Section 51.35 - How can my state equalize the emission inventory effort from year to year?(a) Compiling a triennial inventory means more effort every 3 years. As an option, your state may ease this workload spike by using the following approach:(1) Each year, collect and report data for all Type A (large) point sources (this is required for all Type A point sources).(2) Each year, collect data for one-third of your sources that are not Type A point sources. Collect data for a different third of these sources each year so that data has been collected for all of the sources that are not Type A point sources by the end of each 3-year cycle. You must save 3 years of data and then report all emissions from the sources that are not Type A point sources on the triennial inventory due date.(3) Each year, collect data for one-third of the nonpoint, nonroad mobile, and onroad mobile sources. You must save 3 years of data for each such source and then report all of these data on the triennial inventory due date.(b) For the sources described in paragraph (a) of this section, your state will have data from 3 successive years at any given time, rather than from the single year in which it is compiled.(c) If your state chooses the method of inventorying one-third of your sources that are not Type A point sources and triennial inventory nonpoint, nonroad mobile, and onroad mobile sources each year, your state must compile each year of the 3-year period identically. For example, if a process has not changed for a source category or individual plant, your state must use the same emission factors to calculate emissions for each year of the 3-year period. If your state has revised emission factors during the 3 years for a process that has not changed, you must compute previous years' data using the revised factor. If your state uses models to estimate emissions, you must make sure that the model is the same for all 3 years. 80 FR 8796 , Feb. 19, 2015