Christopher FREY

Ph.D., Engineering and Public Policy, Carnegie Mellon University
Adjunct Professor, Division of Environment and Sustainability

Tel: (852) 2358 8363
Office: Rm 4412(lift 17/18)
Link(s): Personal Home Page

Research Area

Air pollutant emission inventories; prevention and control of air pollutant emissions; human exposure to air pollution; quantification of variability and uncertainty and environmental risk assessment.


Research Interests and Biography

H. Christopher Frey is the Glenn E. Futrell Distinguished University Professor of environmental engineering in the Department of Civil, Construction, and Environmental Engineering at North Carolina State University in Raleigh, NC, USA. Dr. Frey is an Adjunct Professor in the Division of Environment and Sustainability of the Hong Kong University of Science and Technology.  At HKUST, Dr. Frey conducts collaborative research regarding measurement and modeling of human exposure to air pollution and regarding linkages between emissions, air quality, exposure, and adverse effects on human health. Dr. Frey has taught ENVR 2020 Urban Air quality and ENVR 6040 Environmental Exposure and Risk Assessment.

Dr. Frey‘s research interests are measurement and modeling of real-world fuel use and emissions of onroad and nonroad vehicles; measurement and modeling of human exposure to air pollution; modeling and evaluation of advanced energy conversion (e.g., combustion, gasification) and environmental control systems; development and application of methods for quantification of variability and uncertainty and for sensitivity analysis in environmental systems models; and exposure and risk analysis.

At NC State, Dr. Frey teaches CE 476/CE 576 Air Pollution Control, CE 479/CE 579 Air Quality, and CE 772 Environmental Exposure and Risk Assessment.

From 2012 to 2015, Dr. Frey was Chair of the U.S. Environmental Protection Agency’s Clean Air Scientific Advisory Committee (CASAC).  He chaired CASAC review panels on ozone, nitrogen dioxide, and lead.  He currently serves on CASAC review panels for Particulate Matter, Nitrogen Oxides, and Sulfur Oxides.  He is a member of the U.S. EPA Science Advisory Board since 2012. In recent years, he has served on the Board of Environmental Studies and Toxicology of the National Research Council, an EPA Science Advisory Board panel on expert elicitation, an advisory committee on EPA's "MOVES" vehicle emission factor model, National Research Council committees on review of the toxicological assessment of tetrachloroethylene and of EPA’s New Source Review program, a NARSTO assessment of multipollutant air quality management, and a World Health Organization working group on uncertainty in exposure assessment. He was a lead author for 2006 guidance by the Intergovernmental Panel on Climate Change (IPCC) regarding uncertainty in greenhouse gas emission inventories.

Dr. Frey is a Fellow and Past President of the Society for Risk Analysis and a Fellow of the Air & Waste Management Association. Dr. Frey has a B.S. Mechanical Engineering from the University of Virginia, and from Carnegie Mellon University he has a Master of Engineering in Mechanical Engineering and PhD in Engineering and Public Policy.


