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

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.

Butene Emissions From Coastal Ecosystems May Contribute to New Particle Formation

“…A recent study from Rocco et al. (2021) also reported that some VOCs previously thought to be anthropogenic, that is, benzenoids, can be instead emitted by oceanic phytoplankton.…”

“…The Omaruru River delta aquifer, approximately 100 km inland (east) of Henties Bay, receives less than 50 mm/year of precipitation, and acts as a barrier for the river which does not flow at Henties Bay (Geyh and Plothner, 1995). A recent study from Rocco et al (2021) also reported that some VOCs previously thought to be anthropogenic, that is, benzenoids, can be instead emitted by oceanic phytoplankton.…”

“…Rocco et al. (2021) already observed benzenoids in remote oceanic regions. Other abundant VOCs observed during the campaign were isoprene (C 5 H 9 + ), with median mixing ratios of 70 ppt, methanol (CH 5 O + ), the most abundant oxygenated VOC with a median mixing ratio of 1.6 ppb, followed by formic acid (CH 3 O 2 + ), acetone (C 3 H 7 O + ), formaldehyde (CH 3 O + ), acetaldehyde (C 2 H 5 O + ), ethanol (C 2 H 7 O + ) and acetic acid (C 2 H 5 O 2 + ) with median mixing ratios of 1.0 ppb, 470, 420, 290, 250, and 200 ppt, respectively (Figure 1).…”

“…A diverse range of reactive hydrocarbons, mainly mono-and di-unsaturated, were observed, including VOCs previously thought to be markers of anthropogenic emissions such as toluene (Text S2 in Supporting Information S1). Rocco et al (2021) ) with median mixing ratios of 1.0 ppb, 470, 420, 290, 250, and 200 ppt, respectively (Figure 1). For all of these VOCs, higher concentrations were observed when the wind blew from the NW (methanol, acetone, and acetic acid) and NNW (formaldehyde, acetaldehyde, ethanol, butene, and isoprene) directions, consistent with transport of emissions from the Benguela upwelling system.…”

Marine biogenic emissions of benzene and toluene and their contribution to secondary organic aerosols over the polar oceans

“…Recently, Rocco et al (29) suggested a phytoplankton source of benzene and toluene in the surface ocean. They used mesocosm and phytoplankton culture experiments to show that phytoplankton species produce benzene and toluene at variable rates.…”