Ana Filipa Domingues

Monitoring of atmospheric ozone and nitrogen dioxide over the south of Portugal by ground-based and satellite observations.

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.

Measurements of stratospheric ozone and nitrogen dioxide at Èvora, Portugal

The Spectrometer for Atmospheric TRAcers Monitoring (SPATRAM) has been developed as a result of collaboration between the Geophysics Centre of Évora University (CGE-UE), the Institute for Atmospheric Sciences and Climate of the National Research Council (ISAC-CNR) in Italy and the Italian National Agency for New Technologies, Energy and the Environment (ENEA). SPATRAM is a multipurpose ultraviolet (UV)–visible scanning spectrometer (250–950 nm). It has been installed at the Observatory of the CGE, in Évora, since April 2004 and is currently used to carry out measurements of the zenith scattered radiation, the so-called ‘Passive mode’, to retrieve the vertical content and distribution of some atmospheric tracers such as ozone (O3) and nitrogen dioxide (NO2) using Differential Optical Absorption Spectroscopy (DOAS) methodology. The lack of such measurements taken automatically on a routine basis in southwestern European regions, specifically in Portugal, motivated the effort for its installation and constitutes a major driving force for the present work. For continuous NO2 monitoring the 425–455 nm spectral range is investigated. For O3 retrieval the spectral interval 320–340 nm is chosen. The measurements are in good agreement with the photochemical theory of NO2 (O3), showing maximum values during the summer (spring) and minimum values during the winter (autumn) seasons. Moreover, the application of sophisticated inversion schemes to the output of the DOAS program, using the Air Mass Factor (AMF) matrix as the kernel of the inversion algorithm, allowed for the determination of the vertical distribution of NO2 and O3 atmospheric compounds. In addition, the influence of desert dust aerosol absorption on ozone retrieval is assessed, revealing values of about 3.5% for an aerosol optical depth (AOD) of 1.0, in the case simulated. A correction factor is derived and applied whenever desert dust is detected. The ground-based results obtained for the ozone column content are compared with data from the satellite-borne Ozone Monitoring Instrument (OMI), and the two data sets are found to be in good agreement, with a correlation coefficient of 0.96.

Ozone Seasonal Variation with Ground-Based and Satellite Equipments at Évora Observatory: Portugal During 2007–2010

The present study deals with the retrieval and analysis of O3 total columns over the Evora Observatory (South of Portugal) for the period 2007–2010. The data-set presented in this paper is derived from spectral measurements carried out with the UV–Vis. Spectrometer for Atmospheric Tracers Measurements—SPATRAM, installed at the Observatory of the Geophysics Centre of Evora (CGE) –Portugal (38.5oN; 7.9 oW, 300 m asl). The results obtained applying Differential Optical Absorption Spectroscopy (DOAS) methodology to the SPATRAM measurements of zenith sky scattered radiation are presented in terms of seasonal variations of O3. The O3 retrieved with SPATRAM instrument confirms the typical seasonal cycle for middle latitudes reaching the maximum during the spring and the minimum during the autumn. The ground-based results obtained for O3 column are also compared with data from Ozone Monitoring Instrument (OMI) instrument onboard Aura Satellite.

Saharan desert dust radiative effects: a study based on atmospheric modelling

This work investigates the Saharan desert storms direct effect, through the assessment of regional-scale Desert Dust (DD) aerosol Radiative Forcing (RF). Simulated parameters, obtained from atmospheric modelling, are used. The effect over different surfaces on the dust RF is analysed and the stratospheric ozone is considered. In the presence of DD aerosols, a shortwave cooling and a longwave warming effects are found both at the top of the atmosphere and at the surface. The underlying surface seems to interfere in the aerosol RF and the total ozone column changes have small impact on the dust RF at the surface.

Observations of tropospheric compounds at Evora station with multi-axis hyperspectral measurements

The multi purpose UV-Vis. Spectrometer for Atmospheric Tracers Measurement (SPATRAM) is installed at the Observatory of the Geophysics Centre of Evora (38.5º N, 7.9º W) - Portugal, since 2004, measuring the zenith scattered radiation in the 300-550 nm spectral range. The main products are the total column and the vertical profiles of NO2 and O3 obtained with the application of the Differential Optical Absorption Spectroscopy (DOAS) algorithms and with inversion schemes based on the Optimal Estimation methods respectively. Recently (February 2009), the MIGE (Multiple Input Geometry Equipment) was coupled to the SPATRAM instrument allowing for the measurements of the diffused radiation in directions away from the zenith one (Off-Axis). MIGE is an alt-azimuth platform based on a very simple optical layout, using an optical fibre to transmit the radiation inside the monochromator of the SPATRAM equipment. Thanks to the solution adopted in the developing phase, MIGE is able to scan the whole hemisphere. In this work, after a brief description of the MIGE, the first and preliminary results for vertical profiles of NO2 in the Planetary Boundary Layer (PBL), and the values of Slant Column Densities (SCD) of O3 and SO2 measured in Off-Axis configuration at Evora Station, are presented and discussed.

Ozone, nitrogen dioxide, and BrO total columns over Évora-Portugal during 2007-2008

Since the recognition during the seventies of the importance played by the minor atmospheric compounds in the climate system (gases and aerosols), the studies regarding the chemistry and dynamical processes of Ozone (O3) and of nitrogen dioxide (NO2) at high and mid-latitudes, became a fruitful field of research. This work deals mainly with the retrieval and analysis of O3 and NO2 total columns and vertical profiles over the Evora Observatory (South of Portugal) for the period 2007-2008. The products presented in this paper are obtained from spectral measurements carried out with the UV-Vis. Spectrometer for Atmospheric Tracers Monitoring - SPATRAM, installed at the Observatory of the Geophysics Centre of Evora (CGE) since 2004. The application of the Differential Optical Absorption Spectroscopy (DOAS) algorithms to the spectral zenith-sky measurements is presented and discussed. The inversion technique applied to the output of the DOAS procedures (the trace gases content along the optical path of measurements: the slant column densities -SCD- of the analyzed absorber) are examined. The first observations obtained with the SPATRAM instrument regarding stratospheric bromine oxide (BrO) are shown. In addition, the comparison of the ground-based measurements with data derived from satellite equipments (OMI and SCIAMACHY), are discussed.