Optical source apportionment and radiative forcing of light-absorbing carbonaceous aerosol at a tropical marine monsoon climate zone: the importance of ship emissions

Abstract. Source-specific optical properties of light-absorbing carbonaceous (LAC) aerosol are poorly understood owing to its various sources in the atmosphere. Here, a receptor model coupling multi-wavelength absorption with chemical species was utilized to explore the source-specific LAC optical properties at a tropical marine monsoon climate zone. Results showed that biomass burning contributed the largest to LAC absorption on average, but ship emissions became the dominant contributor (44–45 %) when the air masses originated from the South China Sea. The source-specific absorption Ångström exponent indicates that black carbon (BC) was the dominant LAC aerosol in ship and motor vehicle emissions while there was also brown carbon (BrC) existed in biomass-burning emissions. The source-specific mass absorption cross section (MAC) showed that BC from ship emissions had a stronger light-absorbing capacity than biomass burning and motor vehicle emissions. The BrC MAC derived from biomass burning was smaller than BC MAC and highly depended on wavelengths. Radiative effect assessment indicates a comparable atmospheric forcing and heating capacity of LAC aerosol from biomass burning and ship emissions. Our study provides insights into the optical properties of LAC aerosol from various sources and can improve our understanding of the LAC radiative effects caused by ship emissions.