Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published December 2001 | public
Journal Article

The effect of water on gas–particle partitioning of secondary organic aerosol. Part I: α-pinene/ozone system


The effect of relative humidity (RH) on aerosol formation by the semi-volatile oxidation products of the α-pinene/O_3 system has been comprehensively studied. Experiments were performed in the presence of ammonium sulfate (aqueous, dry), ammonium bisulfate seed (aqueous, dry), and aqueous calcium chloride seed aerosols to ascertain their effect on the partitioning of the oxidation products. The yield of organic aerosol varies little with RH, and is not affected by the presence of dry inorganic salt aerosols. Aqueous salt aerosols reduce the yield of organic aerosol compared to that under seed-free or dry seed conditions. The degree of reduction is electrolyte dependent, with aqueous ammonium sulfate leading to the largest reduction and aqueous calcium chloride the smallest. Hygroscopic growth of the organic aerosol from <2% to 85% RH was also monitored, and could be satisfactorily represented as the sum of the individual contributions of the organic and inorganic fractions. The implications of the growth factor measurements for concentration/activity relationships of the condensed phase organic material (assuming a liquid solution) was explored. The formation of the organic aerosol was investigated using a simple two component model, and also one including the 12 product compounds identified in a previous study. The experimental results for <2% and 50% RH (without salt seed aerosols) could be satisfactorily predicted. However, the aqueous salt seed aerosols are predicted to increase the overall yield due to the dissolution of the organic compounds into the water associated with the seed aerosol—the opposite effect to that observed. The implications of two distinct phases existing the aerosol phase were investigated.

Additional Information

© 2001 Elsevier. Received 10 February 2001; accepted 29 July 2001. This work was supported by the US Environmental Protection Agency Center on Airborne Organics, US Environmental Protection Agency Agreement CR827331-01-0, and the Chevron Corporation. David Cocker was supported in part by a NSF Graduate Fellowship. The contribution of Simon Clegg was supported by an Advanced Fellowship from the Natural Environment Research Council of the UK. Special thanks to K.M. Cocker, M. Kalberer, and N.E. Whitlock.

Additional details

August 21, 2023
October 23, 2023