Articles | Volume 17, issue 8
Research article
26 Apr 2017
Research article |  | 26 Apr 2017

Four years (2011–2015) of total gaseous mercury measurements from the Cape Verde Atmospheric Observatory

Katie A. Read, Luis M. Neves, Lucy J. Carpenter, Alastair C. Lewis, Zoe L. Fleming, and John Kentisbeer

Abstract. Mercury is a chemical with widespread anthropogenic emissions that is known to be highly toxic to humans, ecosystems and wildlife. Global anthropogenic emissions are around 20 % higher than natural emissions and the amount of mercury released into the atmosphere has increased since the industrial revolution. In 2005 the European Union and the United States adopted measures to reduce mercury use, in part to offset the impacts of increasing emissions in industrialising countries. The changing regional emissions of mercury have impacts on a range of spatial scales. Here we report 4 years (December 2011–December 2015) of total gaseous mercury (TGM) measurements at the Cape Verde Observatory (CVO), a global WMO-GAW station located in the subtropical remote marine boundary layer. Observed total gaseous mercury concentrations were between 1.03 and 1.33 ng m−3 (10th, 90th percentiles), close to expectations based on previous interhemispheric gradient measurements. We observe a decreasing trend in TGM (−0.05 ± 0.04 ng m−3 yr−1, −4.2 % ± 3.3 % yr−1) over the 4 years consistent with the reported decrease of mercury concentrations in North Atlantic surface waters and reductions in anthropogenic emissions. The decrease was more visible in the summer (July–September) than in the winter (December–February), when measurements were impacted by air from the African continent and Sahara/Sahel regions. African air masses were also associated with the highest and most variable TGM concentrations. We suggest that the less pronounced downward trend inclination in African air may be attributed to poorly controlled anthropogenic sources such as artisanal and small-scale gold mining (ASGM) in West Africa.

Short summary
This paper presents 4 years of total gaseous mercury data obtained from measurements made at the Cape Verde Atmospheric Observatory, a subtropical site in the Atlantic Ocean. The data show a clear decreasing trend in the overall concentrations but in air from sub-Saharan Africa the trend is less significant and the data more variable. We attribute this result to an influence from artisanal small-scale gold mining in this region, a source for which there is uncertain information.
Final-revised paper