Cloud condensation nuclei spectra derived from size distributions and hygroscopic properties of the aerosol in coastal south-west Portugal during ACE-2

Abstract

In this work we propose and test a method to calculate cloud condensation nuclei (CCN) spectra based on aerosol number size distributions and hygroscopic growth factors. Sensitivity studies show that this method can be used in a wide variety of conditions except when the aerosol consist mainly of organic compounds. One crucial step in the calculations, estimating soluble ions in an aerosol particle based on hygroscopic growth factors, is tested in an internal hygroscopic consistency study. The results show that during the second Aerosol Characterization Experiment (ACE‐2) the number concentration of inorganic ions analyzed in impactor samples could be reproduced from measured growth factors within the measurement uncertainties at the measurement site in Sagres, Portugal. CCN spectra were calculated based on data from the ACE‐2 field experiment at the Sagres site. The calculations overestimate measured CCN spectra on average by approximately 30%, which is comparable to the uncertainties in measurements and calculations at supersaturations below 0.5%. The calculated CCN spectra were averaged over time periods when Sagres received clean air masses and air masses influenced by aged and recent pollution. Pollution outbreaks enhance the CCN concentrations at supersaturations near 0.2% by a factor of 3 (aged pollution) to 5 (recent pollution) compared to the clean marine background concentrations. In polluted air masses, the shape of the CCN spectra changes. The clean spectra can be approximated by a power function, whereas the polluted spectra are better approximated by an error function.

Subarctic atmospheric aerosol composition: 3. Measured and modeled properties of cloud condensation nuclei

“…into the CCN prediction algorithm [Covert et al, 1998;Dusek et al, 2003;Ervens et al, 2007;Snider et al, 2003;Zhou et al, 2002]. Some studies assumed internally mixed aerosols but treated clearly bimodal scans separately [Rissler et al, 2004;Vestin et al, 2007], or involved the full GF-PDF [Gasparini et al, 2006;Mochida et al, 2006] similar to our study.…”

“…Most studies assumed internally mixed aerosols, involving only GF mean (D p ,t) instead of the full GF-PDF Figure 7. Closure performances as a function of SS of different CCN activation closure studies for atmospheric aerosols that used HTDMA data as a proxy for the chemical composition [Covert et al, 1998;Dusek et al, 2003;Ervens et al, 2007;Gasparini et al, 2006;Mochida et al, 2006;Rissler et al, 2004;Snider et al, 2003;Vestin et al, 2007;Zhou et al, 2002]. Results obtained in this study (externally mixed approach) are shown as black circles.…”

Calibration of LACIS as a CCN detector and its use in measuring activation and hygroscopic growth of atmospheric aerosol particles

“…Critical super-saturations given in Hudson and Da (1996) for measurements in Reno, Nevada, are 0.3% and 0.23% for particle sizes of 60 and 100 nm, and for measurements done in Sacramento, California, are 0.5% and 0.45% for 60 and 100 nm, respectively. Recently, Dusek et al (2006) obtained a critical diameter of 83 nm at a super-saturation of 0.4% for an air mass that recently had passed over the city of Frankfurt, Germany. Thus, the values measured in this study are in the same range than earlier measurements of the CCN behavior of urban atmospheric aerosol particles.…”

“…In the past, attempts have been made to derive the number of cloud condensation nuclei (CCN) of an aerosol from measurements of hygroscopic properties (e.g., Covert et al, 1998;Dusek et al, 2003). Generally, the derived number of CCN overestimates the number of CCN measured.…”

“…It has been tried to derive cloud particle number concentrations based on measurements of the hygroscopic growth of aerosol particles, either in laboratory experiments or for atmospheric aerosol (e.g., Covert et al, 1998;Brechtel and Kreidenweis, 2000a,b;Dusek et al, 2003;Kreidenweis et al, 2005;Koehler et al, 2006). In general, the derivation was more successful for laboratory studies than for those conducted in the real atmosphere.…”