This contribution focuses on the development and refinement of novel scientific algorithms for th... more This contribution focuses on the development and refinement of novel scientific algorithms for the retrieval of total and tropospheric nitrogen dioxide (NO2) columns for the GOME-2 satellite instrument. NO2 plays significant roles in atmospheric chemistry. It strongly related to ozone destruction in the stratosphere, and is regarded as an important air pollutant and ozone precursor in the troposphere. Total NO2 columns from GOME-2 are retrieved with the Differential Optical Absorption Spectroscopy (DOAS) method using the large 425-497 nm wavelength fitting window in order to increase the signal to noise ratio. The tropospheric NO2 column is derived using an improved Stratospheric-Tropospheric separation (STS) algorithm, followed by an air mass factor (AMF) conversion calculated with the LIDORT model. For the calculation of the tropospheric AMF, improved GOME-2 cloud parameters are used and a new surface albedo (LER) climatology based on GOME-2 observations for 2007-2013 is applied. ...
Atmospheric Chemistry and Physics Discussions, 2017
We present MAX-DOAS measurements of NO<sub>2</sub>, HCHO, and aerosols performed in C... more We present MAX-DOAS measurements of NO<sub>2</sub>, HCHO, and aerosols performed in Central Africa, in the city of Bujumbura, Burundi (3.38° S, 29.3° E). A MAX-DOAS instrument has been operated at this location by BIRA-IASB since late 2013. Aerosol-extinction and trace-gas vertical profiles are retrieved by applying the optimal-estimation-based profiling tool bePRO to the measured…
Total and tropospheric NO 2 columns have been operationally retrieved from the GOME-2/MetOp instr... more Total and tropospheric NO 2 columns have been operationally retrieved from the GOME-2/MetOp instruments since the first MetOp platform was put in orbit in October 2006. GOME-2 NO 2 data products are retrieved in three main steps: (1) a DOAS spectral analysis yielding the total column amount of NO 2 along the slant optical path, (2) an estimation of the stratospheric NO 2 column using tropospheric masking and spatial interpolation, to be subtracted from the total column to derive the tropospheric contribution, and (3) a conversion of the total and tropospheric slant columns into vertical columns based on airmass factor calculations which require a-priori knowledge of the NO 2 vertical distribution and surface albedo, as well as cloud information retrieved from GOME-2 spectra. In this study we combine correlative measurements available from complementary ground-based remote sensing networks to address the geophysical validation of the GOME-2 NO 2 data products. Zenith-sky DOAS/SAOZ me...
ABSTRACT In recent years, ground-based multi-axis differential absorption spectroscopy (MAX-DOAS)... more ABSTRACT In recent years, ground-based multi-axis differential absorption spectroscopy (MAX-DOAS) has shown to be ideally suited for the retrieval of tropospheric trace gases and deriving information on the aerosol properties. These measurements are invaluable to our understanding of the physics and chemistry of the atmospheric system, and the impact on the Earth&#39;s climate. Unfortunately, MAX-DOAS measurements are often performed under (partially) cloudy conditions, causing data quality degradation and higher uncertainties on the retrievals. A high aerosol load and/or a strong cloud cover can introduce additional photon absorption or multiple scattering. The first effect strongly impacts the retrieved differential slant columns (DSCDs) of the trace gases, leading to an underestimation of the atmospheric column density. Multiple scattering, on the other hand, becomes important for low clouds with a high optical depth, and cause a strong increase in the retrieved trace gas DSCDs. The presence of thin clouds can furthermore introduce a degeneracy in the retrieved aerosol optical depth, since they will have similar effect on the MAX-DOAS measurements. In this case, only information on the trace gas DSCDs can be successfully retrieved. If the cloud cover consists of broken or scattered clouds, the MAX-DOAS method becomes very unstable, since the different elevation angels will probe regions of the sky with strongly deviating properties. Here we present a method to qualify the sky and cloud conditions, using the colour index and O4 DSCDs, as derived from the MAX-DOAS measurements. The colour index is defined as the ratio of the intensities at the short- and long-wavelength part of the visible spectral range, typically at 400 nm and 670 nm. For increasing optical thickness due to clouds or aerosols, the colour index values decrease and values for different elevation angles converge. In the case of broken clouds, the colour index shows a strong and rapid temporal variation, which is easily detectable. Additional information is derived from the O4 DSCD measurements, since they are quite sensitive to the change of the light paths due to scattering at different altitudes. For example, thick clouds at low altitude show a very strong increase in the DSCD values due to scattering, combined with a low colour index value due to the intensity screening. In general, our method shows promising results to qualify the sky and cloud conditions of MAX- DOAS measurements, without the need for other external cloud-detection systems such as Brewer instruments or pyrheliometers.
