DEVELOPMENT OF MODELING INVENTORY FACTORS FOR MOBILE SOURCE PARTICULATE ORGANIC CARBON AND SEMI-VOLATILE ORGANIC COMPOUND EMISSIONS

Project No. A-71

Leaders:   R. S. MacArthur    
                  D. R. Lawson

Scope and Objective

The study will evaluate, develop, and demonstrate procedures for adjusting existing primary organic carbon particulate matter (primary OC) and semi-volatile organic compound (SVOC) mobile source emissions.  The objectives include:

1. Evaluating and adjusting the existing emissions inventories for selected metropolitan areas, using stochastic or deterministic methods:

• on-road gasoline fleet (not addressed in item 3), below
• on-road diesel
• off-road gasoline
• off-road diesel

2. Defining objective metrics for intercomparison of emissions inventories, monitored air quality data, and source apportionment model estimates; and
3. Developing adjustments to the on-road LD inventory using vehicle emissions testing results.

Current Status and Future Program

This project approach was developed in cooperation with NREL, LADCO, MARAMA, and EPA.  The main users of the project are expected to be regional organizations such as LADCO and MARAMA for their PM modeling sensitivity studies.

Analyses of nonattainment area monitoring data show that in most areas, the primary chemical constituents of PM2.5 are sulfates, nitrates, organic carbonaceous mass (OC), and elemental carbon (EC).  States are using chemical transport models (CTM) and dispersion models to develop control plans for PM2.5.  While model performance is good for sulfates and nitrates (in the eastern U.S.), model performance for OC is generally poor.  Despite recent efforts to improve model chemistry and emissions for SOA, the model predictions of OC concentrations remain uncertain.  One explanation for such discrepancies are VOC and primary OC emissions inventories and speciation profiles (in particular, mobile sources) which have been identified as major sources of primary OC (and SVOC) in urban areas by source apportionment studies.  Another possible reason is that extensive SOA is being formed not accounted in the chemical reactions used in the modeling.

The emissions inventory adjustments developed in this project will be used to support early planning by states to address upcoming air quality challenges.  It should be noted that EPA is developing a draft MOVES model scheduled for public release in 2008.  This version of MOVES will include updated estimates of on-road gasoline and diesel PM, primarily from the E-69 Kansas City study and CRC E-55, respectively.  This project is expected to provide information which will assist in an independent assessment of MOVES.  We expect the proposed methodology will derive from a combination of analyses related to light-duty spark-ignition (LDSI) vehicular emission factors, source apportionment techniques, and chemical transport modeling of PM.   

The matrix for mapping the adjustment factors from the Kansas City adjusted mobile source inventory to a Detroit inventory and one additional city would be required by season (temperature), vehicle class (LDGV, LDGT), emissions mode (LA92 or from continuous measurement), roadway classification (i.e., driving behavior), and other changes according to differences in on-road vehicle emissions modeling (MOBILE6.2 inputs).

CRC issued a request for proposal for Project A-71 on behalf of anticipated co-sponsors NREL and MARAMA.  The Project Panel reviewed proposals and a decision was made to allow other sponsors to proceed with project funding while CRC funding was directed to other project priorities.

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