The Hestia-Baltimore v1.6 Scope 1 FFCO2 emissions are reported for the 2010 to 2015 (Table 1), with a focus on 2014 (Figure 1). Emissions totaled 1,487.3 kt C (Mg C) in 2014, with a 95% confidence interval (CI) of 1,158.9 to 1,944.9 kt C. The central estimate of annual emissions ranged from a peak of 1,798.3 kt C in 2010 to a minimum of 1,420.0 kt C in 2012. After 2012, the total emission increased each year through 2015. The peak in emissions in 2010 was driven largely by the commercial marine vessel (CMV) sector. The largest emitting sectors in each year except for 2010 were onroad, commercial, residential, and industrial, representing 34.2%, 19.9%, 19.0%, and 11.8% of the total emissions in 2014. In 2010, however, CMV emissions were the second largest emitting sector behind onroad. The electricity production and nonroad sectors each accounted for less than 10% of the total emissions in each year, while rail and aircraft emissions accounted for less than 1%. Table 2 shows the emissions categories organized by sector and scope that were included in Hestia-Baltimore and the City’s 2014 SRI (2020 email from L. McNeilly to S. M. Miller and G. S. Roest, unreferenced, see notes). Hestia-Baltimore includes only Scope 1 FFCO2 emissions while the SRI includes most Scope 1 categories, Scope 2 emissions in buildings and associated with electrified railways, and Scope 3 emissions associated with waste. Our comparison is restricted to only FFCO2 from the common Scope 1 categories.
2.1. Building sectors
The residential sector emissions of 282.5 (195.3 – 417.7) kt C represented 19.0% of the total city emissions in 2014. Natural gas consumption was the source of 86.6% of those emissions while petroleum fuels (liquid fossil fuels, e.g. distillate fuel oil and kerosene) contributed nearly all of the rest. Residential coal consumption was negligible. Figure 2 shows the 200 m gridded annual residential FFCO2 emissions for 2014 and Figure 3 shows the cumulative fraction of emissions in all emitting grid cells. The top 10% of emitting grid cells were responsible for 33.8% of residential FFCO2 in Baltimore, while the top 50% of grid cells accounted for 84.8% of residential emissions.
Residential FFCO2 emissions were only reported for natural gas consumption in Baltimore’s SRI (Table 2). The residential natural gas emissions in 2014 were estimated to be 244.6 (168.9 - 362.2) kt C in Hestia-Baltimore and 204.2 kt C in the SRI. The SRI emissions were within the 95% CI of Hestia-Baltimore emissions with a relative mean difference of 18.0% for the central emission estimate. The 2014 SRI documentation states that residential GHG emissions in Baltimore were estimated using Baltimore Gas and Electric (BGE) utility data on natural gas energy consumption for single- and multi-family residences while petroleum consumption was not estimated, likely due to the fact that home heating oil is often purchased through private transactions instead of from a centralized utility. The exclusion of petroleum is an important data gap in the SRI as 13.4% of residential FFCO2 was associated with petroleum fuels in 2014. The 2011 NEI data, which serves as input to Vulcan and subsequently Hestia (see Section 5), includes estimates of nonpoint criteria pollutant emissions associated with petroleum combustion - hence, the data used by Maryland to report emissions to the NEI, if available, may be useful for developing city-scale GHG emissions estimates.
The commercial sector emissions total of 296.3 (209.9 – 429.4) kt C in 2014 (19.9% of the annual total) made this sector the second largest FFCO2 source in the city, with 77.3% from nonpoint commercial buildings and the remaining 22.7% from commercial point sources. Figure 2 shows the prominence of commercial point sources within high emitting grid cells. The top 10% of emitting grid cells were contained 74.7% of emissions (Figure 3). Natural gas use was associated with 93.2% of commercial FFCO2 emissions with petroleum accounting for 6.8%. Less than 0.1% of commercial FFCO2 was associated with coal.
Commercial sector FFCO2 emissions were also only reported for natural gas consumption in Baltimore’s SRI, under the title ‘Commercial and Institutional Buildings and Facilities’. Emissions in Hestia-Baltimore were 276.0 (195.4 - 400.3) kt C for point and nonpoint commercial natural gas consumption while Baltimore’s SRI reported 130.3 kt C based on BGE utility data – entirely outside the 95% CI of Hestia-Baltimore with a difference of 71.7% for the central emission scenario. The extent to which large point sources are captured in the BGE data is not clear, and there may be differences between Hestia-Baltimore and the BGE utility data in the categorization of commercial and industrial emissions. These potential differences could not be diagnosed with the available data. The sum of commercial and industrial natural gas consumption emissions in the 2014 SRI was 285 kt C – only 6.4% less than the central Hestia-Baltimore emission estimate. Again, the lack of emissions associated with petroleum in Baltimore’s SRI represents a data gap, as petroleum fuel consumption was associated with 6.8% of commercial FFCO2 in Hestia-Baltimore in 2014.
