Geostationary satellite reveals increasing marine isoprene emissions in the center of the equatorial Pacific Ocean

Abstract

Isoprene is the most abundant non-methane biogenic volatile organic compound in the Earth’s atmosphere and has the potential to influence photochemistry in the remote ocean–atmosphere. Marine isoprene emission estimates vary over multiple orders of magnitude using different methods, and the paucity of continuous in-situ measurements makes it challenging to distinguish their spatiotemporal variations. Here we present marine isoprene emission estimates inferred from Himawari-8 observations and model simulation covering the western Pacific Ocean and the eastern Indian Ocean. Although most isoprene emission hotspots were near coasts, we found an unexpected emission pool in the center of the equatorial Pacific Ocean with 18% higher emissions than those in the North and South Pacific Oceans. Remarkably, the isoprene emissions increased by 5.5 ± 0.1% per year in the center of the equatorial Pacific Ocean between August 2015 and December 2020, while no significant trend for emissions in other ocean regions. We investigated marine isoprene oxidation impacts based on satellite observations, and the results suggest NO2 may play a critical role during aerosol formation from isoprene in the remote ocean air.

Important Roles and Formation of Atmospheric Organosulfates in Marine Organic Aerosols: Influence of Phytoplankton Emissions and Anthropogenic Pollutants

“…The roles of biogenic SOAs, especially isoprene-SOA, in marine atmospheres should be reconsidered with the organosulfate groups involved. Biogenic isoprene plays an important role in SOA formation and marine aerosol optical depth over the open oceans, and a remarkable increasing trend of isoprene fluxes by a rate of 5.5% per year has been observed in the center of the equatorial Pacific Ocean between August 2015 and December 2020 . Elevation of seawater-released biogenic VOCs would also lead to a conversion of inorganic-to-organic sulfate aerosols (i.e., organosulfates), accompanied with other biogenic SOA formation, which thus influences the particle hygroscopicity with a decreasing fraction of hygroscopic sulfate .…”

“…Biogenic isoprene plays an important role in SOA formation and marine aerosol optical depth over the open oceans, and a remarkable increasing trend of isoprene fluxes by a rate of 5.5% per year has been observed in the center of the equatorial Pacific Ocean between August 2015 and December 2020. 31 Elevation of seawater-released biogenic VOCs would also lead to a conversion of inorganic-to-organic sulfate aerosols (i.e., organosulfates), accompanied with other biogenic SOA formation, which thus influences the particle hygroscopicity with a decreasing fraction of hygroscopic sulfate. 64 The core−shell morphology formed after the reaction of biogenic VOCs with aged sea spray aerosols or sulfate would further influence the particle hygroscopicity as well as the uptake efficiency of gaseous precursors.…”

“…The reactive uptake of biogenic VOC oxidation products (e.g., isoprene epoxides, monoterpene oxides) by acidified sulfate aerosols represents an important reaction for OS formation, based on lab simulations and continental field observation studies. − A recent lab study reported the isoprene-OS formation in aged sea spray aerosols via the reactive uptake of isoprene epoxydiols onto acidic sodium sulfate . Atmospheric isoprene originating from the ocean is estimated to be 0.1–11.6 Tg·C·year –1 , which plays an important role in organic aerosol formation over remote oceanic areas. − Marine isoprene emissions kept an increasing trend over some regions in the equatorial Pacific Ocean during the past few years . However, the contribution of biogenic SOAs in marine atmospheres was evaluated in previous studies by only considering the widely known and traditional isoprene/monoterpene-SOA tracers (e.g., methylglyceric acid, C 5 -alkene triols, methyltetrols, pinonic acid). − The roles or formation processes of biogenic OSs in marine SOAs are far from clear due to a lack of cruise observation evidence; thus, the importance of marine biogenic SOAs previously recognized might be underestimated.…”

“…28−30 Marine isoprene emissions kept an increasing trend over some regions in the equatorial Pacific Ocean during the past few years. 31 However, the contribution of biogenic SOAs in marine atmospheres was evaluated in previous studies by only considering the widely known and traditional isoprene/monoterpene-SOA tracers (e.g., methylglyceric acid, C 5 -alkene triols, methyltetrols, pinonic acid). 32−35 The roles or formation processes of biogenic OSs in marine SOAs are far from clear due to a lack of cruise observation evidence; thus, the importance of marine biogenic SOAs previously recognized might be underestimated.…”

Enhanced dataset of global marine isoprene emission from biogenic and photochemical processes for the period 2001–2020

“…Previous studies utilized experimentally based parameters to describe the photochemical processes within the SML, as well as a 10-metre windspeed threshold indicating the point at which the SML starts to be torn apart (Ciuraru et al, 2015b;Brüggemann et al, 2017). To date, estimates of global marine isoprene emissions have been derived by considering these two emission pathways (Conte et al, 2020;Zhang and Gu, 2022). However, few long-term datasets with high temporal and spatial resolutions is available for both types of emission till now.…”