Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 11701-11711, 2015
http://www.atmos-chem-phys.net/15/11701/2015/
doi:10.5194/acp-15-11701-2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Oct 2015
Observations of new particle formation in enhanced UV irradiance zones near cumulus clouds
B. Wehner1, F. Werner2,a, F. Ditas1,b, R. A. Shaw3, M. Kulmala4, and H. Siebert1 1Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
2Leipzig Institute for Meteorology, 04103 Leipzig, Germany
3Department of Physics, Michigan Technological University, Houghton, Michigan, USA
4Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
anow at: Joint Center for Earth Systems Technology (JCET), Physics Department, Baltimore, Maryland, USA
bnow at: Max Planck Institute for Chemistry, 55128 Mainz, Germany
Abstract. During the CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados) campaign, the interaction between aerosol particles and cloud microphysical properties was investigated in detail, which also includes the influence of clouds on the aerosol formation. During two intensive campaigns in 2010 and 2011, helicopter-borne measurement flights were performed to investigate the thermodynamic, turbulent, microphysical, and radiative properties of trade-wind cumuli over Barbados. During these flights, 91 cases with increased aerosol particle number concentrations near clouds were detected. The majority of these cases are also correlated with enhanced irradiance in the ultraviolet (UV) spectral wavelength range. This enhancement reaches values up to a factor of 3.3 greater compared to background values. Thus, cloud boundaries provide a perfect environment for the production of precursor gases for new particle formation. Another feature of cloud edges is an increased turbulence, which may also enhance nucleation and particle growth. The observed events have a mean length of 100 m, corresponding to a lifetime of less than 300 s. This implies that particles with diameters of at least 7 nm grew several nanometers per minute, which corresponds to the upper end of values in the literature (Kulmala et al., 2004). Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds (ELVOCs) are probably involved here.

Citation: Wehner, B., Werner, F., Ditas, F., Shaw, R. A., Kulmala, M., and Siebert, H.: Observations of new particle formation in enhanced UV irradiance zones near cumulus clouds, Atmos. Chem. Phys., 15, 11701-11711, doi:10.5194/acp-15-11701-2015, 2015.
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Short summary
During the CARRIBA campaign on Barbados, 91 cases with increased aerosol particle number concentrations near clouds were detected from helicopter-borne measurements. Most of these cases are correlated with enhanced irradiance in the ultraviolet range. The events have a mean length of 100m, corresponding to a lifetime of 300s, meaning a growth of several nm/h. Such high values cannot be explained by sulfuric acid alone; thus extremely low volatility organic compounds are probably involved here.
During the CARRIBA campaign on Barbados, 91 cases with increased aerosol particle number...
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