United States
 Environmental Protection
 Agency
 Research and Development
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
EPA/600/SR-92/001 Feb. 1992
  Project Summary
 Documentation  of AIRS AMS
 National  Methodologies
 E. Sue Kimbrough
   The report provides, to states and
 other participants (e.g., Regional  Of-
 fices, Headquarters, other federal agen-
 cies) and users of the Area and Mobile
 Source Subsystem (AMS), an under-
 standing of the estimation procedures
 that will be used by the national compo-
 nent of AMS to generate emissions esti-
 mates for area  and mobile source
 categories. It discusses general meth-
 odology and assumptions as well as
 the original source of algorithms, activ-
 ity levels, and emission factors neces-
 sary to calculate emissions  for each
 area and mobile  source in AMS. The
 report presents methodologies for all
 identified sources not defined as point
 sources. Area and mobile sources are
 divided into seven major groups: sta-
 tionary source fuel combustion, mobile
 sources, industrial processes, solvent
 utilization, solid waste disposal, natural
 sources, and miscellaneous area
 sources. Historically, these methodolo-
 gies have been referred to as the Na-
 tional Emissions Data System (NEDS)
 methods and to some extent are docu-
 mented in area source documentation
 for the 1985 National Acid Precipitation
 Assessment Program (NAPAP) inven-
 tory; however, the NAPAP documenta-
 tion does not include certain initial data
 calculations. In addition, over the years
 numerous changes have occurred to
the sources of the data that "feed" these
 methodologies. These initial data cal-
culations and source data changes are
 included in the report.
   This Project Summary was devel-
 oped by EPA's Air and Energy Engi-
 neering Research Laboratory, Research
 Triangle Park, NC, to announce key find-
 ings of the research project that is fully
 documented in a separate report of the
 same title (see Project Report ordering
 information at back).

 Introduction
   The U.S. Environmental Protection
 Agency's (EPA's) Office of Air Quality Plan-
 ning and Standards (OAQPS) in Research
 Triangle Park, NC, is in the process of
 developing a nationwide database of esti-
 mated air pollutant emissions from area
 and mobile  sources known as the
 Aerometric Information Retrieval System
 (AIRS) Area and Mobile Source Subsystem
 (AMS).
   The purpose of this document is to
 provide states and other participants and
 users of AMS (e.g., Regional Offices, Head-
 quarters, other federal agencies) with an
 understanding of the estimation procedures
 that will be used by AMS to generate emis-
 sions estimates for area and mobile source
 categories. General methodology and as-
 sumptions are discussed as well as the
 original source of algorithms, activity lev-
 els, and emission factors necessary to cal-
 culate emissions for each area and mobile
 source in AMS.
   The document presents methodologies
 for all identified sources not defined as
 point sources in a specific geographic re-
 gion. Area sources include all mobile
 sources, and stationary sources too small,
difficult, or numerous to classify as point
sources. Area and mobile sources are di-
vided into seven major groups: stationary
                                                 Printed on Recycled Paper

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source fuel combustion, mobile sources,
Industrial processes,  solvent  utilization,
solid waste disposal, natural sources, and
miscellaneous area sources.
   Activity levels are derived primarily from
related information published by other fed-
eral  agencies, supplemented by special
data developed by EPA for the purpose of
developing AMS emission inventories. Pub-
lished  data  such as  fuel use by  state,
motor vehicle miles of travel by state and
county, and forest fire acres burned by
state are used with related data such as
employment, population, and  miscella-
neous  geographic or economic data to
derive  annual county estimates of the ac-
tivity levels for each of the National Emis-
sions Data System (NEDS)  area source
categories. The activity levels derived are
adjusted to account for point source activ-
ity (such as  fuel use by point sources) so
that  the area source  data reflect only the
activity levels (and  resulting  calculated
emissions) that are not  accounted for by
point sources.  The source of this  point
source data is the AIRS Facility Subsystem
(FS). Point source emissions data are sub-
mitted annually by each state to EPA for
Inclusion in the AIRS FS.
   Area and mobile source emissions es-
timates for  seven pollutants—particulate
matter >10  u.m (PM,0). total suspended
particulate matter (TSP), sulfur  dioxide
(SOj), nitrogen oxides (NO,), reactive vola-
tile organic  compounds  (VOCs), carbon
monoxide (CO), and lead (PB)—are calcu-
lated for each area  and mobile source
category utilizing appropriate emission fac-
tors which are contained in the AMS emis-
sion factor file. For many categories, the
same  emission factors are used  for all
counties; however, for some source cat-
egories, state or county specific emission
factors account for local variables that af-
fect emissions. The  more specific  emis-
sion factors are used in AMS calculations
for alJ highway motor vehicle  categories,
fugitive dust categories, and selected other
categories in a few  counties where data
are  available to develop more applicable
emission factors than the national  emis-
sion factors.
    Emissions estimates are updated an-
nually by AMS which first estimates activity
levels for each county and then applies the
appropriate emission factor and any appli-
cable  control efficiency. County emissions
estimates are then summed to produce
 national emissions estimates.

