Stockton school-aged children’s exposures to polycyclic aromatic hydrocarbons (PAHs)

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Human exposure to polycyclic aromatic hydrocarbons (PAH) is associated with significant adverse health outcomes, yet the magnitude and temporal trends in environmental concentrations are not well understood. Stockton, California, in the San Joaquin Valley, experiences some of the highest air pollution levels in the United States due to its valley topography that traps emissions and the influence of regional industry and transportation. This pilot study, performed in December 2021, aimed to characterize exposures to PAH exposures among schoolchildren and to evaluate in-classroom air filtration effectiveness. We conducted a two-week monitoring campaign at a small K-8 parochial school, deploying PAH sampling equipment in four classrooms and at two outdoor locations. Indoor and outdoor PAH levels were measured over 24-hour periods on two consecutive days each week. Portable air cleaners were installed in half of the classrooms. Integrated 24-hour samples for PAHs were collected using Harvard-type impactors (two 37 mm filters) and XAD-2 filled sorbent tubes for highly volatile compounds (e.g., naphthalene). Co-located real-time PM2.5 and black carbon monitors were also deployed indoors and outdoors to capture concentration patterns and assess filtration impacts. Week 1 measurements were significantly higher than Week 2, reflecting heavy rainfall during the second week. Indoor concentrations of volatile, low-molecular weight PAHs (naphthalene and acenaphthene) and oxygenated PAHs (1,3-indanedione, 1,4-anthraquinone, and 5,12-naphthacenequinone) were significantly lower in classrooms with portable air cleaners in Week 1 compared to those without (Kruskal-Wallis p-values < 0.05). Of the 36 PAHs measured, 12 were detected in 100% of samples, including acenaphthene, acenaphthylene, acenaphthenequinone, anthracene, 1,4-anthraquinone, benzo(a)anthracene-7,12-dione, benzo[a]pyrene, 1,3-indanedione, fluorene, 9H-fluoren-9-one, 1,4-naphthoquinone, and phenanthrene. Naphthalene concentrations were highest (indoor median: 257.9 ng/m3; 95th percentile: 344.8 ng/m3; outdoor median: 285.8 ng/m3; 95th percentile: 329.6 ng/m3). The indoor-to-outdoor (I/O) ratio for naphthalene was 1.12, indicating indoor sources predominated. We present results integrating PAH, PM2.5 and black carbon concentration data, highlighting spatial and temporal patterns and the role of filtration in reducing exposures. These findings contribute to understanding pollutant sources and mitigation strategies in school environments located in overburdened communities.

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