Proof-of-concept validation of a cost-effective, occupancy-based 3-day sampling strategy for polycyclic aromatic hydrocarbons in school environments.

Monitoring polycyclic aromatic hydrocarbons (PAHs) in educational settings is crucial for assessing children's health risks, but it is currently constrained by the labour, time, and economic burdens of the standard 5-day active sampling protocol. As a proof-of-concept, this study validated a cost-effective 3-day sampling proxy that is statistically equivalent to the 5-day standard conducted in a rural Belgian primary school during winter. Left-censored PAH concentration data were first reconstructed using a Gibbs sampler based left-censored missing value imputation approach (GSimp), and interchangeability between protocols was assessed via non-parametric Wilcoxon signed-rank two one-sided tests (TOST). Our analysis revealed a clear physicochemical dichotomy. Gaseous pollutants behave as a stable temporal background, while particle-bound pollutants are driven by episodic resuspension dynamics. Therefore, simplified 3-day protocols relying on partial school days generally failed to achieve equivalence for heavy particle-bound PAHs, as they only captured a kinetically incomplete snapshot of the diurnal particle cycle. We demonstrated that the optimal 3-day protocol must consist exclusively of full school days, which covers the complete daily resuspension load, thereby minimising measurement uncertainty. Adopting this approach reduces sampling resources by 40%, from five to three days per week, while preserving statistical equivalence for the eight target PAHs that remained quantifiable after excluding highly censored compounds. As a single-site and single-season proof-of-concept, this study provides a foundation for more resource-efficient PAH monitoring in schools, pending multi-site and multi-season validation before broader epidemiological deployment.