Cloud condensation nuclei (CCN) activity of non-volatile particles in Tokyo

A novel system has been developed to measure cloud condensation nuclei (CCN) activity simultaneously with volatility at 400°E C. The CCN/CN ratios were measured by a combination of a CCN counter and a condensation particle counter, and the volatility was measured by a volatility tandem differential mobility analyzer. This system was connected to a differential mobility analyzer and a hygroscopicity tandem differential mobility analyzer (HTDMA) in tandem to measure these properties of size- and hygroscopicity- selected aerosols. These instruments were deployed in Tokyo in November 2004. The number size distribution of the non-volatile cores in 100 nm aerosols was bimodal: one was a slightly-volatile mode (the decrease of mobility diameter (Δdm) caused by the volatilization was less than 20 nm) and the other was a mostly-volatile mode (Δdm > 20 nm). In Tokyo, the dominant fraction of the non-volatile cores at 400°E C is black carbon (BC). The ratios of aerosol particles not activated as CCN at a supersaturation (SS) of 0.5% are close to the number fraction of slightly volatile particles (FSV). The volatility measurement of HTDMA-selected particles reveals that most of less-hygroscopic particles were slightly-volatile. CCN/CN ratios of slightly volatile particles ((CCN/CN)SV) are estimated from CCN activity and volatility measurements of less-hygroscopic particles. (CCN/CN)SV at SS=0.5% and higher is correlated with the Δdm, and (CCN/CN)SV is nearly equal to unity at a 10nm Δdm. Because the main component of the non-volatile cores is BC, this result indicates that the CCN activity of BC particles depends strongly on the amount of coating.