 Background
    Historically, NEDS has been the com-
 puter  system that the U.S. EPA has used
to calculate, store, and retrieve area and
mobile source emissions for the following
criteria pollutants: TSP, SO2, NOX, VOCs,
and CO. EPA is in the process of design-
ing and developing a new data subsystem
in the AIRS called  the AMS,  which  will
replace NEDS.
   AMS will use state-of-the-art database
management software with  user-friendly
menus and screens. The  goals  of AMS
are:  1) provide storage and reporting ca-
pabilities for area and mobile source emis-
sions and  related data required  by EPA
regulations and the Clean Air Act;  2) re-
place the existing system used  to store
and  report these data with a state-of-the-
art system; 3) promote information sharing
among EPA offices and state and local air
agencies; 4) provide the ability to interact
with  other EPA databases; and 5) provide
enhanced data processing services to the
EPA and state and local user community.
   With  passage of  the  Clean  Air  Act
Amendments (CAAA) of 1990  in  Novem-
ber 1990, a data  system that tracks area
and mobile source emissions inventory data
became critical to the needs of the Agency.
In particular, an area and mobile source
data system will be  needed to  support
implementation of Title I of the CAAA. This
takes the form of 1) storing area  and  mo-
bile source emissions data as reported by
state and local air agencies; and 2) devel-
oping comprehensive capabilities to sup-
port CAAA regulatory reporting,  tracking,
and  analytical requirements.
   Emissions inventory data reported to
AMS by state and local air agencies in
support of Title  I of the CAAA involve
reporting emissions inventory data for non-
attainment areas only. AMS, in addition to
supporting Title I requirements, will include
a national component that will include emis-
sions inventory data that may be used for
regional modeling. Since regional models
require data for both non-attainment and
attainment areas and generally require con-
sistent emission estimation methodologies
throughout the  modeling domain, this na-
tional component will generate  emission
estimates using a consistent methodology
for area and mobile source categories for
all areas of the U.S.—non-attainment and
attainment areas.
    In order to accommodate the need to
support Title I activities and regional mod-
eling needs, a  basic design decision has
been made to develop AMS  using what
 may be described as a "parallel approach."
The definition of  parallel approach is that
 EPA would prepare area and  mobile source
 data for all counties in the U.S. Any state
 data submitted would reside in  "parallel"
 with the EPA prepared data. As a result of
this parallel approach, AMS  will consist of
two components—a national  component
and a state component.
   Ideally, a more integrated or hybrid ap-
proach would be better. (In the hybrid ap-
proach, EPA  would prepare  area and
mobile source data for all counties  in the
U.S. Any state data submitted would re-
place EPA prepared data for source cat-
egories in  those counties.)  However,
implementation of the hybrid approach will
not be attempted in the base system until:
1) better methodologies are available from
emission inventory research projects cur-
rently underway and the states become
familiar with an AMS system, and 2) a
plug-in methodology capability is fully in-
troduced. The emission estimation proce-
dures described below will be 'used within
the national component of AMS.
   Historically, these methodologies have
been referred to  as the NEDS methods
and  are described in area  source  docu-
mentation for the  1985 National Acid Pre-
cipitation Assessment Program (NAPAP)
inventory. Much of the narrative from  that
documentation has been used in the prepa-
ration of this report, since the basic con-
cepts for the estimation of the emissions
have remained comparable to the meth-
ods  described in  earlier documents. Cur-
rently, a number of  emissions inventory
research projects are underway and should
provide improved emission estimation pro-
cedures. When these new procedures are
available, they will be implemented in AMS.

