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Published August 15, 2000 | Published
Journal Article Open

Combustion organic aerosol as cloud condensation nuclei in ship tracks


Polycyclic aromatic hydrocarbons (PAHs) have been sampled in marine stratiform clouds to identify the contribution of anthropogenic combustion emissions in activation of aerosol to cloud droplets. The Monterey Area Ship Track experiment provided an opportunity to acquire data on the role of organic compounds in ambient clouds and in ship tracks identified in satellite images. Identification of PAHs in cloud droplet residual samples indicates that several PAHs are present in cloud condensation nuclei in anthropogenically influenced air and do result in activated droplets in cloud. These results establish the presence of combustion products, such as PAHs, in submicrometer aerosols in anthropogenically influenced marine air, with enhanced concentrations in air polluted by ship effluent. The presence of PAHs in droplet residuals in anthropogenically influenced air masses indicates that some fraction of those combustion products is present in the cloud condensation nuclei that activate in cloud. Although a sufficient mass of droplet residuals was not collected to establish a similar role for organics from measurements in satellite-identified ship tracks, the available evidence from the fraction of organics present in the interstitial aerosol is consistent with part of the organic fraction partitioning to the droplet population. In addition, the probability that a compound will be found in cloud droplets rather than in the unactivated aerosol and the compound's water solubility are compared. The PAHs studied are only weakly soluble in water, but most of the sparse data collected support more soluble compounds having a higher probability of activation.

Additional Information

© American Meteorological Society 2000. Manuscript received 15 May 1996; in final form 7 June 1997. This work was funded by support from the Office of Naval Research Grant N00014-93-1-0872. The authors are grateful to the University of Washington Cloud and Aerosol Research Group for their assistance in collecting aerosol samples aboard the C-131A, in particular Peter Hobbs, Jack Russell, and Don Spurgeon. Support of ONR Grant N00014-92-J-1587 to the University of Washington Cloud and Aerosol Research group for aircraft operations during MAST is also acknowledged.

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