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.
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.
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.
Ivan Kostadinov, L. Grassi, G. Ballista, Giorgio Giovanelli, Rodolfo Guzzi, Daniele Bortoli, W. Di Nicolantonio, C. Lecerf, Andrea Petritoli, Fabrizio Ravegnani, S. Scarpanti
The satellite remote sensing instruments for climatic studies are required to have: (1) fast time sampling, (2) high spectral resolution, (3) high space resolution, (4) wide field of view, (5) broad spectral range, (6) simultaneous measurements in different spectral intervals and/or type of measurements (7) lack of movable mechanical parts, etc. Here it is described the main idea of an input optic of remote sensing UV-VIS-IR instrument aimed for climatic studies form the space. It is attempted with the proposed optical system to satisfy requirements (2), (6), (5), (7) and, at least partially, the rest ones.
In the present paper the possibility of the Copper Bromide (CuBr) laser as an attractive tool in the micromachining of different materials has been demonstrated. High-quality percussion drilling, trepanning, scribing, and precision cutting were demonstrated on metals and ceramics with a negligible heat affected zone (HAZ). These good results were achieved with the combination of high power, short pulses, visible radiation and close to the diffraction-limited beam quality.
The application of Differential Optical Absorption Spectroscopy (DOAS) methodology to the zenith scattered light data collected with the GASCOD spectrometer developed at the ISAC Institute allow for the detection of stratospheric trace gases involved in the ozone cycle such as NO2, OClO, BrO. The instrument was installed in December 1995 in the Italian Antarctic station at Terra Nova Bay (74°26'S, 164°03E', Ross Sea), after several tests both in laboratory and in Antarctic region, for unattended and continuous measurement in extreme high-latitude environment. The GASCOD is still working and producing very interesting data for the study of the denitrification processes during the formation of the so-called ozone hole over the Antarctic region. For the continuous NO2 monitoring for whole the year, also during winter when the station is unmanned, the [407 - 460] nm spectral region is investigated. The results for Nitrogen Dioxide, obtained by application of DOAS algorithms to the data recorded during the year 2001, are presented. ERS-2 was launched in April 1995 into a near-polar sun-synchronous orbit at a mean altitude of 795 km. The descending node crosses the equator at 10:30 local time. GOME is a nadir-scanning double monochromator covering the 237 nm to 794 nm wavelength range with a spectral resolution of 0.17-0.33 nm. The spectrum is split into four spectral channels, each recorded quasi-simultaneously by a 1024-pixel photodiode array. The global spatial coverage is obtained within 3 days at the equator by a 960 km across-track swath (4.5 s forward scan, 1.5 s back scan). The ground pixel size of the measurements is 320 X 40 km2. A comparison of GASCOD and GOME results for NO2 total column is performed.
The measurements of HCl and CH4 atmospheric total abundance is very important, because these minor gases play a fundamental role in the stratospheric ozone cycle and in the climatic change. In fact, the first is considered source and sink for chlorine compounds; the latter is a greenhouse gas (26%) and can contribute to the hydrochloric acid formation. HCl and CH4 present a vibrorotational absorption spectrum in the near infrared (3-4 micron). For this reason it is possible to use a Fabry-Perot interferometer (FPI) as a multiple narrow band filter with an appropriate free spectral range (FSR), so its transmission bands overlap the absorption lines of gas under observation. A remote sensor called NISES (Near Infrared Single-Etalon Sensor) and based on a plane FPI with a dynamic control of the etalon gap, is developing. It utilizes the direct sun radiation collected by a solar tracker to detect atmospheric HCl and CH4 slant columns and its suitable for both ground based and airborne applications. The model MAES (Mathematical Algorithm for Etalon Sensor) has been used to study the main optical characteristics of the FPI (free spectral range, finesse, transmission lines number) and to optimize the instrumental response over a wide range of atmospheric conditions. Moreover, line by line computations of atmospheric layer optical depths and radiances are performed, using HARTCODE (R. Rizzi et al. submitted to Applied optics), so a sequence of different Free spectral Range (FSRs), during the measurements itself, is proposed to minimize the water vapor and gases interfering contribution. The main optical characteristics of an FPI and its deployment for atmospheric sensing are discussed; the result of model simulation and the layout of the HCl sensor are presented as well as some preliminary tests.
