1Instituto Nacional de Técnica Aeroespacial (INTA), Área de Investigación e Instrumentación Atmosférica, Ctra Ajalvir km4, 28850, Torrejón de Ardoz, Madrid, Spain
2Laboratory for Atmospheric and Climate Science, CSIC, Toledo, Spain
3Centro de Investigación Atmosférica de Izaña (Agencia Estatal de Meteorología – AEMET), Sta, Cruz de Tenerife, Spain
Received: 12 Aug 2011 – Discussion started: 12 Oct 2011
Abstract. Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument deployed at the Izaña subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and hence is representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO DSCD of 1.52×1013 molecules cm−2 was observed at the 5° instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-to-day variability of 33% at one standard deviation. Based on the simulation of the DSCDs using radiative transfer calculations with five different hypothesized IO profiles, the IO mixing ratio is estimated to range between 0.2 and 0.4 pptv in the free troposphere. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher IEA, suggesting an enhancement of IO inside the dust cloud.
Revised: 02 Apr 2012 – Accepted: 16 May 2012 – Published: 06 Jun 2012
Puentedura, O., Gil, M., Saiz-Lopez, A., Hay, T., Navarro-Comas, M., Gómez-Pelaez, A., Cuevas, E., Iglesias, J., and Gomez, L.: Iodine monoxide in the north subtropical free troposphere, Atmos. Chem. Phys., 12, 4909-4921, doi:10.5194/acp-12-4909-2012, 2012.