Stationary  Source Fuel
Combustion
   Stationary source fuel combustion which
contributes to area source emissions has
been divided into three  major categories:
Residential Fuel, Commercial and Institu-
tional  Fuel, and  Industrial Fuel.  Collec-
tively, these  categories account  for all
stationary fuel combustion activity not usu-
ally  reported as point sources. Each cat-
egory is further subdivided into the following
fuel types: anthracite coal, bituminous coal,
distillate oil, residual oil, natural gas, lique-
fied petroleum gas (LPG), wood, industrial
coke, and process gas. Methodologies for
 activity level estimation and emission fac-
tor derivation  are discussed for each cat-
 egory and fuel type.
    In the following methodologies  for the
calculation of activity levels, consumption
 is determined for each type of fuel using
two general steps:
  1)   County  consumption is calculated
      using an algorithm which is based on
      significant variables for which county-
      specific data are available (e.g., de-
      gree days, number  or rooms per
      dwelling, number of dwellings).

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  2)  Resulting county consumption esti-
      mates are normalized to reflect pub-
      lished state consumption data by the
      equation:

    NCC = ECC
                ESC
  where:
      NCC  =  Normalized  county con-
               sumption
      ECC  =  Estimated county con-
               sumption
      PSC  =  Published state consump-
               tion
      ESC  =  Estimated  state  con-
               sumption (summation of
               estimated county con-
               sumption)

 Residential Fuel
    The residential fuel category estimates
 emissions for residential  activities which
 utilize fuel for water heating, space heat-
 ing, and  cooking. Emissions contributed
 by residential fuel consumption are broken
 down into six categories according to fuel
 type: anthracite coal, bituminous coal, dis-
 tillate  oil, natural gas, LPG, and  wood.
 Emissions from the residential residual oil
 consumption category are considered to
 be negligible; therefore,  no  methodology
 exists for this category. For each listed fuel
 type, activity levels measured by fuel quan-
 tity consumed in weight  or volume units
 are multiplied by emission factors to obtain
 emissions estimates. Methodologies  for
 activity levels and  emission factors  are
 discussed in turn.

 Commercial and Institutional
   Area source emissions from fuel use
 by commercial and institutional sources
 consist of emissions from all fuel burned in
 stationary sources that are  not included
 under  residential  sources,  industrial
 sources, power plants, or commercial point
 sources. Examples  of commercial/institu-
 tional area sources are hospitals, hotels,
 laundries, schools, and universities. Fuel
 types included in the discussion of activity
 levels and emission factors are anthracite
 coal, bituminous coal, distillate oil, residual
 oil, natural gas, LPG, and wood.
   Activity levels are estimated for anthra-
 cite coal, bituminous coal, distillate oil,  re-
 sidual oil, natural gas, and LPG. Currently,
 AMS does not employ a methodology to
 estimate wood  consumption at commer-
 cial/institutional sources.  Emissions from
 this source are considered negligible com-
 pared to those from  other sources.

 Industrial
   Area source  emissions generated  by
the industrial fuel consumption sector which
 are not accounted for by point source cat-
 egories are discussed for the following fuel
 types: anthracite coal, bituminous coal, dis-
 tillate oil, residual oil,  natural  gas,  LPG,
 wood, and process gas. Methodologies for
 consumption and emission factor compu-
 tation are presented as available.
   A procedure  was developed for the
 allocation of state industrial area source
 consumption of bituminous coal, distillate
 oil, residual oil, natural gas, and LPG. The
 procedure for estimating industrial bitumi-
 nous coal area source consumption has
 been adjusted and applied to  estimating
 industrial anthracite coal area source con-
 sumption. Originally, the procedure for in-
 dustrial natural gas consumption called for
 the inclusion of industrial LPG consump-
 tion. LPG will now  be estimated sepa-
 rately. In addition, industrial natural gas
 consumption by boilers and internal com-
 bustion (1C) engines will be estimated sepa-
 rately.
   Procedures for estimating coke, wood,
 and  process gas  activity levels have not
 been developed.  Industrial area  source
 consumption of these fuels is assumed to
 be negligible.

