Cloud activation properties of aerosol particles in a continental Central European urban environment

• Published in: Atmospheric chemistry and physics 2021-07, Vol.21 (14), p.11289-11302
• Main Authors: Salma, Imre, Thén, Wanda, Vörösmarty, Máté, Gyöngyösi, András Zénó
• Format: Article
• Language: English
• Subjects: Aerosol particles; Aerosols; Analysis; Chemical composition; Cloud condensation nuclei; Clouds; Condensation; Condensation nuclei; COVID-19; Cycles; Diameters; Fine structure; Hygroscopicity; Laboratories; Locations (working); Nucleus; Parameters; Particle counters; Particle size distribution; Properties; Radiation counters; Size distribution; Supersaturation; Time dependence; Ultrastructure; Urban areas; Urban environments; Variability; Water vapor; Water vapour
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-21-11289-2021

Collocated measurements using a condensation particle counter, differential mobility particle sizer and cloud condensation nuclei counter were realised in parallel in central Budapest from 15 April 2019 to 14 April 2020 to gain insight into the cloud activation properties of urban aerosol particles. The median total particle number concentration was 10.1 × 103 cm−3. The median concentrations of cloud condensation nuclei (CCN) at water vapour supersaturation (S) values of 0.1 %, 0.2 %, 0.3 %, 0.5 % and 1.0 % were 0.59, 1.09, 1.39, 1.80 and 2.5 × 103 cm−3, respectively. The CCN concentrations represented 7–27 % of all particles. The CCN concentrations were considerably larger but the activation fractions were systematically substantially smaller than observed in regional or remote locations. The effective critical dry particle diameters (dc,eff) were derived utilising the CCN concentrations and particle number size distributions. Their median values at the five supersaturation values considered were 207, 149, 126, 105 and 80 nm, respectively; all of these diameters were positioned within the accumulation mode of the typical particle number size distribution. Their frequency distributions revealed a single peak for which the geometric standard deviation increased monotonically with S. This broadening indicated high time variability in the activating properties of smaller particles. The frequency distributions also showed fine structure, with several compositional elements that seemed to reveal a consistent or monotonical tendency with S. The relationships between the critical S and dc,eff suggest that urban aerosol particles in Budapest with diameters larger than approximately 130 nm showed similar hydroscopicity to corresponding continental aerosol particles, whereas smaller particles in Budapest were less hygroscopic than corresponding continental aerosol particles. Only modest seasonal cycling in CCN concentrations and activation fractions was seen, and only for large S values. This cycling likely reflects changes in the number concentration, chemical composition and mixing state of the particles. The seasonal dependencies of dc,eff were featureless, indicating that the droplet activation properties of the urban particles remained more or less the same throughout the year. This is again different from what is seen in non-urban locations. Hygroscopicity parameters (κ values) were computed without determining the time-dependent chemical composition of the pa