This contribution focuses on the development and refinement of novel scientific algorithms for th... more This contribution focuses on the development and refinement of novel scientific algorithms for the retrieval of total and tropospheric nitrogen dioxide (NO2) columns for the GOME-2 satellite instrument. NO2 plays significant roles in atmospheric chemistry. It strongly related to ozone destruction in the stratosphere, and is regarded as an important air pollutant and ozone precursor in the troposphere. Total NO2 columns from GOME-2 are retrieved with the Differential Optical Absorption Spectroscopy (DOAS) method using the large 425-497 nm wavelength fitting window in order to increase the signal to noise ratio. The tropospheric NO2 column is derived using an improved Stratospheric-Tropospheric separation (STS) algorithm, followed by an air mass factor (AMF) conversion calculated with the LIDORT model. For the calculation of the tropospheric AMF, improved GOME-2 cloud parameters are used and a new surface albedo (LER) climatology based on GOME-2 observations for 2007-2013 is applied. ...
Atmospheric Chemistry and Physics Discussions, 2017
We present MAX-DOAS measurements of NO<sub>2</sub>, HCHO, and aerosols performed in C... more We present MAX-DOAS measurements of NO<sub>2</sub>, HCHO, and aerosols performed in Central Africa, in the city of Bujumbura, Burundi (3.38° S, 29.3° E). A MAX-DOAS instrument has been operated at this location by BIRA-IASB since late 2013. Aerosol-extinction and trace-gas vertical profiles are retrieved by applying the optimal-estimation-based profiling tool bePRO to the measured…
Total and tropospheric NO 2 columns have been operationally retrieved from the GOME-2/MetOp instr... more Total and tropospheric NO 2 columns have been operationally retrieved from the GOME-2/MetOp instruments since the first MetOp platform was put in orbit in October 2006. GOME-2 NO 2 data products are retrieved in three main steps: (1) a DOAS spectral analysis yielding the total column amount of NO 2 along the slant optical path, (2) an estimation of the stratospheric NO 2 column using tropospheric masking and spatial interpolation, to be subtracted from the total column to derive the tropospheric contribution, and (3) a conversion of the total and tropospheric slant columns into vertical columns based on airmass factor calculations which require a-priori knowledge of the NO 2 vertical distribution and surface albedo, as well as cloud information retrieved from GOME-2 spectra. In this study we combine correlative measurements available from complementary ground-based remote sensing networks to address the geophysical validation of the GOME-2 NO 2 data products. Zenith-sky DOAS/SAOZ me...
ABSTRACT In recent years, ground-based multi-axis differential absorption spectroscopy (MAX-DOAS)... more ABSTRACT In recent years, ground-based multi-axis differential absorption spectroscopy (MAX-DOAS) has shown to be ideally suited for the retrieval of tropospheric trace gases and deriving information on the aerosol properties. These measurements are invaluable to our understanding of the physics and chemistry of the atmospheric system, and the impact on the Earth&#39;s climate. Unfortunately, MAX-DOAS measurements are often performed under (partially) cloudy conditions, causing data quality degradation and higher uncertainties on the retrievals. A high aerosol load and/or a strong cloud cover can introduce additional photon absorption or multiple scattering. The first effect strongly impacts the retrieved differential slant columns (DSCDs) of the trace gases, leading to an underestimation of the atmospheric column density. Multiple scattering, on the other hand, becomes important for low clouds with a high optical depth, and cause a strong increase in the retrieved trace gas DSCDs. The presence of thin clouds can furthermore introduce a degeneracy in the retrieved aerosol optical depth, since they will have similar effect on the MAX-DOAS measurements. In this case, only information on the trace gas DSCDs can be successfully retrieved. If the cloud cover consists of broken or scattered clouds, the MAX-DOAS method becomes very unstable, since the different elevation angels will probe regions of the sky with strongly deviating properties. Here we present a method to qualify the sky and cloud conditions, using the colour index and O4 DSCDs, as derived from the MAX-DOAS measurements. The colour index is defined as the ratio of the intensities at the short- and long-wavelength part of the visible spectral range, typically at 400 nm and 670 nm. For increasing optical thickness due to clouds or aerosols, the colour index values decrease and values for different elevation angles converge. In the case of broken clouds, the colour index shows a strong and rapid temporal variation, which is easily detectable. Additional information is derived from the O4 DSCD measurements, since they are quite sensitive to the change of the light paths due to scattering at different altitudes. For example, thick clouds at low altitude show a very strong increase in the DSCD values due to scattering, combined with a low colour index value due to the intensity screening. In general, our method shows promising results to qualify the sky and cloud conditions of MAX- DOAS measurements, without the need for other external cloud-detection systems such as Brewer instruments or pyrheliometers.
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Papers by Gaia Pinardi