1. Preparation of Fine Particulate Emissions Inventories
Chapter 3 – Onroad Mobile Sources
After this lesson participants will be able to:
describe the EPA’s MOBILE6 model, the National Mobile Inventory Model, and the new MOtor Vehicle Emissions Simulator (MOVES) model
understand the acceptable uses, advantages, and disadvantages of these models for the development of PM inventories
explain how vehicle mileage is used to calculate emissions from onroad vehicles.

2. EPA’s Onroad Models – Overview
MOBILE6
Current official model for SIP emission inventory development
NMIM
Incorporates MOBILE6
VMT is an input to model
Can be used to calculate emission inventory, not just emission factors
MOVES
Significant departure from MOBILE model series
Released in draft form April 2009
Not acceptable for SIP inventories until final version is released by end of 2009
EPA’s Office of Transportation and Air Quality or OTAQ (pronounced O-TAK) has developed onroad emission models
MOBILE6 (and previous MOBILE models) is FORTRAN-based and require the user to develop a text file input file
Both NMIM and MOVES can be accessed via a Graphical User Interface (GUI) which takes the place of the MOBILE6 input file and are both written in Java.
NMIM included the development of a National County Database with default information by county.
MOVES expands on the database concept by including all data in databases that can be revised by the user; this includes not just local information, but also information on emission rates, driving cycles, etc.

3. MOBILE6 Overview Use MOBILE6 model for emission factors
PM2.5, SO2, NOx, NH3, PM10, VOC, and CO
PM2.5 and PM10 emission factors are for primary emissions (PM2.5-PRI and PM10-PRI)
Use VMT data for activity
Map VMT data to corresponding MOBILE6 emission factors
OTAQ developed MOBILE6 to estimate emissions from mobile sources.
The MOBILE6 model:
includes emission factors for PM2.5, SO2, NH3, PM10, VOC and CO.
can be downloaded with its User Guide from
uses PM2.5 and the PM10 emission factors to represent primary emissions.
VMT estimates should be developed by vehicle type and speed (to represent specific road types) and the VMT should then be matched
to the corresponding MOBILE 6 emission factors for the same vehicle type and speed, and representing the same time period, to form the basis of emission calculations.

4. MOBILE6 Modeling Inputs
PM inventories are annual
Contrasts with seasonal ozone or CO inventories
MOBILE6 runs should represent multiple seasons
Generally either 12 sets of monthly inputs or 3 to 4 sets of seasonal inputs
Some MOBILE6 inputs will be same as those used for ozone or CO modeling:
Registration distribution
Control programs
Seasonal (or monthly) inputs are needed for a PM inventory to capture differences in ambient conditions and fuel programs that would affect emissions.
In the case of using 3 seasons, the seasons are generally summer, winter, and spring/fall.
Local registration distributions are important for PM inventories, just as the are for ozone inventories, as these will affect the rate at which new emission standards get incorporated into the fleet. Differences between the MOBILE6 default distribution and actual distributions from local areas can lead to significant differences in the resulting emissions.

5. MOBILE6 Modeling Inputs (cont’d)
Some data needs to correspond to month/season being modeled
Ambient conditions
Fuel parameters
Speeds/speed distributions (may not change by season)
VMT mix (may not change by season)
PM2.5 emission factors fairly insensitive
No temperature or speed correction factors applied in MOBILE6
No deterioration with age in PM emission factors
One additional data input required for MOBILE 6 modeling that was not required in the past is the diesel sulfur content expressed in parts per million.
Also, there are additional commands needed for generating PM2.5 inventories in MOBILE 6.
The commands are described in the MOBILE user’s guides developed by OTAQ.
Note that when you develop a PM inventory, you cannot do a PM2.5 and a PM10 inventory simultaneously.
As a result, it is necessary to specify just one particle size per each run.

