Atmospheric Aerosol and Cloud Condensation Nuclei Formation: A Possible Influence of Cosmic Rays? |
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Authors: | F Arnold |
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Institution: | (1) Atmospheric Physics Division, Max Planck Institute for Nuclear Physics (MPIK), P.O. Box 103980, D-69029 Heidelberg, Germany |
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Abstract: | A physical mechanism which may have a potential to connect climate with cosmic rays (CR) involves aerosol particle formation
by CR generated atmospheric ions followed by new particle growth. Only grown particles can scatter sunlight efficiently and
can eventually act as cloud condensation nuclei (CCN) and thereby may influence climate. Moreover grown particles live longer
as they are less rapidly scavenged by pre-existing larger particles. The present paper discusses aerosol particle formation
and growth in the light of new measurements recently made by our MPIK Heidelberg group. Emphasis is placed upon the upper
troposphere where very low temperatures tend to facilitate new particle formation by nucleation. The new measurements include:
laboratory measurements of cluster ions, aircraft measurements of ambient atmospheric ions, and atmospheric measurements of
the powerful nucleating gas H2SO4 and its precursor SO2. The discussion also addresses model simulations of aerosol formation and growth. It is concluded that in the upper troposphere
new aerosol formation by CR generated ions is a frequent process with relatively large rates. However new particle formation
by homogeneous nucleation (HONU) which is not related to CR also seems to be efficient. The bottleneck in the formation of
upper troposphere aerosol particles with sizes sufficiently large to be climate relevant is not nucleation but growth of small
particles. Our recent upper troposphere SO2 measurements suggest that particle growth by gaseous sulphuric acid condensation is at least occasionally efficient. If so
CR mediated formation of CCN sized particles should at least occasionally be operative in the upper troposphere. |
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Keywords: | aerosols clouds cosmic rays |
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