The UV-Vis DOAS spectrometer GASCOD/A4p (Gas Analyzer Spectrometer Correlating Optical Differences, Airborne version) was installed on board the stratospheric Geophysica aircraft during the APE-THESEO and APE-GAIA campaign in February-March and September-October 1999 respectively. The instrument is provided by five input windows, three of which measure scattered solar radiation from the zenith and from two horizontal windows, 90 degree(s) away from the zenith to perform limb-absorption measurements. Spectra from 290 to 700 nm were processed through DOAS technique to obtain trace gases column amounts. Data from horizontal windows, which are performed for the first time from an airborne spectrometer, are used to retrieve an average concentration of the gases along a characteristic length of the line of sight. An atmospheric Air Mass Factor model (AMEFCO) is used to calculate the probability density function and the characteristic length used to reduce the slant column amounts to in-situ concentration values. The validation of the method is performed through a comparison of the values obtained, with a in-situ chemiluminescent ozone analyzer (FOZAN) which performed synchronous measurements on board Geophysica aircraft. Data from the APE-GAIA campaign was presented and discussed.
GASCODs are UV-Visible ground-based spectrometers developed at the ISAO Institute and used to detect stratospheric trace gases involved in the ozone cycle such as NO2, OClO, BrO, by application of Differential Optical Absorption Spectroscopy (DOAS) methodology to the zenith scattered light collected data. After several tests both in laboratory and in Antarctic region, one of the spectrometers was modified for unattended and continuous measurement in extreme high-latitude environment. The instrument was installed in December 1995 in the Italian Station at Terra Nova Bay (74 degree(s)26'S, 164 degree(s)03E', Ross Sea). The GASCOD is still working and causing very interesting data for the study of the denitrification processes during the formation of the so-called ozone hole over the Antarctic region. When the station is unmanned, to allow for the continuous NO2 monitoring for whole the year without mechanical problems, the fixed [407 - 460] nm spectral region is investigated. The results for Nitrogen Dioxide, obtained by application of DOAS algorithms to the data recorded during the year 2000, are presented. During a leg (December 2000 - January 2001) of the 16th Italian Antarctic Expedition, after the usual instrument check, many measurements were carried out in other spectral regions, with the aim to obtain information about the stratospheric tracers contents. The results obtained for Ozone, Nitrogen dioxide and Formaldehyde at different Solar Zenith Angle are presented.
UV-visible ground-based spectrometers were developed at the ISAO Institute and they are used for application of differential optical absorption spectroscopy (DOAS) methodology to detect stratospheric trace gases involved in the ozone cycle such as NO2, OClO, and BrO. Observations of the light scattered from the zenith-sky were performed with the instrumentation above mentioned, in various stations situated in both the hemispheres. Some problematics connected to data validation and results analysis are introduced. Considerations about the temperature dependency of the cross-section used for the determination of the trace gases slant column are carried out. Results for nitrogen dioxide abundances at different season and various Solar Zenith Angle in their seasonal and diurnal variation are presented and discussed. Finally, the behavior of the sunrise nitrogen dioxide abundance over the sunset slant column is shown and examined.
One of the most important reservoirs of chlorine in the stratosphere is HCl, which sequesters active species and affects the rate of catalytic reactions with ozone. HCl presents a vibro- rotational absorption spectrum, in the near IR; for this reason it is possible to use a Fabry-Perot Interferometer as a multiple narrow band filter with an appropriate free spectral range so its transmission bands overlap the HCl absorption lines.
In ns-putsed longitudinal discharge-excited He-Cu and He-CuBr vapor ion lasers oscillation in the IR spectral range has been obthined. UV laser operation has been obtained only in Ne-CuBr vapor ion laser. An average output power of 210 mW has been measured on the laser line 248.6 nm and a 270 mW on multiline - 248.6, 252.9, 260.0 and 270.3 nm.
We report laser characteristics of a gold ion laser radiating on the lines 282.3nm, 284.7nm, 289.3nm and 291.8nm A longitudinal nanosecond discharge has been used for excitation. Quasi-cw lasing was obtained with 33%/m small-signal gain and 110 mW average output power for the strongest line 282.3nm This average output power corresponds to the record peak power of 1.7W. The investigated laser offers promising prospect for various scientific and technological applications.
A 50 W CuBr laser is reported. Characteristics of the major laser parameters are presented: output power, laser pulse repetition frequency, and laser beam quality. The laser has been designed for precision material processing in industry.
