Emissions Analysis

rev. February 2020

The UrbanFootprint Emissions module estimates greenhouse gas (GHG) emissions associated with passenger vehicle transportation and building energy and water use. Comparative results for greenhouse gas emissions demonstrate differences between land use scenarios due to their travel characteristics and building programs, which impact vehicle miles traveled (VMT), energy use, and water use results. GHG emissions are also subject to technical assumptions for vehicle and building performance, as well as emissions rates of energy sources for transportation and building energy. This documentation focuses on the calculations of emissions alone. The VMT, building energy, and water use calculations with which GHG emissions are estimated are described in the documentation for other modules: Transportation Analysis, Energy Use Analysis, and Water Use Analysis.

Along with transportation GHG emissions, the module estimates criteria pollutant emissions from passenger vehicle transportation, including nitrogen oxides (NOx), particulate matter (PM2.5 and PM10), sulfur oxides (SOx), carbon monoxide (CO), and volatile organic chemicals (VOC). These emissions, which are calculated on the basis of average per-mile factors, are intended to reflect comparative results at the project scale, and not localized (for example, neighborhood-level) emissions impacts.

Emissions into the future are subject to assumptions reflecting fuel economy improvements; GHG emissions rates for transportation fuel, electricity, and natural gas; and criteria pollutant emission rates.

Analysis is run at the scale of the project canvas (generally parcels or census blocks), yielding a spatial output layer and corresponding data table; both can be used within UrbanFootprint for mapping and data exploration, and exported. The module also reports individual and comparative scenario results via summary charts, and generates a spreadsheet summary in Excel format.

Methodology

The module estimates emissions on the basis of the VMT, energy use, and water use outputs generated by the Transportation, Energy Use, and Water Use modules. Please refer to the documentation for these modules for details about how these outputs are calculated.

Estimated emissions are also determined by input assumptions about vehicle performance, transportation fuel emissions, and electricity and natural gas emissions. The following sections describe the calculations and assumptions. Figure 1 depicts the analysis flow from inputs to outputs.

Figure 1. Emissions Analysis Flow

Transportation GHG and Criteria Pollutant Emissions Calculations

The Transportation module estimates annual VMT, annual VMT per household, and annual VMT per capita. Transportation GHG emissions are calculated on the basis of fleet-wide average vehicle fuel economy and an average fuel emission rate. These assumptions can be set separately for the base and individual future-year scenarios.

Fuel economy (in miles per gallon) is applied to VMT to calculate fuel consumption. The fuel emission rate, in pounds of carbon dioxide equivalent (CO2e) per gallon, is applied to fuel consumption for the GHG emissions calculation. The following equation summarizes the calculation:

To estimate air pollutant emissions, the module applies emission factors (in grams per mile) for each pollutant to VMT. For example, the equation for estimating annual SOx emissions is as follows:

Building Energy GHG Emissions Calculations

The Energy Use module estimates electricity and natural gas use for residential and commercial buildings. Building energy GHG emissions from electricity and natural gas use are calculated, in turn, on the basis of emissions rate assumptions that can be set separately for the base and individual future-year scenarios. The equation for calculating GHG emissions generated by residential and commercial buildings’ electricity use is as follows:

The Water Use module estimates residential and commercial indoor and outdoor water use. GHG emissions associated with the treatment and distribution of estimated water use are calculated using assumed indoor and outdoor water-energy use rates (expressed in electricity use per volume of water) and a GHG emissions rate for electricity. Assumptions can be set separately for the base and individual future-year scenarios. The equation for calculating GHG emissions associated with water-energy use is as follows:

Input Parameters

UrbanFootprint comes loaded with a set of default carbon emissions rates for electricity use, natural gas use, and transportation fuel that are derived from U.S. Environmental Protection Agency (EPA) data. The default inputs can be replaced with localized baseline inputs, if available, via the Analysis Assumptions editor. Different energy use inputs can be set for each scenario, and can be used to test the impact of energy efficiency measures into the future. By changing the inputs for future-year scenarios, you can test the impact of more efficient buildings in the context of new growth. You can also create scenarios that replicate the Base Canvas and change the energy use inputs to test the impacts of efficiency measures for existing buildings.

