© Crown copyright 2013. Nitrogen Dioxide and Ultrafine Particles Dominate the Biological Effects of Inhaled Diesel Exhaust Treated by a Catalyzed Diesel Particulate Filter

We studied the impact of a catalyzed diesel particulate fil-ter (DPF) on the toxicity of diesel exhaust. Rats inhaled exhaust from a Cummins ISM heavy-duty diesel engine, with and without DPF after-treatment, or HEPA-filtered air for 4 h, on 1 day (single exposure) and 3 days (repeated exposures). Biological effects were assessed after 2 h (single exposure) and 20 h (single and repeated exposures) recovery in clean air. Concentrations of pollutants were (1) untreated exhaust (−DPF), nitric oxide (NO), 43 ppm; nitrogen dioxide (NO2), 4 ppm; carbon monoxide (CO), 6 ppm; hydrocar-bons, 11 ppm; particles, 3.2 × 105/cm3, 60–70 nm mode, 269 μg/m3; (2) treated exhaust (+DPF), NO, 20 ppm; NO2, 16 ppm; CO, 1 ppm; hydrocarbons, 3 ppm; and particles, 4.4 × 105/cm3, 7–8 nm mode, 2 μg/m3. Single exposures to −DPF exhaust resulted in increased neu-trophils, total protein and the cytokines, growth-related oncogene/ keratinocyte chemoattractant, macrophage inflammatory protein