Fig. 2

Oxidative potential and metal content of exhaust PM derived from petrol diesel and RME blended fuel combustion. Panel a shows superoxide free radical generation using electron paramagnetic resonance (EPR) with the spin-trap Tempone-H (1 mM). All particulates were suspended at an equivalent concentration of 0.1 mg/mL in physiological saline. Pyrogallol (0.1 mM) is used as a positive control to spontaneously generate superoxide. RME100 generated significantly less superoxide than petrodiesel (*p < 0.05) or RME30 (†p < 0.05) (unpaired t-tests, n = 6–10). Panel b represents ascorbate- and glutathione-dependent oxidative potentials (OPAA and OPGSH, respectively) for the PM < 0.2 μm and PM0.2–0.5 μm fractions are illustrated, with the data expressed per μg of extracted PM (n = 3, separate filters, per fraction and fuel type). A total aggregated OP (OP^TOT) is also illustrated reflecting the sum of the OP^AA and OP^GSH measures. Data are illustrated as means with standard deviation, with comparison between groups performed on the sum of the OP for the two fractions combined using the students t-test (P < 0.05): ‘a’ petrol diesel vs, RME30; ‘b’ RME30 vs RME100; no significant differences were observed between petrol diesel and RME100. Panel c represents the concentration of a selection of the measured metals in both PM fractions derived from each fuel type (n = 3). Zn = zinc, Cr = Chromium, V = Vanadium, Mn = Manganese, Cu = Copper, Mo = Molybdenum, Ni = Nickel, Fe = Iron. Asterisks represent significant differences (p < 0.05) in concentration relative to petrodiesel. No significant differences were noted between the fuel types in the PM < 0.2 μm fraction and metal concentrations did not differ between the two fractions under each condition