Transportation Emissions Input Parameters

The Emissions module currently applies an on-road average fuel economy for all cars, and an average emissions rate for gasoline. While the inputs do not directly account for alternative vehicle and fuel types, users could test the impacts of technological advancements by developing composite assumptions in some manner outside of UrbanFootprint (for example, deriving an average vehicle fuel economy based on an assumed distribution of vehicle types into the future). Alternatively, VMT results can be exported from UrbanFootprint to be used as a basis for extended analyses of VMT, transportation energy use, and emissions with respect to projected technological change or policy targets.

Table 1 summarizes the input parameters used to calculate transportation GHG emissions, and the default baseline values used by UrbanFootprint. National average on-road passenger vehicle fuel economy and GHG emissions are based on EPA data. National average criteria pollutant emissions rates are from the EPA Motor Vehicle Emission Simulator (MOVES)³ model. If available, users can input localized baselines and projected future-year values for more accurate and/or policy-oriented analysis.

Table 1: UrbanFootprint Default National Auto Fuel Economy and Emissions Rate Assumptions

Parameters

Default Baseline Values

Average on-road passenger vehicle fuel economy

22 miles/gallon of gasoline

Fuel emissions rate

19.61 lbs CO2e/gallon of gasoline

NOx emissions per mile

0.9018 grams/mile

PM10 emissions per mile

0.0203 grams/mile

PM2.5 emissions per mile

0.018 grams/mile

SOx emissions per mile

0.0087 grams/mile

CO emissions per mile

7.2933 grams/mile

Volatile Organic Compound (VOC) emissions per mile

0.686 grams/mile

Building Energy Emissions Input Parameters

The default electricity GHG emission rates in UrbanFootprint are based on data from the EPA Emissions & Generation Resource Integrated Database 2016 (eGRID). The dataset contains the environmental characteristics of almost all electric power generated in the United States, including emissions rates, net generation, resource mix, and air emission of nitrogen oxides, sulfur dioxide, carbon dioxide, methane, and nitrous oxide. Specifically, the Emissions module uses annual CO2-equivalent (CO2e) total output emission rate averaged by state (measured in pounds per megawatt-hour).

The GHG emissions rate for natural gas is a constant as indicated by the EPA. Table 2 summarizes the input parameters used to calculate building energy GHG emissions and the default baseline values used by UrbanFootprint. Users can input localized baselines and projected future-year values. Future rates can be based on policy targets or energy portfolio scenarios at the local, regional, or broader scales.

Figure 1. Map of eGRID 2016 CO2 Equivalent Emissions Rates by State

Table 2: Default Input Parameters for Building Energy Emissions

Parameters

Default Baseline Values

GHG emissions rate, electricity

Values differ by eGRID subregions

GHG emissions rate, natural gas

11.83 lbs CO2e/therm

The energy use associated with water supply — including treatment and pumping for conveyance and distribution — varies depending on the characteristics of local water systems and source water supply. While there is wide variability across the U.S., the module assumes a default national average that can serve to gauge the order of magnitude of water-energy emissions. The default national rate comes from a study that references EPA Portfolio Manager data for water and wastewater facilities as collected by Lawrence Berkeley National Laboratories (LBNL), assuming water systems with a 5 to 20 million gallon daily (MGD) flow rate. The weighted average water-energy use intensities for systems of other sizes are shown in Table 3.

Table 3. Water Energy-Use Intensities (Weighted Average Values for Water System Parameters from Filtered Energy Star Dataset)

Average Daily Flow Range (million gallons per day, or MGD)

Energy Use Intensity (kWh per million gallons)

< 3 MGD

2,000 kWh/MG

3 to 5 MGD

1,400 kWh/MG

5 to 20 MGD

1,600 kWh/MG

20 to 600 MGD

1,500 kWh/MG

UrbanFootprint assumes the same GHG emissions rate for water-related electricity use as specified for building electricity use.

Table 4 summarizes the input parameters used to calculate water-energy GHG emissions and the default baseline values used by UrbanFootprint. If available, users can input localized baselines and projected future-year values for more accurate and/or policy-oriented analysis.

