 |
NARSTO Workshop on Innovative Methods for Emission Inventory Development and Evaluation University of Texas, Austin October 14-17, 2003 |
 |
Poster 13: Federal Highway Administration's Particulate Matter
Ambient Concentration and Traffic Correlation Study
Kevin N. Black
Federal Highway Administration
Federal Highway Administration (FHWA) has been performing a study to determine if accurate correlations could be made between the vehicle component of particulate matter (PM) emissions and ambient air concentrations. The reason this study is being conducted is to determine whether the current mobile source emission inventories are accurately reflecting the vehicle contribution. Ambient air quality is a function of the emissions of all sources in addition to the weather and the local site geography. The concentrations of pollutants are also a function of the reactivity of the compounds being emitted. Because of the complexity and inter-reactivity of the sources and the atmosphere, trying to correctly apportion the mobile source component is a challenge.
Ambient concentrations are measured to provide “instantaneous” information about air quality conditions in an area. Air quality models are used to “predict” future air quality resulting from specific changes to an area due to demographic changes, economic activity, and air quality improvement programs that have been established to reduce air pollution. The basis of air quality improvement programs begins with an emission inventory establishing the contribution from all sources. The permitting process for stationary sources requires monitors and monitoring programs capable of accounting for air pollution releases generated by the specific permitted industries. Mobile sources do not have this capability and rely on the development of inventories from emission factor models such as the MOBILE model and from traffic data. Both traffic data and emission factors calculated by the MOBILE model have significant variability, measuring traffic volume as a surrogate for monitoring direct emissions and comparing this with the ambient concentrations throughout the day is intended to assess the accuracy of the mobile source emission inventory.
This paper outlines the FHWA Particulate Matter - Traffic Correlation Study and provides comparison data between the emission inventory for a specific area and the correlation effort between vehicles activity and ambient concentration. The study was performed for five cities representing different geographic areas and vehicle fleets. It illustrates how inventory data compares to monitored ambient concentrations and traffic and how these can be used to determine the accuracy of the mobile source component of ambient particulate matter concentrations.