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 ------- 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). ------- 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 ------- 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, ------- 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 ------- 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 ------- 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 ------- 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 EPA/600/SR-92/001 ------- |