Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation by Jasper Kirkby et al., Nature 476 (2011)

Nature 476 (August 2011)

Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation

• Jasper Kirkby,
• Joachim Curtius,
• João Almeida,
• Eimear Dunne,
• Jonathan Duplissy,
• Sebastian Ehrhart,
• Alessandro Franchin,
• Stéphanie Gagné,
• Luisa Ickes,
• Andreas Kürten,
• Agnieszka Kupc,
• Axel Metzger,
• Francesco Riccobono,
• Linda Rondo,
• Siegfried Schobesberger,
• Georgios Tsagkogeorgas,
• Daniela Wimmer,
• Antonio Amorim,
• Federico Bianchi,
• Martin Breitenlechner, 
• André David,
• Josef Dommen,
• Andrew Downard,
• Mikael Ehn,
• Richard C. Flagan
• et al.

Received

 

09 September 2010

 

Accepted

 

24 June 2011

 

Published online

 

24 August 2011

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Atmospheric aerosols exert an important influence on climate¹ through their effects on stratiform cloud albedo and lifetime² and the invigoration of convective storms³. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours⁴, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small^5, 6. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia⁷. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100–1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H₂SO₄–H₂O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.

http://www.nature.com/nature/journal/v476/n7361/full/nature10343.html