Effects of air/fuel ratio and ozone aging on physicochemical properties and oxidative potential of soot particles.

Fuel combustion conditions and atmospheric aging processes can affect the physicochemical properties of soot particles, which further change the oxidative potential (OP) of soot. In this study, we generated two soot samples under higher and lower air/fuel ratio (A/F) conditions, and further treated them with ozone (O) at a level similar to that in the polluted atmosphere. The physicochemical properties and OP values (measured by dithiothreitol (DTT) assay, OP) of fresh and ozonised soot samples were compared to investigate the influences of A/F and O aging. Both A/F and O aging significantly affected soot physicochemical properties and OP values. Lower A/F was favourable for generating soot particles containing more polycyclic aromatic hydrocarbon (PAH), water-soluble organic carbon (WSOC), and light-absorbing organics, but fewer oxygen-containing groups. After O aging, a decline in PAHs and increase in oxygen-containing groups and WSOC were observed in both aged soot samples. In addition, both lower A/F and O aging enhanced soot OP values. Soot generated under lower A/F was more sensitive to O aging, after which there was a significantly greater change in physicochemical characteristics, in turn contributing substantially to the greater OP increase observed in low-A/F soot.