Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa23a1135p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SA23A-1135
Physics
0305 Aerosols And Particles (0345, 4801, 4906), 0320 Cloud Physics And Chemistry, 1650 Solar Variability (7537), 2104 Cosmic Rays, 3311 Clouds And Aerosols
Scientific paper
Experimental studies of aerosol nucleation in air, containing trace amounts of ozone, sulphur dioxide, and water vapor at concentrations relevant for the Earths atmosphere are reported. The production of new aerosol particles is found to be proportional to the negative ion density. These results suggest that ions are important for nucleation processes in the atmosphere and cloud cover -- and may thus link cosmic rays to Earth's climate. The production of aerosols in the Earth's atmosphere is an unresolved and challenging problem. Atmospheric and experimental observations have shown that the nucleation of aerosol particles can occur under conditions that cannot be explained by classical nucleation theory. Several ideas have been put forward to solve the nucleation problem, e.g., Ion-induced Nucleation and Ternary Nucleation. However, experimental investigations exploring the role of ions in particle production are scarce, and often at conditions far removed from those relevant for the lower part of the atmosphere. In our laboratory we have performed1 an experimental investigation of nucleation that confirms the importance of ions under conditions that do prevail in the lower atmosphere. The measurements were performed in a 7 m3 reaction chamber, which was continuously flushed with dry purified air. Variable concentrations of water vapor (H2O), ozone (O3), and sulphur dioxide (SO2) could be added to the chamber, where the pressure was held a few Pa above atmospheric pressure, and the temperature fixed at 296 K. UV-lamps (253.7 nm) were used to initiate a photochemical reaction that transforms (H2O), ozone (O3), and sulphur dioxide (SO2) to sulphuric acid (H2SO4). Ions were produced in the chamber by galactic cosmic radiation. This natural production of ions could be enhanced with gamma sources, mounted outside of the chamber. A Gerdien tube was used to measure the ion current, and aerosols generated in the chamber were measured with a TSI Ultra Fine Condensation Particle Counter (3--150 nm). The experimental data indicate that particle production rates scale with the negative ion density and the results thus suggest that ions play a fundamental role in the production of new aerosol particles in the Earths atmosphere and cloud cover. (1) H. Svensmark et al., Proc.~Roy.~Soc.~London A, 463, 385--396 (2006), DOI: 10.1098/rspa.2006.1773.
Enghoff Martin B.
Pedersen J. O.
Svensmark Henrik
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