Reactive gases monitoring program at Izaña






Visitors for reactive gases studies




The objective is to perform a continuous monitoring of reactive gases related to climate forcing and air quality on multi-decadal time scales in the subtropical North Atlantic free troposphere. For this purpose, ozone, carbon monoxide, sulphur dioxide and nitrogen oxides are monitored in a continuous basis. This project is being developed within the framework of the Global Atmospheric Watch Program of the World Meteorological Organization.


The instrumentation used for performing the in-situ reactive gases measurement are placed thorough the tower of the observatory’s building, exactly in the second, third and sixth floors.


Two inlets are use for reactive gases measurements. One is used for collecting ozone samples and the other is used for collecting carbon monoxide, sulphur dioxide and nitrogen oxides. Vertical laminar flow manifolds are used to take the sample air assuring residence times of the air masses less than 10 seconds.


Fig. 1. Inlets and an example of the vertical laminar flow manifolds of reactive gases at Izaña.


Zero checks are made during 15 minutes in a daily period. In the case of carbon monoxide, this zero check is carried out each half an hour to minimize the influence of temperature fluctuations.
Multipoint calibrations are made each three months. A primary standard 49C-PS is used to calibrate the ozone analyzers, while a dilution system with cylinders is used to calibrate the rest of compounds. In addiction a GPT system is used to calibrate NO2 measurements.

Fig. 2. Scrubbers of the 43C, 48C ad 42C models, respectively.


The methodologies used by these analyzers have been declared as reference methods by the Environmental Protection Agency of USA and the European Union.

Instrument pictures
Ozone concentration is measured by UV Photometric absorption.
Model 49C (Thermo Electron Corporation).

Carbon monoxide is measured by a gas filter correlation analyzer.
Model 48C-TL (Thermo Electron Corporation).

Sulphur Dioxide is measured by pulsed fluorescence analyzer.
Model 43C-TL (Thermo Electron Corporation).
Nitrogen oxides are measured by a chemiluminescence technique. The molybdenum converter has been replaced by a photolytic converter to minimize nitrogen species interferences.
Model 42C-TL (Thermo Electron Corporation).

More details on the measurements are provided at GAWSIS


Reactive gases at Izaña Observatory are focused on the characterization of these gases in the free troposphere, its trends, the analysis and detection of the long range transport mechanism and its influence as precursors of nanoparticles formation.

The characterization of reactive gases in the free troposphere

A minimum in summer and autumn time (≈70 ppb) and maximum in winter and spring (≈140 ppb) are observed for CO measurements:

Fig. 3. Time series of carbon monoxide (2006-2008).

At Izaña station a trace level analyzer for nitrogen oxides measurements with a molybdenum converter was installed in a first stage. Molybdenum converters are non specific for determination of nitrogen dioxide (NO2), because their response to other nitrogen-containing compounds as peroxyacetyl nitrate (PAN) and a variety of other organic nitrates and nitric acid, which provokes an overestimation of NO2 measurement, specially, when sampling photochemically aged air masses or in remote locations, where NOx is small compared with NOy (Winer et al., 1974, Steinbacher et al., 2007). Because of this, the output was understood as a good approximation of the total gas phase “nitrogen oxides” (NOy). In a second stage, the molybdenum converter was replaced by a photolytic one which uses ultraviolet light, which allows a better measurement of NO2 in this location.

Nitrogen oxides do not reveal a seasonal pattern, which is explained by the conjunction of opposite processes: the thermally induced vertical transport and the chemical lifetime of NOx (Zani et al., 2007). SO2 does not present a seasonal pattern too.

The upward orographic flows provoke the transport of polluted boundary layer air to the height of Izaña in a daily cycle between 10h to 18h. This mixing with the boundary layer air provokes an increase of NOX mixing ratios and SO2, and a decrease in O3 mixing ratios.

Out of this time period, we could expect to measure the representative troposphere levels in the tropical region of reactive gases, unfortunately, in the case of sulphur dioxide and nitrogen oxides, this estimation is a difficult matter because they remain under the detection limits ( <60pptv and <50 pptv, respectively).