 Mobile Sources
   Mobile sources which contribute to area
 source emissions  are divided into five ma-
jor categories: Highway Vehicles, Off-High-
way  Vehicles, Railroad  Locomotives,
Aircraft, and Marine Vessels. For each of
the above categories, methodologies for
activity level and  emission factor estima-
tion are discussed.

 Highway Vehicles
   AMS disaggregates motor vehicles into
eight EPA vehicle  categories on the basis
of use and gross vehicle weight for the
purpose of calculating emissions:
     Light Duty
     Gasoline Vehicles       LDGV
     Light Duty Gasoline
     Trucks -1              LDGT1
     Light Duty Gasoline
     Trucks - 2              LDGT2
     Heavy Duty
     Gasoline Vehicles       HDGV
     Motorcycles             MC
     Light Duty
     Diesel Vehicles          LDDV
     Light Duty
     Diesel Trucks          LDDT
 •   Heavy Duty
     Diesel Vehicles         HDDV
    LDGVs are defined as gasoline pow-
 ered passenger  vehicles weighing 8500
 Ib* or less. LDGT1 s include gasoline cargo
 vehicles weighing 6000 Ib or less. LDGT2s
 include gasoline  cargo vehicles weighing
 between  6001 and 8500 Ib. Heavy duty
 vehicle categories separate diesel  and
 gasoline powered trucks and buses weigh-
 ing more than 8500 Ib. MCs are defined as
 any motor vehicles designed to travel with
 not more than three wheels in contact with
 the ground, and weighing less than 1,500
 Ib. LDDVs are defined as diesel powered
 passenger vehicles weighing 8500 Ib or
 less. LDDTs include diesel cargo vehicles
 weighing 8500 Ib or less.
    While vehicle miles travelled (VMT) are
 determined for each vehicle class and road
 class, fuel consumption is determined only
 for each vehicle class.  Emission factors in
 grams per mile obtained from the execu-
 tion of the MOBILE model are applied so
 as to determine emissions for vehicle type
 and speed class. VMT is determined for
 the following road classes:
 Assumed
 Speed,
 mph**
 55
 55
 55

 55

 55

 55
 55


 45
 45
 45


 19.6
 19.6
    Road Class


Urban Interstate
Rural Interstate
Urban Other Freeways and
    Expressways
Urban Other Principal
    Arterials
Rural Other Principal
    Arterials
Urban Minor Arterials
Rural Minor Arterials


Rural Major Collector
Rural Minor Collector
Rural Local


Urban Collector
Urban Local
Off-Highway Vehicles
   Emissions from off-highway vehicles are
generated by activities  of  gasoline and
diesel vehicles which  do not utilize  road
systems. Vehicles contributing to off-high-
way emissions are divided into six general
                                           1 !b = 0.454 kg
                                           1 mph = 1.609km/h

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categories: farm equipment, construction
equipment, industrial equipment, lawn and
garden equipment, motorcycles, and snow-
mobiles. While gasoline is consumed by all
sbc categories, diesel fuel is utilized only by
farm equipment, construction equipment,
and industrial equipment.
   In general, consumption is estimated
by one of the following methods:
 1)  Apportionment of national fuel con-
     sumption to counties on the basis of
     employment, population, etc.
 2)  Calculation of county  or state totals
     by applying fuel consumption rates
     to average usage figures and equip-
     ment populations.
   Consumption estimation  methodologies
are described for each category by fuel
type.

Aircraft
   Emissions  estimates for aircraft are di-
vided into  three  categories:  commercial,
military, and civil. Activity levels and emis-
sion factors, measured relative to units of
aircraft landing and takeoff cycles (LTOs)
by county, are multiplied  by emission fac-
tors to obtain emissions estimates.
   Activity level is measured  by LTOs us-
ing either operation records  from  county
airports or aircraft  registration data,  de-
pending on the location of Federal Aviation
Administration (FAA) airports. For these
calculations, an operation,  as defined by
the FAA, consists of either a takeoff or a
landing.
   Weighted average emission factors are
computed for each type  of aircraft within
each aviation category.  In some catego-
ries, flying hours are used as a  unit of
measure assuming  that the number of fly-
ing hours are  proportional to  LTOs. Emis-
sion  factors  are then combined  using
aircraft type population data from Jane's
and FAA Aviation Forecasts to form  one
factor for each pollutant.

