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

ZERO CHECKS AND CALIBRATIONS

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.

INSTRUMENTS

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

Parameters	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 The molybdenum converter has been replaced by a photolytic converter to minimize nitrogen species interferences.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

Research

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).

Fig. 5. Five-minutes averaged values of N_3-10, 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 NO_y 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.

Scientists

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.