Background: Health effects research of air pollution has little clarity in the relationship between particles and noise exposures. Sources of particle pollution tend to also produce high levels of noise pollution. Disentangling the effects of chemical and non-chemical exposures may be difficu however, targeted intensive sampling of both in relevant microenvironments provides insight to effect modification or confounding in health effect assessments. Aim: Describe the relationship of noise as a predictor of particle pollution in the vehicular microenvironment through intensive sampling. Methods: Two scenarios, where air and noise pollutants were measured for ～2 hours, were examined six times each: 1) a stationary vehicle near a highway and 2) a mobile vehicle on the highway. In both scenarios, windows were alternated from opened to closed at 15 minute intervals. PM2.5 mass, ultrafine particles, and particles bound with polycyclic aromatic hydrocarbons (PAHs) were measured. Audio was measured in decibels. Linear mixed effect regression models were developed for each pollutant parameter-noise pair, and were grouped by sampling session. Results: In-cabin PM2.5 mass concentrations in our experiments were driven primarily by mobility. There was high heterogeneity in the sampling session effects, but the estimate of the average effect of mobility was still significant, 1.03 (0.70,1.36)95%. No association was found with noise. Our study measured ultrafine particles in two different instruments with varying sensitivity to particle size. The prior two minutes of ultrafine concentrations were significant predictors of current minute concentrations (2.96-9.98, t = 1.73-4.98). Notably, noise was positively associated with ultrafine particle concentrations as measured by a condensation particle counter under all conditions of the sampling scenarios. Conclusions: Noise was found to be predictive for certain pollutant parameters, particularly ultrafine particle measurements. Conditions of vehicle activity were important modifiers of observed concentrations.
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