Aircraft measurements of the vertical distribution and activation property of aerosol particles over the Loess Plateau in China

For the first time, comprehensive aircraft measurements of atmospheric aerosols and cloud condensation nuclei (CCN) were made over the Loess Plateau in Shanxi, China. Data from six flights in July and August 2013 were analyzed. Fine aerosols were predominant over the region. On the one hazy day, the fraction of fine particles in the total aerosol load was the greatest. Aerosol number concentration decreased exponentially with altitude. Inversion layers caused low-level aerosol accumulation zones. The mean aerosol particle size increased with altitude, and the larger particles were mainly found above 2 km. Aerosol number size distributions at different height ranges showed two or three peaks. The aerosol number size distribution from 0.01 μm to 20 μm can be fitted with three log-normal distribution functions. The number concentration of CCN (NCCN) decreased with altitude. NCCN was linearly related to the CN concentration (NCN). The fraction of CCN to CN (fCCN/CN) at 0.3% SS was half of that at 0.4% SS. The fCCN/CN on the hazy day was lower than on the clear days. Vertical profiles of fCCN/CN and the effective diameter (ED) were similar, although the fCCN/CN increased with altitude.