Observational study on the distribution of cloud condensation nuclei and its causes in drought region.

Using a droplet measurement technologies (DMT) cloud condensation nuclei (CCN) counter,distributions of CCN on the ground and in the air in Yanchi and Yinchuan of Ningxia Hui Autonomous Region were obtained.It was concluded that CCN had a distinctive diurnal cycle.The high concentration appears in the early morning and evening,affected by human activities.There was a positive correlation of CCN concentration with temperature during the day,and a negative correlation at the night.Heavy rainfall had a scavenging effect on CCN concentration,while dust aerosol did not increase CCN concentration effectively.With respect to other regions in North China,the CCN concentration in Yanchi was relatively low.With increasing supersaturation,more particles were activated.According to the expression N=CS k,the fitted spectra parameters in Yinchuan showed continental characteristic.In the air,CCN concentration decreased with height,especially in the cloud,which was due to scavenging while an inversion layer tended to increase CCN concentration.