Air and Radiation EPA420-R-05-017 

December 2005 

NR-004c 

Seasonal and Monthly

Activity Allocation

Fractions for Nonroad 

Engine Emissions Modeling 
EPA420-R-05-017 

December 2005 

Seasonal and Monthly Activity Allocation Fractions for

Nonroad Engine Emissions Modeling

NR-004c

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

NOTICE

This technical report does not necessarily represent fi nal EPA decisions or positions.

It is intended to present technical analysis of issues using data that are currently available.

The purpose in the release of such reports is to facilitate the exchange of

technical information and to inform the public of technical developments which

may form the basis for a fi nal EPA decision, position, or regulatory action.
Introduction 

The United States Environmental Protection Agency (EPA) has developed a national 

nonroad air emissions inventory model called NONROAD. The model uses estimates of annual 

activity for each equipment type, e.g., generally expressed in terms of hours of operations or 

gallons of fuel used per year, to calculate yearly emission inventories. It will also calculate 

inventories on a seasonal (i.e., summer, fall, winter, spring), monthly, or daily (i.e., weekday or 

weekend day) basis by allocating annual activity to these smaller time periods. This report 

documents the seasonal and monthly activity allocation fractions used by the model. Daily 

activity allocation fractions are addressed in a separate technical report. The only substantive 

change from draft NONROAD2004 is the seasonal allocation of construction equipment, 

described in the Methodology/Results section below. Seasonal inputs have also been added for 

Puerto Rico and the U.S. Virgin Islands, simply by assigning them to the Southeast region and 

using those existing values. The EPA currently considers these seasonal fractions to be final 

inputs for the draft NONROAD2005 model. 

The remainder of this report is organized into two parts. The first part contains a basic 

description of the overall approach and sources of information that are used to develop the 

requisite temporal allocation fractions. The second part explains how this information is used 

and describes the final default values for each state. 

Background 

The draft NONROAD2005 model allocates annual activity for the various equipment 

categories to each month of the year based on the general climate and geographic location of the 

state and the time of year in which the equipment is used. Seasonal inventories are computed by 

combining the monthly activity fractions that comprise each of the four seasons as shown in 

Table 1. 

Table 1 

Season and Month Correspondence

Season Month 

Summer June, July, and August 

Fall September, October, and November 

Winter December, January, and Februarya 

Spring March, April, and May 

a When running the model for the winter season, it assumes January, February, and December all in the same year, rather 

than the preceding December. 

1 
The monthly activity allocation fractions used in NONROAD were derived from the 

seasonal activity factors contained in the November 1991 Nonroad Engine and Vehicle Emission 

Study1 (NEVES) and monthly activity factors contained in a technical report for the California 

Air Resources Board (CARB) nonroad emissions model - OFFROAD.2

 The EPA decided to 

develop the activity allocation fractions based on these two documents as default values for the 

NONROAD model. To the best of the EPA’s current knowledge, these two sources of 

information represent the most comprehensive work that has been done to date concerning the 

distribution of activity by season and month for a broad range of nonroad equipment categories 

on a statewide (CARB) and nationwide (EPA) basis. The EPA recognizes that states and other 

users of NONROAD may have more detailed information on their local activity levels by season 

and month. Such users of NONROAD may substitute activity allocation fractions derived for a 

state, county, or air quality management district based on surveys or other studies for any of the 

equipment categories. 

The data from NEVES can be found in Appendix L, Tables L-02, L-03, and L-04 of that 

document, which contain percentages of activity for summer and winter use only (Attachment 

1).b

 More specifically, Table L-02 contains summer and winter activity allocations for 

agricultural, construction, industrial, lawn and garden (excluding chainsaws), 

snowblower/snowmobile, commercial marine, airport service, logging (including chainsaws), 

and light commercial equipment. These percentages were derived from a paper written by Hare 

and Springer,3 1987 state implementation plan (SIP) inventories, and the CARB Technical 

Support Document for proposed regulations applicable to lawn and garden equipment.4 Separate 

summer and winter activity allocations for these general equipment categories are provided for 

three climatological and geographical regions (cold/northern, medium/central, and 

warm/southern). These regions are defined by the average January temperature and latitude 

criteria shown in Table 2. 

