Cap Verde

The Cape Verde Atmospheric Observatory (CVAO), at Calhau on the island of São Vicente. The CVAO is a World Meteorological Organisation-Global Atmospheric Watch (WMO-GAW) global station and provides quality-assured atmospheric data.

An Aero-Laser AL5001 instrument for the measurement of carbon monoxide mixing ratios in background air has been installed at the National Centre for Atmospheric Science (NCAS) Cape Verde Atmospheric Observatory (CVAO) since October 2006 and there are no plans for the measurements to stop in the foreseeable future. At the University of York we also have an AL5002 instrument which is used for shorter deployments (e.g. for NAMBLEX and OP3 and has in the past been used as a back-up for both the Cape Verde system and the FAAM aircraft system. 

The aim of the project is to monitor the background concentration of CO (along with other trace gases) in the tropical marine boundary layer, to gain increased understanding of the oxidation capacity in this region.  The CVAO site is a “Global” Global Atmospheric Watch site which means that it meets the requirements to provide data required to address environmental issues of global scale and importance.

Some of these requirements include the following:

  1. The station location is regionally representative and is normally free of the influence of significant local pollution sources.
  2. There are adequate power, air conditioning, communication and building facilities to sustain long term observations with greater than 90% data capture (i.e. <10% missing data). 
  3. The GAW CO observation made is of known quality and linked to the GAW CO Primary Standard. 
Inside the CVAO station.

CO data is presently submitted in near-real-time to the MACC (Monitoring Atmospheric Composition and Climate) project which is part of the European GMES (Global Monitoring for Environment and Security) programme. The concentration of CO in the marine boundary layer is mainly controlled by the hydroxyl radical (OH) concentration. Deviations occur as a result of long-range transport from more polluted areas and the occasional biomass burning input from the Canary Islands.

Instrument rack containing an AL5001 CO-monitor.

Publications

Publication single view

Article

Title: Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean
Authors: K.A. Read, A.S. Mahajan, L.J. Carpenter, M.J. Evans, B.V.E. Faria, D.E. Heard, J.R. Hopkins, J.D. Lee, S.J. Moller, A.C. Lewis, L. Mendes, J.B. McQuaid, H. Oetjen, A. Saiz-Lopez, M.J. Pilling and J.M.C. Plane
Journal: Nature Lett.
Year: 2008
Volume: 453
Pages: 1232
DOI: 10.1038/nature07035
Web URL: http://www.nature.com/nature/journal/v453/n7199/full/nature07035.html
Abstract: Increasing tropospheric ozone levels over the past 150 years have led to a significant climate perturbation; the prediction of future trends in tropospheric ozone will require a full understanding of both its precursor emissions and its destruction processes. A large proportion of tropospheric ozone loss occurs in the tropical marine boundary layer and is thought to be driven primarily by high ozone photolysis rates in the presence of high concentrations of water vapour. A further reduction in the tropospheric ozone burden through bromine and iodine emitted from open-ocean marine sources has been postulated by numerical models, but thus far has not been verified by observations. Here we report eight months of spectroscopic measurements at the Cape Verde Observatory indicative of the ubiquitous daytime presence of bromine monoxide and iodine monoxide in the tropical marine boundary layer. A year-round data set of co-located in situ surface trace gas measurements made in conjunction with low-level aircraft observations shows that the mean daily observed ozone loss is ~50 per cent greater than that simulated by a global chemistry model using a classical photochemistry scheme that excludes halogen chemistry. We perform box model calculations that indicate that the observed halogen concentrations induce the extra ozone loss required for the models to match observations. Our results show that halogen chemistry has a significant and extensive influence on photochemical ozone loss in the tropical Atlantic Ocean boundary layer. The omission of halogen sources and their chemistry in atmospheric models may lead to significant errors in calculations of global ozone budgets, tropospheric oxidizing capacity and methane oxidation rates, both historically and in the future.

Back to the list view