Future emissions regulations will dictate limits to smoke mass concentrations as well as particle sizes. Current methods are not able to predict the soot emissions and particle sizes distributions accurately. Existing measurements show that lean burn architectures to be featured in geared large and medium civil turbofan engines can lead to very large numbers of small particulates. Moreover, lean burn calls for operation in pilot and pilot/main modes; the switch from pilot to main operation has to be based on accurate estimation of pollutant species like smoke, CO, and UHC. A programme of work is proposed to deliver accurate and reliable predictive methods for all pollutant species, based on development of advanced emissions and spray models, as the spray has a major effect on emissions. Please refer to the full topic descriptions document published in this call.