Robert A. Harley

Carl W. Johnson Professor of Civil and Environmental Engineering

Contact Information


Mailing Address:
Department of Civil and Environmental Engineering, 760 Davis Hall
University of California, Berkeley, CA 94720-1710 USA

Biographical Sketch

Robert Harley is a Professor in the Department of Civil and Environmental Engineering at the University of California, Berkeley, where he has been on the faculty since 1993. He holds a bachelor's degree in Engineering Science (Chemical Engineering option) from the University of Toronto, and both M.S. and Ph.D. in Environmental Engineering Science from the California Institute of Technology (Caltech). Harley's research focuses on air quality and sustainable transportation; he is an author of over 100 papers published in peer-reviewed scientific journals. He is the inaugural holder of the Carl W. Johnson Endowed Chair in Civil and Environmental Engineering at Berkeley, awarded in recognition of his record of scholarship and university and professional service. Harley has been a visiting scientist at the University of Colorado / NOAA Aeronomy Lab in Boulder (1999-2000) and at the Max Planck Institute for Chemistry in Mainz, Germany (2011), and served as Chair of the CEE Department at UC Berkeley (2015-2018).


Courses I have taught at Berkeley include
  • E 7 (freshman level), Introduction to Computer Programming for Scientists and Engineers.
    Elements of procedural and object-oriented programming. Induction, iteration, and recursion. Real functions and floating-point computations for engineering analysis. Introduction to data structures. Representative examples are drawn from mathematics, science, and engineering. The course uses the MATLAB programming language.

  • CEE 11 (sophomore level), Engineered Systems and Sustainability.
    An introduction to key engineered systems (e.g., energy, water supply, buildings, transportation) and their environmental impacts. Basic principles of environmental science needed to understand natural processes as they are influenced by human activities. Overview of concepts and methods of sustainability analysis. Critical evaluation of engineering approaches to address sustainability.

  • CEE 100 (junior level), Elementary Fluid Mechanics.
    Principles of mechanics as applied to the statics and dynamics of incompressible fluids; open channel flow, fluid measurements, forces on submerged objects, pumps, turbines. Individual laboratory experiments conducted by the student.

  • CEE 218A (graduate level), Air Quality Engineering.
    Quantitative overview of the characterization and control of air pollution problems. Summary of fundamental chemical and physical processes governing pollutant behavior. Analysis of key elements of the air pollution system: sources and control techniques, atmospheric transformation, atmospheric transport, modeling, and air quality management.

Teaching Schedule 2020-21

Semester Course no. Course title Meeting times
Fall 2020CEE 218AAir Quality EngineeringMWF 10-11
Spring 2021CEE 11Engineered Systems and SustainabilityTBD

Research (Link to Publication List)

The atmosphere carries a heavy burden of air pollution, with large contributions to the problem coming from the combustion of coal and petroleum-derived fuels. As a society, we need to evolve towards a more sustainable, environmentally benign approach to meeting growing demands for energy. My research group uses mathematical models and data from field experiments to help understand air pollution problems and related issues in atmospheric chemistry, climate change, and emission source characterization and control.

Atmospheric Modeling

Some air pollutants are formed in situ from other precursor emissions by photochemical reactions in the atmosphere. Air pollution problems of this type, including tropospheric ozone and some components of airborne particulate matter, have complex relationships to precursor emissions. We use mathematical models to synthesize understanding of relevant processes that take place in the real atmosphere.

I am interested in development and use of diagnostic tools to assess source contributions to air pollutant concentrations, as there are typically multiple source types and regions that contribute to the problem. We quantify model sensitivity and uncertainty with respect to underlying processes and model input data (see Publication List, refs 14, 23, 41, 50-51, 53, 58, 65, 70). We use models to illuminate the reasons for observed atmospheric responses to changes in emissions that occur on various time scales ranging from diurnal to decadal (refs 15, 40, 51, 60).

An example of research on this topic is the paper by Martien and Harley (2006), Adjoint Sensitivity Analysis for a Three-Dimensional Photochemical Model: Application to Southern California. Environmental Science & Technology 40, 4200-4210.

