Abstract:This study established an experimental system that combined an ultrasonic nebulizer with a photo-acoustic soot spectrometer and a scanning mobility particle sizer for measuring light absorption of water-soluble organic matter (WSOM) in PM2.5. PM2.5 samples were collected in the summer of 2011 in Shenzhen, and aerosols were re-generated from the water extracts using the ultrasonic nebulizer. The light absorption of the aerosols was then detected by the photo-acoustic soot spectrometer. The results show that the average mass concentration of WSOM during the campaign was (4.3±2.3) μg/m3, accounting for 11.9%±4.8% of PM2.5 and 49.2%±18.5% of OM, respectively. The Mass Absorption Efficiency (MAE) of WSOM at the wavelengths of 405, 532 and 781nm was (0.55±0.31), (0.54±0.31) and (0.21±0.13) m2/g, respectively. Further calculations show that the light absorption of WSOM at the wavelengths of 405, 532and 781nm was (2.30±1.08), (2.25±1.26) and (0.86±0.45) Mm-1, respectively, which contributed 7.6%, 10.6% and 5.8% to the entire PM2.5 light absorption at the corresponding wavelengths, respectively. The contribution of WSOM to aerosol light absorption is potentially important and more studies on the role of organic aerosol in visibility deterioration should be carried out.