The second is the progressive tightening of, and an advance notice system on, permissible emission levels. Permissible emission levels have been specified for 26 substances; they are being progressively tightened after accounting for the development rate of industrial technologies and reduction ability and advance notices are given to allow establishments to prepare ahead of time. The advance notice system began with an announcement in 1991 regarding tightened permissible emission levels applicable from 1995. Since then permissible emission levels have been progressively tightened in 1999, 2005, and 2010. The tightened permissible emission levels applicable from January 1, 2015 were announced on December 31, 2012.