ARB Research Seminar

This page updated April 18, 2017

Identifying Urban Designs and Traffic Management Strategies for Southern California that Reduce Air Pollution Exposure

Photo of Suzanne Paulson

Suzanne Paulson

Photo of J. R. DeShazo

J. R. DeShazo

Photo of Akula Venkatram

Akula Venkatram

Suzanne Paulson, Ph.D., Professor, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles; J. R. DeShazo, Ph.D., Professor and Vice Chair, Department of Public Policy, Luskin School of Public Affairs, University of California, Los Angeles; Akula Venkatram, Ph.D. Professor, Department of Mechanical Engineering, University of California, Riverside.

May 18, 2017
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


This project investigates the direct and quantitative effects of complicated urban built-environment on near-road dispersion and levels of on-road air pollution at scales from a few meters away from the center of the street to several city blocks. This was studied using ultrafine particle (UFP) concentrations as a surrogate for on-road air pollution, as it is an excellent proxy for motor vehicle emissions at short time scales. The project studies design features of transit oriented developments (TODs); types of development that are needed to move California communities toward improved public health combined with SB 375 (SB 375, Sustainable Communities and Climate Protection Act of 2008) goals of sustainability. TODs are a type of mixed-use community development that includes housing, office, retail and/or other amenities integrated into a walkable neighborhood, located within a half-mile of quality public transportation.

The project explored seven measurement sites in the greater Los Angeles area with different built-environments but similar mesoscale meteorology. At the sub-block scale, the data was used to explore the decay of air pollution away from roadway intersections to find the optimal location of transit stops relative to the intersection, which lies approximately 40 m away from the center of the intersection. This project also led to the development of a detailed statistical micro-dynamics model, able to closely reproduce second-by-second observations of UFP concentrations to disentangle the contributions of on-coming and on-going traffic, light and heavy-duty vehicles, traffic movements, building heights, and other features that impact air pollution concentrations in built-environments. The project also developed an approach to address several of the challenges associated with making high-resolution maps from mobile air pollution concentration measurements, including the question of how many repeats of a mobile monitoring route are needed to determine representative concentrations.

The results suggested that the largest impact of the built-environment is at the scale of several blocks. On the scale of a small neighborhood (several large city blocks), it was determined that after controlling for traffic, UFP concentrations were generally higher in the morning than those in the afternoon due to limited dispersion capacity combined with a relatively stable surface layer. In the calm mornings, the areal aspect ratio (Arₐᵣₑₐ) developed in this study for real urban configurations showed a strong relationship with block-scale UFP concentrations. Arₐᵣₑₐ includes the building area-weighted building height (or effective building height), the amount of open space, and the building footprint. In the afternoon, however, when wind speeds were generally higher and turbulence was stronger, the standard deviation of vertical velocity fluctuations, σw, was the most effective factor controlling UFP concentrations. The surrounding built-environment appears to play an indirect role in observed UFP concentrations by affecting surface-level micrometeorology. The effects are substantial; after controlling for traffic, differences in Arₐᵣₑₐ and building heterogeneity were related to differences in UFP concentrations by factors of two to three among the five study sites. Moving to the scale of a single street, part of the study focused on street canyon-like urban built-environments. This work suggests that for this specific configuration, street-level concentrations of vehicle-related air pollutants can be estimated with a model that assumes that vertical turbulent transport of emissions dominates the governing processes. The project developed a semi-empirical Vertical Dispersion Model (VDM) to describe the data collected in street canyons located in Hannover, Germany and Los Angeles. VDM indicates that magnification of concentrations relative to those in the absence of buildings is most sensitive to the aspect ratio of the street (the ratio of the effective building height to the street width). VDM estimates also indicate that the presence of the buildings in a street canyon configuration can potentially magnify street-level concentrations by as much as a factor of 3.5 relative to those in the absence of buildings. VDM equations were translated into an easy to use spreadsheet tool and python code that allows city planners to use VDM to conduct sensitivity analysis, generate concentration estimates, and develop mitigation strategies that aim to reduce the pedestrian exposure to air pollution within TODs. The results from this project have significant implications for pedestrian exposure to motor vehicle emissions as well as transit-oriented urban planning.

Speaker Biography

Suzanne Paulson, Ph.D., is a Professor in the Department of Atmospheric and Oceanic Sciences and a Professor in the Institute of the Environment at UCLA, where she serves as the director of the Center for Clean Air. Dr. Paulson's current research studies the impact of naturally occurring and human-made particles on public health and the Earth's climate. Her research also focuses on the influences of the built-environment on air pollution levels in complex urban areas. Professor Paulson teaches climate change and air pollution to undergraduate and graduate students and has given numerous invited public lectures on related topics. She was featured in numerous radio, print, and video interviews for her work in air quality in the Los Angeles area. Currently, Professor Paulson serves on the Research Screening Committee for the California Air Resources Board and serves as an Airport Commissioner for the City of Santa Monica. She has received a National Science Foundation CAREER award for her research. Professor Paulson earned a B.A. in Chemistry from the University of Colorado and a Ph.D. in Environmental Engineering Science from the California Institute of Technology (Ph.D.).

J. R. DeShazo, Ph.D., is the Director of the Luskin Center for Innovation and Professor and Vice Chair of the Department of Public Policy in the Luskin School of Public Affairs at UCLA. Professor DeShazo is an expert in economics, public finance, and organizational governance. Professor DeShazo's recent research has focused on local public finance, regulatory reform, climate change policy, solar energy policy, and plug-in electric vehicle policy. His work also supports the California Air Resources Board and the Southern California Association in their effort to implement AB 32, the Global Warming Solutions Act, and its complementary SB 375, transportation and land use bill. He advises the Los Angeles City Council and the Metropolitan Water District of Southern California, among key agencies. Dr. DeShazo has previously advised the U.S. Environmental Protection Agency and the United Nations, among others. Professor DeShazo holds a Ph.D. in Urban Planning from Harvard University and a M.Sc. in Economics from Oxford University.

Akula Venkatram, Ph.D., is a Professor at the Department of Mechanical Engineering at University of California, Riverside. Dr. Venkatram is an expert in micro-meteorology and air pollution dispersion modeling. Dr. Venkatram has over a decade of experience at ENSR Consulting and Engineering and served as the Head of Department at Ontario Ministry of the Environment in Toronto, Canada, before accepting his current position at UCR. Professor Venkatram pursues research in comprehensive modeling of systems governing air quality, theoretical aspects of small-scale dispersion, application of micro-meteorology to dispersion problems, and development of simplified models for complex urban systems. Professor Venkatram's current research focuses on air quality impacts of various anthropogenic sources in urban environments. Professor Venkatram has received Scientific and Technological Achievement Award from the U.S. Environmental Protection Agency for his contribution in air pollution research. Dr. Venkatram earned his B.S. in Mechanical Engineering from the Indian Institute of Technology at Madras, India, and his Ph.D. in Mechanical Engineering from Purdue University at West Lafeyette, Indiana (Ph.D.).

For a complete listing of the ARB Research Seminars and the related documentation
for the seminars please view the Main Seminars web page