Abstract
The SPATRAM (Spectrometer for Atmospheric TRAcers Monitoring) instrument has been developed as a result of the collaboration between CGE-UE, ISAC-CNR and Italian National Agency for New Technologies, Energy and the Environment (ENEA). SPATRAM is a multi-purpose UV-Vis-scanning spectrometer (250 - 950 nm) and it is installed at the Observatory of the CGE, in Evora, since April 2004. A brief description of the instrument is given, highlighting the technological innovations with respect to the previous version of similar equipment. The need for such measurements automatically taken on a routine basis in south-western European regions, specifically in Portugal, has encouraged the development and installation of the equipment and constitutes a major driving force for the present work. The main features and some improvements introduced in the DOAS (Differential Optical Absorption Spectroscopy) algorithms are discussed. The results obtained applying DOAS methodology to the SPATRAM spectrometer measurements of diffused spectral sky radiation are presented in terms of diurnal and seasonal variations of nitrogen dioxide (NO(2)) and ozone (O(3)). NO(2) confirms the typical seasonal cycle reaching the maximum of (6.5 +/- 0.3) x 10(+15) molecules cm(-2) for the sunset values (PM), during the summer season, and the minimum of (1.55 +/- 0.07) x 10(+15) molecules cm(-2) for the sunrise values (AM) in winter. O(3) presents the maximum total column of (433 +/- 5) Dobson Unit (DU) in the spring season and the minimum of (284 +/- 3) DU during the fall period. The huge daily variations of the O(3) total column during the spring season are analyzed and discussed. The ground-based results obtained for NO(2) and O(3) column contents are compared with data from satellite-borne equipment (GOME - Global Ozone Monitoring Experiment; SCIAMACHY - Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY; TOMS - Total Ozone Monitoring Spectrometer) and it is shown that the two data sets are in good agreement. The correlation coefficient for the comparison of the ground-based/satellite data for O(3) is of 0.97.
Highlights
In the last forty years, the stratospheric ozone (O3) in the Northern Hemisphere (NH) midlatitudes has suffered a significant decrease
The Vertical Column Density (VCD) of both NO2 and O3 are obtained through Eq (7), where the Air Mass Factor (AMF) is calculated with the AMEFCO radiative transfer model [24]
AMEFCO is based on the Intensity Weighted Optical Path (IWOP) method and is a single-scattering model using ray tracing in a spherical two-dimensional atmosphere with optical paths integrated over individual shells
Summary
In the last forty years, the stratospheric ozone (O3) in the Northern Hemisphere (NH) midlatitudes has suffered a significant decrease. Studies of O3 profile temporal series in the NH show that the annual average of O3 concentration has increased in the troposphere and decreased in the low stratosphere [1]. Other authors confirm these results [2,3], emphasizing that, in Southern Europe, the trend of O3 loss per decade is higher than the one found in the United States, considering areas at the same latitudes and with equal values of surface nitrogen oxides. The hypothesis of the air mass transport from the polar vortex towards lower latitudes cannot be completely applied to the NH. The decrease of stratospheric O3 during summer time at northern high latitudes is caused by chemical reactions and transport processes [5]
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