Last updated 9 Apr 2021

This is a brief description of how these 2021 emissions inventories for the 
final Revised CSAPR Update were created by EPA.

The following sector inventories are simple interpolations of the 2016fh 
and 2023fh inventories to 2021: afdust, ag, rail, rwc, onroad_can, onroad_mex,
othafdust, othptdust

airports: 2021 inventories were developed using 2016-2021 projection 
factors consistent with other version 1 platform projections. 
Also, for this simulation, the 2016 airports inventory used as
the baseline for this projection includes corrections consistent with 
the June 2020 version of 2017NEI, and also an update at the 
Hartsfield-Jackson (ATL) airport provided by the state of Georgia.

cmv_c1c2 and cmv_c3: 2021 inventories were developed using 2016-2021 projection 
factors consistent with other version 1 platform projections. Non-AIS-based 
Canada CMV inventories were interpolated between 2015 and 2023.

nonpt: Mostly a 2016-2023 interpolation, except that the 2023 cellulosic
inventory is omitted completely. 

np_oilgas and pt_oilgas: A brand new 2021 projection was developed, using 
methods consistent with other version 1 platform projections. 

onroad / onroad_ca_adj: For version 1 platform, MOVES was previously run for 
2020. To make use of that data without rerunning MOVES for 2021, onroad 
emissions were prepared using 2020 activity (projected from 2016 using methods
consistent with other version 1 platform years), 2020 emission factor tables
from MOVES, and a set of 2020->2021 national adjustment factors applied in 
SMOKE-MOVES. California emissions were interpolated from 2016 and 2023.

ptegu: Uses a brand new EGU inventory for 2021.

ptnonipm: Most sources were interpolated from 2016 and 2023, except:
- The interpolation is not based directly on 2016fh and 2023fh, but on newer 
  versions of 2016 and 2023 which include a few updates each.
- A new closures packet was applied for 2021.
- An inventory which includes new units fom 2018NEI was also included,
  used as is without projections.

othar: Mostly a 2016-2023 interpolation like other Canada and Mexico sectors,
except there is a standalone area source EPG inventory for 2023 with no 2016
equivalent; that inventory is being used for 2021 as-is. 

othpt: Mostly a 2016-2023 interpolation like other Canada and Mexico sectors,
except for Canadian point sources which can not be easily interpolated; for
those sources we use 2023 emissions.