Oceanic phytoplankton are a potentially important source of benzenoids to the remote marine atmosphere

Manon Rocco,Stacy Deppeler,Cliff Law,Neill Barr,Jonathan Williams,Andrew Marriner,Karl Safi,Erin Dunne,James Harnwell,Maija Peltola,Alexia Saint-Macary,Karine Sellegri,Aurélie Colomb

doi:10.1038/s43247-021-00253-0

Abstract

Benzene, toluene, ethylbenzene and xylenes can contribute to hydroxyl reactivity and secondary aerosol formation in the atmosphere. These aromatic hydrocarbons are typically classified as anthropogenic air pollutants, but there is growing evidence of biogenic sources, such as emissions from plants and phytoplankton. Here we use a series of shipborne measurements of the remote marine atmosphere, seawater mesocosm incubation experiments and phytoplankton laboratory cultures to investigate potential marine biogenic sources of these compounds in the oceanic atmosphere. Laboratory culture experiments confirmed marine phytoplankton are a source of benzene, toluene, ethylbenzene, xylenes and in mesocosm experiments their sea-air fluxes varied between seawater samples containing differing phytoplankton communities. These fluxes were of a similar magnitude or greater than the fluxes of dimethyl sulfide, which is considered to be the key reactive organic species in the marine atmosphere. Benzene, toluene, ethylbenzene, xylenes fluxes were observed to increase under elevated headspace ozone concentration in the mesocosm incubation experiments, indicating that phytoplankton produce these compounds in response to oxidative stress. Our findings suggest that biogenic sources of these gases may be sufficiently strong to influence atmospheric chemistry in some remote ocean regions.

Highlights

Benzene, toluene, ethylbenzene and xylenes can contribute to hydroxyl reactivity and secondary aerosol formation in the atmosphere
Current global and regional trace gas emission inventories and chemistry-climate models generally include a limited number of marine volatile organic compounds (VOCs) emissions that are known to be important to particle formation, remote OH reactivity and halogen-ozone chemistry
As part of the 2020 Sea2Cloud campaign aboard the R/V Tangaroa[15], experiments were undertaken in which ~1 m3 samples of surface seawaters were collected in three distinct locations in the Southwest Pacific east of New Zealand and studied in situ in two Air-Sea Interaction Tanks (ASIT)

Summary

Introduction

Toluene, ethylbenzene and xylenes can contribute to hydroxyl reactivity and secondary aerosol formation in the atmosphere. Current global and regional trace gas emission inventories and chemistry-climate models generally include a limited number of marine volatile organic compounds (VOCs) emissions that are known to be important to particle formation, remote OH reactivity and halogen-ozone chemistry These include dimethyl sulfide (DMS)[1,2,3,4], isoprene[5,6], C2-C3 hydrocarbons[7], amines[8], organohalogens, and monoterpenes[6,9]. In addition to emissions from terrestrial plants, Misztal et al.[11] reported benzenoids emissions from marine phytoplankton from a series of laboratory, mesocosm, and ship-borne experiments For their relevance to climate, marine emissions of such aromatic compounds in remote ocean regions, may contribute to local ozone photochemistry, OH reactivity, and secondary organic aerosol formation[12]. To unravel some of these complex systems requires multiscale studies from the laboratory to the open ocean in order to understand their biological production pathways and the drivers of their seasonal and spatial variations for use in regional and global ocean-atmosphere models

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Results

Conclusion