December 2008, Automotive Fleet - Feature
Step 1 to a Greener Fleet: Measuring Emissions
By Jason Mathers
Step by Step: How to Measure Emissions
Step 1. Set a Baseline.
Among the first steps to creating a solid system for tracking emissions is deciding a baseline year and emission reduction goals. When first developing a GHG baseline, companies should calculate emissions for the past several years. Although eventually a single year is selected as the baseline, managers should look at multiple years to identify unusual trends and ensure the right starting point is selected.
Step 2. Aggregate total amount of fuel consumed by type.
Through fuel card records, driver receipts, or other sources, managers can calculate the amount of fuel consumed by the company fleet. Fuel should be tracked by type and volume, such as gallons of gasoline.
Step 3. Identify carbon dioxide coefficients.
When combusted, each fuel type releases a specific amount of carbon dioxide in the atmosphere. For example, gasoline emits 19.42 lbs. per gallon. (See Table 1 on page 6.) Information on these and other types of fuel is available through the EPA. For easy calculation, coefficients are presented by volume, not by energy content.
Step 4. Calculate carbon dioxide emissions.
To calculate the total amount of CO2 emitted by a fleet, multiply the total volume consumed of each type of fuel by the fuel-specific carbon dioxide coefficient. For example:
1,000 gallons of gasoline x 19.42 lbs. CO2 = 19,420 lbs. of CO2
This calculation covers the vast majority of a fleet’s overall emissions.
Step 5. Estimate remaining emissions.
Refrigerant leaks and CH4 and N2O emissions are also factors in a vehicle’s greenhouse gas emissions. Each of these gases is a significantly more potent greenhouse gas than CO2. However, they are typically emitted in much smaller quantities. Calculating these emissions is more complicated than CO2 emissions since they are dictated by other factors than the amount of fuel consumed.
Under normal operating circumstances, these gases make up a few percentages of a passenger vehicle fleet’s emissions. Managers can approximate these emissions by assuming they equate to 5.7 percent of CO2. Thus, total emissions can be calculated by using the following equation:
Total CO2 x 1.057 = Total Emissions
To continue the previous example, a fleet that emits 19,420 lbs. of CO2 is estimated to emit the equivalent of 1,107 lbs. of CO2 in the form of other GHG emissions. In the example fleet, total emissions are 20,527 lbs. CO2 equivalent (CO2e).
Companies that want to fully calculate CH2, N2O, and refrigerant emissions can follow the protocol developed by the EPA Climate Leaders program, www.epa.gov/stateply/basic/index.html.