A presentation file titled "SMOG: The Movie" posted here shows an animated series of 24 hourly ozone maps for Southern California, along with a few introductory slides summarizing motivation and key features of mathematical models for photochemical smog.

Time Series Analysis

Analysis of measured pollutant concentrations provides a complementary perspective to model-based studies. Unfortunately, the signals that we seek to detect are often hard to separate from natural variability in the system that occurs from day to day and on seasonal time scales. Changes in air pollution observed on weekly and decadal time scales may be more readily linked to changes in emissions (refs 38-39, 47-48, 52, 56). We use receptor-based models together with online measurement methods to infer, for example, temperature effects on pollutant emissions (ref 49). This is important to understanding the role of day-to-day meteorological variability in affecting air pollution levels, and also in considering possible effects of climate change.

An example of research on this topic is the paper by Rubin et al. (2006), Temperature Dependence of Volatile Organic Compound Evaporative Emissions from Motor Vehicles. Journal of Geophysical Research 111, D03305, doi: 10.1029/2005JD006458.

See also Marr and Harley (2002), Spectral Analysis of Weekday-Weekend Differences in Ambient Ozone, Nitrogen Oxide, and Non-methane Hydrocarbon Time Series in California. Atmospheric Environment 36, 2327-2335.

Sustainable Transportation

The transportation sector involves movement of both passengers and freight. This sector currently relies on petroleum-derived fuels such as gasoline and diesel. My research group has made a series of field measurements at a California highway tunnel (Caldecott, hwy 24) that document emission trends over time and, in particular, the effects of improved emission control technologies and gasoline reformulation on vehicle emissions (refs 11, 20-21, 52, 55, 59). While there has been major progress in control of emissions from gasoline-powered cars and light trucks, efforts to control emissions from large trucks and off-road diesel engines have not yet advanced so far.

I have also been a lead developer of the "fuel-based" approach to estimating vehicle emissions, in which vehicle activity is measured by fuel consumption, and emission rates are expressed per unit of fuel burned rather than per km traveled or per unit time (refs 10, 15, 17, 22, 31, 33, 48, 67, 73). Emission rates for many pollutants (e.g., CO, NOx, as well as CO2 of course) vary less over wide ranges of vehicle weight and driving conditions when normalized to fuel consumption (ref 42). This line of research has contributed to policy-relevant revisions in national and state-level air pollution emission inventories.

The freight transport sector relies heavily on diesel fuel, in contrast to passenger travel where gasoline is the dominant fuel. My research group has been working to describe the amount of diesel-related air pollution (previous estimates were flawed in various ways), and the spatial and temporal patterns of those emissions (refs 16-17, 24-25, 31, 48, 55, 59, 62, 71, 72, 76). Advanced diesel emission controls such as continuously regenerating particle traps have been installed on new engines as standard equipment since 2007, and have been retrofit on some older engines as well. Control of diesel emissions in the freight transport sector continues to raise many challenging technical and policy questions.

Mobile Laboratory
Mobile lab used to measure Port truck emissions

We are now using the Port of Oakland as a laboratory for studying coming statewide and national changes in diesel engine emissions. Because of the large numbers of marine, locomotive, and heavy truck engines operating in and around the Port, there are extra concerns about exposure to diesel exhaust in the surrounding community. We reported on the effects of an early clean-up effort to replace or install exhaust filters on Port trucks (Dallmann et al., ref. 76). A non-technical summary providing more background on this issue and a summary of research findings is available: see Berkeley Transportation Letter (Winter 2012 edition).

A paper by Millstein and Harley (ref. 67) has influenced policy on the control of emissions from off-road diesel-powered construction equipment such as bulldozers and backhoes. The scale of impact is on the order of one billion dollars statewide in California. Previous emission estimates for nitrogen oxides (NOx) and exhaust particulate matter (PM) from this sector were too high (see our paper for details). Rules that would have required retrofit or replacement of older in-use construction equipment/engines have been revised, and will take effect more gradually. These policy changes followed from different counting methods being used to estimate emissions, and also due to the weak economy.