The industrial sector’s emissions of 175.3 (132.1 – 240.7) kt C in 2014 (11.8% of the city total) were dominated by point sources (79.1% of the industrial total), evident in Figure 2 as relatively few grid cells with high emissions. The point sources occupied only sixteen grid cells out of 6,066 grid cells that overlap with the city of Baltimore (0.2%). Nonpoint industrial buildings and processes accounted for the remaining 20.9%. The top 10% of emitting grid cells contained 89.9% of industrial emissions (Figure 3). Unlike the commercial and residential sectors, petroleum was associated with most of the industrial FFCO2 (83.6%) while natural gas use made up the remaining 16.4%.
The industrial sector was difficult to compare between the SRI and Hestia-Baltimore due to apparent differences data sources and categorization. Again, only natural gas use was reported for ‘Manufacturing Industries and Construction’ emissions in Baltimore’s SRI. Baltimore’s SRI reported 155.6 kt C FFCO2 for natural gas use in this sector while the industrial natural gas use in Hestia-Baltimore was only 28.8 (22.1 – 38.8) kt C. Again, this discrepancy is likely due to differences in commercial and industrial building categorization between the SRI and Hestia-Baltimore. However, 83.6% of industrial emissions in Hestia-Baltimore were from petroleum fuel use in 2014 – not natural gas. It is possible that some of the ‘Manufacturing Industries and Construction’ emissions in the 2014 SRI were categorized as (e.g.) commercial sector emissions in Baltimore-Hestia. Furthermore, the dominance of industrial point sources in Hestia-Baltimore highlights the need to include major point source facilities. Another category called Industrial Processes and Product Use (IPPU) was not reported in the SRI, which is allowed under the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC) standard when data availability prevents an estimate.
2.2. Electricity production
Scope 1 FFCO2 from electricity generation totaled 129.1 (112.3 – 145.9) kt C in 2014 (8.7% of the city total), making it the fifth largest sector from 2011 to 2015. Petroleum combustion was responsible for 75.5% of these emissions while the remaining 24.5% was derived from natural gas combustion. Specifically, Hestia-Baltimore contains ten facilities that reported non-zero FFCO2 emissions within the city of Baltimore. CO2 emissions from biofuel-based energy generation are not included in Hestia-Baltimore. No emissions from coal use are reported for this sector within Baltimore. Figure 4 shows the electricity producing point sources, which are clustered near the central core of the city and around the harbor. Baltimore contains two facilities that report hourly emissions to the Clean Air Markets Division (CAMD) which burn natural gas (3.7% of electricity production emissions in 2014). Three facilities that burn natural gas and/or petroleum have emissions estimated from monthly fuel consumption data from the Energy Information Administration in the US Department of Energy (DOE/EIA, 96.3% of sector total in 2014). Table 3 shows the central estimate of FFCO2 emissions from the CAMD and EIA facilities from 2010 to 2015. Additionally, nine electricity producing facilities are reported in the 2011 NEI point sector, though only five of these report non-zero emissions (less than 0.1% of sector total in 2014). Table 4 shows emissions for these facilities in 2014. The Wheelabrator Baltimore Refuse facility is the largest producer of FFCO2 from electricity production in the city (71% of Scope 1 power plant emissions and 6.2% of city total emissions in 2014), with FFCO2 emissions coming from petroleum-based solid waste, which is included in Baltimore-Hestia due to the fossil-fuel origin of the waste. However, the facility’s actual CO2 emissions are much higher due to additional combustion of biogenic solid waste (29).
Baltimore’s SRI contains emissions for several electricity producing facilities, though only six of these facilities were located within the city limits of Baltimore (Table 5). Electricity consumption for the other facilities should be quantified in Scope 2 emissions and therefore are not included in our comparison with Hestia-Baltimore. Of the six facilities in Baltimore’s SRI within the city boundary, five overlapped with Hestia-Baltimore facilities, though the Trigen Leadenhall St facility was categorized as an industrial point source in Hestia-Baltimore with FFCO2 emissions of zero in all six years. The remaining facility (Trigen North Central Ave) was not included in the Hestia-Baltimore data. The reason for the differences in emissions for the remaining facilities is not clear, though it is likely due to different data sources – CAMD CO2 data and EIA fuel consumption in Hestia-Baltimore vs. USEPA Flight Database in the SRI. The difference is especially notable for the Wheelabrator facility, which is the largest electricity producing facility within the city of Baltimore. Furthermore, the second largest facility in Hestia-Baltimore – the Domino Sugar facility – was not included in the SRI under electricity producing facilities, though it may have been included in the industrial or commercial sectors. Overall, Hestia-Baltimore estimated Scope 1 FFCO2 emissions of 129.1 (112.3 – 145.9) kt C from electricity producing facilities within the city boundary, while the SRI reported 103.0 kt C – a difference of 22.5% compared to the central emission estimate. Meanwhile, the SRI reported total Scope 1 powerplant emissions of 2,186.7 kt C from facilities both within and outside of the city boundary.
