Cloud condensation nuclei measurements in the high troposphere and in jet aircraft exhaust

Extensive measurements of cloud condensation nuclei (CCN) spectra (1 to 0.02% supersaturation; S) at altitudes up to 12 km are presented. These were similar to many marine boundary layer measurements when normalized to standard sea level pressure. Extremely low CCN concentrations (<10 cm −3 ) were sometimes found in association with very high CN (condensation nuclei) concentrations (>3000 cm −3 ). This was suggestive of cloud scavenging of CCN and production of small particles. Measurements in the exhaust of a B‐757 jet aircraft showed very high CCN/CN ratios and enhancements of CCN concentrations for all S. This suggests a greater impact of jet aircraft on clouds and climate than previous measurements.