Atmos. Chem. Phys. Discuss., 10, 8009-8049, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Novel method of generation of Ca(HCO3)2 and CaCO3 aerosols and first determination of hygroscopic and cloud condensation nuclei activation properties
D. F. Zhao1,2, A. Buchholz2, Th. F. Mentel2, K.-P. Müller2, J. Borchardt2, A. Kiendler-Scharr2, C. Spindler2, R. Tillmann2, A. Trimborn3, T. Zhu1, and A. Wahner2
1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China
2Forschungszentrum Jülich, Institut für Chemie und Dynamik der Geosphäre–2: Troposphäre, 52425 Jülich, Germany
3Aerodyne Research Inc., 45 Manning Rd, Billerica, MA 01821, USA

Abstract. Atmospheric mineral aerosols contain CaCO3 as a reactive component. A novel method to produce CaCO3 aerosol was developed by spraying Ca(HCO3)2 solutions, which were generated from CaCO3 suspensions and CO2. By aerosol mass spectrometry the freshly sprayed aerosol was characterized to be Ca(HCO3)2 which under annealing in a tube furnace transformed into CaCO3. Transmission Electron Microscopy demonstrated that the particles produced were spherical. The method is easy to operate and was able to generate aerosol of sufficient concentration and proper size for the study of physiochemical properties as was demonstrated for hygroscopicity and CCN activity measurements, and investigations of heterogeneous reactions of mineral aerosol. Fresh Ca(HCO3)2 particles are somewhat more hygroscopic than CaCO3 particles although both have small growth factors of 1.03 and 1.01, respectively, at 95% relative humidity. The CCN activity of Ca(HCO3)2 aerosol is remarkably higher than that of CaCO3 aerosol and only slightly less than that of Ca(NO3)2. Experiments in the Large Jülich Aerosol Chamber showed that Ca(HCO3)2 can exist for several hours under dry atmospheric conditions which is in contrast to the current believe that Ca(HCO3)2 is unstable in the atmosphere. We conclude that Ca(HCO3)2 maybe be formed in the atmosphere in cloud droplets of activated mineral dust by reaction of CaCO3 with CO2 and H2O. The presence of Ca(HCO3)2 and as a consequence an enhanced CCN activity may alter the influence of mineral aerosol on global climate.

Citation: Zhao, D. F., Buchholz, A., Mentel, Th. F., Müller, K.-P., Borchardt, J., Kiendler-Scharr, A., Spindler, C., Tillmann, R., Trimborn, A., Zhu, T., and Wahner, A.: Novel method of generation of Ca(HCO3)2 and CaCO3 aerosols and first determination of hygroscopic and cloud condensation nuclei activation properties, Atmos. Chem. Phys. Discuss., 10, 8009-8049, doi:10.5194/acpd-10-8009-2010, 2010.
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