Apologies for the late response. Thank you @eyth.alison for confirming that N2O is not in the EQUATES onroad inventory data on the ftp site. I am also able to confirm that there is not another version of these inventories for the NEI years that contain N2O.
I was able to find out that we do have these onroad inventories for all EQUATES years (2002-2019) but they are not yet publicly posted. N2O is not in the 2002-2017 EQUATES onroad invtories but is available for 2018 and 2019. We can work to get this full set publicly posted in case that might be helpful.
In terms of context for why N2O is not available in the 2002-2017 files, @callen, who is one of the emissions experts that prepares these inventory packages, provided this context:
N2O was not included in the 2002-2017 EQUATES onroad inventories because the packages were developed before N2O was added in Emissions Modeling Framework (EMF) system for processing FF10-format emissions files (sometimes called “AQ-style” onroad inventories). As for why N2O has not always been included in these files, it’s a greenhouse gas that doesn’t affect AQ modeling and hasn’t always been a focus for what we do. MOVES output has included N2O for many years now, and we have been including it in our SMOKE-MOVES runs for many years as well, but we have not always included it in our post-processing products such as the AQ-style onroad inventories. As interest in GHGs has increased, we have started including N2O in some of our more recent post-SMOKE-MOVES onroad datasets, and this included the EQUATES 2018 and 2019 files.