Marine Vessels
    Marine vessel  categories for  which
emissions estimates are discussed include
coal vessels, distillate oil vessels, residual
oil vessels, and gasoline  vessels. Final
estimates are measured  in gallons of fuel
consumed. Emissions from  coal vessels
have not been estimated because emis-
sions from this source are considered neg-
ligible compared to other  area sources.
Consumption  methodologies and emission
factor derivation are presented for each
category.

 Railroad Locomotives
    This category includes  fuel utilized by
railroad locomotives and fuel used by rail-
road stations and workshops for space
heating. The latter fuel consumption has
been included primarily because it is diffi-
cult to separate from total railroad fuel use
and  is considered insignificant compared
to locomotive consumption.  The primary
fuel consumed by railroad locomotives is
distillate oil (diesel fuel). The activity  level,
measured in thousands of gallons, is multi-
plied by emission factors to produce emis-
sions estimates.
   The methodology used to estimate dis-
tillate oil consumption involves the alloca-
tion  of published state  consumption  of
distillate oil by railroad locomotives to the
county level on the basis of current popu-
lation distribution.

Gasoline Marketing Operations
   This source category  covers evapora-
tive losses of VOCs from gasoline market-
ing operations such as filling losses from
loading underground storage tanks at ser-
vice stations, and spillage and filling losses
from filling  automobile tanks. Gasoline
evaporative losses at refineries or  bulk
distribution  terminals  are  not included.
Emissions from refineries are assumed to
be accounted for in point source catego-
ries.
   The activity level for this category, mea-
sured  by  retail gas sales in  thousands of
gallons, is multiplied by emission factors to
generate emissions estimates.
   Retail sales of gasoline include all sales
of gasoline for highway use, aviation use,
and for use by the construction equipment,
industrial  equipment, and farm equipment
off-highway subcategories.  Sales to the
above user categories are estimated  sepa-
rately and summed to generate total county
sales.
   State retail sales of gasoline for high-
way and marine use are allocated to each
county according to the  county's propor-
tion of the statewide gross dollar receipts
from gasoline service stations. Published
state aviation retail sales of gasoline are
allocated  to the county according to the
total LTO cycles in the county for each of
the  military, civilian, and commercial air-
craft categories.
    County retail sales of gasoline for off-
highway sources are assumed to be the
same  as consumption derived in the activ-
ity levels section of Farm Equipment, Con-
struction Equipment,  and Industrial
Equipment under Off-Highway Sources

 Unpaved Roads
    Vehicle traffic over unpaved roads, park-
ing  areas, and recreational areas gener-
ates fugitive dust  emissions which are
estimated in NEDS. Primary factors  which
affect the amount of dust generated are
vehicle speed, surface type, wind speed,
surface moisture, and type of vehicle. Meth-
odologies for the estimation of activity level
measured in vehicle miles travelled (VMT)
and for emission factor derivation are de-
scribed.
   The methodology developed to deter-
mine the county VMT on unpaved roads is
based on regression analysis of data col-
lected for VMT per county and  mileage of
unpaved roads per county.  County road
mileages for this study were obtained from
state  transportation  or  highway  depart-
ments. VMT was found to be  dependent
on the county population and  mileage of
unpaved roads in the county.

Industrial Processes
   Industrial processes  are very properly
considered as point sources in  most emis-
sion  inventories and in the recent past
have  not been considered to be significant
contributors to area source emissions. How-
ever,  there may be  many  industrial pro-
cesses that are too small to be  considered
point  sources, but collectively may contrib-
ute substantially to the overall total. At the
present time, no methodologies are  avail-
able to estimate activity levels on a county
basis.

