Atmos. Chem. Phys. Discuss., 10, 21653-21681, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Water content of aged aerosol
G. J. Engelhart1, L. Hildebrandt1, E. Kostenidou2,4, N. Mihalopoulos3, N. M. Donahue1, and S. N. Pandis1,2,4
1Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
2Department of Chemical Engineering, University of Patras, Patra, Greece
3University of Crete, Environmental Chemical Processes Laboratory (ECPL), Heraklion, Greece
4Institute of Chemical Engineering and High Temperature Chemical Processes (ICE-HT), Foundation of Research and Technology (FORTH), Patra, Greece

Abstract. The composition and physical properties of aged atmospheric aerosol were characterized at a remote sampling site on the northern coast of Crete, Greece induring the Finokalia Aerosol Measurement Experiment in May 2008 (FAME-2008). A reduced Dry-Ambient Aerosol Size Spectrometer (DAASS) was deployed to measure the aerosol water content and volumetric growth factor of fine particulate matter. The particles remained wet even at relative humidity (RH) as low as 20%. The aerosol was acidic during most of the measurement period, which likely contributed to the water uptake at low RH. The water content observations were compared to the thermodynamic model E-AIM, neglecting any contribution of the organics to aerosol water content. There was good agreement between the water measurements and the model predictions. Adding the small amount of water associated with the organic aerosol based on monoterpene water absorption did not change the quality of the agreement. These results strongly suggest that the water uptake by aged organic aerosol is relatively small (a few percent of the total water for the conditions of FAME-08) and generally consistent with what has been observed in laboratory experiments. The Q-AMS water concentration was well correlated with the DAASS measurements and in good agreement with the predicted values for the RH of the Q-AMS inlet. This suggests, that at least for the conditions of the study, the Q-AMS can provide valuable information about the aerosol water concentrations if the sample is not dried.

Citation: Engelhart, G. J., Hildebrandt, L., Kostenidou, E., Mihalopoulos, N., Donahue, N. M., and Pandis, S. N.: Water content of aged aerosol, Atmos. Chem. Phys. Discuss., 10, 21653-21681, doi:10.5194/acpd-10-21653-2010, 2010.
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