United States Air and Energy Engineering

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

E AP Project Summary

Comparison of the 1985 NAPAP

Emissions Inventory with the

1985 EPA Trends Estimate for

Industrial SO2

 Sources

Research and Development EPA/600/SR-94/012 March 1994

Section 406 of the 1990 Clean Air Act

Amendments (CAAA) requires that the

Administrator of the Environmental Protection Agency (EPA) transmit a report

to Congress containing a national inventory of annual sulfur dioxide (SO2)

emissions from industrial sources, as

well as emission projections for the

next 20 years, not later than 1995. The

requirement stems from the 5.6 million

ton emissions cap on SO2

 from industrial sources that is contained in Title

IV of the CAAA and based on estimated 1985 emissions from the National

Acid Precipitation Assessment Program

(NAPAP). This report presents analyses of 1985 industrial SO2

 emissions

from two available data sources: the

NAPAP inventory and the EPA Trends

report. These analyses conclude that

the two data sources estimate comparable emissions in the aggregate, but

estimates for specific categories and

for processes within those categories

vary widely. The Trends method is

limited to source categories that emit

10,000 tonnes per year of SO2. In general, the Trends method overestimates

emissions from these source categories due primarily to the absence of

SO2

 control efficiency assumptions.

Overestimation of emissions in the

Trends data set is offset by the inclusion of additional source categories in

the NAPAP inventory with the final aggregate estimates within less than 10%

of each other. (NOTE: Trends methodology is being changed for 1993, using

the 1985 NAPAP emissions inventory

as a base.)

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

documented in a separate report of the

same title (see Project Report ordering

information at back).

Introduction

Section 406 of the 1990 Clean Air Act

Amendments (CAAA) requires that the

Administrator of the Environmental Protection Agency (EPA) transmit a report to

Congress containing “a national inventory

of annual sulfur dioxide emissions from

industrial sources not later than January

1, 1995 for all years for which data are

available, as well as the likely trend in

SO2

 emissions over the following twenty

year period (1995 to 2015).” The CAAA

also establishes an emissions cap of 5.6

million tons per year from industrial

sources; this annual cap is equivalent to

the 1985 industrial SO2 estimate from the

National Acid Precipitation Assessment

Program (NAPAP) inventory. To provide

the analysis mandated by Congress, the

1985 baseline data must first be examined to identify strengths and weaknesses

in the available emission and supporting

data. The purpose of the overall study

was to understand the similarity and differences between existing data sets and

determine which data are suitable to serve

as a baseline for the SO2

 emission projections. This paper presents the initial analysis of two major sources of industrial data

currently available: the 1985 NAPAP emission inventory and the 1985 national emisDavid Zimmerman and Rebecca Battye
2

sion estimates, referred to as the Trends

emission estimates.

Overview of the Data Sets

The 1985 NAPAP emission inventory

effort supported acid deposition research,

including atmospheric modeling, through

comprehensive, detailed source emission

estimates provided by local and state

agencies. It is a bottom-up inventory and

a 1985 snapshot. The SO2

 emission data

for significant (>100 tons per year) sources

were systematically quality assured, with

greater effort expended on larger sources.

The inventory included a unique confirmation step, allowing individual plants emitting at least 2500 tons per year to review

their emission estimates prior to finalization.

Prior to 1993, EPA prepared an annual

emissions Trends report representing both

current and historic emissions (1940 to

present). Industrial emission estimates

were derived from national, published activity data and standard, process-level

emission factors; historic estimates were

altered based on the most recent activity

data and emission factors to better represent the most current understanding of

emission processes. For the industrial

sector, activity data were obtained primarily from the Department of Energy, Energy Information Administration; the Department of the Interior, Bureau of Mines;

and the Department of Commerce, Bureau of Census. It is essentially a topdown approach designed to follow category emissions through time and not a

true inventory. It presents a consistently

derived national emission estimate at the

emission category level (e.g., industrial oil

combustion) rather than the source (e.g.,

boiler) level.

Due to findings discussed here, as well

as other factors, the Trends methodology

has been revised as of 1993. References

to Trends in this paper will no longer be

valid for years 1985 and beyond, effective

with the 1993 edition of the Trends report.

The reader is cautioned that comments

herein on the Trends report are valid only

for editions prior to 1993.

Methodology

The 1985 NAPAP and Trends industrial

emission estimates were directly compared. The 1985 NAPAP-published emission estimates as well as the annual U.S.

point source file were used as the basis

for the analysis. The 1992 report National

Air Pollutant Emission Estimates, 1900-

1991, and the background procedures

(Procedures Document for the Development of National, Regional and Preliminary Air Pollutant Emissions Trends Report) formed the basis of the analysis of

the published Trends estimates. (Note

that the Trends estimates are updated

annually; the Trends procedures themselves have also been revised in 1993.

This analysis uses the Trends procedures

used through 1992, but does not include

the new Trends procedures that will be

reflected in the forthcoming 1993 report.)

This study of industrial SO2

 emissions verified emission estimates and activity (i.e.,

throughput) where possible based on the

original source materials.

