2007 Volume 42 Issue 6 Pages 339-349
Hygroscopic properties of atmospheric aerosol particles at Kagurazaka in Tokyo were investigated in four seasons. A tandem differential mobility analyzer system wasused to measure the dependence of particle size on relative humidity (RH) for monodisperse aerosols with dry mobility diameter of 100nm. In summer, the average of number fraction of growth particles at 65%RH and 70%RH was only 23% and 28%, respectively; however that at 78%RH and 83%RH was 50% and 61%, respectively. In the typical case, number fraction and growth factor in summer suddenly increase over 75-80%RH that were near deliquescence relative humidity of (NH4) 2SO4, NaCl or NaNO3. In autumn, number fraction and growth factor at any relative humidity were almost always smaller than those of other seasons. Number fraction of growth particles at 65%RHwas 41% and 59% in spring and winter, respectively, and similarly that at 70%RH was more than in autumn and summer. Especially in winter, number fraction and growth factor at any relative humidity were large. Number fractions at 70%RH were larger when atmospheric temperatures were low or atmospheric relative humidities were high, which suggests that secondary particles production process from gases relates to existence of particles that grow at low relative humidity.
