The Environmental Protection Agency (EPA) is revising some of the regulations that were originally promulgated in 1998 to implement the NO<INF>X</INF> SIP Call. The revisions give covered states greater flexibility concerning the form of the nitrogen oxides (NO<INF>X</INF>) emissions monitoring requirements that the states must include in their state implementation plans (SIPs) for certain emissions sources. Other revisions remove obsolete provisions and clarify the remaining regulations but do not substantively alter any current regulatory requirements.