The comparison of NAPAP and Trends

analyzed the derivation of individual industrial category estimates. Such analyses were complicated by several factors:

• NAPAP is comprehensive and includes all reported industrial emission

categories; Trends is limited to categories thought to emit at least 10,000

tonness SO2 (uncontrolled) annually.

• NAPAP is source and plant specific;

Trends is national and category specific. No opportunity exists to match

individual data values between the

inventories; in fact, category definitions differ between the two inventories.

• The 1985 NAPAP inventory is a

single-year inventory and is not updated; Trends adjusts historical emission estimates based on the most

current information.

Results of the Comparison

This research led to a highly detailed

view of the two sets of emission estimates

on a category basis, principally relying on

emission and activity (throughput) data.

The authors attempted to reproduce the

1985 Trends emissions estimates and

noted any irregularities between the calculated and published data. The analyses proved complex, especially when disaggregating data to create comparable

categories between NAPAP and Trends

data sets, and raised a number of questions.

Table 1 summarizes the differences between the NAPAP and Trends estimates.

Overall, the two 1985 estimates (NAPAP

and Trends) compare favorably: NAPAP

estimates 5.6 million tons SO2 (as reflected

in the CAAA), and Trends estimates 6.0

million tons. However, Table 1 shows

distinct variability in the category-level estimates between the two data sets. The

major industrial SO2

 emission producing

categories, industrial combustion, non-ferrous metals, iron and steel, petroleum refineries, oil and natural gas production,

pulp and paper, and cement manufacturing are discussed in detail in the report.

Summary

As these two data sets are reviewed

and compared, the genesis and purpose

of each methodology must be considered.

The 1985 NAPAP inventory was a comprehensive emissions inventory designed

to reflect actual conditions in 1985, with

great emphasis on the gathering and quality assurance of the emission estimate at

the plant and process level. It was assembled mainly at the state and local level

by professionals familiar with the individual

sources and with significant review by the

major sources. The Trends methodology

was designed to provide a longitudinal

view of the direction and probable magnitude of emission changes. It was assembled from standard emission factors

and national activity data in most cases

and was not intended to reflect actual

conditions for individual plants or source

types at any given time. A de minimus

level of 10,000 tonnes SO2 (uncontrolled)

was established for inclusion of a source

category, so Trends is not intended to be

comprehensive. The Trends methodology reviewed and presented here is currently in transition; subsequent Trends reports will reflect a fundamental shift in the

estimation approach.

The two 1985 estimates, Trends and

NAPAP, provide reasonable agreement,

within less than 10%, when viewed as an

aggregate industrial SO2

 estimate. There

is greater divergence when the data sets

are compared at the category and subcategory levels. Because the data sets were

developed from different data sources and

with different purposes, disagreement at

disaggregated category levels primarily

reflects the inherent differences in the

methodologies.

The overall agreement appears to be

due to a balance between Trends overestimates where subcategories overlap between Trends and NAPAP and the inclusion of more categories and more individual emission points in NAPAP. The

systematic Trends overestimate, relative

to the NAPAP inventory, is due in part to

the absence of SO2

 control efficiency estimates in the methodologies. SO2

 control

technologies have been applied to most

of the large industrial SO2 categories

through the promulgation of New Source

Performance Standards (NSPS), issuance

of operating permits, and New Source
3

Review Permits. The strengths and weaknesses revealed in this review are presented below.

NAPAP Data Set

• The 1985 NAPAP inventory still represents the most comprehensive and

accurate emissions estimates for 1985

because of its rigorous quality assurance of emissions and bottom-up nature. The inventory accounts for individual source operating characteristics, controls and emission factors.

• Activity data in the 1985 NAPAP inventory were not subject to the same

standard of quality assurance or completeness. Some data were unreported due to confidentiality restrictions, and activity data for small

sources (i.e., <100 tons per year)

passed only the grossest quality assurance checks. There are known

reporting problems among miscellaneous fuels and other categories. The

accuracy and representativeness of

activity data in the NAPAP inventory

are best evaluated source by source;

category-level summaries are unreliable without adjustments.

• It is still possible to locate questionable data values in the 1985 NAPAP

emission inventory when examined on

a source by source basis, especially

for smaller emitters.

Trends Data Set

• Some industrial emission categories,

notably iron and steel foundries, are

missing from the Trends method. As

such, the inventory is not comprehensive, although few major gaps

were found under close scrutiny.

• As a top-down approach, broad assumptions of emission factors and

controls are used across a category.

Frequently, estimates make no adjustment for controls. Accommodating individual source operating characteristics, including emission factors,

is impossible.

• The underlying industrial activity data

are largely reliable and probably far

superior to the corresponding NAPAP

estimates at the category level. Any

method for 1995 and beyond should

take advantage of these independent

data sources.

