Preprints
https://doi.org/10.5194/egusphere-2023-956
https://doi.org/10.5194/egusphere-2023-956
25 Jul 2023
 | 25 Jul 2023

Microphysics of radiation fog and estimation of fog deposition velocity for atmospheric dispersion applications

Rachid Abida, Narendra Nelli, Diana Francis, Olivier Masson, Ricardo Fonseca, Emmanuel Bosc, and Marouane Temimi

Abstract. Fog augments the wet deposition of airborne particles entrained in its hydrometeors. This article aims to characterize fog deposition processes around the Barakah nuclear power plant (BNPP), in the United Arab Emirates (UAE), and assess the potential impact of fog on the deposition rate of radionuclides in case of an accidental release. To this end, the microphysics of twelve radiation fog events, typical in such arid climate, were measured during the winter seasons of 2021 and 2022 using a fog monitor that was deployed at the BNPP. The impact of fog deposition on the settling of radionuclides is investigated based on model simulations using the Weather Research Forecasting (WRF) model with the MYJ PBL scheme and FLEXPART.

All fog events are found to share a common feature of a bimodal distribution in droplet number concentration (Nc), with modes at 4.5 μm and 23.16 μm. It was pointed out that despite the high proportion of smaller droplets in the fog associated with the fine mode, the greatest contribution to the liquid water content (LWC) comes essentially from medium to large droplets between 10 and 35 μm. The deposition flux of fog water at the site and the fog droplet deposition velocity were estimated using an Eddy Covariance (EC) onsite. Typical mean values for fog droplet deposition velocity are found to range between 2.11 and 7.87 cm s-1. The modeling results show that fog deposition contributed by 30–40 % to the total ground deposition of 137Cs, highlighting the importance of incorporating fog deposition as an additional scavenging mechanism in dispersion modeling under foggy conditions.

Rachid Abida, Narendra Nelli, Diana Francis, Olivier Masson, Ricardo Fonseca, Emmanuel Bosc, and Marouane Temimi

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-956', Anonymous Referee #3, 10 Aug 2023
    • AC1: 'Reply on RC1', Diana Francis, 20 Oct 2023
  • RC2: 'Comment on egusphere-2023-956', Anonymous Referee #1, 21 Aug 2023
    • AC2: 'Reply on RC2', Diana Francis, 20 Oct 2023
  • RC3: 'Comment on egusphere-2023-956', Anonymous Referee #2, 08 Sep 2023
    • AC3: 'Reply on RC3', Diana Francis, 20 Oct 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-956', Anonymous Referee #3, 10 Aug 2023
    • AC1: 'Reply on RC1', Diana Francis, 20 Oct 2023
  • RC2: 'Comment on egusphere-2023-956', Anonymous Referee #1, 21 Aug 2023
    • AC2: 'Reply on RC2', Diana Francis, 20 Oct 2023
  • RC3: 'Comment on egusphere-2023-956', Anonymous Referee #2, 08 Sep 2023
    • AC3: 'Reply on RC3', Diana Francis, 20 Oct 2023
Rachid Abida, Narendra Nelli, Diana Francis, Olivier Masson, Ricardo Fonseca, Emmanuel Bosc, and Marouane Temimi
Rachid Abida, Narendra Nelli, Diana Francis, Olivier Masson, Ricardo Fonseca, Emmanuel Bosc, and Marouane Temimi

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Short summary
This study is the first application of the Eddy Covariance (EC) framework to measure the fog droplet deposition velocity in a hyperarid coastal site. The average deposition velocity of fog droplets is around 3 cm s-1. The ratio of the time-integrated ground deposition of 137Cs under foggy conditions to that under clear sky conditions, showed that the fog contributed to the total ground deposition of 137Cs by up to 40 %.