Dependence of CCN activity of less volatile particles on the amount of coating observed in Tokyo

Abstract

A novel observation system has been developed to measure cloud condensation nuclei (CCN) activity simultaneously with volatility of aerosol particles at 400°C. CCN/CN ratios were measured using a CCN counter and a condensation particle counter, and volatility was measured with a volatility tandem differential mobility analyzer (VTDMA). This system was connected to a hygroscopicity tandem differential mobility analyzer in tandem to measure these properties of hygroscopicity‐selected particles. These instruments were deployed in Tokyo in November 2004. In Tokyo, the dominant fraction of nonvolatile cores at 400°C has been found to be black carbon (BC). Therefore the number size distribution measured by VTDMA represents the mixing state of black carbon particles. The VTDMA measurement of hygroscopicity‐selected particles revealed that most of the less hygroscopic particles were less volatile, while more hygroscopic particles were more volatile. CCN/CN ratios of less volatile particles [(CCN/CN) LV ] are estimated from CCN activity and volatility measurements of less hygroscopic particles. (CCN/CN) LV at SS = 0.5% is correlated with the decrease of peak diameter due to volatilization (Δ d m ), and (CCN/CN) LV is nearly equal to unity at Δ d m = 10 nm. This result suggests that the CCN activity of BC particles significantly depends on the amount of coating.