Does distance from the vehicle headlight change the properties of particulate matter?

Understanding factors affecting particulate matter (PM), particularly light exposure from vehicle headlights, is essential for addressing air quality challenges. However, no comprehensive studies are available. This research, therefore, aims to investigate whether light produced by the vehicle headlight (Halogen type; 12V-55w) at various distances (120 cm, 70 cm, and 20 cm) for 1 hr affects the physical and thermal features of PM obtained from a gasoline vehicle at idle speed. The findings indicate that light can significantly change the properties of PM, especially at a close distance of 20 cm. However, as the distance increases, the effectiveness of light decreases, showing almost no impact at 120 cm. At 20 cm, PM shows higher primary particle diameters (42.1 %), core size/particle size ratio (15.2 %), fringe separation distance (12.4 %), low-volatile substances (9.4 %), non-volatile substances (21.4 %), heat required for 5 %, 50 %, and 95 % reductions in PM mass (14.4 %, 41.7 %, and 13.7 %, respectively), and frequency factor (80.3 %), as well as lower shell size/core size ratio (17.4 %), fringe length (9.9 %), PM mass (21.4 %) and high-volatile substances (8.1 %) compared to no light condition. While, fractal dimension, mean radius of gyration, length/width ratio, roundness, fringe tortuosity, soot ignition temperature, and activation energy are almost identical.