United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/036 Nov. 1985
Project Summary
Framework for Uncertainty
Analysis of the NAPAP
Emissions Inventory
Carmen Benkovitz
The objective of this project is to
develop a methodologies framework to
assess the uncertainties associated with
the emissions values as presented in the
National Acid Precipitation Assessment
Program (NAPAP) emissions inventory
and to implement a prototype computer
system to estimate the uncertainties
associated with the base NAPAP emis-
sions values. Previous projects that
addressed the assignment of quantita-
tive values to the uncertainties in emis-
sions data were reviewed, and a statis-
tical methodology was developed that
allows the computation of more accu-
rate uncertainty values. Auxiliary data
required to carry out the computations
were identified, and the prototype
computer system to implement the
calculations has been designed and is
being implemented.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park. NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The NAPAP emissions inventory was
based on the National Emissions Data
System (NEDS) currently operated by the
Office of Air Quality Planning and Stand-
ards (OAQPS) of EPA (National Air Data
Branch, 1983). NEDS provided the basic
data from which all other levels of aggre-
gation or disaggregation will be calcu-
lated. The basic NEDS data are statistical
averaged parameters which allow the
calculation of yearly emissions of the five
criteria pollutants (particulates, SO,, NO,,
hydrocarbons, and CO) on an individual
source/process basis for point sources
and on a county level for area sources.
Current plans call for the application of
spatial, temporal, and species disaggre-
gation algorithms which will be based on
disaggregation factors (or modifications
thereof) developed for the Northeast
Corridor Regional Modeling Project
(NECRMP). Higher levels of aggregation
will be calculated as sums of the NEDS
data.
Calculation of the uncertainty of the
emissions values will be based on the
statistical formulas expressing the vari-
ance of a function based on the expected
values and variances of the parameters
used to calculate the function. Application
of these techniques will start with the
algorithms used to calculate the yearly
emissions values and will be extended to
include currently known algorithms for
spatial and temporal aggregation and
spatial, temporal, and species disaggre-
gation, as applicable.
Theoretical Background
The statistical formulas to be used are
those expressing the variance of a func-
tion based on the expected values and the
variances of the parameters used to
calculate the function. For N independent
parameters and a function of the form x =
N
I UK, the variance is given by:
k=1
N
V(x)=I V(UK) (1)
k=1
N
For a function of the formx= n Uk, the
k=1
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variance is given by:
N
V(x)= TT {[EdJJP
N
- TT [E(U,)]*(2)
where E( } represents the expected value
and V( ) represents the variance of a
population. The sample mean and the
sample variance can be used as estima-
tors of the population expected value and
variance; equations (1) and (2) are exact
for these estimators as they are for the
population moments.
Review of Previous Work
Several previous projects have address-
ed the problem of assigning, in statistical
terms, quantitative values to the errors in
emissions data. Final reports from the
following projects were reviewed.
1. Weighted Sensitivity Analysis of
Emissions Data, project conducted
by IBM Corporation under contract
to the Office of Air Quality Planning
and Standards (OAQPS), EPA, July
1973.
2. Source Inventory and Emission
Factor Analysis (SIEFA) project
conducted by PEDCo - Environmen-
tal Specialists, Inc., under contract
to OAQPS, September 1974.
3. Emissions Inventory for the SURE
Region, project conducted by GCA
Corporation under contract to the
Electric Power Research Institute
(EPRI), April 1981.
4. Emissions, Costs and Engineering
Assessment, Work Group 3B, US-
Canada Memorandum of Intent
(MOI) on Transboundary Air Pollu-
tion, June 1982.
5. Preliminary Evaluation of Acidic
Deposition Assessment Uncertain-
ties, project conducted by Argonne
National Laboratory (ANL) under
contract to the U.S. Department of
Energy, November 1982 (prelimi-
nary report).
All these projects have based their
calculations on the statistical formulas
for error propagation as derived for
"small" values of the errors; i.e., the
Taylor series expansion included only the
first derivatives of the function. Some of
the error values used in subsequent
calculations have been as high as 80-
90% of the mean. For errors of this size,
the exact equations derived in this project
represent more accurate solutions.
Implementation of Prototype
Computer System
The final task of this project addresses
the design and implementation of the
basic framework of computer software
needed to calculate uncertainties associ-
ated with yearly emissions values for
both point and area sources. The con-
ceptual design is independent of the
software system used to support the
NAPAP inventory; the design and imple-
mentation of the software modules will
allow portability between computer sys-
tems and will be as independent as
possible of the current NAPAP inventory
software system. Figure 1 is a schematic
of this design.
Conclusion
Detailed quantification of the uncer-
tainties associated with emissions values
in the scale required by the NAPAP
researchers has never been attempted
before. In this project, methodologies
have been developed to allow quantifica-
tion of these uncertainties, and computer
software has been developed to perform
these calculations.
NAPAP Emissions
Inventory
Data Files
Uncertainty
Data File
Emissions Reports
—emissions values
—uncertainty values
Figure 1. Implementation based on the current NAPAP emissions inventory system.
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Carmen Benkovitz is with Brookhaven National Laboratory, Upton, NY 11973.
J. David Mobley is the EPA Project Officer (see below).
The complete report, entitled "Framework for Uncertainty Analysis of the NAPAP
Emissions Inventory," (Order No. PB 86-112 570/AS; Cost: $9.95, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/6
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