Completed Ph.D. Dissertations

  • Tom Kirchstetter (B.S. in Atmospheric Science and Math, SUNY Albany; UC Berkeley Ph.D. 1998)
    Impact of reformulated fuels on motor vehicle emissions

  • Brett Singer (B.S. in Mechanical Engineering, Temple University; UC Berkeley Ph.D. 1998)
    A fuel-based approach to estimating motor vehicle exhaust emissions

  • Doug Black (B.S. in Electrical Engineering, University of Michigan; UC Berkeley Ph.D. 2000)
    Development and application of a sensor for real-time microenvironmental and personal ozone measurements

  • Linsey Marr (B.S. in Engineering Science, Harvard; UC Berkeley Ph.D. 2002)
    Changes in ozone sensitivity to precursor emissions on diurnal, weekly, and decadal time scales

  • Andrew Kean (B.S. in Mechanical Engineering, Cooper Union; UC Berkeley Ph.D. 2002)
    Effects of vehicle speed and engine load on emissions from in-use light-duty vehicles

  • Phil Martien (B.A. in Physics, UC Santa Cruz; B.S. in Environmental Engineering, Humboldt State; UC Berkeley Ph.D. 2004)
    Forward and adjoint sensitivity analysis in Eulerian photochemical air quality models

  • George Ban-Weiss (B.S. in Mechanical Engineering, UC Berkeley; UC Berkeley Ph.D. 2008)
    Characterization of gas- and particle-phase emissions from on-road motor vehicles

  • Ling Jin (B.S. in Physical Geography, Peking University; UC Berkeley Ph.D. 2008)
    A seasonal perspective on regional air quality in central California

  • Dev Millstein (B.S. in Economics, Vassar College; UC Berkeley Ph.D. 2009)
    Air quality responses to changes in black carbon and nitrogen oxide emissions

  • Drew Gentner (B.S. in Chemical and Environmental Engineering, Northwestern University; UC Berkeley Ph.D. 2012)
    Gas-phase organic carbon and tropospheric pollution: sources, emissions, and implications for air quality

  • Juli Rubin (B.S. in Civil and Environmental Engineering, Cornell University; UC Berkeley Ph.D. 2012)
    Investigation of aerosol sources, lifetime and radiative forcing through multi-instrument data assimilation

  • Tim Dallmann (B.S. in Civil and Environmental Engineering, University of Wisconsin; UC Berkeley Ph.D. 2013)
    Evaluation of mobile source emissions and trends

  • Sharon Shearer (B.S. in Civil and Environmental Engineering, University of Texas at Austin; UC Berkeley Ph.D. 2013)
    An improved chemical mechanism for photochemical air quality modeling

  • Brian McDonald (B.S. in Civil and Environmental Engineering, Virginia Tech; UC Berkeley Ph.D. 2014)
    High-resolution mapping and long-term trends for motor vehicle emissions

  • Ivy Tao (B.S. in Physics, Bryn Mawr/Haverford College; UC Berkeley Ph.D. 2016)
    Changes in mobile source emissions and ambient air quality in California

  • Lucas Bastien (B.S. in Energy and Environmental Engineering, Institut National des Sciences Appliquées, Lyon, France; UC Berkeley Ph.D. 2016)
    Adjoint sensitivity analysis of air pollution problems

  • Chelsea Preble (B.S. in Environmental Science, UC Berkeley; UC Berkeley Ph.D. 2017)
    Effects of advanced after-treatment control technologies on heavy-duty diesel truck emissions

  • Matthew Vannucci (B.S. in Physics, Rutgers University; UC Berkeley Ph.D. 2018)
    Human-centric indoor air quality

  • Regan Patterson (B.S. in Chemical Engineering, UCLA; UC Berkeley Ph.D. 2019)
    Effects of diesel emission control measures and truck routing on air quality, environmental equity and justice