California Air Resources Board

Principal Investigator/Author: Suzanne Paulson

Contractor: University of California, Los Angeles

Contract Number: 12-308

Project Status: Completed

Relevant CARB Programs: Atmospheric Processes, Climate Change

Topic Areas: Behavioral Change, Mobile Source Strategy, Modeling, Monitoring, Transport

Research Summary:

This project investigated the impact of the built environment on concentrations of roadway pollutants, specifically ultrafine particles. The report emphasizes the configurations that arise around transit, mode shifting and transit-oriented development, and types of development that are needed to move California communities toward improved public health combined with Senate Bill (SB) 375 goals of sustainability. As higher density communities and transit-oriented developments are built, there is potential to create situations that expose more people to more roadway emissions. We seek to understand features of the built environment that may be adjusted to avoid or mitigate potential unintended consequences. Built environment effects are considered on several different scales: (1) sub-street scale within few meter of a road, (2) street scale looking at entirety of a single street, and (3) multi-block scale that spans over several blocks. The analyses were based on extensive field measurements made in several communities in the Los Angeles area during 2013, 2014 and 2015, most of it at high spatial and temporal resolution. In some cases, other datasets were used either from a 2008 study, also in Downtown Los Angeles and also supported by CARB, or from a longer term study in Hanover, Germany performed by other investigators. The communities in the Los Angeles area included four sites in Downtown Los Angeles, and sites in Temple City, Beverly Hills and Koreatown.

Exposure to elevated levels of roadway pollutants has been associated with a wide range of adverse health outcomes. Freshly emitted vehicular pollution is a complex mixture of gases and particles, of which ultrafine particles (UFP) is a major component. While the components of fresh vehicle emissions that cause adverse health effects is not well established, UFP are both an excellent proxy for roadway emissions and may potentially be a significant contributor to roadway-related toxicity.

The analyses presented below begin at the sub-street scale and conclude at the multi-block scale. A summary for urban planners and policymakers is also provided.

*Along with the Final Report, there is a zipped folder containing four files that make up the vertical dispersion model (VDM). This folder must be extracted (unzipped) prior to running the model. Please read the instructions prior to use.

Final Report & Model: Please email research@arb.ca.gov to request the final report and VDM generated by this research contract: