Retrieval of vertical ozone content using the Chappuis band with high spectral resolution solar radiation measurements

A method based on the absorption of the Chappuis band in the visible region has been developed in order to retrieve column ozone content together with aerosol optical depth by means of direct solar irradiance measurements of high spectral resolution. Due to the great sensitivity in the visible Chappuis band region of ozone to aerosol contribution and viceversa a careful supervised fitting using adequate windows is carried out. The fit is according to the Angstrom formula and the correct behaviour of the aerosol optical thickness in the 350-1000 nn spectral range supports the adequate retrieval of the ozone values. These values are obtained by means of a nonlinear least square fitting between experimental and modelled data of the aerosol optical thickness (without Rayleigh contribution). Analysing the retrieved ozone values for every wavelength in the Chappuis band a standard deviation of 0.035 atm-cm in the retrieved ozone value must be assigned. Results during the year of 1995 are shown in a rural site (Boecillo), 25 km away from the city of Valladolid located in the center of the Castilla-Leon Region (Spain). Our retrieved values of ozone content show a constant shift (around 0.03 atm-cm) and less scatter compared with those of the Arenosillo (a Spanish station belonging to the Global Ozone Observing System of WMO). Seasonal variation during this measured period of a year are clearly manifested with a maximum around April and a minimum in October. Diurnal variations of 0.03 atm-cm are easily observed and interdiurnal variations of 0.04 atm-cm are also very frequent.