Table 4: Default Input Parameters for Water Use Emissions

Parameters

Default Baseline Values

Indoor water supply electricity use (indoor water-energy use intensity)

1,600 kWh/million gallons

Outdoor water supply electricity use (outdoor water-energy use intensity)

1,600 kWh/million gallons

GHG emissions rate, electricity

Values vary by eGRID subregions

Output Metrics

The Emissions module generates a spatial output layer and corresponding data table; both can be used within UrbanFootprint for mapping and data exploration, and exported. The module also reports individual and comparative scenario results via summary charts, and generates a spreadsheet summary in Excel format. The attributes of the spatial output/data table are summarized in Table 5.

Table 5: Emissions Module Outputs

Attribute(s)

Description

Residential Water GHG Emissions

Annual GHG emissions associated with residential water use.

Commercial Water GHG Emissions

Annual GHG emissions associated with commercial water use.

Total Water GHG Emissions

Total GHG emissions from residential and commercial water use.

Residential Water GHG Emissions per Capita

Annual GHG emissions from residential water use, per capita in a parcel or census block.

Commercial Water GHG Emissions per Employee

Annual GHG emissions from commercial water use, per employee in a parcel or census block.

Water GHG Emissions per Household

Annual GHG emissions from residential water use, per household in a parcel or census block.

Transportation GHG Emissions

Annual GHG emissions from passenger vehicle transportation.

Residential Building Energy GHG Emissions

Total annual GHG emissions from residential building energy use.

Commercial Building Energy GHG Emissions

Total annual GHG emissions from commercial building energy use.

Total Building Electricity GHG Emissions

Total annual GHG emissions from residential and commercial building electricity use.

Building Natural Gas GHG Emissions

Total annual GHG emissions from residential and commercial building natural gas use.

Total Building Energy GHG Emissions

Total annual GHG emissions from residential and commercial building energy use.

Residential Building Energy GHG Emissions per Capita

Annual GHG emissions from residential building energy use, per capita.

Commercial Building Energy GHG Emissions per Employee

Annual GHG emissions from commercial building energy use, per employee.

Residential Building Energy GHG Emissions per Household

Annual GHG emissions from residential building energy use, per household.

Passenger Vehicle Emissions per Household

Annual GHG emissions from residential passenger vehicle transportation, per household.

Passenger Vehicle Emissions per Capita

Annual GHG emissions from residential passenger vehicle transportation, per capita.

Total Passenger Vehicle Emissions

Annual GHG emissions from residential passenger vehicle transportation.

Total GHG Emissions

Annual total GHG emissions from passenger vehicle transportation, building energy use, and water use.

GHG Emissions per Capita

Annual GHG emissions from residential passenger vehicle transportation, residential building energy use, and residential water use, per capita.

GHG Emissions per Employee

Annual GHG emissions from commercial building energy and commercial water use, per employee.

Total NOx Emissions

Annual NOx emissions associated with residential VMT attributed to households in parcel or census block.

Total PM10 Emissions

Annual PM10 emissions associated with residential VMT attributed to households in parcel or census block.

Total PM2.5 Emissions

Annual PM2.5 emissions associated with residential VMT attributed to households in parcel or census block.

Total SOx Emissions

Annual SOx emissions associated with residential VMT attributed to households in parcel or census block.

Total CO Emissions

Annual CO emissions associated with residential VMT attributed to households in parcel or census block.

Total VOC Emissions

Annual VOC emissions associated with residential VMT attributed to households in parcel or census block.

Total Pollutant Emissions

Total annual criteria pollutant emissions, including NOx, PM10, PM2.5, SOx, CO, and VOCs, attributed to households in parcel or census block.

Endnotes

  1. Electricity Use and Management in the Municipal Water Supply and Wastewater Industries, Electric Power Research Institute and the Water Research Foundation, 3002001433, Final Report, November 2013. Available at https://www.waterrf.org/research/projects/electricity-use-and-management-municipal-water-supply-and-wastewater-industries

  2. Ibid.