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 in the marine boundary layer. While the abundance of MOA primarily-emitted from sea spray or secondarily-formed in the atmospheres has not been well quantified, which hindered our understanding on the climate effects of marine aerosols. Here, based on shipboard cruises over the Northwest Pacific Ocean, we explored a framework to separate the primary and secondary MOA using a combined parameterization of observed [Na+] in marine aerosols and [Chl-a] in surface seawater, the indicators of sea salt emission and marine biological activity. The performance of source function was validated through comparing the estimated primary MOA with the water-insoluble organics and protein-like organics in marine aerosols, both primarily generated by sea spray. Primary MOA accounted for 59% of the total organic aerosols, and their fractions varied along latitude and across seasons driven by marine biological activity and meteorological conditions.