Andrea Petritoli, Giorgio Giovanelli, Paolo Bonasoni, Tiziano Colombo, Franco Evangelisti, U. Bonafe, Daniele Bortoli, Ivan Kostadinov, Fabrizio Ravegnani
A UV/Vis DOAS spectrometer (GASCOD, Gas Analyzer Spectrometer Correlating Optical Differences) was installed at Monte Cimone station in 1993 and since then it has been measuring zenith scattered solar radiation at sunset and sunrise. During 1995 it was possible to investigate two spectral regions, about 50 nm width, centered at 365 nm and 436 nm while later we only have measurements at 436 nm available. The spectra obtained during the 1995 - 96 period have been processed with DOAS technique to obtain column amounts of NO2 and O3. The seasonal and diurnal variation of the NO2 column amounts is shown with a summer maximum (about 1.2 X 1017 mol(DOT)cm-2 for p.m. value and 6 X 1016 mol(DOT)cm-2 for a.m.) and winter minimum (about 2 X 1016 mol(DOT)cm-2 for a.m. and 5 X 1016 mol(DOT)cm-2 for p.m.). An anomalous spring increase in p.m. NO2 value during 1995 is investigated through a vertical distribution analysis. The gas profile is retrieved through a Chahine inversion algorithm applied to the slant columns measured at different solar zenith angle. In fact the air mass factor variation with solar zenith angle can be used to extract information about the gas concentration at each atmospheric layers. A consistent and frequent tropospheric increase in NO2 a.m. concentration is evident. The method and the results obtained are discussed.
The present paper deals with the factors influencing the accuracy of the DOAS and in particularly, with the changing of the depolarization ratio of the zenith scattered radiation and related variations of the retrieved NO2 slant column. Ground based measurements carried out during 1997 and 1998 of the polarization state of the zenith- scattered radiation and the NO2 slant columns have been obtained in 4075 angstrom - 4640 angstrom spectral interval. The depolarization ratio is calculated from the spectra registered with a sheet linear polarizer, inserted into the instrument. A linear regression analysis is applied to retrieve NO2 slant columns. The obtained results are analyzed and discussed.
A UV/Vis spectrometer (named GASCOD) for Differentiated Optical Absorption Spectroscopy (DOAS) has been developed at ISAO Institute and deployed for ground based measurements of stratospheric trace gases for several years at mid-latitudes and the Antarctic region. An airborne version, called GASCOD/A has been installed on board a M55-Geophysica airplane, a stratospheric research platform, capable of flying at an altitude of up to 20 Km. After a test campaign in Italy, the GASCOD/A performed successfully during the Airborne Polar Experiment in the winter 95/96. More recently, the instrument was upgraded to achieve higher sensitivity and reliability. Two additional radiometric channels were added. The input optics can turn in order to collect solar radiation from five different channels: one for detection of the zenith scattered radiation through the roof window (for DOAS measurement), two for direct and diffused radiation through two lateral windows and two for radiometric measurements through two 2(pi) optical heads mounted on the upper and bottom part of the aircraft and linked to the instrument by means of optical guides. The radiometric channels give us the possibility of calculating the photodissociation rate coefficients (J-values) of photochemical reactions involving ozone and nitrogen dioxides. The mechanical and optical layout of the instrument are presented and discussed, as well as laboratory tests and preliminary results obtained during flights onboard the M55- Geophysica.
Livio Scarsi, Primo Attina, Osvaldo Catalano, Carlo De Marzo, Salvatore Giarrusso, Ivan Kostadinov, Boris Krenov, David Lamb, John Linsley, Piero Mazzinghi, Roberto Stalio, Yoshiyuki Takahashi
One of the most challenging tissues in Astroparticle Physics is represented today by the observation of the energy spectrum of the Extreme Energy Cosmic Radiation. The very existence of particles with energy above 1020 eV and of neutrinos of comparable energy raises fundamental scientific questions in connection with their origin and propagation in the interstellar/intergalactic space. These particles can be detected through the gain showers produced in the Earth Atmosphere. The shower development is accompanied by emission of fluorescence in the atmosphere, in particular that induced in Nitrogen with characteristics spectral lines in the UV. Following a first suggestion by J. Linsley in the early 1980's, taken over by Y/ Takahashi, the fluorescence observation can be advantageously carried out by space. By using wide angel optics with large collecting surface, we can monitor a target area of atmosphere of the order of millions square kilometers x sr and corresponding mass above 1013 tons, allowing the detection of the very small flux values typical of the EECR and making possible the search of the elusive high energy neutrinos. AIRWATCH follows this approach. We describe the main scientific goals for the investigation of the EECR, High Energy neutrinos and of the Gamma Ray Bursts, together with the relevant connections to the problem of their origin. The experimental framework is outlined and a description is given of the space mission and of the observational strategy.
