5.7 Summary of quality assurance methods

EPA performed a series of checks and comparisons against both the inputs and the resulting emissions to quality assure the onroad inventory. These checks are in addition to the ones described on the underlying CDBs. The following is a list of the more significant checks that were performed:

• Review of SPGM data prior to becoming EPA Defaults

  • EPA identified missing motorhomes and motorcycles, as well as misclassified trucks.
  • SPGM provided additional data to correct this.

• Review of StreetLight data prior to becoming MOVES inputs

  • EPA generated plots of monthly/daily/hourly VMT and average hourly speeds, comparing trends by month, vehicle type, hour, and day type. EPA performed limited gap-filling where necessary.
  • EPA found that some months of data showed irregular VMT patterns or high average speeds. Affected months were excluded from final calculations.

• Review of S/L/T agency MOVES inputs

  • EPA created plots of age distributions to check that the distributions looked like year 2023 and that population totals reasonably matched with SPGM; where discrepancies existed, EPA contacted the S/L/T agency for clarification of the registration data year (age distributions) and/or revised population estimates.
  • Previously discussed QA script and findings (Section 5.5.2).

• The 2023 NEI emissions were compared to the 2022v2 platform emissions to make sure that all SCCs, counties, and pollutants were covered and as a general quality assurance of the emissions.

• Comparisons of 2023 with 2022v2 emissions were done using spreadsheets that compared emissions from the two years using various groupings, including but not limited to county-level, the first 6 digits of the SCC (fuel + MOVES source type), and grouping by light-duty and heavy-duty.

• Maps of county-level CAP emissions were prepared for each MOVES source type, including maps of the difference between 2023 emissions versus 2022v2 emissions. Similar plots of gridded CAP emissions were prepared for each rate (e.g., RPD), and of county-level emission rates (emissions divided by activity) for select CAPs by MOVES source type and rate.

The maps and spreadsheets helped to identify areas with suspect activity data or emission factors, and EPA followed up on any suspect areas to investigate further and resolve problems if any were found. Folders containing a number of QA maps, plots, and summaries are referenced as part of the supporting data in Table 5.17.