Table 2 

Seasonal Activity Allocation Fraction Regions Defined by Hare and Springer 

Region 

Average January 

Temperature (EF) Latitude 

Cold/Northern < 35E 43E and north 

Medium/Central 35E - 44E 37E to 43E

Warm/Southern > 45E 37E and south 

Table L-03 contains summer and winter activity allocations for recreational marine 

equipment from a boat usage survey done for the National Marine Manufacturers Association 

b The derivation of allocation factors for the fall and spring using the NEVES summer and winter values is explained in 

the next section. 

2 
(NMMA).5

 The factors in this table are arranged into eight geographical regions: Northeast, 

Southeast, Mid-Atlantic Coast, Great Lakes, Southwest, Rocky Mountains, Northwest, and West 

Coast. 

Table L-04 contains summer and winter activity allocations for recreational equipment 

from a survey done for the Motorcycle Industry Council (MIC).6 Table L-04 lists twelve 

regions. However, the list of regions was subsequently found to be in error, based on a list 

received from the MIC that defines the geographical regions used for its survey. The corrected 

information was used in the development of the allocation scheme for NONROAD. 

The MIC organized the seasonal activity usage results into four regions (East, Midwest, 

South, West), which the MIC further divided into eight subregions: New England and Middle 

Atlanticc

 (East); East Central and West Central (Midwest); Southeast and Southwest (South); and 

Rocky Mountains and Pacific (West). In Table L-04, the allocations for the main regions are 

averages of the two subregions that form each of the main regions. 

The CARB model has activity allocations for the State of California, which are expressed 

in monthly form (Attachment 2). The allocation fractions are described in the OFFROAD 

model’s technical support document. The CARB factors differ from those contained in NEVES 

for agriculture, construction, industrial, lawn and garden, snowblowers/snowmobile, and 

recreational equipment. The CARB technical document did not contain allocations for certain 

categories (i.e., commercial and recreational marined

), and it differed from NEVES in that it 

contained separate factors for tillers, chainsaws less than or equal to five horsepower and 

transportation refrigeration units. CARB and NEVES had equivalent allocations for the 

remaining categories where usage was judged to be essentially uniform over the year. As 

described in the next section, the CARB allocation factors are used directly for most equipment 

categories in the draft NONROAD2005 to model emissions in the State of California. 

In NEVES, Middle Atlantic was changed to be Mid-Atlantic Coast. However, in the documentation of the geographic 

definitions received from the MIC, it is labeled at Middle Atlantic. 

d

For commercial marine, as well as aircraft and locomotives, baseline emissions in tons per day were directly entered into 

the OFFROAD model and a growth factor was used to project emissions into the future. Therefore, seasonal activity 

allocation fractions were not needed. No explanation is given for why no seasonal activity allocation fractions are listed for 

recreational marine equipment. 

3 

c
Methodology/Results 

NEVES-Based Regional Activity Allocations 

Because each of the seasonal allocation tables in NEVES contains different numbers and 

types of geographical regions, composite regions were created for use in NONROAD by 

geographically matching the less defined regions from Tables L-02 and L-03 to those in Table L04. This correspondence is shown in Table 3. The resulting ten composite regions represent an 

attempt to reconcile and link the regions defined in each of the three tables so that they are 

geographically coherent and compatible. 

Table 3 

Mapping of Seasonal Activity Allocation Regions From NEVES to NONROAD

NEVES 

General 

Equipment 

Table L-02 

NEVES 

Recreational Marine 

Table L-03 

NEVES 

Recreational Equipment 

Table L-04 

NONROAD 

Composite 

Regions 

Cold/Northern Northeast, Great Lakes, 

Northwest, Rocky Mountains 

Midwest, New England, 

Rocky Mountains, East 

Central 

Northeast/New England, 

Great Lakes/Midwest, 

Rocky Mountains, 

Northwest 

Medium/Central Mid-Atlantic Coast, West 

Coast 

Mid-Atlantic Coast, West 

Central, Pacific, 

Middle Atlantic, West 

Coast, Central West 

Warm/Southern Southeast, Southwest South, Southeast, Southwest Southeast, Southwest, 

South Central 

There were two exceptions in regard to the general method of defining the regions 

discussed above. The first involved a decision to leave out the East Central region found in 

Table L-04 for recreation equipment from the composite regions because the region that it 

defined could be included in and reasonably characterized by the Great Lakes/Midwest region. 

