Robert Harley

The atmosphere carries a heavy burden of air pollution, with large contributions to the problem coming from the combustion of fossil fuels. As a society, we need to evolve towards a more sustainable, environmentally benign approach to meeting growing demands for energy. Harley’s 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. Here are a few of the research projects Hansen is currently working on below: 

• 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 many of the major components of airborne fine particulate matter or PM2.5, have complex relationships to precursor emissions. Harley’s research group uses mathematical models to synthesize an understanding of precursor emissions and relevant processes that take place in the atmosphere.

• Air Pollution from Mobile Sources - The transportation sector involves the movement of both passengers and freight. This sector currently relies on petroleum-derived fuels such as gasoline and diesel. Harley’s research group has made a series of field measurements at a California highway tunnel that document emission trends over time and the effects of improved emission control technologies and gasoline reformulation on vehicle emissions. 

  The freight transport sector relies heavily on diesel fuel, in contrast to passenger travel, where gasoline is the dominant fuel. Harley’s research group has been working to understand how diesel-related air pollution has changed following the introduction of particle filters and catalytic converters (i.e., selective catalytic reduction systems for NOx control). His group also works on mapping vehicle activity and modeling the impacts of traffic-related emissions on ambient air pollution at high spatial resolutions (e.g., 50-150 m, ~1 km, and 4 km).

• "Fuel-based" Approach to Estimating Motor Vehicle Emissions - Harley’s research group has also developed a new approach to motor 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 of time. 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. This line of research has contributed to policy-relevant revisions in national and state-level air pollution emission inventories.