Readme File for TIER2.EXE - Version of MOBILE5b used in Tier 2 Study

5/18/98
U.S. Environmental Protection Agency
Office of Transportation and Air Quality

EPA is releasing the version of MOBILE5b used in support of the draft

Tier 2 study, consisting of an executable version of the modified

model (TIER2.EXE) and input files for the four geographic regions used

in the study (NRTHEAST.IN, CHICAGO.IN, ATLANTA.IN, ATTAIN.IN).  In

doing so, EPA intends to share the modeling tools and assumptions used

in developing the air quality assessment in the study.  Several

caveats apply to this model which the user needs to be aware of:



1.   This version of MOBILE5b is a tool used solely for the purpose of

regulatory analysis.  It is not being released for use in SIPs or

other purposes for which the MOBILE model is required, and does

not constitute EPA guidance for such applications.  EPA will not

provide extensive support in the use of this model. 



2.   The "Modified MOBILE5b" model, as such, consists of the TIER2.EXE

model run in conjunction with the provided input files.  The

input files contain the substantive revisions made to the model,

and implicitly account for some factors (such as I/M) through the

use of adjusted basic emission rates (BERs).  For this reason,

many of the adjustments contained within the conventional

MOBILE5b model are not valid when used with the revised input

files (for example: I/M credits, methane offsets, additional load

corrections).



3.   The "with I/M" scenarios approximate the benefits of an IM240

test, based on a combination of I/M assumptions from OTAG

modeling and ARB's CALIMFAC model.  The I/M assumptions are not

meant to reflect the program details for any particular

geographic case modeled.



4.   The modified MOBILE5b model will change as updated information

regarding changes proposed for MOBILE6 becomes available. 



One note regarding execution of the model: TIER2.EXE is simply

MOBILE5b modified to accept a greater number of basic emission rates

(BERs) and provide flexibility for the point at which the second

deterioration rate (DR2) of the BER is implemented.  Thus, TIER2.EXE

is run in an identical fashion to MOBILE5b, and requires the same

external files to be present as MOBILE5b (F77L3.EER, TECH12.D,

IMDATA.D; all are included in the download of MOBILE5b).  Documentation

for TIER2.EXE is contained in TIER2DOC.WPD (or TIER2DOC.PDF). 



Details regarding the development of the inputs used in the modified

MOBILE5b model are contained in EPA Report EPA420-R-98-004,

"Methodology for Modifying MOBILE5b in the Tier 2 Study," available on

the OTAQ Web Site, 

http://www.epa.gov/otaq/regs/ld-hwy/tier-2/index.htm. 


Model Documentation

Download TIER2 model and documentation: [320K ZIP]

Email Contact: tier2-study@epa.gov

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Readme File for TIER2.EXE - Version of MOBILE5b used in Tier 2 Study

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