 The second exception pertained to the allocation factors used for the general equipment 

categories included in the Rocky Mountains category for NONROAD. In Table L-02, the 

general equipment categories used in this geographic area would have been classified as 

Medium/Central by the criteria previously shown in Table 2. This classification may seem 

reasonable since the Rocky Mountains region is generally located in the central part of the U.S. 

However, the climatic conditions found in most of the Rocky Mountains more closely resemble 

the northern part of the U.S. than the central section of the country. Therefore, NONROAD uses 

the Cold/Northern seasonal activity allocation factors from Table L-02 for the general equipment 

categories included in the Rocky Mountains category. This rationale is also supported by Table 

L-01 in NEVES, which classified the nonattainment area of Denver as being within a cold 

region. 

4 
Since the seasonal allocation factors for all of the categories except recreational 

equipment were arranged in more general regions than the ten composite regions described 

above, these values were used multiple times based on the matching strategy in Table 3. For 

example, the cold/northern fractions from Table L-02 are used in the Northeast/New England, 

Midwest/Great Lakes, Rocky Mountains, and Northwest regions. 

Because the allocation tables in NEVES include only summer and winter factors, it was 

also necessary to develop allocations for the remaining two seasons. These allocations were 

determined by taking the sum of the summer and winter allocation percentages for each 

equipment category and geographical region represented in the NEVES tables, and subtracting 

this value from one hundred. The resulting value was then divided by two to obtain the fall and 

spring allocation percentages. 

The monthly allocation fractions required by NONROAD can be computed from the 

NEVES-based seasonal allocation percentages by first dividing the seasonal percentages for each 

equipment category and region described above by 100 to convert from percentile to fractional 

form. Second, each seasonal allocation fraction was then divided by three to produce the 

allocation fraction for each month of the respective season (Table 1). The resulting monthly 

allocation fractions by equipment category for all regions except the West Coast, which is 

described below, are shown in Table 4. 

This approach assumes that the four seasons are contained in specific three month 

periods, within which usage in each category is constant. For example, this results in 

NONROAD apportioning the use of snow-related equipment to December, January, and 

February because these are defined as the winter months. However, it is common knowledge 

that significant snow can occur in late fall and early spring in certain areas. While the NEVESbased method does not optimally reflect such conditions, in the absence of more specific regional 

or local data, the method provides a reasonable and logical approximation of the seasonal 

impacts on nonroad equipment usage for a national emission inventory model. 

CARB-Based Regional Activity Allocations 

An exception to the NEVES-based approach described above resulted from using the 

available fractions from the CARB OFFROAD technical support document for the State of 

California, which is represented in NONROAD by the West Coast region. Recreational marine 

was not included in the CARB model, so NONROAD uses allocations derived from NEVES. 

The resulting monthly allocation fractions by equipment category for the West Coast and for 

each of the other regions are shown in Table 4. 

Construction Value-Based Regional Activity Allocations 

The one industry segment that has been updated from the NEVES and CARB-based 

approaches described above is construction equipment. The county level construction dollar 

value data7 that EPA acquired to update the geographic allocations for draft NONROAD20058 

also included a breakout of construction expenditures by month. For consistency with the other 

seasonal inputs and to minimize effects of any potentially anomolous data at the individual state 

and month level, EPA aggregated these data into the seasons defined in Table 1 and the regions 

5 
defined in Table 5. The main change in these seasonal allocations relative to prior versions of 

NONROAD is a decrease in the difference between summer and winter activities. The new data 

indicate that a greater portion of construction activity occurs in winter months than was the case 

with the older data. 

