Emissions Estimation Methods
That Have Changed Since the Last Report

Year of Inventory

Pollutant

Category

Methodology Change

1990

CO, VOC, NO_x

Primarily nonutility point sources and 17 states worth of area sources

A combination of Ozone Transport Assessment Group ( OTAG), Grand Canyon Visibility Transport Commission Inventory ( GCVTC), and Aerometric Information Retrieval System ( AIRS) data was added to inventory, replacing some units but primarily just adding more units. (Ozone season daily data received was developed into annual data).

1990

PM₁₀, PM_2.5, SO₂

As above

State data received as above was augmented with PM and SO₂ data through an SO₂ and PM to NO_x uncontrolled emission factor ratio.

1991-1995

All but Pb

Primarily nonutility point sources and 17 states worth of area sources

NAPAP, AIRS data, GCVTC and Grand Canyon projections from the 1990 inventory using Bureau of Economic Analysis ( BEA) growth indicators.

1990

All but Pb

on-road mobile

1990, 1995, 1996 use state-supplied MOBILE model inputs where applicable. See Reference 1 for a list of States supplying model inputs.

1990

All but Pb

on-road mobile

Used state supplied vehicle miles traveled ( VMT) where applicable. See Reference 1 for a list of States providing VMT.

1985-1989

All but Pb

chemical and allied

Removed rule effectiveness from pre-1990 chemical and allied product emissions.

1985-1994

NO_x

utilities

Used NO_x emission rates from Acid Rain Division (ARD) instead of AP-42 emission factors.

1994-1998

NO_x, SO₂

utilities

Based Phase I units on CEM data from ARD, remaining units are from DOE767 survey data (small amount of units).

1996

All but Pb

nonutility point (35 states) and area sources (14 states)

Added state-supplied data directly received from states or retrieved from AIRS as part of the PEI inventory effort, as directed by the states.

5 State submittals were select cities only.

1997-1998

All but Pb

nonutility point and area sources

Projected through 1998 based on the 1996 PEI enhanced database using EGAS derived growth factors and BEA growth factors where applicable.

1970, 1975, 1980

All but Pb

non-road sources

Generated national-level nonroad emission estimates based on category-specific ratios of 1996 NONROAD model outputs to previous year national estimates.

1985-1998

All but Pb

non-road sources

Ran the beta version of the NONROAD model for all counties in U.S. for 1996. Used the NONROAD model to calculate national emissions for the other years and then used SCC-specific ratios for the other years relative to 1996 (year in question/1996) to determine county-level estimates.

1985-1998

All but Pb

non-road sources

For commercial marine diesel, EPA’s OTAQ provided revised national VOC, NO_x, CO, and PM emission estimates for commercial marine diesel engines. National estimates were distributed to counties using the geographic distribution in the existing NET.

1990-1998

All but Pb

Miscellaneous -agric. forestry

Revised allocation of Census of Agriculture activity data between the 1990 and 1997 census: used agricultural surrogates instead of economic surrogates.

1990-1998

PM

Miscellaneous -agric. crops

Began using tillage activity data using the Conservation Technology Information Center, Purdue University, data, and also changed silt value methodology from 1990 onward.

1989-1998

PM

Miscellaneous -managed burning

Based on USDA Forest Service inventory of PM from prescribed burning. Public percentage of acres burned projected from 1990 using national-level growth factor developed from total U.S. acres burned, while private portion held constant.

1990-1998

PM

Miscellaneous -construction

Changed the emission factor in 1990: changed from using a former AP-42 value to using latest AP-42 findings report: "Improvement of Specific Emission Factors" - change occurred in Trends year 1997.

1990-1998

PM

paved roads

The rain correction factor in the paved road equation was reduced by 50 percent for the years 1990 onward due to uncertainty associated with the actual reduction in emissions due to precipitation on paved road surfaces.

1990-1998

All but Pb

structural fires

For non-OTAG States, revised 1990 and 1996 emissions based on new loading factor value. Projected all States using EGAS regression equations, which relate State-level population to the amount of material burned in structure fires.