6. MOBILE6 Modeling Inputs (cont’d)
Additional data required for PM modeling in MOBILE6
Diesel sulfur content (in parts per million [ppm])
Additional commands needed for MOBILE6
Described in MOBILE6 User’s Guide
PM2.5 and PM10 emission factors cannot be calculated in same scenario – particle size must be specified in each scenario
One additional data input required for MOBILE 6 modeling that was not required in the past is the diesel sulfur content expressed in parts per million.
Also, there are additional commands needed for generating PM2.5 inventories in MOBILE 6.
The commands are described in the MOBILE user’s guides developed by OTAQ.
Note that when you develop a PM inventory, you cannot do a PM2.5 and a PM10 inventory simultaneously.
As a result, it is necessary to specify just one particle size per each run.

7. National Mobile Inventory Model (NMIM)
Creates emission inventories at the national level or for any combination of states/counties
Consolidated emissions modeling system
Combines a graphical user interface, MOBILE6, NONROAD, and a county database
Database contains most recent information used in the NEI
National Mobile Inventory Model:
a tool developed by OTAQ to create national or sub-national emission inventories for any calendar year
uses county-specific input parameters
a consolidated emissions modeling system for EPA’s MOBILE and NONROAD models
combines a graphical user interface, MOBILE6, NONROAD, and a database with modeling information for each county in the United States.
Currently this database contains the most recent information (e.g., fuel parameters, registration data, temperatures, etc.) used by EPA to generate the default National Emission Inventory estimates for each county.
EPA has used NMIM to prepare historical and projection year emission inventories for a number of recent rulemakings.

8. National Mobile Inventory Model (NMIM) (cont’d)
Calculates criteria pollutants and HAP emissions (whereas MOBILE6 only calculates emission factors)
All estimates based on same input parameters
Used to generate 2002, 2005, and draft 2008 NEI
Optional for states
Available for general use in 2004
Produces same results as MOBILE6 and NONROAD
NMIM:
can calculate both criteria (including ammonia) and HAPs for the source categories included in the MOBILE6 and NONROAD models.
consolidates all the model inputs into a single data base such that all the estimates are based on the same input parameters in each county (e.g., fuel programs, inspection/maintenance, humidity, temperatures).
is an optional tool for states to use in estimating mobile source inventories by organizing and automating emission inventory development for highway vehicles and NONROAD categories.
is not a substantively different approach than directly using MOBILE 6 and NONROAD.
This tool was developed to make creating inventories easier and does not change the answers that are obtained from running MOBILE or NONROAD individually.
State use:
States may wish to customize all or part of their own inventory generation process to the NMIM model approach.
This will allow them to take advantage of its efficiency and transparency, and to align the NEI inventory results more closely with their own inventory estimates.
State and local agencies will be able to use the database to view the county-level default values and to replace them with data that better represents their geographic areas.

9. Sources of VMT Data State Department of Transportation
Metropolitan Planning Organization
2002/2005 NEI VMT Data based on:
State-provided VMT
FHWA HPMS data summaries
By roadway type and State
By roadway type and Urban Area
Nationally by Vehicle Type
State departments of transportation typically provide VMT data.
Metropolitan planning organizations track these data for certain areas. However, VMT data should be used from whatever source it is available.
MPO transportation modeling generally validates local VMT estimates against FHWA’s Highway Performance Modeling System VMT data.
State DOTs are required to submit VMT data for certain road types to FHWA annually.
Summaries of the annual FHWA HPMS data can be found online in FHWA’s Highway Statistics publications

10. VMT Approach
Distributions of VMT by roadway type, vehicle type, by hour of day can be applied directly to VMT or included within MOBILE6 input files
Also need to have speeds matched to roadway types either as average speeds or as speed distributions by speed ranges
In the case of the NEI, the VMT data was developed for use in conjunction with MOBILE 6 by using the distributions of VMT by roadway type and vehicle type. In some cases this activity data may be available by hour of the day.
Regardless of the format, these fractions can be applied directly to the total VMT, or they can be included within the MOBILE 6 input files in order to generate a weighted emission factor in MOBILE 6.
It is important to have speeds matched to the roadway types, either as an average speed or as speed distributions by speed ranges.
This latter approach is the approach needed for link-based VMT development and some transportation demand models.

