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Preprints
https://doi.org/10.5194/acp-2020-49
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-49
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 06 Feb 2020

Submitted as: research article | 06 Feb 2020

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A revised version of this preprint was accepted for the journal ACP.

Identifying a regional aerosol baseline in the Eastern North Atlantic using collocated measurements and a mathematical algorithm to mask high submicron number concentration aerosol events

Francesca Gallo1, Janek Uin2, Stephen Springston2, Jian Wang3, Guangjie Zheng3, Chongai Kuang2, Robert Wood4, Eduardo B. Azevedo5, Allison McComiskey2, Fan Mei6, Jenni Kyrouac7, and Allison C. Aiken1 Francesca Gallo et al.
  • 1Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, USA
  • 2Environment and Climate Science Department, Brookhaven National Laboratory, Upton, NY, USA
  • 3Center for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, USA
  • 4Department of Atmospheric Sciences, University of Washington, Seattle, USA
  • 5Centre of Climate, Meteorology and Global Change (CMMG), University of Azores, Portugal
  • 6Atmospheric Measurement and Data Sciences, Pacific Northwest National Laboratory, Richland, WA, USA
  • 7Environmental Science Division, Argonne National Laboratory, Argonne, IL, USA

Abstract. High time-resolution measurements of in situ aerosol and cloud properties provide the ability to study regional atmospheric processes that occur on timescales of minutes to hours. However, one limitation to this approach is that continuous measurements often include periods when the data collected are not representative of the regional aerosol. Even at remote locations, submicron aerosols are pervasive in the ambient atmosphere with many sources. Therefore, periods dominated by local aerosol should be identified before conducting subsequent analyses to understand aerosol regional processes and aerosol-cloud interactions. Here, we present a novel method to validate the identification of regional baseline aerosol data by applying a mathematical algorithm to the data collected at the U.S. Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) User Facility in the Eastern North Atlantic (ENA). The ENA Central facility (C1) includes an Aerosol Observing System (AOS) for the measurement of aerosol physical, optical, and chemical properties at time resolutions from seconds to minutes. A second temporary Supplementary facility (S1), located ~ 0.75 km from C1, was deployed for ~ 1 year during the Aerosol and Cloud Experiments (ACE-ENA) campaign in 2017.

First, we investigate the local aerosol at both locations. We associate periods of high submicron number concentration (Ntot) in the fine mode Condensation Particle Counter (CPC) and size distributions from the Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) as a function of wind direction using a meteorology sensor with local sources. Elevated concentrations of Aitken mode (< 100 nm diameter) particles were observed in correspondence with the wind directions associated with airport operations. At ENA, the Graciosa airport and its associated activities were found to be the main sources of high concentration aerosol events at ENA, causing peaks in one-minute Ntot that exceeded 8000 cm−3 and 10 000 cm−3 at C1, in summer and winter, respectively, and 5000 cm−3 at S1 in summer. Periods with high Ntot not associated with these wind directions were also observed. As a result, the diverse local sources at ENA yielded a poor relationship between Ntot measurements collected at C1 and S1 (R2 = 0.03 with a slope = 0.05 ± 0.001). As a first approach to mask these events, the time periods when the wind direction was associated with the airport operations (west to northwest and southeast to south at C1 and east to south at S1) were applied. The meteorological masks removed 38.9 % of the data at C1 and 43.4 % at S1, and they did not significantly improve the relationship between the two sites (R2 = 0.18 with a slope = 0.06 ± 0.001).

Due to the complexity of high Ntot events observed at ENA, we develop and validate a mathematical ENA Aerosol Mask (ENA-AM) to identify high Ntot events using one-minute resolution data from the AOS CPC at C1 and S1. After its parametrization and application, ENA-AM generated a high correlation between Ntot in the summer at C1 and S1 (R2 = 0.87 with a slope = 0.84 ± 0.001). We identified the regional baseline at ENA to be 428 ± 228 cm−3 in the summer and 346 ± 223 cm−3 in the winter. Lastly, we compared masked measurements from the AOS with the ARM Aerial Facility (AAF) during flights over C1 in the summer to understand submicron aerosol vertical mixing over C1. The high correlation (R2 = 0.71 with a slope of 1.04 ± 0.01) observed between C1 and the AAF Ntot collected within an area of 10 km surrounding ENA and at altitudes < 500 m indicated that the submicron aerosol at ENA were well mixed within the first 500 m of the marine boundary layer during the month of July during ACE-ENA. Our novel method for determining a regional aerosol baseline at ENA can be applied to other time periods and at other locations with validation by a secondary site or additional collocated measurements.

Francesca Gallo et al.

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Francesca Gallo et al.

Data sets

Eastern North Atlantic Aerosol Mask (ENA-AM) with the Condensation Particle Counter (CPC) at Supplementary Facility (S01) A. Aiken and F. Gallo https://doi.org/10.5439/1581730

Eastern North Atlantic Aerosol Mask (ENA-AM) with the Condensation Particle Counter (CPC) at Central Facility (C1) during Summer 2017 F. Gallo and A. Aiken https://doi.org/10.5439/1579567

Eastern North Atlantic Aerosol Mask (ENA-AM) with the Condensation Particle Counter (CPC) at Central Facility (C1) during Winter 2017 F. Gallo and A. Aiken https://doi.org/10.5439/1579568

Francesca Gallo et al.

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Short summary
Continuous high-time resolution ambient data can include periods when aerosol properties do not represent regional aerosol processes due to high concentration local events. We develop a novel aerosol mask at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Facility in the Eastern North Atlantic (ENA). We use two ground sites to validate the mask, include a comparison with aircraft overflights, and provide guidance to increase data quality at ENA and other locations.
Continuous high-time resolution ambient data can include periods when aerosol properties do not...
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