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Black carbon concentrations and sources in the marine boundary layer of the tropical Atlantic Ocean using four methodologies
Pohl, K., M. Cantwell, P. Herckes, AND R. Lohmann. Black carbon concentrations and sources in the marine boundary layer of the tropical Atlantic Ocean using four methodologies. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 14(6):7431-7443, (2014).
Black carbon (BC) is the byproduct of the incomplete combustion of biomass and fossil fuels making it ubiquitous in the environment. Atmospheric BC is an important forcing factor with respect to climate change, second only to carbon dioxide. It is a strong absorber of sunlight and its deposition to ocean sediments is a potential long-term sink for fixed carbon and organic pollutants. Black carbon is rarely measured in remote environments causing aerosol models to deal with significant uncertainty in their predictions. Instead, results are often extrapolated to estimate BC concentrations in remote regions. This uncertainty is further exacerbated by the fact that BC results are operationally defined by the selected analytical method. In this study, sediment samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols. Findings indicate that to better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions.
Combustion-derived aerosols in the marine boundary layer have been poorly studied, especially in remote environments such as the open Atlantic Ocean. The tropical Atlantic has the potential to contain a high concentration of aerosols, such as black carbon, due to the African emission plume of biomass and agricultural burning products. Atmospheric particulate matter samples across the tropical Atlantic boundary layer were collected in the summer of 2010 during the southern hemispheric dry season when open fire events were frequent in Africa and South America. The highest black carbon concentrations were detected in the Caribbean Sea and within the African plume, with a regional average of 0.6 μgm−3 for both. The lowest average concentrations were measured off the coast of South America at 0.2 to 0.3 μgm−3. Samples were quantified for black carbon using multiple methods to provide insights into the form and stability of the carbonaceous aerosols (i.e., thermally unstable organic carbon, soot like, and charcoal like). Soot-like aerosols composed up to 45% of the carbonaceous aerosols in the Caribbean Sea to as little as 4% within the African plume. Charcoal-like aerosols composed up to 29% of the carbonaceous aerosols over the oligotrophic Sargasso Sea, suggesting that non-soot-like particles could be present in significant concentrations in remote environments. To better apportion concentrations and forms of black carbon, multiple detection methods should be used, particularly in regions impacted by biomass burning emissions.