Impact of vehicle lights on physicochemical properties of particulate matter from diesel vehicles

This study investigates the effect of irradiation from the two most widely used vehicle lights, namely, High-intensity discharge (HID) and Light-emitting diode (LED), on the physical and chemical properties of both aged and fresh PM emitted from a diesel vehicle under idle and full throttle engine operating conditions. The PM samples were exposed to vehicle light for 1, 6, and 12 h at a constant distance of 10 cm while PM samples without exposure (0 h) served as the control. The results of physical microscopic and chemical analyses of PM samples show that HID light exposure for 1, 6, and 12 h increases the average sizes of aged PM particles by 8.6%, 15.5%, and 27.6%; PM particles at idle engine speed by 26.3%, 58.0%, and 68.4%, and; PM particles at full throttle condition by 13.6%, 45.5%, and 68.2%, respectively. Similarly, LED light exposure for 1, 6, and 12 h, increases the average sizes of aged PM particles by 5.2%, 6.9%, and 17.2%; PM particles at idle engine speed by 21.1%, 47.4%, and 73.6%, and PM particles at full throttle by 9.1%, 36.4%, and 54.5%, respectively. Furthermore, chemical properties of PM samples show remarkable changes.