Biogenically driven marine organic aerosol production over the West Pacific Ocean

Abstract. Marine organic aerosols play crucial roles in cloud formation and climate regulation within the marine boundary layer. However, the abundance of marine primary organic carbon (MPOC) generated by sea spray and secondary organic carbon (MSOC) formed via gas-to-particle conversion or atmospheric oxidation/aging processes remains poorly quantified, which hinders our understanding on the climate effects of marine aerosols. In this work, two shipboard cruises were conducted over the West Pacific Ocean to estimate abundance and compositions of marine organic aerosols. We propose an observation-based approach to quantify the MPOC and MSOC using a combined parameterization of the observed Na+ in fine aerosol particles and the surface chlorophyll-a (Chl-a), an indicator of marine biological activity. The parameterization approach of MPOC using [Chl-a] × [Na+]0.45 was validated through comparing with the water-insoluble organic carbon in the aerosol samples. The estimated MPOC (0.33 ± 0.32 µgC m−3) averagely accounted for 56 %–66 % of the total organic carbon in the collected samples, which was mainly attributed to the protein-like substances transferred into the sea spray aerosols from seawater. Over the West Pacific Ocean, the MPOC and MSOC displayed peak concentrations over the regions 5° S–5° N (0.64 ± 0.56 and 0.44 ± 0.32 µgC m−3) and 35–40° N (0.46 ± 0.35 and 0.51 ± 0.30 µgC m−3). The variation and spatial distribution of MPOC and MSOC along the latitude were driven by the marine biological activities. High MSOC concentrations were also observed over the region of 15–20° N (0.35 ± 0.41 µgC m−3), which was due to an additional contribution by the oxidation of volatile organic precursors from the photochemical production of seawater organics. This study proposes a parameterization approach to quantify the MPOC and MSOC over the Pacific Ocean or other oceanic areas. Our results highlight the marine biogenically driven formation of marine organic aerosols, and different quantitative relations of MPOC with seawater Chl-a and other parameters are needed based on in-situ observations across oceanic regions.