• Based on the Trends documentation,

the actual Trends execution contains

minor to moderate errors in calculaTable 1. Magnitude Differences Between 1985 Trends and NAPAP SO2

 Emission Estimates

Trends NAPAP Delta Delta

Source Category a (tons) (tons) (tons) (percent)

Coal b 1,840,000 1,721,000 119,000 6.9

Oil c 540,000 713,000 -173,000 -24.3

Natural Gas d 0 33,000 -33,000 -100.0

Wood 10,000 42,000 -32,000 -76.2

Miscellaneous Fuel 80,000 14,000 66,000 471.4

Other Fuel Combustion Emissions

Reported through NAPAP 74,000 -74,000 -100.0

1° Copper 650,000 655,000 -5,000 -0.8

1° Lead and Zinc 240,000 106,000 134,000 126.4

2° Lead 30,000 21,000 9,000 42.9

1° Aluminum 70,000 58,000 12,000 20.7

Other Primary and Secondary

Metals Emissions Reported through NAPAP 42,000 -42,000 -100.0

Iron and Steel 360,000 204,000 156,000 76.5

Iron and Steel Foundries 16,000 -16,000 -100.0

Oil and Natural Gas Production 160,000 332,00 -172,000 -51.8

Pulp and Paper 250,000 130,000 120,000 92.3

Cement 620,000 291,000 329,000 113.1

Glass 30,000 23,000 7,000 30.4

Lime 30,000 32,000 -2,000 -6.3

Sulfuric Acid 210,000 217,000 -7,000 -3.2

Carbon Black 10,000 28,000 -18,000 -64.3

Petroleum Refineries 830,000 640,000 190,000 29.7

Other Industrial Process Emissions

Reported through NAPAP 220,000 -220,000 -100.0

Total 5,960,000 5,612,000 348,000 6.2

a Except where noted, the emissions for a source category represent process level emissions only and do not include emissions from the combustion of fuel. b Excludes bitumnous coal and lignite consumed at cement and lime manufacturing facilities. c Excludes both distillate and residual oil consumed at cement plants and petroleum refineries and residual oil consumed at iron and steel mills. d Excludes natural gas consumed in cement manufacturing, petroleum refining, the iron and steel industry, glass manufacture, and at crude petroleum and natural gas production

facilities
4

tion of activity and emissions. Trends

could also benefit from recently revised standard emission factors and

updated sources of activity data.

Conclusion

The 1985 NAPAP SO2 emission estimates remain the most reliable emission

estimate baseline because that was one

of the intentions of the inventory effort.

Reliable emission projections of the 1985

data, especially to 1995 and beyond, are

difficult because the activity data in the

NAPAP inventory are incomplete due, in

part, to confidentiality and other restrictions. Because it is a 1985 inventory,

emission factors and activity data do not

reflect current or future operations for these

source categories.

The Trends methodology reflected in

this review is poorly suited to provide a

baseline estimate for industrial emissions,

fundamentally due to its design and primary objectives. Its strengths lie in the

identification and use of the underlying

industrial activity data which would provide a firm foundation for year-to-year projection of specific industrial activities and

their baseline emissions.

Results using the new Trends method

could not be reviewed in the scope of this

research. Due to findings discussed here,

as well as other factors, the Trends methodology has been revised as of 1993.

References to Trends in this paper will no

longer be valid for years 1985 and beyond, effective with the 1993 edition of

the Trends report. The reader is cautioned that comments herein on the Trends

report are valid only for editions prior to

1993.

Several additional sources of data that

may provide more recent data and fill data

gaps for an analysis of industrial SO2 emissions were identified: Information Collection Requests obtained in support of the

Maximum Achievable Control Technology

(MACT) standards developed under Title

III of the CAAA, SO2

 state implementation

plan (SIP) inventories, and ozone/carbon

monoxide SIP inventories. Of these, the

MACT data are the most promising because many of the significant industrial

SO2 source categories are under MACT

development; the data collected from the

sources have been targeted for and will

therefore be accessible from the

Aerometric Information Retrieval System;

and major sources, production data, and

control equipment information can be identified from the data collected.

Finally, the 1985 NAPAP data were analyzed to determine whether individual

source tracking would be a feasible option

to improve the reliability of the emission

estimates and the projections through time.

Such an option would improve and update the baseline estimate and provide

current information on processes and control equipment. It could also be used with

the industrial activity data available from a

variety of sources to project the remainder of the inventory. Figure 1 shows that

relatively few sources (about 130) account

for approximately 50% of the total industrial SO2 emissions. To capture 80% of

the SO2

 emissions, approximately 500

sources would need to be inventoried.

5,000,000

4,000,000

3,000,000

23,000,00

13,000,00

0

1,000 2,000 3,000 4,000

Cumulative SO2 emissions (tons)

# of plants

Figure 1. Cumulative sulfur dioxide emissions in the 1985 NAPAP inventory versus number of plants.
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D. Zimmerman and R. Battye are with EC/R, Inc., University Tower, Suite 404, 3101

Petty Road., Durham, NC 27707.

Charles C. Masser is the EPA Project Officer (see below).

The complete report, entitled "Comparison of the 1985 NAPAP Emissions Inventory

with the 1985 EPA Trends Estimate for Industrial SO2

 Sources," (Order No.

PB94-152220/AS; Cost: $36.50, subject to change) will be available only from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

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

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