6 
Table 4 

Monthly Seasonal Activity Allocation Fractions

(Based mostly on Tables L-02, L-03, and L-04 in Appendix L in NEVES, but construction is based on 2003 value of constru

Northeast/New England 

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Construction 0.059 0.059 0.093 0.093 0.093 0.095 0.095 0.095 0.086 0.Industrial 0.067 0.067 0.083 0.083 0.083 0.100 0.100 0.100 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.003 0.003 0.052 0.052 0.052 0.230 0.230 0.230 0.052 0.Recreational Equipment 0.047 0.047 0.070 0.070 0.070 0.146 0.146 0.146 0.070 0.

7 
Table 4 Continued 

Great Lakes/Midwest

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.

Construction 0.061 0.061 0.089 0.089 0.089 0.099 0.099 0.099 0.086 0.

Industrial 0.067 0.067 0.083 0.083 0.083 0.100 0.100 0.100 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.000 0.000 0.050 0.050 0.050 0.233 0.233 0.233 0.050 0.Recreational Equipment 0.027 0.027 0.077 0.077 0.077 0.153 0.153 0.153 0.077 0.

Rocky Mountains 

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Construction 0.066 0.066 0.079 0.079 0.079 0.100 0.100 0.100 0.089 0.Industrial 0.067 0.067 0.083 0.083 0.083 0.100 0.100 0.100 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.000 0.000 0.052 0.052 0.052 0.230 0.230 0.230 0.052 0.Recreational Equipment 0.027 0.027 0.080 0.080 0.080 0.147 0.147 0.147 0.080 0.

8 
Table 4 Continued 

Mid-Atlantic

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.090 0.090 0.090 0.133 0.133 0.133 0.090 0.Construction 0.072 0.072 0.079 0.079 0.079 0.098 0.098 0.098 0.085 0.Industrial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.090 0.090 0.090 0.133 0.133 0.133 0.090 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.007 0.007 0.068 0.068 0.068 0.190 0.190 0.190 0.068 0.Recreational Equipment 0.040 0.040 0.078 0.078 0.078 0.137 0.137 0.137 0.078 0.

Southeast 

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.100 0.100 0.100 0.113 0.113 0.113 0.100 0.Construction 0.078 0.078 0.080 0.080 0.080 0.089 0.089 0.089 0.086 0.Industrial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.100 0.100 0.100 0.113 0.113 0.113 0.100 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.023 0.023 0.075 0.075 0.075 0.160 0.160 0.160 0.075 0.Recreational Equipment 0.057 0.057 0.080 0.080 0.080 0.117 0.117 0.117 0.080 0.

9 
Table 4 Continued 

Northwest

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Construction 0.069 0.069 0.081 0.081 0.081 0.102 0.102 0.102 0.080 0.Industrial 0.067 0.067 0.083 0.083 0.083 0.100 0.100 0.100 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.073 0.073 0.073 0.167 0.167 0.167 0.073 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.016 0.016 0.063 0.063 0.063 0.190 0.190 0.190 0.063 0.Recreational Equipment* 0.043 0.043 0.073 0.073 0.073 0.143 0.143 0.143 0.073 0.

West Coast 

Note: West Coast table uses CARB OFFROAD Seasonal Activity Allocation Fractions except for marine and construction. 

Equipment Category January February March April May June July August September OcAgricultural 0.054 0.054 0.086 0.086 0.108 0.108 0.108 0.108 0.108 0.Construction 0.072 0.072 0.088 0.088 0.088 0.090 0.090 0.090 0.083 0.Industrial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Lawn and Garden excl. chainsaws 0.057 0.067 0.086 0.086 0.095 0.095 0.095 0.095 0.095 0.Snowblowers/Snowmobiles 0.200 0.200 0.180 0.060 0.020 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine* 0.023 0.023 0.075 0.075 0.075 0.160 0.160 0.160 0.075 0.Recreational Equipment 0.060 0.060 0.070 0.080 0.090 0.100 0.100 0.100 0.090 0.

*CARB OFFROAD did not have marine seasonal allocation fractions, so NEVES data are used for these. 