Construction
   Road and  building construction activi-
ties generate particulate emissions. Princi-
pal activities in construction which cause
dust emissions are land clearing, excava-
tion,  and vehicle traffic around  the con-
struction site. Variables known  to affect
emissions are soil type, moisture, wind
speed, and type of operations on-stte. At
present, no methodology is available to
estimate activity level at the county level.
However,  emission factors  are  available
from  AP-42.

Solvent Utilization
   This area source category  documents
the estimation procedures for evaporative
losses of  VOCs from solvent usage by
area  sources. Organic solvent  usage is
divided into seven major categories: sur-
face  coating operations, dry cleaning op-
erations,  degreasing operations, graphic
arts,  rubber and plastics,  miscellaneous
industrial operations, and  miscellaneous
non-industrial operations. Surface coating
is further divided into the following subcat-
egories: architectural coatings, auto refin-
ishing, textile products, flatwood products,
wood furniture, metal furniture, paper, plas-
tic products, cans, metal coils,  miscella-
neous finished  metals, electrical,  large
appliances, magnet  wire, motor vehicles,

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 aircraft, marine, railroad, and miscellaneous
 manufacturing  operations. In each cat-
 egory, use of specific solvents is identified
 and enumerated to compute  total solvent
 usage in tons per year.
    The methodology for allocating organic
 solvent consumption by county consists of
 apportioning national consumption  of 20
 primary solvent groups by major user cat-
 egory according to county population  or
 employment data.  User  categories are
 listed in Table 1. Table 2 lists the primary
 solvent groups used to determine losses
 from  organic solvent consumption. The
 category "Special Naphthas"  includes the
 aliphatic naphthas such as V. M. P.  naph-
 thas, Stoddard solvent, rubber solvents,
 and mineral spirits.
    National consumption  of  the  primary
 solvent groups is distributed to each of the
 user categories according to the percent-
 age of total solvent consumption used by
 the user category. Percentage usage ob-
 tained from published sources is compiled
 for each user category in Table 2. National
 area source solvent use estimates are de-
 termined by subtracting point source sol-
 vent  use  or emissions  for each user
 category from total solvent use for each
 user category.
   County consumption for each  solvent
 group and user category is then computed
 by allocating calculated  national area
 source consumption on the basis of appli-
 cable county SIC area source employment
 or population as  shown in Table  1. For
 example, in the degreasing processes use
 category, total solvent use is  allocated to
 each  county in proportion to the county
 area source employment  for  SIC groups
 34 through 39. Area source employment is
 determined by  subtracting point  source
 employment from total county employment
 for each SIC category.  For dry cleaning
 applications, the county-wide allocation  is
 made on the basis of total employment  in
 SIC  groups 7215, 7216,  and 7218. To
 reflect the unequal solvent use in particu-
 lar establishments within SIC groups, con-
 sumption is multiplied by  a factor which
 compares the number of individuals in the
 county in each area source user category
to the number of individuals in the nation in
 each area  source user category.  County
consumption of each solvent type is then
 summed for each county  to  yield a total
county consumption.

Solid Waste Disposal
   The area source category  for  solid
waste disposal includes on-sfte refuse dis-
posal activities by residential, commercial/
institutional, and industrial  sectors. In this
section, emissions from the disposal prac-
 Table 1.      User Categories

     User Categories
     Population or Employment by SIC
        Used for Country Allocation
 Surface Coating
     Architectural Coatings
     Auto Refinishing
     Textile Products
     Flatwood Products
     Wood Furniture  (SIC 25 partial)
     Metal Furniture  (SIC 25 partial)
     Paper
     Plastic Products
     Cans
     Metal Coils
     Misc. Finished Metals
     Electrical
     Large Appliances
     Magnet Wire
     Motor Vehicles
     Aircraft
     Marine
     Railroad
     Miscellaneous Mfg.
            County Population
            SIC 7535
            SIC 22
            SIC 243 +244
            SIC 26
            SIC 308
            SIC 341
            SIC 3498
            SIC 34-(341 + 3498)
            SIC 35
            SIC 363
            SIC 36 - 363
            SIC 371
            SIC 372
            SIC 373
            SIC374
            Total Mfg. - Above SIC
                     employment
 Degreasing
 Dry Cleaning
 Graphic Arts
 Rubber & Plastics
 Miscellaneous Industrial

 Miscellaneous Non-Industrial
            SIC 34 thru 39
            SIC (7216x2) = 7215+ 7218
            SIC 264 + 265 + 27
            SIC 30
            Summation ofCBP' employment
            in SIC's 20 thru 39
            County Population
 * County Business Pattern
tices of open burning and on-sfte incinera-
tion are discussed separately. Solid waste
generation in hundreds of tons is used as
a measure of activity level.

