Executive Summary

Hot-spot analysis, also known as project-level analysis, assesses impacts of transportation emissions on local air pollution of carbon monoxide (CO) and particulate matter (PM). It is required for regional transportation plans (RTP), transportation improvement programs (TIP) and transportation project development/modification by transportation conformity rules and NEPA process. Such transportation conformity studies are particularly important in non-attainment areas and locales with concentrated and heavily traveled transportation infrastructures (e.g., major transportation corridors, border crossings, congested intersections, etc.). Gaussian plume dispersion models of line sources have been widely used in quantitative hot-spot analysis of CO from transportation sources. These models incorporate the effects of dispersion caused by dilution and air movement. These models have proven successful in modeling inert gaseous pollutants such as CO with sound scientific basis satisfying empirical accuracy.

However, the Gaussian dispersion models do not account for any chemical reactions or other physical dynamics such as condensation, coagulation and deposition; which have been shown critical for quantitative modeling of particulate matter (PM) on hot-spot spatial scales. To the best of the PIs’ knowledge, quantitative hot-spot modeling tools do not exist to adequately characterize gradients in concentrations of PM, PM components (such as black carbon), and PM precursors near roadways. On the other hand, fast growing evidence of the adverse effects of fine particles on public health, especially of those near roadways, has pushed the imperative need for such tools that can be used in transportation planning, air quality management and exposure assessment.

We propose to develop an advanced process-based hotspot analysis model of fine particulate matters (< 2.5 ?m in aerodynamic diameter, PM2.5). By “process-based”, the model aims to take into account key chemical reactions and physical dynamics that govern the evolution of fine particles as they disperse from road sources to near road receptors. We will first develop an advanced single-link, processes-based dispersion model (SPDM). To apply it in the multi-link environment typical of major metropolitan areas, we will divide the roadway system within the study area into discrete segments of varying link geometry so that each segment can be effectively treated as a single, straight line source. Thus the SPDM can be employed for each element. The impact of each element will be integrated to yield the total of multiple highways. The resultant product is a multi-link, processes-based dispersion model (MPDM).

For urban and regional (km-scale) background PM concentrations to be used in hot-spot analysis, we will employ a state-of-science grid-based air quality model, CMAQ-UCD, which has incorporated an advanced PM module previously developed and validated by the PI. A microscale emission inventory will be created by coupling the MOVES model and microscopic traffic simulation models. Next improved wind field will be constructed by assimilating measured wind data into the existing wind field. Finally all these inputs will be fed into the MPDM to conduct hotspot modeling. The study has been motivated by the transportation and air pollution problems in the South Bronx, New York City (NYC). As a case study, this model will be applied to the South Bronx, which is encircled by major highways. The Bronx has been the New York City borough with the highest overall rates of asthma hospitalizations, deaths and prevalence among children as well as adults. Recent studies have linked asthma to exposure to diesel particulate matters from transportation emissions in the South Bronx. We will compare the model results of PM2.5 and black carbon concentrations from hot-spot analysis to intensive measurement data previously collected by researchers from New York University.

The advanced features of the MPDM include that 1) it is able to simulate both transport and transformation of mobile emissions, and 2) it is capable of dealing with complicated geometry and interactions of multiple highways. Although this study focuses on the South Bronx for a case study, the methodologies and models developed can be readily applied in other hot-spot analyses. The study will mark a critical step toward the next generation hotspot modeling, providing transportation policy makers a scientifically sound and quantitative tool for environmental assessment of transportation projects.