Assessment of cloud supersaturation by size-resolved aerosol particle and cloud condensation nuclei (CCN) measurements

Abstract

Abstract. In this study we show how size-resolved measurements of aerosol particles and cloud condensation nuclei (CCN) can be used to characterize the supersaturation of water vapor in a cloud. The method was developed and applied during the ACRIDICON-Zugspitze campaign (17 September to 4 October 2012) at the high-Alpine research station Schneefernerhaus (German Alps, 2650 m a.s.l.). Number size distributions of total and interstitial aerosol particles were measured with a scanning mobility particle sizer (SMPS), and size-resolved CCN efficiency spectra were recorded with a CCN counter system operated at different supersaturation levels.During the evolution of a cloud, aerosol particles are exposed to different supersaturation levels. We outline and compare different estimates for the lower and upper bounds (S low , S high ) and the average value (S avg ) of peak supersaturation encountered by the particles in the cloud. A major advantage of the derivation of S low and S avg from size-resolved CCN efficiency spectra is that it does not require the specific knowledge or assumptions about aerosol hygroscopicity that are needed to derive estimates of S low , S high , and S avg from aerosol size distribution data. For the investigated cloud event, we derived S low ≈ 0.07-0.25 %, S high ≈ 0.86-1.31 % and S avg ≈ 0.42-0.68 %.

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

“…According to Krüger et al (2014), the error in N CCN is based on the counting error of the measured particle number and is 10 % of N CCN for large concentrations; given that mostly low concentrations prevailed, the mean error was about 20 % of N CCN .…”

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 2: Variability and characteristic differences under near-pristine, biomass burning, and long-range transport conditions

“…For clarity throughout the discussion, we subdivided the S range according to Reutter Furthermore, we marked the range, in which average peak supersaturations at cloud base, Scloud (DH,κ), in the ATTO region are expected. The Scloud(DH,κ) results were obtained according to Krüger et al (2014) and can be found in our part 1 study as well as in Table 2 of the present work. The relevant Scloud(DH,κ) range spans from ~0.18 % to ~0.34 % and, thus, overlaps with the interphase between low and intermediate S regimes.…”

“…For further CCN-relevant information, we refer the reader to Rose et al (2008) and Krüger et al (2014). The CCN efficiency spectra parameterization as introduced in part 1 plays a key role in the present manuscript.…”

“…Illustrative examples can be found during days with strong rain showers, such as 27 April, 05 May, and 06 May. Note that the 'depth of the notches', corresponding to the smallest activated particles, could in principle be used to estimate the S levels during the corresponding events (compare procedure in Krüger et al, 2014). Further note in this context that besides depletion of the accumulation relative to the Aitken mode, aerosol activation and cloud processing are known to also 35 foster the opposite effect: The growth of Aitken mode particles into the accumulation mode via formation of aqueous phase reaction products (i.e., sulfate and aqueous phase SOA) in the cloud droplets, followed by droplet re-evaporation and deposition of the newly formed compounds onto the particles (e.g., Ervens, 2015;Farmer et al, 2015).…”

Comparing parameterized versus measured microphysical properties of tropical convective cloud bases during the ACRIDICON–CHUVA campaign

“…According to Krüger et al (2014), the error in N CCN (S) based on the counting error in the measured particle number ( c = √ c + 1) can be calculated by…”