Natural Sources
    Natural sources are known to be sig-
nificant contributors to area source emis-
sions. Natural  sources may include:
biogenic  sources, wind erosion, lightning,
geothermal sources,  and  open-water
sources.  However, while there are numer-
ous methodologies for estimating emis-
sions from natural sources, there remains
disagreement among the experts as to the
most appropriate methodology to  use for
estimating emissions from this category.

Miscellaneous Area Sources
   Area sources which are not defined by
Stationary Source Fuel Combustion,  Mo-
bile Sources,  Industrial Processes, Sol-
vent Utilization, Solid Waste Disposal, or
Natural Sources categories are compiled
in  the  miscellaneous area sources  cat-
egory.  The importance of these area cat-
egories is that, while total emissions from
 each source are relatively small compared
 to the major categories, emissions at a
 particular time may be significant.
   As presented, identified miscellaneous
 area sources include: Acres Under Culti-
 vation (Land Tilling), Agricultural Burning,
 Forest Wildfires, Managed Burning,  and
 Structural Fires.

 Agriculture Production—Crops

 Acres Under Cultivation
 (Land Tilling)
   Fugitive dust emissions result from vari-
 ous  soil preparation operations which in-
 clude rough plowing, mulch plowing,  and
 the cutting of narrow slits into the sod for
 seed and/or fertilizer. Variables known to
 affect the quantity of dust generated are
 soil type, surface moisture, resulting  tool
 speed, type of equipment, and wind speed.
 However,  no methodology has been de-
 veloped to adequately estimate emissions.
 For previous inventories, activity levels are
 estimated using the number of acres tilled
 as obtained from the Census of Agricul-
ture. It was assumed that each acre of

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Tablo 2.     Percentage End Use of Solvents by Major Solvent Category
Solvent Type
Special Naphthas
Porchtoroothylene
Elhanol
Trichbroalhyfone
Isopropanol
Acotono
Gtycol Ethers
Cydohoxanona
Mothy! Ethyl Kotona
Ethyl Benzene
Propytono Glycol
Mothanol
Butyl Acotato
EthylAcatato
Butyl Alcohols
Mothyl Isobutyl Ketona
Monochtorobenzane
o-Dtchlorobenzene
p~Dhhlorobenzene
AH Other Solvents'
Surface Dry Graphic
Coating Degreasing Cleaning Arts
48.7 6.7 2.0 6.4
10.0 53.0

80.0
15.0
17.0
43.0

69.4



65.0 5.0
41.0
15.5
65.5
21.0



Rubber & Miscellaneous
Plastics Industrial
9.6 7.1

26.0

9.0

10.0
5.0
10.0

54.0 4.0
8.0

8.0
1.8
8.0
21.0
25.0
23.0

Miscellaneous
Non-Industrial
10.7
4.0

5.0
37.0
11.5



0.5
6.0
15.0
3.0
13.0
1.3
18.0
11.0
5.0
46.0

  miscellaneous non-industrial.
 harvested cropland is tilled three times per
 year. The resultant activity levels were re-
 ported In thousands of acres.

 Agricultural Burning
   This miscellaneous area source cat-
 egory estimates  emissions from agricul-
 tural burning practices routinely  used to
 clear and/or prepare land for planting. Spe-
 cific operations include grass stubble burn-
 Ing, burning of agricultural crop residues,
 and burning of standing field crops as part
 of harvesting (e.g., sugarcane). Emissions
 estimates are generated by multiplying the
 number of acres burned in each county by
 a fuel loading factor and the emission fac-
 tor for each pollutant.
   The original methodology estimated the
 1974 activity level in terms of acres burned
 per state. It is assumed that the total quan-
 tity of agricultural products burned in 1974
 Is the same quantity  which  will  be con-
 sumed by fire each year. If no specific crop
 data were available, it was assumed  that
 the  number of  acres burned annually are
 divided equally between sugar cane  and
 field crops. For the purposes of these cal-
 culations, fuel  loadings for grass burning
are 1 to 2 tons per acre;* for sugar cane
burning, fuel loadings range from 6 to 12
tons per acre.
   If new state, regional, or national esti-
mates are  available, the existing county
data will be updated by the same percent-
age as the relative state, regional,  or na-
tional percentage increase or decrease.

