Third generation air system was the three level air. In Europe the use of three levels of air feeding with primary and secondary below the liquor guns started about 1980. At the same time stationary firing gained ground. Use of about 50% secondary seemed to give hot and stable lower furnace. Higher black liquor solids 65 – 70% started to be in use. Hotter lower furnace and improved reduction were reported. With three level air and higher dry solids the sulfur emissions could be kept in place.