Ozone trends
Ozone is an important trace gas in the troposphere because it affects the oxidizing capacity of the troposphere (Logan 1985; Thompson, 1992), it is a phytotoxicant that can affect public health in polluted areas (Tiao et al., 1975), and it is an important greenhouse gas (Mitchell, 1989).
The distribution of ozone in the troposphere is highly variable in time and space because of the numerous sources and sinks and because of the many production/destruction reactions with other atmospheric constituents.
At Izaña station located in the free troposphere on Tenerife, in the Canary Islands, continuous measurements of ozone and related species has been made since 1987. This long-term record provides unique insights into the meteorological processes that affect ozone concentrations over this region of the subtropical North Atlantic Ocean.
Fig. 4. Time series of surface ozone (1987-2008).

The influence of reactive gases as precursors of nanoparticles formation

New particle formation is observed almost every day in the upward orographic flows that are developed during daylight around Tenerife Island. The transport of water vapour and gaseous precursors due to upward flows from the boundary layer the low free troposphere results on new particles of a few nanometres.

Fig. 5. Five-minutes averaged values of N3-10, SO2, water vapour concentrations and relative humidity during two events (16 November 2007 and 1 October 2007)


Fig. 6. Hourly median values and percentiles for each month of 2007 of: (A) relative humidity (RH), water vapour (H2O) and temperature (T), (B) SO2 and NOy concentrations, (C) global (G) and UV-B radiation, (D) N10, N3 and N3−10 concentrations, and (E) percentiles 70-th, 90-th and 85-th of N3−10, and (F) percentiles 15-th and 25-th of N3−10.


Mrs. Yenny González Ramos (Lead, PhD student) (link to personal page)
Dr. Emilio Cuevas Agulló (link to personal page)
Dr. Sergio Rodríguez González (link to personal page)
Ramón Ramos López (link to personal page)

Visitors for reactive gases studies (since 2004)

Name Institution Period
Dr. C. Zellweger
and Dr. J. Klausen
Global Atmosphere Watch
World Calibration Centre for Surface Ozone
Carbon Monoxide and Methane, EMPA
30/11/2004 – 4/12/2004
María Elena Barlasina

Ushuaia GAW Station

01/09/2008 – 01/10/2008
Ricardo Daniel Sánchez Servicio Meteorológico Nacional de Argentino 01/09/2008 – 01/10/2008
Dr. C. Zellweger Global Atmosphere Watch
World Calibration Centre for Surface Ozone
Carbon Monoxide and Methane, EMPA
4/03/2009 – 11/03/2009

Publications based on reactive gases observations at Izaña

Rodríguez, S., González, Y., Cuevas, E., Ramos, R., Romero, P.M., Abreu-Afonso, J., Redondas, A., Atmospheric nanoparticle observations in the low free troposphere during upward     orographic flows at Izaña Mountain Observatory. Atmospheric Chemistry and Physics Discussions, 9, 10913–10956, 2009. Still in open discussion period !!! (download pdf)

Gil; M., M. Yela, L. N. Gunn, A. Richter, I. Alonso, M. P. Chipperfield, E. Cuevas, J. Iglesias, M. Navarro, O. Puentedura, and S. Rodríguez, NO2 climatology in the northern subtropical region: diurnal, seasonal and interannual variability, Atmos. Chem. Phys., 8, 1635-1648, 2008.
Oltmans, S. J.., A. S. Lefohn, J. M. Harris, I. Galbally, H. E. Scheel, G. Bodeker, E. Brunke, H. Claude, D. Tarasick, B. J. Johnson, P. Simmonds, D. Shadwick, K. Anlauf, K. Hayden, F. Schmidlin, T. Fujimoto, K. Akagi, C. Meyer, S. Nichol, J. Davies, A. Redondas, E. Cuevas, Long-term Changes in Tropospheric Ozone, Atmos. Environ., 40, 3156-3173, 2006.
Rodríguez, C. Torres, J.C. Guerra, E. Cuevas, Transport Pathways to Ozone to Marine and Free-Troposphere Sites in Tenerife, Canary Islands, Atmos. Environ., 38, 4733-4747, 2004.
Oltmans, S.J., A.S. Lefohn, H.E. Scheel, J.M.   Harris, H. Levy II, I.E. Galbally, E.G. Brunke, C.P. Meyer, J.A. Lathrop, B.J. Johnson, D.S. Shadwick, E.Cuevas, F.J. Schmidlin, D.W. Tarasick, H. Claude, J.B. Kerr, O. Uchino, V. Mohnen, Trends of Ozone in the Troposphere, Geophys. Res. Lett., Vol. 25, 2, 139-142, 1998.

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