ZAMG - Sonnblick Observatorium

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, A. Kasper-Giebl, , A. Koch, , R. Hitzenberger and , H. Puxbaum (2000), "Scavenging Efficiency of ‘Aerosol Carbon’ and Sulfate in Supercooled Clouds at Mt. Sonnblick (3106 m a.s.l., Austria)", Journal of Atmospheric Chemistry, 35: 33-46.

Abstract:
Cloud water and interstitial aerosol samples collected at Mt. Sonnblick (SBO) were analyzed for sulfate and lsquoaerosol carbonrsquo to calculate in-cloud scavenging efficiencies. Scavenging efficiencies for sulfate (epsiSO) ranged from 0.52 to 0.99 with an average of 0.80. lsquoAerosol carbonrsquo was scavenged less efficiently with an average value (epsiAC) of 0.45 and minimum and maximum values of 0.14 and 0.81, respectively. Both epsiSO and epsiAC showed a marked, but slightly different, dependence on the liquid water content (LWC) of the cloud. At low LWC, epsiSO increased with rising LWC until it reached a relatively constant value of 0.83 above an LWC of ap 0.3 g/m3. In the case of lsquoaerosol carbonrsquo, we obtained a more gradual increase of epsiAC up to an LWC of ap 0.5 g/m3. At higher LWCs, epsi_ remained relatively constant at 0.60. As the differences between epsiSO and epsiA varied across the LWC range observed at SBO, we assume that part of the lsquoaerosol carbonrsquo was incorporated into the cloud droplets independently from sulfate. This hypothesis is supported by size classified aerosol measurements. The differences in the size distributions of sulfate and total carbon point to a partially external mixture. Thus, the different chemical nature and the differences in the size and mixing state of the aerosol particles are the most likely candidates for the differences in the scavenging behavior.

Keywords:
scavenging efficiency, lwc, total carbon, sulfate