Preprints
https://doi.org/10.5194/acp-2021-471
https://doi.org/10.5194/acp-2021-471

  22 Jun 2021

22 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Aerosol Responses to Precipitation Along North American Air Trajectories Arriving at Bermuda

Hossein Dadashazar1, Majid Alipanah2, Miguel Ricardo A. Hilario3, Ewan Crosbie4,5, Simon Kirschler6,7, Hongyu Liu8, Richard H. Moore4, Andrew J. Peters9, Amy Jo Scarino4,5, Michael Shook4, K. Lee Thornhill4, Christiane Voigt6,7, Hailong Wang10, Edward Winstead4,5, Bo Zhang8, Luke Ziemba4, and Armin Sorooshian1,3 Hossein Dadashazar et al.
  • 1Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, USA
  • 2Department of Systems and Industrial Engineering, University of Arizona, Tucson, AZ, USA
  • 3Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
  • 4NASA Langley Research Center, Hampton, VA, USA
  • 5Science Systems and Applications, Inc., Hampton, VA, USA
  • 6Institute for Atmospheric Physics, DLR, German Aerospace Center, Oberpfaffenhofen, Germany
  • 7Institute for Atmospheric Physics, University of Mainz, Mainz, Germany
  • 8National Institute of Aerospace, Hampton, VA, USA
  • 9Bermuda Institute of Ocean Sciences, 17 Biological Station, St. George’s, GE01, Bermuda
  • 10Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA

Abstract. North American pollution outflow is ubiquitous over the western North Atlantic Ocean, especially in winter, making this location an ideal natural laboratory for investigating the impact of precipitation on aerosol particles along air mass trajectories. We take advantage of observational data collected at Bermuda to seasonally assess the sensitivity of aerosol mass concentrations and volume size distributions to accumulated precipitation along trajectories (APT). The mass concentration of particulate matter with aerodynamic diameter less than 2.5 µm normalized by the enhancement of carbon monoxide above background (PM2.5/∆CO) at Bermuda was used to estimate the degree of aerosol loss during transport to Bermuda. Results for December–February (DJF) show most trajectories come from North America and have the highest APTs, resulting in significant reduction (by 53 %) in PM2.5/∆CO under high APT conditions (> 13.5 mm) relative to low APT conditions (< 0.9 mm). Moreover, PM2.5/∆CO was most sensitive to increases in APT up to 5 mm (−0.044 µg m−3 ppbv−1 mm−1) and less sensitive to increases in APT over 5 mm. While anthropogenic PM2.5 constituents (e.g., black carbon, sulfate, organic carbon) decrease with high APT, sea salt in contrast was comparable between high and low APT conditions owing to enhanced local wind and salt emissions in high APT conditions. The greater sensitivity of the fine mode volume concentrations (versus coarse mode) to wet scavenging is evident from AERONET volume size distribution data. A combination of GEOS-Chem model simulations of 210Pb submicron aerosol tracer and its gaseous precursor 222Rn reveal that (i) surface aerosol particles at Bermuda are most impacted by wet scavenging in winter/spring (due to large-scale precipitation) with a maximum in March, whereas convective scavenging plays a substantial role in summer; and (ii) North American 222Rn tracer emissions contribute most to surface 210Pb concentrations at Bermuda in winter (~75–80 %), indicating that air masses arriving at Bermuda experience large-scale precipitation scavenging while traveling from North America. A case study flight from the ACTIVATE field campaign on 22 February 2020 reveals a significant reduction in aerosol number and volume concentrations during air mass transport off the U.S. East Coast associated with increased cloud fraction and precipitation. These results highlight the sensitivity of remote marine boundary layer aerosol characteristics to precipitation along trajectories, especially when the air mass source is continental outflow from polluted regions like the U.S. East Coast.

Hossein Dadashazar et al.

Status: open (until 03 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-471', Anonymous Referee #1, 05 Jul 2021 reply

Hossein Dadashazar et al.

Hossein Dadashazar et al.

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Short summary
This study investigates precipitation impacts on long-range transport of North American over the western North Atlantic Ocean (WNAO). Our results demonstrate that precipitation scavenging plays a significant role in modifying surface aerosol concentrations over the WNAO, especially in winter/spring months due to large-scale scavenging processes. This study highlights how precipitation impacts surface aerosol properties with relevance for other marine regions vulnerable to continental outflow.
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