Thermal stability analysis of particles incorporated in cirrus crystals and of non-activated particles in between the cirrus crystals: comparing clean and polluted air masses

[摘要] A thermal volatility technique is used to provide indirect information aboutthe chemical composition of the aerosol involved in cirrus cloud formation.The fraction of particles that disappears after being heated to 125°Cis termed volatile and the fraction that disappears between 125 and250°C is termed semi-volatile. Particles that still remain after beingheated to 250°C make up the non-volatile fraction. The thermalcomposition of residual particles remaining from evaporated cirrus crystalsis presented and compared to interstitial aerosol particles (non-activatedparticles in between the cirrus crystals) for two temperature regimes (cold:T< -38°C, warm: -38≤T< -23°C), based on in-situobservations. The observations were conducted in cirrus clouds in theSouthern Hemisphere (SH) and Northern Hemisphere (NH) midlatitudes duringthe INCA project. In the cold temperature regime, the non-volatile fractionof the residual particles was typically in the range 10 to 30% in the NHand 30 to 40% in the SH. In the warm temperature regime, the non-volatileresidual fraction was typically 10 to 30% (NH) and 20 to 40% (SH). Athigh crystal number densities the non-volatile fraction in both temperatureregimes was even higher: in the range of 30 to 40% (NH) and 40 to 50%(SH). The semi-volatile fraction was typically less than 10% in bothhemispheres, causing the volatile fraction to essentially be a complement tothe non-volatile fraction. In terms of the fractioning into the three typesof particles, the SH cold case is clearly different compared to the otherthree cases (the two warm cases and the cold NH case), which share manyfeatures. In the NH data the distribution of different particle types doesnot seem to be temperature dependent. In all the cases, the non-volatilefraction is enriched in the residual particles compared to the fractionsobserved for the interstitial particles. This enrichment corresponds toabout 15 (NH) and 30 (SH) percent units in the two cold cases and to 15-25(NH) and 25-35 (SH) percent units in the two warm cases. In the NH coldcase, there is a clear relation between the fractions observed in theinterstitial particles and what is observed in the residual particles. Theobserved large fractions of non-volatile particles show that particlesforming ice crystals are not entirely made up of water-soluble sulfateparticles.

[学科分类] 大气科学