The Advanced Energy Systems Group

Populations near roads are exposed to a mixture of traffic-related primary and secondary pollutants. Approximately 30–45% of urban populations in the United States are likely exposed to elevated pollution levels near major roadways. In many countries with densely populated urban areas, this figure is likely higher. Emission reduction programs implemented by government agencies throughout the world have significantly reduced emission rates of air pollutants from motor vehicles. In spite of these reductions, motor vehicles still significantly contribute to pollution in urban areas, often due to large increases in vehicle use offsetting per vehicle emission reductions.

Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry Model (CTAG)

Our modeling framework is called Comprehensive Turbulent Aerosol Dynamics and Gas Chemistry (CTAG), a computational fluid dynamics (CFD)-based environmental turbulent reacting flow model designed to simulate the transport and transformation of multiple air pollutants on and near roadways. Figure 1 describes the structure and the components in CTAG. A brief introduction is given below. On the pollutant transport side, CTAG is designed to capture the major turbulentmixing processes in the roadway environments: vehicle-induced turbulence (VIT) and road-induced turbulence (RIT) and atmospheric boundary layer turbulence (ABLT). RIT includes turbulence due to roadway configuration, road surface properties and roadside structures. On the transformation side, currently CTAG has incorporated NOx chemistry and aerosol processes such as nucleation, condensation/evaporation, and coagulation. Additional chemical mechanisms such as detailed photochemical reactions of volatile organic carbon VOC) can be added on. The on-road and near-road simulations are linked by implements a multi-scale structure in CTAG.

In addition to numerical simulations, researchers at EERL also conducted field measurements charactering the air pollution gradients near the intersection of I-81 and I-690 in downtown Syracuse, and the Impact of local traffic exclusion on near-road air quality in New York City.

Figure 1: CTAG framework and components

CTAG implements a multi-scale structure (Figure 2) based upon the mechanistic roadway air quality modeling framework proposed by Zhang and Wexler (2004). CTAG resolves aerosol dynamics and gas-phase chemistry in the on-road domain (i.e., “tailpipe-to-road”) and near-road domain (i.e., “road-to-ambient”), respectively. The turbulent mixing process on the on-road domain is dominated by VIT, and is dominated by RIT and ABLT for the near-road domain. CTAG first resolves the plume dynamics behind individual vehicles, and the subsequent interactions of multiple plumes in the on-road domain. The processed on-road emissions will serve as inputs to the near-road domain simulations, where CTAG resolves the dynamics of roadway plumes in the roadside micro-environments. The processed roadway plume profiles on the near-road domain can be used as inputs to regional-scale air quality simulations. This multi-scale structure enables CTAG to serve as an advanced analytical tool for a variety of applications.

Reference

Yan Wang. Modeling the evolution of vehicle exhaust plume near road and in laboratory dilution systems using the CTAG model. Ph.D. dissertation. 2012.