Characterization and integration of a new oxidative flow reactor for use in biological exposure systems with diesel exhaust and other aerosols

Freshly emitted air pollutants may not represent real-world exposures in human studies, especially for communities exposed to aged pollutants. This study presents the characterization and simulation of diesel exhaust (DE) atmospheric aging in a new oxidative flow reactor (OFR) named Fast-oxidation Box (FoxBox, volume: 1019 L) and the effect of aging on biological systems through in vitro cellular studies. We examined: (a) residence time distribution (RTD) for DE-derived CO₂, SO₂, and particles, (b) DE particle transmission efficiency, (c) losses of low-volatile organic compounds (LVOC), and (d) photochemical oxidation of DE (from OH exposure of (1.9 to 9.5)×10¹¹ molec cm⁻³ s). Our results demonstrate turbulent flow-like conditions in FoxBox with a narrower RTD for particles than gases. The particle transmission efficiency was greater than 80% for mobility diameters from 40 to 615 nm. LVOC losses to FoxBox walls were negligible. The changes in particle size distributions, such as new particle formation, and chemical composition–particularly secondary aerosol formation like nitrate, ammonium, semi-volatile oxygenated organic aerosol (OA)–during photochemical oxidation were like those observed in the atmosphere and other OFRs. The O:C values for newly formed OA in FoxBox were unlike those for ambient low-volatile oxygenated OA, likely due to high PM_2.5 loading used for aging. A549 cell exposures revealed increased cytotoxicity and reactive oxygen species formation compared to incubator controls, due to photochemical aging. In the future, we plan to conduct more complex biological research, particularly controlled human studies, which will provide crucial insights and establish a unique capability globally.