Other Combustion
   Area  sources which  are defined  as
Other Combustion include such categories
as forest wildfires, managed burning, and
structural fires. The importance of these
area categories is that, while total emis-
sions from each source are relatively small
compared to the major categories, emis-
sions at  a  particular time may  be signifi-
cant.

Forest Wildfires
   Each year emissions are generated by
forest wildfires covering large tracts of for-
ested  land. For  this category, emission
estimates are generated by  multiplying the
number of acres burned per county by a
fuel loading factor and then the emission
factor.
   In the original methodology, state esti-
mates of wildfire activity were allocated to
the county level  on the basis of forest
acreage per county. These wildfire statis-
tics were obtained, reported in number of
acres burned, from contact with state for-
estry officials and from state land use maps
for the  base  year  1974. Since  1974, the
wildfire  activity level for each county from
the previous year has been updated with
wildfire  statistics from the U.S. Forest Ser-
vice.  Regional fuel loading  factors in tons
per acre for each EPA region are applied
to state averages within each region to
yield tons consumed.

Managed Burning (Slash/
Prescribed Burning)
   Managed  burning activities included in
this area source category are slash burn-
ing and prescribed burning. In slash burn-
ing  operations,  waste  from logging
operations is burned under controlled con-
ditions to reduce fire hazards and remove
  1 ton/acre « 0.224 kg/m2

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brush considered to host destructive in-
sects.  Prescribed burning  is used as  a
forest management practice to establish
favorable  seedbeds,  remove competing
underbrush,  accelerate nutrient  cycling,
control tree pests,  and contribute other
ecological benefits.
   For this category, emissions estimates
are generated by multiplying the  number
of acres burned in each county by a fuel
loading factor and the emission factor for
each pollutant.
   Original state estimates of acreage con-
sumed by both managed  burning tech-
niques were determined  for the NEDS
inventory  year of 1974. Individual state
officials and the U.S. Forest Service were
contacted to provide estimates of  acreage
burned, burning technique, and fuel load-
ing ratios. AMS uses state data generated
for 1974 which was allocated to the county
level according to forest acreage per county
as obtained from contact with local officials
or state land use maps. If not provided,
fuel  loadings for slash burning and pre-
scribed burning are 75  and 3 tons  per
acre, respectively.
   If new state, regional, or national esti-
mates  are available, the existing county
data will be updated by the same percent-
age as the relative state, regional, or na-
tional percentage increase or decrease.

Structural Fires
   Structural fires have been included in
AMS because building fires  have been
identified  in the production of short-term
emissions of air contaminants. Activity level
for this category, measured  by the total
number of fires per county, is multiplied by
a loading factor and the emission factor to
obtain emissions estimates.
   The  total number of  building fires is
obtained from the most  recent statistics
from the National Fire Protection Associa-
tion  (NFPA). In absence of county level
allocation  data, it is assumed, based on
the nationwide NFPA figures, that an aver-
age  of four fires per 1,000 population oc-
cur each year. Estimates of the material
burned is obtained by multiplying the num-
ber structural fires by a fuel factor of 6.8
tons* of material per fire.
   If new state, regional, or national esti-
mates are available, the existing county
data will be updated by the same percent-
age  as the relative state, regional, or na-
tional percentage increase or decrease.
                                                                                      *  1 ton = 907 kg
                                                                           *US. GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40162

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  E Sue Kfmbrough is  the EPA Project Officer, (see below).
  The complete report, entitled "Documentation of AIRS AMS National Methodologies,"
    (Order No. PB92-132869/AS; Cost: $26.00, 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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
     BULK RATE
POSTAGE & FEES PAID
 EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
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