The present work deals with UV/Vis up-welling and down-welling irradiation measurements carried out in the lower
Antarctic stratosphere by means of GASCOD-A/4pi spectroradiometer on board the M55-Geophysica aircraft during the
APE-GAIA campaign. Very few such measurements have been performed in the lower stratosphere. The experimental
data are used for the calculation of NO2 photodissociation rate coefficients in the upper troposphere and lower
stratosphere along the altitude of the flight. A detailed description of the measurement method, instrumentation and
calibration procedures is presented. Experimental results are presented and discussed too.
The emissions of the cruise ships, in terms of nitrogen dioxide (NO2) and sulphur dioxide (SO2), are evaluated with the DOAS scanning spectrometer TropoGAS (Tropospheric Gas Analyser Spectrometer) developed at ISAC CNR in close
collaboration with the CGE-UE. The slant columns amounts of the above mentioned compounds are obtained with the
application of the Differential Optical Absorption Spectroscopy (DOAS) technique to the spectral measurements carried
out with the TropoGAS instrument. This last is linked with an optical fibre to a simple scanning optical system allowing
for measurements in multiple axis configurations. The measurements are carried out across the Giudecca Channel in
Venice, during two field campaigns performed in July and in October 2007. The instrumental setup, the DOAS method
and the technique for the evaluation of the ships emissions, are described. The results of flow rate emissions for NO2 and
SO2 are presented and discussed. Their mean values are about 12g/s and 4 g/s for NO2 and SO2 respectively.
KEYWORDS: NOx, Atmospheric modeling, Spectroscopy, Data modeling, Single crystal X-ray diffraction, Aerosols, Lamps, Polonium, Systems modeling, 3D modeling
A simple method to determine the vertical distribution of a pollutant gas, namely NO2, by means of the spectral
measurements obtained with a scan-DOAS spectrometer, is presented. The developed technique can be summarized as
follows: i) a series of quasi simultaneous measurements in the zenith and in others directions allowing for the
determination of the Slant Column Density of NO2 for different elevation angles; ii) an active DOAS measurement for
the determination of the NO2 concentration at the ground; iii) a set of Radiative Transfer Model (RTM) calculation of the
scattering distance from the spectrometer, for a set of visibility values; iv) a recursive procedure of profile calculation
starting from the first measurement and subtracting the value of NO2 Slant Column Density (SCD) retrieved from the
measurement taken at the previous angle of sight. Measurements are carried out during summer 2007 in S. Pietro
Capofiume (Bologna-Italy). The vertical distribution for NO2 obtained with the above described method has been
compared with the profiles calculated with the GAMES (Gas Aerosol Modelling Evaluation System) model. The results
of this comparison show some differences between the modelled and the measured profiles, probably due to box
approximations in RTM calculation for measured profiles and to the large pixel grid (about 10x10 km2), for model evaluation.
In the frame of DOAS, a Monte Carlo code has been developed, to calculate, for a given detector with assigned diameter
and field of view, the single and multiple scattering radiance. Very general 3-D geometry is foreseen. Spatial distribution
along the detector axis for the single and total scattering radiance are computed. Ground reflected contributions to the
solar radiance are estimated. Differential effects due to small perturbations in physical parameters, such as ozone density,
can simultaneously be taken into account in the same calculation. The code has been applied to ToTaL-DOAS
(Topographic Target Light scattering-Differential Optical Absorption Spectroscopy) measurements.
The GASCOD (Gas Analyzer Spectrometer Correlating Optical Differences) has been installed at the 'Mario Zucchelli'
Antarctic station since 1996. It measures the zenith sky radiation in the 405-465 nm spectral range in unattended and
automatic mode. The application to the spectral data of the DOAS (Differential Optical Absorption Spectroscopy)
algorithms coupled with a Radiative Transfer Model (RTM) for the computation of the Air Mass Factor (AMF), allows
for the retrieval of the total content of the main absorber in this spectral range, namely nitrogen dioxide (NO2).
Moreover, the application of sophisticated inversion schemes to the output of the DOAS program, using the AMF matrix
as the kernel of the inversion algorithm, permits the determination of the vertical distribution of the above mentioned
compound. The full dataset of the spectral data obtained with GASCOD during the period 1996-2008, was re-analyzed
with a modified version of the software tool previously utilized. Even if the spectral range examined with GASCOD is
not the most favorable for the ozone total column and vertical profile retrieval, the re-processing of the spectral data
allowed for the determination of the total ozone columns (TOC). The uncertainties range from 4% to 8% for ozone and
3% to 6% for NO2. The peculiar features of the seasonal variation of NO2 total columns (i.e. the normal decreasing
during the austral fall and the irregular growing towards the summer month) are presented and discussed. The
confirmations of the significant declining of the ozone total columns during the 'Ozone Hole' periods (mid-August to
mid-October) are reported. The vertical distributions obtained for the preceding atmospheric compounds are shown and
examined.
In this paper we present a methodology for the retrieval of the vertical profile of atmospheric gas pollutants in the
boundary layer from ground based remote sensing measurements. Nitrogen dioxide (NO2) and ozone (O3) slant column
amounts have been obtained with the Differential Optical Absorption Spectroscopy (DOAS) technique used in the
multiple axis configuration (the so called MAX-DOAS). The measurements have been carried out in the Presidential
Estate at Castel Porziano (Rome) in the period from September to November 2006 in the frame of a programme started
in 1994 for studying and monitoring the Estate's environment. The retrieval of information on the vertical profile of trace
gases from their slant column amounts requires: (1) the simulation of the radiative transfer in the atmosphere for Air
Mass Factor (AMF) calculation; (2) the application of inversion schemes. In this paper the vertical profiles of NO2 and
O3 obtained from multiple axis DOAS measurements and their daily evolution are presented and discussed. The day
under study is the 29th of October, 2006.
LIDAR (LIght Detection and Ranging) is an optical active remote sensing technology with many applications in
atmospheric physics. Modelling of LIDAR measurements appears useful approach for evaluating the effects of various
environmental variables and scenarios as well as of different measurement geometries and instrumental characteristics.
In this regard a Monte Carlo simulation model can provide a reliable answer to these important requirements. A
semianalytic Monte Carlo code for modelling LIDAR measurements has been developed at ISAC-CNR. The
backscattered laser signal detected by the LIDAR system is calculated in the code taking into account the contributions
due to the main atmospheric molecular constituents and aerosol particles through processes of single and multiple
scattering. The contributions by molecular absorption, ground and clouds reflection are evaluated too. The code can
perform simulations of both monostatic and bistatic LIDAR systems. To enhance the efficiency of the Monte Carlo
simulation, analytical estimates and expected value calculations are performed. Artificial devices (such as forced
collision, local forced collision, splitting and russian roulette) are moreover foreseen by the code, which can enable the
user to drastically reduce the variance of the calculation.
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