Recent and Representative Publications
  • Khan, T., and H.C. Frey, “Comparison of Real-world Versus Certification Emission Rates for Light Duty Gasoline Vehicles,” Science of the Total Environment (2018)
  • Li, Z., W. Che, H.C. Frey, A.K.H. Lau, “Characterization of PM2.5 Exposure Concentration in Transport Microenvironments Using Portable Air Monitors,” Environmental Pollution, 228:433-442 (2017).
  • H.C. Frey, M. Delavarrafiee, and S. Singh, “Real-World Freeway and Ramp Activity and Emissions for Light Duty Gasoline Vehicles,” Transportation Research Record, 2627:17-25 (2017). 
  • Li, Z., W. Che, H.C. Frey, A.K.H. Lau, “Factors Affecting Variability in PM2.5 Exposure Concentrations in a Metro System,” Environmental Research, 160C:20-26 (2017).
  • Khan, T., and H.C. Frey, “Evaluation of Light Duty Gasoline Vehicle Rated Fuel Economy Based on In-Use Measurements,” Transportation Research Record, 2570:21-29 (2016).
  • Graver, B.M., and H.C. Frey, “Comparison of Over-the-Rail and Rail Yard Measurements of Diesel Locomotives,” Environmental Science and Technology, 49(21):13031-13039 (2015), DOI: 10.1021/acs.est.5b02497.
  • Zhou, X., S. Tanvir, H. Lei, J. Taylor, B. Liu, N.M. Rouphail, and H.C. Frey, Integrating a Simplified Emission Estimation Model and Mesoscopic Dynamic Traffic Simulator to Efficiently Evaluate Emission Impacts of Traffic Management Strategies, Transportation Research – Part D, 37(2015):123-136.
  • Liu, B., and H.C. Frey, “Variability in Light Duty Gasoline Vehicle Emission Factors from Trip-Based Real-World Measurements,” Environmental Science & Technology, 49(20):12525-12534.  DOI:  10.1021/acs.est.5b00553 (2015)
  • Jiao, W., and H.C. Frey, “Method for Measuring the Ratio of In-Vehicle to Near-Vehicle Exposure Concentrations of Airborne Fine Particles,” Transportation Research Record, 2341:34-42 (2013).
  • Mannshardt, E., K. Sucic, W. Jiao, F. Dominici, H.C. Frey, B. Reich, and M. Fuentes, Comparing Exposure Metrics for the Effects of Fine Particulate Matter on Emergency Hospital Admissions, Journal of Exposure Science and Environmental Epidemiology, 23:627-636 (doi:10.1038/jes.2013.39). (2013)
  • Che, W., H.C. Frey, and A.K.H. Lau, “Comparison of Sources of Variability in School Age Children Exposure to Ambient PM2.5,” Environmental Science and Technology, 2015, 49(3):1511–1520.
  • Jiao, W., and H.C. Frey, “Comparison of Fine Particulate Matter and Carbon Monoxide Exposure Concentrations for Selected Transportation Modes,” Transportation Research Record, 2428(2):54-62 (2014).
  • Che, W., H.C. Frey, and A. Lau, “Assessment of the effect of population and diary sampling methods on estimation of school-age children exposure to fine particles,” Risk Analysis, 34(12):2066-2079 (December 2014), DOI: 10.1111/risa.12238.
  • Chang, H.H., M. Fuentes, and H.C. Frey, “Time Series Analysis of Personal Exposure to Ambient Air Pollution and Mortality Using an Exposure Simulator,” Journal of Exposure Science and Environmental Epidemiology, 22, 483-488 (2012) doi:10.1038/jes.2012.53. 
  • Cao, Y., and H.C. Frey, “Geographic differences in inter-individual variability of human exposure to fine particulate matter,” Atmospheric Environment, 45(32):5684-5691 (2011)
  • Liu, X., and H.C. Frey, “Modeling Of In-Vehicle Human Exposure to Ambient Fine Particulate Matter,” Atmospheric Environment, 45(27):4745-4752 (2011).
  • H.C. Frey, K. Zhang, and N.M. Rouphail, “Vehicle-Specific Emissions Modeling Based Upon On-Road Measurements,” Environmental Science and Technology, 44(9):3594-3600 (2010).
  • H.C. Frey, H. Zhai, and N.M. Rouphail, “Regional On-Road Vehicle Running Emissions Modeling and Evaluation for Conventional and Alternative Vehicle Technologies,” Environmental Science and Technology, 43(21):8449–8455 (2009).
  • Pang, S.H., H.C. Frey, and W.J. Rasdorf, “Life Cycle Inventory Energy Consumption and Emissions for Biodiesel versus Petroleum Diesel Fueled Construction Vehicles,” Environmental Science and Technology, 43(16):6398-6405 (August 15, 2009).
  • Ozkaynak, H., H.C. Frey, J. Burke, and R.W. Pinder, “Analysis of coupled model uncertainties in source to dose modeling of human exposures to ambient air pollution: a PM2.5 case-study,” Atmospheric Environment, 43(9): 1641-1649 (March 2009).
  • H.C. Frey, W.J. Rasdorf, K. Kim, S.H. Pang, P. Lewis, “Comparison of Real-World Emissions of B20 Biodiesel Versus. Petroleum Diesel for Selected Nonroad Vehicles and Engine Tiers,” Transportation Research Record, 2058:33-42 (2008).  DOI: 10.3141/2058-05.
  • Zhai, H., H.C. Frey, and N.M. Rouphail, “A Vehicle-Specific Power Approach to Speed-  and Facility-Specific Emissions Estimates for Diesel Transit Buses,” Environmental Science and Technology, 42(21):7985-7991 (2008).
  • Mokhtari, A., H.C. Frey, and J. Zheng, “Evaluation and recommendation of sensitivity analysis methods for application to Stochastic Human Exposure and Dose Simulation (SHEDS) models,” Journal of Exposure Science and Environmental Epidemiology, 16(6):491-506 (Nov 2006).
  • Zheng, J., and H.C. Frey, “Quantitative Analysis of Variability and Uncertainty with Known Measurement Error:  Methodology and Case Study,” Risk Analysis, 25(3):663-676 (2005).
  • H.C. Frey, and Y. Zhao, “Quantification of Variability and Uncertainty for Air Toxic Emission Inventories With Censored Emission Factor Data,” Environmental Science and Technology, 38(22):6094-6100 (2004).
  • Zheng, J., and H.C. Frey, “Quantification of Variability and Uncertainty Using Mixture Distributions:  Evaluation of Sample Size, Mixing Weights and Separation between Components,” Risk Analysis, 24(3):553-571 (June 2004).
  • H.C. Frey, A. Unal, N.M. Rouphail, and J.D. Colyar, “On-Road Measurement of Vehicle Tailpipe Emissions Using a Portable Instrument,” Journal of Air & Waste Manage. Assoc., 53(8):992-1002 (August 2003).
  • H.C. Frey, and S.R. Patil, “Identification and Review of Sensitivity Analysis Methods,” Risk Analysis, 22(3):553-578 (June 2002).
  • H.C. Frey, and D.S. Rhodes, “Characterizing, Simulating, and Analyzing Variability and Uncertainty:  An Illustration of Methods Using an Air Toxics Emissions Example,” Human and Ecological Risk Assessment: an International Journal, 2(4):762-797 (December 1996).
  • H.C. Frey, and E.S. Rubin, “Evaluation of Advanced Coal Gasification Combined-Cycle Systems Under Uncertainty,” Industrial and Engineering Chemistry Research, 31(5):1299-1307 (May 1992).