In-situ observations of aerosol particles remaining from evaporated cirrus crystals: Comparing clean and polluted air masses

[摘要] In-situ observations of aerosol particles contained in cirrus crystals are presented andcompared to interstitial aerosol size distributions (non-activated particles in between thecirrus crystals). The observations were conducted in cirrus clouds in the Southern and NorthernHemisphere mid-latitudes during the INCA project. The first campaign in March and April2000 was performed from Punta Arenas, Chile (54°S) in pristine air. The second campaign inSeptember and October 2000 was performed from Prestwick, Scotland (53°N) in the vicinityof the North Atlantic flight corridor. Size distribution measurements of crystal residuals(particles remaining after evaporation of the crystals) show that small aerosol particles(D_p< 0.1 mm) dominate the number density of residuals. The crystal residual size distributionswere significantly different in the two campaigns. On average the residual size distributionswere shifted towards larger sizes in the Southern Hemisphere. For a given integral residualnumber density, the calculated particle volume was on average three times larger in theSouthern Hemisphere.This may be of significance to the vertical redistribution of aerosolmass by clouds in the tropopause region. In both campaigns the mean residual size increasedslightly with increasing crystal number density. The form of the residual size distribution didnot depend on temperature as one might have expected considering different modes ofnucleation. The observations of ambient aerosol particles were consistent with the expectedhigher pollution level in the Northern Hemisphere. The fraction of residual particles onlycontributes to approximately a percent or less of the total number of particles, which is thesum of the residual and interstitial particles. Excellent agreement between the CVI andFSSP-300 probes was found supporting the assumption that each crystal is associated with only oneresidual particle.

[学科分类] 大气科学