H. Christopher Frey

Research Interests



Current and Recent Projects

Past Projects

Computer Laboratory

Frey Research Group

Professional Activities

Real-World Vehicle Emissions

Areas of Research Interest

Dr. Frey’s research interests are broadly in the area of energy and the environment, and specifically in:  (1) measurement and modeling of in-use vehicle activity, fuel use, and emissions for onroad and nonroad vehicles; (2) modeling and evaluation of fossil-fuel-fired power generation systems and associated air pollution control technologies; (3) environmental exposure and risk analysis; and (4) quantification of variability and uncertainty in environmental systems and models.

Measurement and Modeling of Activity, Fuel Use, and Emissions of Onroad and Nonroad Vehicles


Dr. Frey leads research at NC State to characterize and evaluate fuels, technologies, and strategies for reducing vehicle fuel consumption and emissions in the real-world.  His research addresses on-road light (e.g., cars, minivans, SUVs) and heavy vehicles (including trucks, transit buses, and school buses), as well as construction vehicles and diesel locomotives.  He is a leader in the use of Portable Emission Measurement Systems (PEMS) that can be temporarily installed on a vehicle in order to collect data on vehicle activity, fuel use, and emissions under real-world conditions.  He applies this methodology to policy-related research questions of local, national, and international importance.   His work includes life cycle assessment of energy use and emissions for the entire fuel cycle, not just for the vehicle.  His results provide insight into priorities for choices among fuels, technologies, traffic management strategies and improvements to duty cycles in order to reduce fuel use and emissions.  For example, we have found that improved signal timing and coordination reduce emissions by 10 to 20 percent.  Relieving congestion reduces emissions by as much as 50 percent.  Replacing older vehicles with newer vehicles reduces emissions by as much as 60 to 70 percent, while improving fuel economy.  Dr. Frey’s comparison of soy-based B20 to petroleum diesel for 35 in-use shows consistent reductions in tailpipe NO emissions, as well as confirming 20 to 25 percent reductions in emissions of CO, HC, and PM.  He is also evaluating other alternative fuels, additives, lubricants, and technologies.  Dr. Frey provides an objective and quantitative method for real-world evaluation of new fuels and vehicle technologies to accurately inform the policy debate regarding energy, air pollution, and climate change.

Air Pollution Characterization, Prevention, and Control for Power Generation and Other Sources

Much of Dr. Frey’s work involves characterizing emission rates from various types of emission sources, including major stationary sources such as power plants, and mobile sources such as highway vehicles. He is interested in identifying methods for preventing the formation of air pollution, such as through better process design in the case of power generation or through better management in the case of highway systems. Air pollution control technologies are sometimes the most effective approach for reducing emissions of air pollutants. For more than 20 years, he has done work in modeling and assessment of air pollution control technologies. This work has been primarily with respect to coal-based power generation technologies, but includes air pollution control from natural gas and oil-fired power plants as well as from a wide variety of other emission sources.

Electricity is often the preferred form of energy delivery. Global growth in demand for power generation provides an opportunity to introduce more efficient and environmentally cleaner technologies. Dr. Frey’s research on advanced power generation technologies has focused on coal-based systems, including: (a) advanced environmental control technologies for conventional coal-fired power plants; (b) coal gasification-based technologies, such as Integrated Gasification Combined Cycle (IGCC); and (c) other power generation cycles, such as the externally-fired combined cycle. This work has typically involved the development of detailed performance, emissions, and cost models of each technology alternative and applications of the models to answer key questions about technology feasibility and research needs. A key feature of this work has been a quantitative approach to characterizing uncertainty inherent in making predictions about the future performance and cost of technologies that are currently in early stages of research and development.

Exposure and Risk Assessment

In exposure assessment, it is important to take into account interindividual variability, which refers to the real differences in activity patterns and other characteristics of one individual versus another. These differences lead to variation in the frequency and duration with which individuals come into contact with chemicals in various types of environments (e.g., outdoors, home, work). Uncertainty refers to the lack of knowledge that may exist due to limitations of existing data, including small sample sizes, measurement errors, and lack of representativeness. All of these sources of variation in exposure, and in our ability to accurately predict exposures, pose significant challenges in performing exposure assessments. Additional variability and uncertainty exists in making predictions of the likelihood that an exposure will result in an adverse effect. Dr. Frey is interested in the development and application of better methods for quantifying and analyzing both variability and uncertainty in the context of exposure and risk assessment.

Quantitative Analysis of Uncertainty and Variability


Dr. Frey’s research includes a common theme of quantitative analysis of variability and uncertainty in energy and environmental systems. This type of analysis is important in bridging the gap between technical analysis and public policy making. Many times, scientists and engineers are asked to provide information to policy makers that is not yet on a solid empirical and theoretical foundation. Alvin Weinberg discusses this dilemma in detail in his article, "Transscience" (published in the journal Minerva). Thus, partly as a matter of professional integrity, but also because it helps focus research and enables decision makers to understand the risks of being wrong, it is important to convey both what is known and what is not known about the technical aspects of policy-related problems.

Dr. Frey has developed or contributed to several software tools for evaluation or control of environmental pollution, including the Integrated Enviromental Control Model, AUVEE, and AuvTool.  The latter are probabilistic tools for quantifying variability and uncertainty in emission inventories and for data sets, respectively.  He has also contributed to international guidance documents on uncertainty, such as for NARSTO, IPCC, and WHO.


Updated November 5, 2008