Preprints
https://doi.org/10.5194/acp-2021-990
https://doi.org/10.5194/acp-2021-990
 
09 Feb 2022
09 Feb 2022
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Measurement Report: Spectral and statistical analysis of aerosol hygroscopic growth from multi-wavelength lidar measurements in Barcelona, Spain

Michaël Sicard1,2, Daniel Camilo Fortunato dos Santos Oliveira1, Constantino Muñoz-Porcar1, Cristina Gil-Díaz1, Adolfo Comerón1, Alejandro Rodríguez-Gómez1, and Federico Dios Otín1 Michaël Sicard et al.
  • 1CommSensLab, Dept. of Signal Theory and Communications, Universitat Politècnica de Catalunya (UPC), 08034-Barcelona, Spain
  • 2Ciències i Tecnologies de l’Espai-Centre de Recerca de l’Aeronàutica i de l’Espai/Institut d’Estudis Espacials de Catalunya (CTE-CRAE/IEEC), Universitat Politècnica de Catalunya (UPC), 08034-Barcelona, Spain

Abstract. This paper presents the estimation of the hygroscopic growth parameter of atmospheric aerosols retrieved with a multi-wavelength lidar, a micro pulse lidar and daily radiosoundings in the coastal region of Barcelona, Spain. The hygroscopic growth parameter, γ, parametrizes the magnitude of the scattering enhancement in terms of the backscatter coefficient following Hänel parametrization. After searching for time co-located lidar and radiosoundings measurements, a strict criterion-based procedure (limiting the variations of magnitudes such as water vapor mixing ratio, potential temperature, wind speed and direction) is applied to select only cases of aerosol hygroscopic growth. A spectral analysis (at the wavelengths of 355, 532 and 1064 nm) is performed with the multi-wavelength lidar, and a climatological one, at the wavelength of 532 nm, with the database of both lidars. The spectral analysis shows that below 2 km (regime of local pollution and sea salt) γ decreases with increasing wavelengths. This behaviour can be attributed to the aerosol size: the smaller the aerosol, the more hygroscopic. Above 2 km (regime of regional pollution and residual sea salt) the values of γ at 532 nm are nearly the same than below 2 km, and its spectral behaviour is flat. This analysis and others from the literature are put together in a table presenting, for the first time, a spectral analysis of the hygroscopic growth parameter of a large variety of atmospheric aerosol hygroscopicities going from low (pure mineral dust, γ < 0.2) to high (pure sea salt, γ > 1.0) hygroscopicity. The climatological analysis shows that, at 532 nm, γ is rather constant all year round and has a large monthly standard deviation suggesting the presence of aerosols with different hygroscopic properties all year round. The annual γ is 0.55 ± 0.23. The height of the hygroscopic layers shows an annual cycle with a maximum in summer and a minimum in winter. Former works describing the presence of re-circulation layers of pollutants injected at various heights above the PBL may explain why γ, unlike the height of the hygroscopic layers, is not season-dependent. The sub-categorization of the whole database into No cloud and Below-cloud cases reveals a large difference of γ in autumn between both categories (0.71 and 0.33, respectively), possibly attributed to a depletion of inorganics at the point of activation into cloud condensation nuclei in the Below-cloud cases. Our work calls for more in-situ measurements to synergetically complete such studies based on remote sensing.

Michaël Sicard et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-990', Anonymous Referee #3, 19 Feb 2022
    • AC1: 'Reply on RC1', Michael Sicard, 26 Apr 2022
  • RC2: 'Comment on acp-2021-990', Anonymous Referee #1, 28 Feb 2022
    • AC2: 'Reply on RC2', Michael Sicard, 26 Apr 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-990', Anonymous Referee #3, 19 Feb 2022
    • AC1: 'Reply on RC1', Michael Sicard, 26 Apr 2022
  • RC2: 'Comment on acp-2021-990', Anonymous Referee #1, 28 Feb 2022
    • AC2: 'Reply on RC2', Michael Sicard, 26 Apr 2022

Michaël Sicard et al.

Michaël Sicard et al.

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Short summary
Atmospheric particles can absorb water vapor and this water uptake may change their properties, e.g. their size. In the coastal region of Barcelona, Spain, we observe that 1) smaller particles absorb more water vapor, in relative terms, than larger particles; 2) the particle capacity to absorb water vapor has no annual tendency probably because the site background is quite constant (urban + marine aerosol regime).
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