A method for the measurement of the water solubility distribution of atmospheric organic aerosols is presented. This method is based on the extraction of organic aerosols collected on filters, using different amounts of water and measurement of the corresponding water-soluble organic carbon concentration. The solubility distribution is then estimated using the solubility basis set. The method was applied on both ambient and source-specific aerosols. Approximately 60% of the atmospheric urban organic aerosol analyzed had water solubility higher than 0.6 g L-1. Around 10% of the fresh cooking organic aerosol had water solubility higher than 10 g L-1, while 80% of the total fresh cooking organic aerosol had solubility lower than 0.1 g L-1. The ambient measurements suggested that the solubility distributions are roughly consistent with the positive matrix factorization analysis results determined during the analysis of the high-resolution time-of-flight aerosol mass spectrometry data. Most of the oxidized organic aerosol appears to have water solubility above 0.6 g L-1, while the hydrocarbon-like organic aerosol and cooking organic aerosol have water solubility less than 0.002 and 0.1 g L-1, respectively. The biomass burning organic aerosol seems to have mostly intermediate solubility in water, between 0.04 and 0.6 g L-1. The proposed approach can quantify the solubility distribution in the 0.002-15 g L-1 range. Future extension of the method to higher solubility ranges would be useful for capturing the complete solubility range for atmospheric cloud condensation studies (0.1-100 g L-1).
Keywords: atmospheric organic aerosol; positive matrix factorization; water solubility distribution.