Emission and optical characteristics of brown carbon in size-segregated particles from three types of Chinese ships

Brown carbon (BrC) is one of the important light absorption substances that have high light absorption ability under short wavelength light. However, limit studies have focused on the BrC emission from ships. In this study, size-segregated particulate matters (PM) were collected from three different types of ships, light absorption characteristics and size distribution of methanol-soluble BrC and water-soluble BrC in PM from ship exhausts were investigated. Results showed that four-stroke low-power diesel fishing boat (4-LDF) had the highest mass concentrations of methanol-soluble organic carbon (MSOC) and water-soluble organic carbon (WSOC), followed by 2-stroke high-power heavy-fuel-oil vessel (2-HHV), and four-stroke high-power marine-diesel vessel (4-HMV). While 2-HHV had obviously higher light absorption coefficients of methanol-soluble BrC (Abs_365,M) and water-soluble BrC (Abs_365,W) in unit weight of PM than the other two types of ships. The tested ships presented comparable or higher absorption efficiency of BrC in water extracts (MAE_365,W) compared with other BrC emission sources. Majority of BrC was concentrated in fine particles, and the particle size distributions of both Abs_365,M and Abs_365,W showed bimodal patterns, peaking at 0.43–0.65 µm and 4.7–5.8 µm, respectively. However, different particle size distributions were found for MAE_365,M between diesel and heavy fuel oil ships. Besides, different wavelength dependence in particles with different size were also detected. Ship exhaust could be confirmed as a non-ignorable BrC emission source, and complex influencing factor could affect the light absorption characteristics of ship emissions. Particle size should also be considered when light absorption ability of BrC was evaluated.