11. Level of Detail of VMT Data
By county
By roadway type (or link level)
By vehicle type
Appropriate time period
Ideally, the level of VMT data that should be used is by county and by the various roadway types or link level if modeling at that level is planned.
Using data by vehicle type is important since emission rates can vary greatly among the different vehicle types.
Using vehicle type data will allow the adjustments to be made to the national defaults that are typically used.
It is important to match the VMT data (daily or hourly) to the appropriate time period for modeling.

12. Calculating Onroad Emissions
Match VMT to corresponding MOBILE6 emission factor
Map according to speed, roadway type (RT), vehicle TYPE (VT), time period
Emis = VMT  EF  K
Emis = emissions in tons by RT, VT
VMT = vehicle miles traveled on RT by VT in miles
EF = emission factor in grams/mile by RT, VT
K = conversion factor
VMT data should be matched to a corresponding MOBILE 6 emission factor and mapped according to speed, roadway type, vehicle type, and time period.
Emissions are calculated by multiplying the VMT data by an emissions factor as shown in the equation on this slide.

13. MOVES MOVES is a completely new model
New data, structure, capabilities
New fleet and activity defaults
Updated emission rates based on recent test data
Significant PM testing of light-duty gas vehicles through Kansas City Study
496 light-duty gas cars and trucks tested from model years
Vehicles tested in summer and winter conditions
Results of study indicate that MOBILE6 underestimated PM, particularly at cold temps
MOVES is not a carry-over from MOBILE6. It was built from the ground up.
Other new test data have also been included in MOVES
Because MOVES is database-oriented, it can easily be updated by EPA (or others) as additional new testing data become available.

14. Preparing for MOVES
Can be run at a national, county, or project level of detail
Converters and importers available with draft MOVES2009
Can be used to convert MOBILE6 inputs to MOVES-formatted data (e.g., for age-based registration distributions) in near-term
For long-term use, states should collect data that better maps to MOVES
MOVES can be run either through the GUI or via a batch mode using run scripts.
The databases are in MySQL, which is free and non-proprietary.
State agencies and MPOs should develop staff capabilities in using MySQL and the associated query language. This is the easiest way to customize MOVES output to the needs of an individual agency, for both importing local inputs and manipulating model outputs.
EPA has prepared several converters to convert data in MOBILE6 format to MOVES format: registration distributions, speed distributions
Agencies should learn to use the County Data Manager in MOVES in order to easily pull in local data into the MOVES database.
When run at the county level, data sets for each county that an area needs to model must be imported separately, but there are ways to automate this process somewhat.
MOVES includes several scripts for developing reports. Users can develop their own customized scripts which can then be run on any MOVES output database.
Agencies should plan to attend one of EPA’s MOVES training sessions.

15. Preparing for MOVES National trends Local inputs important
PM emissions substantially higher than MOBILE6
NOx emissions generally higher than MOBILE6
HC, CO emissions similar to or lower than MOBILE6
Local inputs important
Fleet mix, fuels, activity
Temperature significantly affects PM
EPA performed an analysis of 3 metropolitan areas, comparing MOVES results to MOBILE6 results.
Each area was modeled using 1 county within the area as a surrogate for that area.
Emissions were calculated for January and July monthly conditions with each result multiplied by six and then summed together to represent annual conditions. Results were analyzed separately for light-duty and heavy-duty vehicles.
Results are shown on the next 3 slides.

16. City-Specific PM2.5 Emissions
Source: EPA, 2009

17. City-Specific NOx Emissions
Source: EPA, 2009

18. City-Specific HC Emissions
Source: EPA, 2009

19. MOVES Schedule Draft MOVES2009 released April 2009
No official uses for this model
Official MOVES2009 to be released by end of 2009
Use will be required for
Next round of SIPs (due 2012 and 2013)
Regional conformity analysis following conformity grace period of 3-24 months
Project level conformity following grace period
NEPA analysis (e.g., air toxics)

20. Additional Resources MOBILE6 website: http://www.epa.gov/otaq/m6.htm
MOVES website:
There are a number of online resources to consult when developing an emissions inventory for onroad sources.
The above sites include available background documents.
Information on MOVES training sessions is available at the MOVES web site above. It also contains the materials from the EPA training course, which can be a valuable resource in getting started in running MOVES.