Observations of Cloud Condensation Nuclei in North China

Using a DMT (Droplet Measurement Technologies) continuous flow streamwise thermal gradient cloud condensation nuclei (CCN) counter mounted on a Cheyenne IIIA aircraft, about 20 flights for aircraft measurements of CCN over North China were conducted in the autumn of 2005 and spring of 2006. According to the design for aircraft observation, the method of spiral ascent or descent in the troposphere was used for the vertical measurement of CCN, and some certain levels were chosen for horizontal measurement. The vertical distributions of CCN concentrations show that most CCN particles are concentrated in the low level of troposphere and CCN concentration decreased with height increasing. It suggests that the main source of CCN is from the surface. This result is consistent with former studies during 1983-1985 in China with a static thermal gradient CCN counter. The comparison of vertical observations between polluted rural area near Shijiazhuang and non-polluted rural area near Zhangjiakou shows that there is about five times difference in CCN concentration. But over two polluted cities, Shijiazhuang and Handan, there is no notable difference in CCN concentration. The horizontal flight measurements for penetrating the cumulus clouds experiment show the apparent decrease of CCN in clouds. It confirms that cloud has a de nite consumptive effect on CCN particles because some CCN particles can form cloud droplets.The surface measurements of CCN in Shijiazhuang City were made during June-August 2005. The statistical CCN data show the great difference in concentration at the same supersaturation (S) in Shijiazhuang summertime. The minimum CCN concentrations were 584, 808, and 2431 cm-3, and the maximum concentrations were 9495, 16332, and 21812 cm-3 at S=0.1%, 0.3%, and 0.5%, respectively. CCN has a diurnal variation cycle. From 0600 BT, the concentration began to increase and reached the maximum at about noon. Then it generally decreased throughout the afternoon. The reason maybe is related to the onset of emissions from vehicular traffic in the morning followed by the photochemical production of secondary organics that condense on the primary particles. The precipitation has an obvious scavenging effect on CCN particles. With the increase of rainfall rate, the CCN concentrations decrease quickly. The high surface CCN concentrations in Shijiazhuang should be related to the serious air pollution and then influenced by anthropogenic sources.According to the expression N = CSk, the CCN spectra can be derived. The fitted spectral parameters of C (more than 1000) and k (about 0.7) show that they are classified to the continental CCN in North China.