The present work deals with the problem regarding the improvement of the differential optical absorption spectroscopy (DOAS), applied to study the stratospheric ozone and other trace gases involved in this chemistry. In particular, the temperature dependence of the Ring effect and the related changes of the NO2 slant column caused by this dependence is verified. The temperature dependence of NO2 is also taken into account. It is shown that the stratospheric temperature variations of about +/- could modify the Stokes and anti-Stokes Raman component and hence modify the Ring effect. The presented results demonstrate that, if such temperature variations are ignored, the related NO2 slant column could be over- or underestimated of about 10 percent.
During the last few years UV-Vis spectrometers were developed at the FISBAT Institute and are used for application of differential optical absorption spectroscopy method to detect many atmospheric trace gases playing important roles in the stratospheric chemistry. After several test both in laboratory and in Antarctic region, one of the spectrometers, called GASCOD2/2, was modified in collaboration with ENEA for unattended and automatic measurement in extreme high-latitude environment. The instrument was installed in December 1995 in the Italian Station at Terra Nova Bay. The aim of this research is to study the dentrification processes during the formation of the so-called ozone hole over the Antarctic region. The preliminary results for the first year of nitrogen dioxide measurement are presented and discussed.
A monitoring campaign of atmospheric pollutants was conducted in February 1993 by several of Italy's CNR institute in heavily polluted greater Milan. This metropolitan area, the largest one in northern Italy, is situated in the northernmost part of the Po Valley and, because of its topography and orography is frequently marked by low ventilation and inversion phenomena, a fast that promotes the accumulation and vertical layering over the city of pollutants. The need for more detailed information on air circulation and changes occurring in the lower atmospheric layers, as well as to understand why air-mass exchange does not take place, thereby impeding the dispersion of pollutants, was the project's goal- orientation. Measurement of NO2, SO2, O3, HNO2 were carried out over a 1.7 Km path in the city center by means of a DOAS system called GASCOD developed by remote sensing group of FISBAT-CNR at Bologna. The light source has been equipped with a remote-controlled occulting devices in order to separate the sky light scattered into the field of bye of the receiving system, which can interfere with the lamp spectra during daytime. The light from the source is collected by a Cassegrain telescope and focused on the spectrograph's entrance slit receiving system; the detector is a linear image sensor featuring an array of 512 MOS photodiodes. Data recorded in the same and boundary areas by a conventional analyzer from city's air-pollution monitoring network are reported for comparison. The statistical correlation of concentration values to the main weather and atmospheric stability parameters are stressed.
The problems of the stratospheric ozone decline during the last decades is the subject of scientific efforts to discover the main factors influencing the processes leading to its disappearance. The exact understanding of chemical- physical processes in the Earth's atmosphere needs high- quality representative measurements for time-series and modeling study. The present paper deals with the problems of the polarization characteristics of DOAS instruments and the corresponding requirements for instrumental orientation relative to the scattered plane. To avoid the polarization effects upon the measurement's accuracy the instrument has to be 'unpolarized'. A fiber optic and an appropriate diffraction grating are used to do this. Experimental measurements have been carried out to check the possibility to use a fiber optic bundle for DOAS applications. The results obtained from this experiments how that the tested fiber bundles do not completely destroy the polarization state of the incoming radiation. At the fiber exit the degree of the polarization reaches up to 10-15 percent in the measured spectral intervals. On the other hand, accordingly to some of the existing methods, to remove Ring effect from the measured zenith spectra, the DOAS instrument used has to be strongly 'polarized'. This achieved by means of a polarizer inserted into the instrument. The assumption is that, applying such kind of measurements makes it possible to separate the Rayleigh from the Raman scattering. The latter e is assumed as unpolarized, which is in conflict with the theory. A new method base on the deconvolution is offered by use as a possible way of overcoming the problems with the Ring effect.
A photodiode-array spectrometer for the detection of atmospheric trace gases has been developed to take diffuse solar zenith and, using a n artificial light source, horizontal long path measurements. Of the numerous factors involved in determining the minimum amount of a detectable gas, including its spectral characteristics, atmospheric phenomena and the algorithm used, the present study examines only the features of the spectrometer and sensor. The spectrometer's spectral dispersion is accurately calculated and its internal stray light kept to a minimum. The linear image sensor's dynamic range and aperture-response function are analyzed along with those phenomena that can alter the actual signal such as veining glare, blooming, etaloning and dark current; the latter two are treated in depth. Etaloning is linked to optical interference in the sensor's passivating layer. A simple model of it, as well as a check of the relative stability over time of the transmission peaks, are included. The analysis of the dark current indicates the existence of a photo-induced component that is inversely proportional to the incident radiation flux. It yields a simple analytical equation describing the phenomenon for the sensor's various elements. This makes it possible to derive the correct dark current value in relation to both the incident radiant energy and the spectral range investigated.
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