Aircraft Measurements of Summer Vertical Distributions of Aerosols and Transitions to Cloud Condensation Nuclei and Cloud Droplets in Central Northern China

Aerosols greatly influence the cloud’s microphysical properties and climate change by acting as cloud condensation nuclei (CCN). Properties of vertical distribution, size distribution, and source regions of aerosols, as well as their transition relationships with the CCN and cloud droplet number concentration, are investigated using nine flights of aircraft measurements under clear and cloudy conditions in Shanxi, central northern China. Results indicate that the atmospheric boundary inversion layer structure has an important impact on the vertical distributions of aerosols and CCN. Size distributions under different weather conditions are similar in the upper atmospheric layers but quite different in the lower layers. There is a high positive linear correlation between the aerosol number concentrations and CCN number concentrations at 0.3% supersaturation in the vertical. A linear regression of y=1.3x−616.3 is established between the cloud droplet number concentrations and aerosol number concentrations near cumulus cloud bases with a correlation coefficient of 0.96. Moreover, the conversion rate from aerosol number concentrations to cloud droplet number concentrations was about 47%. A good linear regression of y=1.6x−473.8 is also found between the CCN number concentrations and cloud droplet number concentrations near cumulus cloud bases with a correlation coefficient of 0.96 at 0.3% supersaturation. The conversion rate is found to be about 69%.