Use of Models and Facility-Level Data in Greenhouse Gas Inventories

Use of Models and Facility-Level Data in Greenhouse Gas Inventories
• For source categories with thresholds, a large fraction of the industry may not be subject to reporting. One goal
of the GHGRP, after all, was to maximize emissions coverage while minimizing the number of reporters to the
program. EPA will need to consider how representative reported data are of national practices? For some
industries the fact that only large industries are reporting may not be relevant, as the same practices, fuels, etc.,
may be used at smaller facilities as well. For other industries, the larger facilities subject to the rule may have
vastly different practices and some data obtained from them may not be sufficient for applying to the smaller
sources.
The availability of plant-level data could address or partially address many of the current challenges associated with
Inventory development. Overall, the GHGRP will help improve the national Inventory by:
• Directly provide the combustion and process-related emissions for some source categories (e.g. ammonia,
cement, aluminum) on an annual basis.
• Allowing the United States to better disaggregate national emissions by industry; disaggregate the current
stationary combustion estimates by manufacturing sector per reporting guidelines (e.g., iron and steel, nonferrous
metals, chemicals, etc.).
• Ensuring that the underlying data for certain source categories are gathered following very specific
methodologies; methodologies that can subsequently be readily reviewed by review teams.
• Enabling the Inventory Agency to develop a relationship with the facilities directly, as opposed to relying on a
third party national statistics organization.
• Reducing reliance on default emission factors; develop country-specific (or even more refined) emission factors.
• Providing substantial supporting information in addition to the GHG emissions data that will enable us to verify
emissions reported.
• Gather underlying data that can help affirm, or bring into question, previous assumptions used in the Inventory.
• Provide an additional data source to conduct quality assurance/quality control checks.
• Refine the uncertainty analysis by allowing us to rely more on data and less on expert judgment.
Nevertheless, we can already anticipate a number of challenges with incorporating reported GHG emissions information
into the national inventory. Some key challenges anticipated include:
• Time Series Consistency. Ensuring time series consistency will be a key issue for all source categories,
although some will be more difficult than others (e.g., combustion-related emissions information received from
facilities using CEMS, petroleum and natural gas systems). Will have to assess source category by source
category whether Tier 3 data obtained through the GHGRP is applicable for earlier years. This may be the
case where there is minimal penetration of technologies and minimal fuel variability over time.
• Comparability. As discussed above, there are only so many ways to quantify emissions from various source
categories. Although the uncertainty bands around emissions estimates will narrow as the United States and
other countries start implementing higher-tiered and country-specific methods, determining comparability may
become more challenging as it may be difficult for inventory reviewers to assess the comparability of methods.
• Transparency. There is still uncertainty over how much of the data will be required to be held confidential. EPA
is currently undertaking a rulemaking to determine how the data will be handled. Our goal is to make as much
available as possible, thereby facilitating transparent review of the data. Nevertheless, some data will inevitably
be held as confidential. The extent to which this affects transparency is yet to be determined. In addition,
some methods employed by facilities within a given source category may actually result in less verification data
reported to EPA, which in turn could introduce challenges with ensuring transparent data presented in the
Inventory.
Conclusions
The United States has an unprecedented opportunity to collect more comprehensive GHG emissions information as a
result of the first annual GHG reports submitted by facilities in 2011 under the Greenhouse Gas Reporting Program.
One can only imagine all of the ultimate uses of the data generated through this program (e.g., project, corporate,
IPCC Expert Meeting Report 116 TFI