Enhanced light absorption due to aerosol particles in ship plumes observed at a seashore site

Abstract

This study investigates the existence of light-absorbing organic aerosols in ship emissions measured at a seashore site. In-situ measurements of aerosol light absorption at a port of Gangneung located on the East Sea on the Korean Peninsula were made using a multi-wavelength aethalometer for approximately 10 days. Moreover, 7- to 24-hr integrated filter-based measurements were performed to analyze the concentration of water-soluble organic carbon (WSOC). During the study period, short-term excursions of black carbon (BC) concentrations at 880 nm (BC880) and aerosol light absorption coefficients at 370 nm (babs,370) occurred repeatedly, as did absorption Ångström exponent (AAE) values at 370–520 nm (AAE370-520). The babs,370 values during the excursions were 4.8 times higher than the background absorption levels. The AAE370-520 values were close to 1.0 at the onset of the excursion; however, they increased to 1.9–2.3 during the excursion. Furthermore, the contribution of brown carbon (BrC) light absorption at 370 nm (BrC babs,370) to the total light absorption ranged from 2.5–11.0% at the onset of the excursion to 45.2–59.8% during the excursion. The WSOC showed good-to-strong correlation with the babs,370, babs,880, and BrC babs,370, with R2 of 0.63–0.77. This suggests that primary combustion sources contributed to the aerosol light absorption. Enhanced BC880, babs,370, AAE370-520, and contribution of BrC absorption at the seashore site without traffic and industrial sources could be attributed to the light-absorbing organic aerosols in ship emissions. It was observed that absorption by BrC in ship engine exhaust can be as important as BC absorption in shorter visible wavelengths.