Observation-based source function suggests biogenically driven primary marine organic aerosol formation

Marine organic aerosols (MOA) play crucial roles in cloud formation and climate regulation over remote ocean, while the abundance of primary MOA has not been well quantified in observation or modelling studies. In this work, we explored a framework to estimate the primarily-emitted organic carbon in marine aerosols (POCM) based on shipboard cruise observations over the Northwest Pacific Ocean. The concentration of POCM in marine aerosols could be well estimated using the observed [Na+] in marine aerosols and [Chl-a] in surface seawater, the indicators of sea salt emission and marine biological activity. The estimated POCM were 0.04−1.57 μgC/m3, averagely accounting for 59% of the total OC, which matched well with the water-insoluble OC concentration and variation of protein-like organics fraction in marine aerosols, both primarily generated by sea spray. The novel source function of primary MOA would help to improve the parametrization scheme of marine aerosols in global climate models.