Background: Gasoline-powered vehicles and equipment are an important source of air pollution in California. Many gasoline-related pollutants pose significant health concerns. The California Air Resources Board strictly regulates the state’s gasoline formulation and vehicle emissions. Objective: To investigate exposure trends for gasoline-related air pollutants between 1996 and 2014, capturing the period before and after the removal of methyl t-butyl ether (MTBE). Methods: We identified gasoline-related chemicals with known or suspected health concerns and adequate ambient air monitoring data. Average exposures to the general public were estimated from 1996 to 2014 in five major air basins and statewide. We determined the fractions of exposures attributable to gasoline use and evaluated cancer and non-cancer risks for chemicals with available cancer potencies and health reference values. Results: We found that average gasoline-attributable cancer risks for the general California population from the most highly emitted carcinogens (acetaldehyde, benzene, 1,3-butadiene, and formaldehyde) declined by over 80% between 1996 and 2014. This decline occurred despite roughly constant statewide gasoline sales, an increase in vehicle miles traveled, and an approximately 10% increase in vehicle registrations over this same period. Naphthalene, measured as a volatile organic compound (VOC), was the most abundant gasoline-related polycyclic aromatic hydrocarbon (PAH). From 1996 to 2014, gasoline-attributable cancer risks for naphthalene were estimated to drop approximately threefold in the South Coast Air Basin. Exposures to gasoline-related chemicals associated with non-cancer health effects, such as chronic respiratory toxicity or neurotoxicity, were generally below levels of concern. The exception was acrolein, with gasoline-related exposures in 2014 estimated to be high enough to pose risks for respiratory toxicity. Impact statement: Our historical analysis demonstrated the success of California’s regulatory efforts to reduce gasoline-related air pollutant exposures and risks to the general public. New efforts are focused on addressing gasoline-related and other air pollution in heavily impacted communities affected by multiple environmental and social stressors.

Background: Diesel exhaust (DE) exposures pose concerns for serious health effects, including asthma and lung cancer, in California communities burdened by multiple stressors. Objective: To evaluate DE exposures in disproportionately impacted communities using biomonitoring and compare results for adults and children within and between families. Methods: We recruited 40 families in the San Francisco East Bay area. Two metabolites of 1-nitropyrene (1-NP), a marker for DE exposures, were measured in urine samples from parent–child pairs. For 25 families, we collected single-day spot urine samples during two sampling rounds separated by an average of four months. For the 15 other families, we collected daily spot urine samples over four consecutive days during the two sampling rounds. We also measured 1-NP in household dust and indoor air. Associations between urinary metabolite levels and participant demographics, season, and 1-NP levels in dust and air were evaluated. Results: At least one 1-NP metabolite was present in 96.6% of the urine samples. Detection frequencies for 1-NP in dust and indoor air were 97% and 74%, respectively. Results from random effect models indicated that levels of the 1-NP metabolite 6-hydroxy-1-nitropyrene (6-OHNP) were significantly higher in parents compared with their children (p-value = 0.005). Urinary 1-NP metabolite levels were generally higher during the fall and winter months. Within-subject variability was higher than between-subject variability (~60% of total variance versus ~40%, respectively), indicating high short-term temporal variability. Impact: Biomonitoring, coupled with air monitoring, improves understanding of hyperlocal air pollution impacts. Results from these studies will inform the design of effective exposure mitigation strategies in disproportionately affected communities.

The San Joaquin Valley in California has some of the nation’s worst air quality. Health effects from elevated outdoor air pollution may be compounded by poor indoor air quality due to use of certain consumer products or individual activities. The BiomSPHERE study measured air pollution-related urinary exposure biomarkers in residents of Stockton and Fresno, California. Urine samples were collected from 64 adult–child pairs in 2023. Metabolites of four polycyclic aromatic hydrocarbons (PAHs) and five volatile organic compounds (VOCs) were measured in urine. Questionnaires were administered to collect information on demographics and potential exposure sources. Metabolites of all PAHs (fluorene, naphthalene, phenanthrene, and pyrene) and four VOCs (acrolein, acrylonitrile, crotonaldehyde, and propylene oxide) were detected in >85% of the samples. 2-Hydroxynaphthalene (2-NAP) was the only PAH metabolite that had higher concentrations in BiomSPHERE adults and children compared with nationally representative levels reported by the U.S. National Health and Nutrition Examination Survey (NHANES). Concentrations of 2-NAP were significantly correlated (p < 0.05) between adults and children, suggesting a common exposure source. Concentrations of 2-NAP were also significantly higher among Hispanic/Latino participants and among participants who recently used cleaning products, air fresheners, and scented personal care products (p < 0.05). For non-smoking adults, metabolites of the VOCs acrolein, acrylonitrile, and propylene oxide were significantly higher in BiomSPHERE compared with NHANES. Further research is needed to identify the sources of elevated 2-NAP and VOC urinary metabolite concentrations.