Greenhouse Gas Reporting Program

EMISSION CALCULATION METHODOLOGIES

The Greenhouse Gas Reporting Program (GHGRP) prescribes methodologies that must be used to determine greenhouse
gas (GHG) emissions from each source category. Reporters generally have the flexibility to choose among several methods
for computing GHG emissions. The decision of which method to use may be influenced by the existing environmental
monitoring systems in place and other factors. Reporters can change emission calculation methods from year to year, as
long as they meet the requirements for use of the method selected.

Direct-Emitting Facilities

Direct-emitting facilities report emissions from each source category (rule subpart) included in the GHGRP and these
emissions can generally be categorized as either combustion or process emissions. Emissions from fuel combustion comprise
carbon dioxide (C02), methane (CH4), and nitrous oxide (N20) emitted from combustion of a fossil fuel (e.g., coal, natural gas,
petroleum products) or biomass feedstock (e.g., wood, landfill gas). Process emissions generally include emissions from
chemical transformation of raw materials and fugitive emissions. The chemical transformation of raw materials often releases
greenhouse gases such as C02, CH4 and N20. These processes include iron and steel production, cement production,
petrochemical production, and nitric acid production, among others. Fugitive emissions refer to emissions of gases due to
leaks or other unintended or irregular releases. Fugitive CH4 releases occur from petroleum and natural gas systems and
underground coal mines. Fugitive emissions of fluorinated gases occur from industrial gas production, electrical equipment
production and use, electronics manufacturing, aluminum production, and magnesium production. These processes typically
release hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).

~ Emissions from fuel combustion are determined by facilities by using a continuous emission monitoring system
(CEMS), measured fuel composition data, or default emission factors. A CEMS is a device that continually collects
information on the quantity of a gas being emitted. CEMS are generally thought to be the most accurate way to
determine emissions for heterogeneous fuels like municipal solid waste, and collect accurate information on
emissions from standard fuels as well. Site-specific fuel composition data can also be used to calculate emissions. A
facility using this methodology would measure for each fuel type the high heating value (HHV), carbon content,
and (for gaseous fuels) molecular weight of a representative sample of the fuel they combust and determine their
emissions by multiplying these parameters by the quantity of fuel consumed. Facilities using default emission
factors use an emission factor supplied by the GHGRP that is a representative average emission factor based on
many samples of the fuel that have been taken across the country. For homogeneous fuels such as pipeline quality
natural gas, default emission factors often provide a very accurate emissions estimate.

~ Process emissions are determined by facilities using a variety of methods including a CEMS, a mass balance
approach, or site-specific or default emission factors. The methods specified in the rule vary by source category,
and are the methods determined to be most appropriate for that source. For example, facilities with a large share
of their emissions emanating from a single or small number of stacks (e.g., cement production) monitor and
determine their emissions differently than those with numerous small emissions sources spread over a large spatial
area (e.g., fugitive leaks from a natural gas distribution system). In cases where a facility has a CEMS-monitored
stack through which both combustion and process C02 are emitted, it may not be possible, based on GHGRP data,
to determine the allocation of combustion and process emissions.

The mass balance approach generally measures the carbon exiting the process through products and entering the process
through feedstocks, calculates the difference between these two values, and assumes that unaccounted for carbon is either
directly released or oxidized and released as C02 Site-specific emission factors for process emissions are determined either by
measuring the carbon content of feedstocks or by performing periodic (e.g., annual) stack tests. Default emission factors are
provided by the GHGRP and are based on the average emissions that occur per unit of consumption of raw material (e.g.,
limestone feedstock) or per unit of output (e.g., glass produced).

https://www.epa.gov/ghgreporting

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Suppliers

Suppliers of certain fossil fuels and industrial gases report the emissions that would occur if the products
that they place into the economy were fully released or oxidized. The emissions can be determined generally
using mass balance methods based on either default emission factors (based on quantities produced,
imported, or exported), reporter-specific emission factors derived from testing, or direct measurement of
carbon quantities (flow and concentration). Reporters are generally allowed to determine quantities of
product supplied by using standard industry practices for business transactions.

C02 Injection Facilities

Facilities that inject C02 underground for sequestration or other purposes are required to report the quantity
of C02 that they receive for injection. Reporters are allowed to determine the mass of C02 received for
injection by using standard industry practices for mass and volumetric flow calculations. Facilities that conduct
geologic sequestration are required to report information on the C02 received for injection and must develop
and implement an EPA-approved monitoring, reporting, and verification (MRV) plan for reporting the amount
of C02 geologically sequestered using a mass balance approach.

Best Available Monitoring Methods (BAMM)

When the rule first became into effect, facilities and suppliers had the option to use BAMM to determine
emissions from specific emissions sources for a limited amount of time. The use of BAMM was allowed
because it was not always feasible for a facility to acquire, install, and operate all of the required monitoring
equipment by the required date. EPA's BAMM provision provided time for facilities to install monitoring
equipment in a way that could minimize impacts to normal business operations. Over time, facilities are
expected to operate all monitoring equipment required by the GHGRP and determine emissions using the
methods specified by the GHGRP. Learn more about Best Available Monitoring Methods (BAMM).

https://www.epa.gov/ghgreporting

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