Spatio-Temporal Analysis of the Roadside Transportation-Related Air Quality (StarTraq 2024): Time-Series Analysis

Abstract

Transportation-related air pollution remains a significant environmental and public health challenge in California’s San Joaquin Valley. This report presents a spatio-temporal analysis of roadside transportation-related air quality in Fresno County, California, from 1985 to 2023 with projections from 2024 through 2032. Using historical emissions inventories, projected vehicle miles traveled (VMT), infrastructure data, and land cover analysis, the study examines how transportation activity and urban expansion have influenced air quality across the region over time. Findings reveal that while PM10, PM2.5, NOx, SOₓ, CO, and CO₂ emissions from on-road mobile sources have declined significantly due to regulatory programs and cleaner technologies, the contribution of passenger vehicles has become proportionally more significant in recent years. Additionally, the study found that Fresno County experienced substantial land-use changes. These include the conversion of more than 130 km² of agricultural land into urban development and major losses in evergreen forest cover in the Sierra Nevada region, correlated with drought and wildfires, and tree mortality. At the same time, continued low-density residential growth has contributed to increased vehicle travel and ongoing air quality challenges. The findings highlight the interconnected relationship between transportation systems, land-use change, environmental conditions, and public health outcomes. This report calls for coordinated land-use planning, sustainable transportation investments, freight and emissions regulation, and environmental equity strategies to support healthier and more resilient communities throughout Fresno County and the broader San Joaquin Valley.