Condensation nuclei (CN) and ultrafine CN in the free troposphere to 12 km: A case study over the Jungfraujoch High‐Alpine Research Station

Condensation nuclei (CN) were measured in the free troposphere (FT) above the Jungfraujoch (JFJ) high‐alpine research station (3454 m; Switzerland) from 4.5 to 12 km asl in a case study on July 30, 1997. Vertical profiles of CN concentration for d ≥ 5 nm ( N ≥5 ), d ≥ 15 nm ( N ≥15 15) were measured, and indicated that ultrafine CN (UCN; 5 ≤ d ≤ 15 nm; N 5‐15 ) exhibited a distinct increase with altitude. Some evidence for near‐constant values of d(logCN)/dz within discrete layers was found, which generally coincided with different airmasses as delineated by changes in the lapse rate dθ/dz at ∼ 5.5, 6.4, 9.0 and 10.6 km asl. In addition, CN concentration was mapped over a 40 × 75 km horizontal domain at 8.0 km asl centered above the JFJ. A pronounced variation in N ≥5 , N ≥15 and specific humidity, but not in UCN, exhibited quasi‐stationary 2‐D features and was attributed to the chance encounter of a mountain wave. The case study provides further evidence that the upper FT may be a source of new particles.