Spatio-Temporal Analysis of Roadside Transportation-Related Air Quality (StarTraq 2021): A Characterization of Bike Trails and Highways in the Fresno/Clovis Area

Kwon, Jaymin; Ahn, Yushin; Chung, Steve · 2022 · ROSA P / Mineta Transportation Institute

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Summary

This study addresses the critical public health issue of transportation-related air pollution in the San Joaquin Valley, specifically the Fresno/Clovis area, which frequently exceeds federal and state clean air standards for particulate matter (PM) and ozone. Motivated by the need to support alternative transportation planning and understand personal exposure risks, the research characterizes spatio-temporal variations in air quality across different transportation modes. It specifically compares active transportation (cycling) against motorized driving, examining how microenvironments—such as bike trails, vehicle interiors, and vehicle exteriors—affect exposure to pollutants like PM2.5, PM1, PM10, and black carbon (BC). The methodology involved comprehensive field sampling using real-time aerosol monitors (DustTrak DRX II and microAeth AE51) and low-cost sensors. For active transportation, researchers carried backpack-mounted sensors while cycling on Woodward Park and Old Clovis trails, alongside stationary reference monitors in a residential backyard to control for sensor drift. For motorized transportation, sensors were installed both on the roof of a vehicle (“On-Road”) and inside the cabin (“In-Vehicle”) to compare exposure levels. Data collection occurred across six local roadway routes in Fresno/Clovis and five intercity trips connecting Fresno with Berkeley and Los Angeles. GPS data was logged via Tracksticks and GoPro cameras, which also captured visual data for source identification. All data streams were time-synchronized using MATLAB to align pollution concentrations with specific geographic coordinates. The results revealed distinct patterns in pollutant distribution and exposure. First, PM10 and PM1 concentrations closely mirrored PM2.5 levels, suggesting that roadside particles are predominantly small, likely originating from combustion sources. Second, air quality variability was significantly higher on bike trails and in On-Road samples compared to backyard and In-Vehicle samples. Third, vehicle cabins provided substantial protection against pollutants; average In-Vehicle PM2.5 concentrations were only 31% of On-Road levels, while In-Vehicle BC was merely 5.5% of On-Road levels. Specifically, On-Road PM2.5 was 2.9 to 4.3 times higher than In-Vehicle levels, and On-Road BC was 62 to 65 times higher. Finally, intercity trips demonstrated that the San Joaquin Valley consistently exhibited higher ambient PM2.5 and BC levels than the Bay Area, regardless of daily air quality fluctuations. The significance of this research lies in its detailed characterization of personal exposure risks associated with different transportation modes. The findings highlight that while active transportation offers health benefits, cyclists face higher and more variable exposure to traffic-related pollutants compared to drivers. The substantial difference between On-Road and In-Vehicle concentrations underscores the protective effect of vehicle cabins against combustion-derived particles. These insights provide data-driven evidence for urban planners to design safer bike trails that minimize exposure to roadway emissions and inform public health policies regarding transportation-related air quality in highly polluted regions.

Key finding

On-road particulate matter and black carbon concentrations were significantly higher than in-vehicle levels, and the San Joaquin Valley exhibited consistently elevated ambient pollution compared to the Bay Area.

Methodology

field_study

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• exposure measurement