Cape Point GAW Field Campaign

Aerosol chemical composition in a coastal polluted area

picture2.jpgThe Cape Point Global Atmosphere Watch station is maintained by the South African Weather Service (SAWS). In collaboration with SAWS we are collecting size-segregated aerosols twice weekly at Cape Point. The research aims are to i) diagnose the sources, size, and formation chemistry of ammonium aerosols and ii) characterize the sources and composition of organic aerosols.

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Human activities have doubled the size of the global nitrogen (N) cycle since the preindustrial era due to fossil fuel combustion and fertilizer production. There are significant detrimental impacts of this excess N on many terrestrial and aquatic ecosystems, known as the ‘nitrogen cascade’, though little is known about the impact on the remote ocean. Global models indicate that the human-derived N emissions that reach the ocean through atmospheric transport and deposition could have a large and direct impact on global climate change through biology and the oceanic carbon dioxide (CO2) sink. However, these global models are difficult to validate due to a lack of measurements in the marine environment, especially in the southern hemisphere. Measurements in the subtropical North Atlantic ocean have shown significant anthropogenic influence on nitrate deposition to the ocean, but recent work has shown that ammonium and organic N in atmospheric deposition may derive primarily from surface ocean biological activity. This suggests that the paradigm whereby the ocean is a passive recipient of anthropogenic N deposition requires re-examination, as the impacts on ocean fertility, oceanic CO2 removal, and nitrous oxide (N2O) emissions may currently be overestimated. This project aims to investigate the surface ocean and lower atmosphere N cycle in a truly remote region of the ocean.

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NOAA HYSPLIT air mass back trajectory showing clean marine air masses reaching Cape Point

Cape Point receives a mixture of very clean marine air masses (right) that have traveled for weeks over the Southern Ocean, and mixed coastal pollution air masses (left) that have traveled over the city of Cape Town. Using a sector collector, we aim to only collect aerosol samples from very clean marine air masses.

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NOAA HYSPLIT air mass back trajectory showing mixed pollution/marine air masses reaching Cape Point

 

This work is funded by the South African National Research Foundation Competitive Program for Rated Researchers. Partners in this research include co-Principal Investigator Casper Labuschagne (SAWS), Dr. Warren Joubert (SAWS), and postgraduate students Kurt Spence and Brandon Opie.