Evaluating Diesel Exhaust Exposure in California Homes Using 1-Nitropyrene in Indoor Air and Dust

Diesel exhaust (DE) is a major traffic-related pollutant linked to adverse health outcomes, but existing methods for estimating indoor DE exposure are not validated. DE exposure indicators such as black carbon (BC), NOx, and PM2.5 are not sufficiently specific to diesel sources. 1-Nitropyrene (1-NP), an NPAH preferentially formed during diesel combustion, has rarely been studied as an indoor exposure indicator. We measured 1-NP and isomeric NPAHs (2-nitropyrene, 2-nitrofluoranthene) in indoor air and house dust from 40 homes in the eastern San Francisco Bay Area, CA, and conducted continuous indoor BC monitoring. We assessed 1-NP’s utility as a DE exposure indicator using summary statistics, diagnostic NPAH ratios, correlations with monitored pollutants, and single-predictor mixed-effects models relating 1-NP to spatial DE predictors. 1-NP was frequently detected in air (74%) and dust (97%), with median concentrations of 0.42 pg/m3 (IQR 0.32–0.54) and 340 pg/g (IQR 190–620), respectively. Air and dust 1-NP were moderately correlated (r = 0.40, p = 0.02), as was BC with 1-NP (air r = 0.38, dust r = 0.47; p < 0.01). Diagnostic ratios (2-NFl:1-NP < 5) indicated dominant primary emission sources. Dust 1-NP showed numerous significant associations with spatial DE predictors, while air 1-NP showed fewer. Overall, 1-NP shows promise as a diesel-specific indoor exposure indicator. Future studies with larger, geographically diverse cohorts are needed to further validate this metric.