, 65409, USA
  • bnow at: School of Environment, Harbin Institute of Technology, Harbin, Heilongjiang, China
  • cnow at: JUUL Labs, San Francisco, CA, 94107, USA

Abstract. The Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) investigated properties of aerosols and subtropical marine boundary layer (MBL) clouds. Low subtropical marine clouds can have a large effect on Earth's radiative budget, but they are poorly represented in global climate models. In order to understand their radiative effects, it is imperative to understand the composition and sources of the MBL cloud condensation nuclei (CCN). The campaign consisted of two intensive operation periods (IOP) (June–July, 2017 and January–February, 2018) during which a fully instrumented G-1 aircraft was deployed from Lajes Field on Terceira Island in the Azores, Portugal. The G-1 conducted research flights in the vicinity of the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) atmospheric observatory on Graciosa Island. An Aerodyne HR-ToF Aerosol Mass Spectrometer (AMS) and Ionicon Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) were deployed aboard the aircraft, characterizing chemistry of non-refractory aerosol and trace gases, respectively. The Eastern North Atlantic region was found to be very clean, with average non-refractory aerosol mass loading of 0.6 μg m−3 in the summer and 0.1 μg m in the winter, measured by the AMS. Average concentrations of trace reactive gases methanol and acetone were 1–2 ppb; benzene, toluene and isoprene were even lower, < 1 ppb. Mass fractions of sulfate, organics, ammonium and nitrate in the boundary layer were 69 %, 23 %, 7 % and 1 % and remained largely similar between seasons. The aerosol chemical composition was dominated by sulfate and highly processed organics. Particulate methanesulfonic acid (MSA), a well-known secondary biogenic marine species was detected, with an average boundary layer concentration of 0.021 μg m−3, along with its gas-phase precursor, dimethyl sulfide (DMS). MSA accounted for no more than 1 % of the sulfate and no more than 3 % of the total aerosol in the boundary layer. Examination of vertical profiles of aerosol and gas chemistry during ACE-ENA reveals an interplay of local marine emissions and long-range transported aged aerosol. A case of transport of biomass burning emissions from North American fires has been identified using back-trajectory analysis. In the summer, the non-refractory portion of the background CCN budget was heavily influenced by aerosol associated with ocean productivity, in particular sulfate formed from DMS oxidation. Episodic transport from the continents, particular of biomass burning aerosol, periodically increased CCN concentrations in the free troposphere. In the winter, with ocean productivity lower, CCN concentrations were overall much lower and dominated by remote transport. These results show that anthropogenic emissions perturb CCN concentrations in remote regions that are sensitive to changes in CCN number and illustrate that accurate predictions of both transport and regional aerosol formation from the oceans is critical to accurately modeling clouds in these regions.

Maria A. Zawadowicz et al.

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Short summary
This paper describes the results of a recent field campaign in the Eastern North Atlantic, where two mass spectrometers were deployed aboard a research aircraft to measure the chemistry of aerosols and trace gases. Very clean conditions were found, dominated by local sulfate-rich acidic aerosol and very aged organics. Evidence of long-range transport of aerosols from the continents has also been identified.
This paper describes the results of a recent field campaign in the Eastern North Atlantic, where...
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