10 
Table 4 Continued 

Central West

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.090 0.090 0.090 0.133 0.133 0.133 0.090 0.Construction 0.070 0.070 0.089 0.089 0.089 0.094 0.094 0.094 0.080 0.Industrial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.090 0.090 0.090 0.133 0.133 0.133 0.090 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.023 0.023 0.075 0.075 0.075 0.160 0.160 0.160 0.075 0.Recreational Equipment 0.027 0.027 0.080 0.080 0.080 0.147 0.147 0.147 0.080 0.

Southwest 

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.100 0.100 0.100 0.113 0.113 0.113 0.100 0.Construction 0.075 0.075 0.084 0.084 0.084 0.091 0.091 0.091 0.084 0.Industrial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Lawn and Garden excl. chainsaws 0.020 0.020 0.100 0.100 0.100 0.113 0.113 0.113 0.100 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.023 0.023 0.075 0.075 0.075 0.160 0.160 0.160 0.075 0.Recreational Equipment 0.040 0.040 0.085 0.085 0.085 0.123 0.123 0.123 0.085 0.

11 
Table 4 Continued 

South Central

Equipment Category January February March April May June July August September OcAgricultural 0.020 0.020 0.100 0.100 0.100 0.113 0.113 0.113 0.100 0.Construction 0.068 0.068 0.092 0.092 0.092 0.091 0.091 0.091 0.082 0.Industrial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Lawn and Garden (excl. chainsaws) 0.020 0.020 0.100 0.100 0.100 0.113 0.113 0.113 0.100 0.Snowblowers/Snowmobiles 0.333 0.333 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.Airport Service 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Logging (incl. chainsaws) 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Light Commercial 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.Recreational Marine 0.023 0.023 0.075 0.075 0.075 0.160 0.160 0.160 0.075 0.Recreational Equipment 0.050 0.050 0.082 0.082 0.082 0.120 0.120 0.120 0.082 0.

12 
As a general practice, EPA welcomes and encourages the use of locally-derived activity 

allocation data in place of national or regional default data. It is the EPA’s judgment that state or 

local agencies, such as CARB, are usually in a better position than EPA to collect, assess, and/or 

develop local nonroad activity-oriented data that more realistically mirror local conditions. In the 

specific case of California, the use of the CARB fractions will help to ensure that EPA’s 

NONROAD model produces compatible results with those from California’s OFFROAD model 

when it is run for California. If possible, EPA will incorporate data from other local sources in 

future model revisions when such information becomes available. 

Assignment of Regional Activity Allocations to States 

The final task involves assigning states to each of the regions. These assignments are shown 

in Table 5. The West Coast region consists of California (since most of the seasonal allocation data 

comes from CARB) and Hawaii (due to lack of other specific data, and assuming that at least 

southern California has some similarity to Hawaii). Many of the other states have logical 

assignments. However, some states do not clearly belong in a particular region because they span 

more than one of the defined regions and/or have several climatic tendencies that resemble more 

than one region. New York could be included in the Great Lakes/Midwest, Northeast/New England, 

or Middle Atlantic regions. Pennsylvania could be included in the Great Lakes/Midwest or Middle 

Atlantic regions. Wyoming could be included in the Central West, Rocky Mountain, or Northwest 

regions. In these cases, the EPA’s best judgment was used based on general knowledge of the 

state’s climate, general geographical position, and information from the NEVES report. Alaska, 

which has two CO nonattainment areas (Fairbanks and Anchorage), presented another problem. It 

should have its own unique seasonal allocation fraction data. However, lacking this data, it seemed 

logical to classify it as a Midwest/Great Lakes state, since the climatic conditions in Alaska bear the 

closest resemblance to the states assigned to that region. 

13 
Table 5 

Mapping of States to Regions Used For Defining Monthly Activity Allocation Fraction 

