According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), aerosols and clouds have been identified as one of the largest uncertainties in understanding the atmospheric and climate system. On the global scale, atmospheric aerosols, which are liquid or solid particles suspended in the atmosphere, have a major impact on how Earth absorbs and reflects heat energy from the sun. There is a high concentration of sea salt aerosols that have a significant effect on the climate and air quality. However, there exist major gaps in knowledge when it comes to understanding the organic matter present in aerosol particles in the organic microlayer found at the ocean surface. These aerosols form the link between ocean biogeochemistry and aerosol formation, which then impacts the climate. The EU-funded MARSU project set up specialised experiments in Cape Verde, Morocco and east China to determine the organic composition of aerosol particles. The team set out to understand the evolution of these aerosol particles at the marine boundary layer and to create a revised picture of the effect of sea salt aerosols on the climate. This research was undertaken with the support of the Marie Skłodowska-Curie programme. “The MARSU participants represent an interdisciplinary team of chemists, physicists and analytical chemists,” says project coordinator, Wahid Mellouki. “The consortium brings together expert scientists conducting cutting-edge laboratory, atmospheric simulation chamber studies, field sampling and analysis, analytical method development and modelling studies.”
The contribution of abiotic reactions
MARSU researchers studied the production of volatile organic compounds (VOCs) by means other than through biological processes (abiotic). They found that chemical reactions activated by the sun at the air-water interface produce organic vapours that enhance aerosol particle formation in the atmosphere. This result is significant because previous models only accounted for biological not abiotic processes producing these aerosols. Project work demonstrated that these chemical reactions activated by the sun at the ocean surface are a major source of VOCs on a global scale. Competing with the amounts produced by marine biology, these processes were found to have the potential for producing more than 60 % of these organic aerosols.
Identifying the mechanisms that drive organic aerosol production
The team studied the links between the organic aerosols produced at the ocean surface and the mechanisms of how they affect clouds and the troposphere, the region of Earth’s atmosphere where weather happens. MARSU found that these particles were highly concentrated in cloud water, but that better models are needed because marine biology alone could not account for the high concentration of this organic matter.
Pioneering the first north African field measurement site
The researchers established a new observation site that showed how strongly emissions from urban, desert, marine and terrestrial sources affect the ambient particulate matter and the organic content of the atmosphere. “With the new Atlas observation site, it was possible for the first time to obtain new insights into drivers of atmospheric composition in a high-altitude remote region in northern Africa, a region which is not covered by field characterisations up to now,” Mellouki remarks. The researchers plan to continue the research with more sites throughout Africa.
MARSU, climate, organic aerosol, ocean surface, marine, VOCs, IPCC, volatile organic compounds