Global marine isoprene emissions: A field, lab, and model study synthesis

Isoprene, a biogenic trace gas produced both on land and in the ocean, is an important precursor of secondary organic aerosol (SOA)/cloud condensation nuclei (CCN). Although the marine source of isoprene to the atmosphere is smaller than the land source, it may still be important for CCN/SOA formation in the remote marine boundary layer (RMBL), because isoprene is usually supersaturated in the open ocean and is highly reactive in the atmosphere (1 hour lifetime). It is known that the marine emissions to the atmosphere are critically controlled by surface ocean biogeochemical and physical factors which are poorly quantified and unpredictable. Once emitted to the atmosphere, isoprene undergoes fast oxidation processes to produce SOA, which may make a large regional impact. However, the strength of this impact is controversial, since only a few studies have measured isoprene directly in the surface ocean.

The focus of this study is to use direct measurements in three different oceans (Atlantic Ocean, Indian Ocean, Pacific Ocean), as well as incubation experiments assessing the production and consumption ratios of isoprene in the surface ocean, to compare the results to model output based on simple parametrizations using remotely-sensed input parameters. With this comparison of modeled data and direct measurements of isoprene it is possible to evaluate global marine isoprene emissions and to estimate the importance of marine derived isoprene as a precursor to RMBL CCN formation.