FIPS State Region 

1. Alabama Southeast 

2. Alaska Great Lakes/Midwest* 

4. Arizona Southwest 

5. Arkansas South Central 

6. California West Coast 

8. Colorado Rocky Mountains 

9. Connecticut Mid-Atlantic 

10. Delaware Mid-Atlantic 

11. District of Columbia (Washington, D.C.) Mid-Atlantic 

12. Florida Southeast 

13. Georgia Southeast 

15. Hawaii West Coast 

16. Idaho Northwest 

17. Illinois Great Lakes/Midwest 

18. Indiana Great Lakes/Midwest 

19. Iowa Great Lakes/Midwest 

20. Kansas Central West 

21. Kentucky South Central 

22. Louisiana Southeast 

23. Maine Northeast/New England 

24. Maryland Mid-Atlantic 

25. Massachusetts Northeast/New England 

26. Michigan Great Lakes/Midwest 

27. Minnesota Great Lakes/Midwest 

28. Mississippi Southeast 

29. Missouri Great Lakes/Midwest 

30. Montana Northwest 

31. Nebraska Central West 

32. Nevada Central West 

14 
FIPS State Region 

33. New Hampshire Northeast/New England 

34. New Jersey Mid-Atlantic 

35. New Mexico Southwest 

36. New York Northeast/New England 

37. North Carolina Mid-Atlantic 

38. North Dakota Great Lakes/Midwest 

39. Ohio Great Lakes/Midwest 

40. Oklahoma South Central 

41. Oregon Northwest 

42. Pennsylvania Mid-Atlantic 

44. Rhode Island Mid-Atlantic 

45. South Carolina Southeast 

46. South Dakota Great Lakes/Midwest 

47. Tennessee South Central 

48. Texas Southwest 

49. Utah Central West 

50. Vermont Northeast/New England 

51. Virginia Mid-Atlantic 

53. Washington Northwest 

54. West Virginia Mid-Atlantic 

55. Wisconsin Great Lakes/Midwest 

56. Wyoming Rocky Mountains 

72. Puerto Rico Southeast* 

78. Virgin Islands Southeast* 

*Although Alaska should have unique seasonal adjustment fractions, for the purpose of default data, Alaska has been 

assigned to the Midwest/Great Lakes profile because of a lack of data at this time. Similarly, Puerto Rico and the U.S. 

Virgin Islands have been assigned to the Southeast regional profile due to lack of data specific to those territories. 

National Average Seasonal and Monthly Activity Allocations 

Since seasonal activity fractions can vary considerably with region, they are most useful 

when performing state or county level model runs. However, the NONROAD model does have the 

capability to model seasonal and monthly emissions for a nationwide scenario, even though such 

results would lack the seasonal specificity of state or county level runs. To estimate national average 

seasonal and monthly activity allocations the monthly activity allocations were used as described 

15 
below. The resulting values are included in the SEASON.DAT input data file with the region 

designation of "US." 

Due to the different seasonal activity allocations and different geographic allocations of the 

various types of equipment, the national average seasonal allocations are calculated as follows. Any 

set of equipment that has the same temporal and geographic allocations can be handled together, 

which is why there are not more than about 75 different types of equipment for this purpose. 

1) Do twelve "50STATE" model runs (one for each month of the year) including all equipment 

types to generate activity (and emission) estimates for each state for each month for every type of 

equipment. Use the same temperature and fuel properties for all runs, since the seasonal allocation 

factors are just meant to allocate activity, regardless of emissions. 

2) Aggregate the activity outputs from Step 1 across all states by SCC and month. This yields one 

activity value for each SCC and month (approximately 75 x 12 = 900). 

3) Also aggregate those activity outputs across all states and months by SCC to get one national 

annual total activity value for each SCC (approximately 75 values). 

4) For each of the equipment types listed in SEASON.DAT find the ratio of each month's activity 

from Step 2 to the annual total from Step 3. 

5) In the /MONTHLY/ packet of SEASON.DAT, in the "US" section for the US total allocations, 

put the twelve monthly ratios from Step 4 into each appropriate line (using the global SCC where 

possible, such as 2270002000 for all diesel construction equipment, or individual SCCs where 

necessary due to equipment specific temporal activity profiles). 

16 
References 

1. Environmental Protection Agency, Office of Air and Radiation. Nonroad Engine and Vehicle 

Emission Study, 21A-2001, November 1991. 

2. Energy and Environmental Analysis. Documentation of Input Factors For the New Off-Road 

Mobile Source Emissions Inventory Model - Draft. Prepared for the California Air Resources 

Board, August 1995. OFFROAD was formerly know as MVOFF 

3. Hare, C.T., and K.J. Springer. Exhaust Emissions from Uncontrolled Vehicles and Related 

Equipment Using Combustion Engines, Part 5, No. APRD-1494. San Antonio, TX:Southwest 

Research Institute, October 1973. 

