| Data source | Years | Counties |
|---|---|---|
| EQUATES | 2002 - 2019 | Anoka, Carver, Chisago, Dakota, Hennepin, Pierce, Ramsey, Scott, Sherburne, St. Croix, Washington |
| National Emissions Inventory | 2020 | Anoka, Carver, Chisago, Dakota, Hennepin, Pierce, Ramsey, Scott, Sherburne, St. Croix, Washington |
| Air Emissions Modeling | 2021 - 2022 | Anoka, Carver, Chisago, Dakota, Hennepin, Pierce, Ramsey, Scott, Sherburne, St. Croix, Washington |
| Interpolation | 2023 - 2049 | Anoka, Carver, Chisago, Dakota, Hennepin, Pierce, Ramsey, Scott, Sherburne, St. Croix, Washington |
| Expected change in emissions in similar county | 2050 | Chisago, Pierce, Sherburne, St. Croix |
| RTDM and EPA MOVES4 | 2050 | Anoka, Carver, Dakota, Hennepin, Ramsey, Scott, Washington |
2 Methodological framework
2.1 On-road
Transportation emissions are available for motorcycles, passenger cars, intercity buses, light commercial trucks, single unit long-haul trucks, refuse trucks, single unit short-haul trucks, transit buses and school buses using EPA data sources. We use a geographic, or territorial accounting method, aligning with Scope 1 in the Greenhouse Gas Protocol. Geographic methods account for any transportation emissions taking place within a geographic boundary, regardless of origin or destination (Fong et al. 2021). Various methodologies are explored in Appendix F.
Geographic emissions are essential for quantifying air pollution experienced by people living in the area, but they do not give information on the logistic decisions of individuals.
All data sources are detailed in Chapter 3.
The Met Council also completed city-level VMT estimates for cities within the 7-county metro area. More information is available in Section 3.4.
All data processing for transportation is compiled using _run_all_transportation.R, ensuring all disparate datasets and sequential processing requirements are correct.
2.1.1 Limitations
Geographic accounting methods do not account for the decisions or travel behavior of individuals within the geographic boundaries. Within the Twin Cities region, this method will show high emissions per capita in low population areas with significant vehicle traffic, such as a lower-population county with major freeway traffic.
2.1.2 Validation
We would expect counties with higher population to have higher emissions and VMT.
2.2 Aviation
2.2.1 Minneapolis-St. Paul International Airport (MSP)
Aviation emissions are derived from three data sources: Metropolitan Airport Commission (MAC) fuel distribution (2005, 2021), MAC Aircraft emission estimates (2016-2020), and MPCA state GHG inventories.
Fuel distribution at the airport is the most straight-forward approach, as it involves applying a direct emission factor for jet fuel to the total amount of fuel distributed. As aircraft are generally only fueled for one flight at a time, we are effectively capturing emissions for aircraft flights departing MSP. The assumption is that any given airport (MSP in this case), should be responsible for half of emissions for each arrival and departure, with the complementary departure/recipient airport being responsible for the other half.
The second data source, MAC provided emissions are also a highly useful source, with the one overlapping year (2021) resulting in an almost identical emission estimate. However, because it lacks the explicit activity data, we prefer using the fuel distribution.
The final data source, which we used to in-fill interstitial years, 2006-2015, relies on MPCA statewide aviation emission estimates. Here, we calculated the proportion of MSP aviation emissions relative to statewide emissions, and used a time-series imputation method to fill in the interstitial years’ proportions. Then, we recalculated MSP emissions by multiplying the interpolated proportion by the statewide emission estimate. This method proved superior to directly imputing the MSP emissions between 2005 and 2016-2021 (i.e. not using the state data in any form), as those interpolations resulted in three years with MSP emission estimates exceeding the statewide emission estimate.