Size-segregated aerosol fluxes, deposition velocities, and chemical composition in an Alpine valley

Riccardo Marzuoli, Giacomo Alessandro Gerosa, Rossella Urgnani, Angelo Finco, Maria Chiesa, Laura Bignotti, Angelo Riccio, Elena Chianese, Giuseppina Tirimberio, Lorenzo Giovannini, Dino Zardi

Risultato della ricerca: Contributo in rivistaArticolo in rivistapeer review

Abstract

The paper presents eddy covariance measurements of aerosol fluxes performed above an Alpine pasture in the Camonica Valley (Italian Alps) during summer 2019 and winter 2020. Vertical fluxes and deposition velocities (vds) were computed for nine aerosol size classes, with geometric mean diameters (GMDs) ranging from 10 nm to 0.76 μm, employing a fast-response electrical low-pressure impactor (ELPI+, Dekati, FI). At the end of each campaign, the concentration of water-soluble ions was estimated from the ion chromatography chemical speciation performed on the multi-impactor filters. K+ concentrations tripled in winter, evidencing the impact of biomass burning emissions, while nitrate, nitrite, ammonium, and sulphate were ascribed to secondary inorganic aerosol (SIA) formation. During summer, classes characterized by downward net daily fluxes presented a high percentage of SIA (> 70%) deposited on the respective filters. Phenomena of growth or coagulation of particles were also detected from the steady increase in concentrations during the day in classes with GMD ≥ 20 nm. Turbulence favoured intense aerosol exchange during the day. During summer nights, low friction velocities (u∗) led to weaker fluxes, while a strong, stable stratification in winter determined aerosol trapping at ground level and non-negligible, mostly negative, fluxes during nighttime. The trends of vds versus aerosol GMDs showed prevailing deposition phenomena under stable atmospheric conditions, with relative humidity higher than or equal to 90%, friction velocity lower than 0.15 m s−1, or wind speed lower than 2 m s−1. Cluster analysis identified groups of days with or without nucleation events and highlighted a rainout effect in summer during a period characterized by intense precipitation.
Lingua originaleEnglish
pagine (da-a)N/A-N/A
RivistaAtmospheric Research
DOI
Stato di pubblicazionePubblicato - 2022

Keywords

  • Aerosol fluxes
  • Eddy covariance
  • Water-soluble ions
  • Secondary inorganic aerosol
  • Pasture

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