4. California Air Resources Board. Technical Support Documents for California Exhaust 

Emission Standards and Test Procedures for 1994 and Subsequent Model Year Utility and Lawn 

and Garden Equipment Engines. Attachment C to CARB Mailout #90-64. El Monte, CA:State 

of California, December 1991. 

5. Irwin Broh & Associates, Inc. NMMA Boat Usage Survey. Prepared for the National Marine 

Manufacturers Association, Des Plaines, IL, August 1991. 

6. Burke Marketing Research. 1990 Survey of Motorcycle Ownership and Usage: Final Results 

Waves 1-12, Volume II. Conducted for the Motorcycle Industry Council, Inc. May 1991. 

7. Construction valuation data for 2003 purchased by EPA from McGraw-Hill Construction 

(formerly F.W. Dodge Company). 

8. Geographic Allocation of State Level Nonroad Engine Population Data to the County Level, 

NONROAD model report NR-014d, 2005. 

17 
Attachment 1 

NEVES Seasonal Activity Allocation Fractions 

Table L-02. Summer and Winter Percentages of Yearly Activity

Equipment Category 

Cold/Northern Medium/Central Warm/Southern 

Summer 

(%) 

Winter 

(%) 

Summer 

(%) 

Winter 

(%) 

Summer 

(%) 

Winter 

(%) 

Agricultural 50 6 40 6 34 6 

Construction 43 10 38 15 33 20 

Industrial 30 20 25 25 25 25 

Lawn and Garden (excl. chain saws) 50 6 40 6 34 6 

Snowblowers/Snowmobiles 0 100 0 100 0 100 

Commercial Marine 25 25 25 25 25 25 

Airport Service 25 25 25 25 25 25 

Logging (including chain saws) 25 25 25 25 25 25 

Light Commercial 25 25 25 25 25 25 

Table L-03. Summer and Winter Percentages of Yearly Activity for 

Recreational Marine Equipment

Region % During Summer % During Winter 

Northeast 68 1 

Southeast 48 7 

Mid-Atlantic Coast 57 2 

Great Lakes 70 0 

Southwest 48 7 

Rocky Mountains 69 0 

Northwest 57 5 

West Coast 48 7 

A-1
Table L-04. Summer and Winter Percentages of Yearly 

Activity for Recreational Equipment* 

Region % During Summer % During Winter 

East 42 12 

Midwest 46 8 

South 36 15 

West 44 11 

New England 44 14 

Mid-Atlantic Coast 41 12 

East Central 48 9 

West Central 44 8 

Southeast 35 17 

Southwest 37 12 

Rocky Mountains 44 8 

Pacific 43 13 

National Average 42 12 

* Excluding snowmobiles 

A-2
ATTACHMENT 2 

CARB OFF-ROAD EQUIPMENT USE BY MONTH OF YEAR

Equipment Category 

Fraction of Annual Use 

Jan Feb Mar Apr May June July Aug Sep Oct 

Recreational Vehicles 0.061 0.061 0.071 0.081 0.091 0.101 0.101 0.101 0.091 0.091 Construction Equipment 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 Industrial Equipment 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 Lawn and Garden Equipment 0.057 0.067 0.086 0.086 0.095 0.095 0.095 0.095 0.095 0.086 Farm Equipment 0.054 0.054 0.086 0.086 0.108 0.108 0.108 0.108 0.108 0.0.75 Light Commercial Equipment 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 Logging Equipment 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 Aircraft GSE 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 Transportation Refrigeration Units 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 0.083 Snowmobiles & Snowblowers 0.200 0.200 0.180 0.060 0.020 0.000 0.000 0.000 0.000 0.000 Chainsaws (#5 HP) 0.090 0.090 0.090 0.050 0.050 0.040 0.080 0.090 0.090 0.110 Tillers 0.030 0.030 0.040 0.150 0.150 0.150 0.110 0.110 0.110 0.040 

A-3