Emissions Analysis
The Analyst 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, yielding a spatial output layer and corresponding data table; both can be used within Analyst 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. Emissions Analysis Flow depicts the analysis flow from inputs to outputs.
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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:
Water-Related GHG Emissions Calculations
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
Analyst 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 comes loaded with national averages for passenger vehicle fuel economy, and greenhouse gas and air pollutant emissions per gallon of gasoline. The default input for fuel economy is an on-road average for light-duty vehicles with short and long wheel bases (including passenger cars, light trucks, vans, pickup trucks, and sport/utility vehicles) as published by the Bureau of Transportation Statistics (BTS)1 for the year 2022.
The default input for greenhouse gas emissions is a carbon dioxide-equivalent (CO2e) emission rate per gallon of gasoline. The CO2 emission rate, and the ratio of CO2 to CO2e emissions used to calculate the overall CO2e emissions rate inclusive of methane and nitrous oxide, are those used by the Environmental Protection Agency (EPA) Greenhouse Gas Emissions Calculator2.
The default inputs for criteria pollutant emissions per gallon are national averages for passenger vehicles, as sourced from the EPA Motor Vehicle Emission Simulator (MOVES) model3.
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 Analyst (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 Analyst 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.
Analyst Default National Auto Fuel Economy and Emissions Rate Assumptions summarizes the input parameters used to calculate transportation GHG emissions, and the default values used by Analyst. If available, users can input localized baselines or projected future-year values for more accurate and/or policy-oriented analysis.
Parameters | Default Baseline Values |
|---|---|
Average on-road passenger vehicle fuel economy | 22.8 miles/gallon of gasoline |
Fuel emissions rate | 19.73 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 Analyst are based on data from the EPA Emissions & Generation Resource Integrated Database (eGRID) for the year 2022, as released by the EPA in January 2024.4. The dataset contains the environmental characteristics of almost all electric power generated in the United States, including net generation, resource mix, and emissions of carbon dioxide, nitrogen oxides, sulfur dioxide, methane, and nitrous oxide. Specifically, the Emissions module uses the annual carbon dioxide-equivalent (CO2e) total output emission rates averaged by state, measured in pounds per megawatt-hour (lbs/MWh).
The GHG emissions rate for natural gas is a constant as indicated by the EPA5. Parameters Default Baseline Values summarizes the input parameters used to calculate building energy GHG emissions and the default baseline values used by Analyst. 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.
Parameters | Default Baseline Values |
|---|---|
GHG emissions rate, electricity | Values differ by eGRID subregions |
GHG emissions rate, natural gas | 11.83 lbs CO2e/therm |
Water-Related Emissions Input Parameters
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 national average values for the “embedded energy” or “water-energy intensity" of water to gauge the magnitude of water-energy emissions. Different factors are assumed for Northern and Southern California.
The default national factors for water-energy use are based on the values for drinking water and wastewater cited by the Environmental Protection Agency (EPA) for the WaterSense program6. They were derived by the EPA from a study that references EPA Portfolio Manager data for water and wastewater facilities as collected by Lawrence Berkeley National Laboratories (LBNL)7
The default factors for water-energy use in Northern and Southern California are those estimated by the California Energy Commission (CEC) in a 2005 report, California’s Water-Energy Relationship8, and a 2006 refinement of the report’s original factors9. The water-energy use factors for Southern California are higher because most of the water used there is transported over longer distances, requiring much more energy for water supply and conveyance.
Analyst assumes the same GHG emissions rate for water-related electricity use as specified for building electricity use.
Default Input Parameters for Water Use Emissions summarizes the input parameters used to calculate water-energy GHG emissions and the default baseline values used by Analyst. If available, users can input localized baselines and projected future-year values for more accurate and/or policy-oriented analysis.
Parameters | Default Baseline Values |
|---|---|
Indoor water supply electricity use factor, national average | 4,590 kWh/million gallons |
Outdoor water supply electricity use factor, national average | 2,068 kWh/million gallons |
Indoor water supply electricity use factor, Northern California | 5,411 kWh/million gallons |
Outdoor water supply electricity use factor, Northern California | 3,500 kWh/million gallons |
Indoor water supply electricity use factor, Southern California | 13,022 kWh/million gallons |
Outdoor water supply electricity use factor, Southern California | 11,111 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 Analyst 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 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. |
1https://www.bts.gov/content/average-fuel-efficiency-us-light-duty-vehicles
2https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator-calculations-and-references
3https://www.epa.gov/moves
6https://www.epa.gov/watersense/data-and-information-used-watersense
7Electricity 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.epri.com/research/products/000000003002001433. The energy use factor for indoor water use is calculated as the total of the EPA factors for drinking water and wastewater, assuming that water used indoors subsequently requires treatment as wastewater. For outdoor water use, the EPA factor for drinking water is applied, assuming the water does not require subsequent treatment as wastewater.
8http://www.energy.ca.gov/2005publications/CEC-700-2005-011/CEC-700-2005-011-SF.PDF
9http://www.energy.ca.gov/2006publications/CEC-500-2006-118/CEC-500-2006-118.PDF