The onroad sector was the largest individual Hestia-Baltimore emission sector, with 508.9 (436.7 – 581.2) kt C in 2014 (34.2% of the city total). Gasoline usage accounted for 82.2% of onroad FFCO2 while diesel fuel represented the remaining 17.8%. Figure 5 shows the 2014 annual onroad emissions for all road segments in the city, normalized to segment length. Emissions along interstates and major arterial roadways were distinct among a backdrop of roadways with generally lower emissions. The downtown core of Baltimore also had higher emissions than the less densely populated suburban outskirts in the northern part of the city and along the eastern and western boundaries. The top 10% of emitting grid cells accounted for 43.2% of onroad emissions (Figure 2, Figure 3) while the 10% of road length with the highest emissions per meter were responsible for 54.0% of emissions (Figure 5).
The difference between the Hestia-Baltimore onroad emissions and the city’s SRI estimate was small relative to other categories reported here, with Hestia emissions of 508.9 (436.7 – 581.2) kt C in 2014 and 589.6 kt C in the SRI – a difference of -14.7% compared to the central emissions estimate and outside of Hestia-Baltimore’s 95% CI. The 2014 SRI provides estimates of ‘vehicle miles travelled’ (VMT) from the USEPA’s MOVES model, which are combined with vehicle-class-specific emission factors to estimate emissions. Hestia-Baltimore also uses data from the MOVES model, but instead of VMT, the FFCO2 output from the MOVES model in the 2011 NEI is used directly. Thus, the difference in the total onroad emissions are likely due to differing estimates of (e.g.) traffic volume and/or emission factors used in versions of the MOVES model. Nonetheless, Hestia-Baltimore’s distribution of onroad emissions to all road segments within the city provides insight into the high-emission onroad corridors that should be considered for sustainable transportation planning.
2.4. Commercial marine vessels
For the years 2011 to 2015, commercial marine vessels (CMV) emissions within ports were the sixth largest FFCO2 emission sector in Baltimore, behind Scope 1 electricity generating sources. Note that no ‘underway’ shipping (shipping lanes along coast or towards open water) emissions were included within the city boundary as these emissions were allocated to Baltimore County in the 2011 NEI. FFCO2 emissions totaled 63.4 (42.8 – 95.8) kt C in 2014, representing 4.3% of the city total. However, CMV emissions in 2010 were 431.3 (291.2 - 652.1) kt C, or 24.0% of the city total, only behind the onroad sector with 511.7 (439.0 – 584.3) kt C (28.5% of the city total). The maximum in 2010 reflects annual fuel sales data from the EIA ‘vessel bunkering use’ and residual fuel oil sales for transportation (16). CMV emissions were not reported in the SRI.
2.5. Aircraft, nonroad, and rail
The nonroad, rail, and aircraft sectors cumulatively represented slightly more than 2% of the city’s total emissions in 2014. Nonroad emissions were the largest sector among the three with 27.2 (26.1 – 28.2) kt C in 2014 (1.8% of the city total), while rail emissions (4.0 (3.3 – 5.2) kt C, 0.3% of the city total) and aircraft emissions (0.6 (0.5 – 0.9) kt C, <0.1% of the city total) were the smallest emitting sectors within the city. The relatively low aircraft emissions reflect the fact that the Baltimore/Washington International Airport (BWI) lies within neighboring Anne Arundel County and is therefore not included in the Scope 1 Hestia-Baltimore emissions.
Scope 1 emissions from these sectors were not included the SRI – a practice which is compliant with the GPC protocol when data are not available. Several of these sources are outside of the regulatory purview of the city, but are Scope 1 FFCO2 emissions nonetheless. Emissions from aircraft and rail both accounted for less than 1% of emissions in Hestia-Baltimore. However, nonroad emissions account for nearly 2% of FFCO2 in Hestia-Baltimore. Again, the USEPA NEI serves as an indirect source of FFCO2 emissions in the absence of centralized data (e.g. from a utility).