Differential Optical Absorption Spectroscopy Technique Research Articles

인공위성 (SCIAMACHY) 데이터를 이용한 대류권 SO2, NO2측정: 2006년 동북아시아 지역의 계절적 SO2, NO2변화 추세

Anthropogenic emissions of nitrogen oxides and sulfur dioxide in Northeast Asia are of great concern because of their impact on air quality and atmospheric chemistry on regional and intercontinental scales. Satellite remote sensing based on DOAS (Differential Optical Absorption Spectroscopy) technique has been preferred to measure atmospheric trace species and to investigate their emission characteristics on regional and global scales. Absorption spectra obtained by the satellite-born instrument, SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) have been utilized to retrieve the information of and over Northeast Asia. levels over Northeast Asia were in order of East China, Yellow Sea, South Sea and Korean Peninsula with mean vertical columns of , , , , respectively. levels were in order of East China, Yellow Sea, Korean Peninsula, and South Sea with mean vertical columns of , , , , respectively. High levels of and were observed over East China, in particular in winter by the contribution of heating fuel combustion exhausts. The and levels over East China were the highest in January with 34% and 42% higher over the annual means. Low levels of ranged over Korean peninsula, while levels were relatively high, in particular in winter. The and levels over Yellow Sea were relatively higher compared to those over Korean peninsula and South Sea, which could be mainly attributed to their transport from East China.

Ten-year measurements of gaseous pollutants in urban air by an open-path analyzer

Object of this study is the versatility of a remote-sensing measurement system through experimental survey of the levels of primary and secondary pollutants in urban areas. For the first time a long-range measurement of different pollutant for a long period are reported in the urban area of Rome. Over 10 years of data collection, levels of NO2, O3, SO2, benzene and toluene are measured and discussed by means of a differential optical absorption spectroscopy (DOAS) system installed at ground level.The period is interesting because it represents one of the most important life-changes in Europe and in Italy: in fact, during the 1990s some significant decrees introduced the catalytic pots and limited the amount of benzene and sulfur dioxide in the fuel. The paper will describe how the main primary and secondary pollutants are changed during all the period: particularly, benzene and SO2 are not over a big social problem for the human health whereas the secondary pollutants, ozone and nitrogen dioxide, have the same trends during the period, meaning a no contribution to their evolution from the atmospheric processes.The DOAS technique is resulted very useful and versatile: comparisons with other traditional analyzers (i.e., GC-PID for benzene and toluene investigations) demonstrate how it allows to have information over all the territory saving the qualitative trends and giving a similar quantitative result. In this respect the authors show that the difference is due to the different sampling ways (the traditional analyzers are punctual whereas the DOAS is a remote-sensing technique covering a wide area) and does not influence the atmospheric process interpretation.Finally, it should be considered that the pollutant trends have been interpreted using the concentration measurements of natural radioactivity as tracer of the dynamic properties of the atmospheric boundary layer.

High precision measurement of formaldehyde in air with differential optical absorption spectroscopy

The formaldehyde (HCHO) measurement is described by differential optical absorption spectroscopy (DOAS) technique and the data processing method is discussed in detail, including the selection of retrieval wavelength band, the removing of interfering structures, the steps of data processing and the spectrum dealing with nonlinear method. The HCHO concentration retrieved in different wavelength bands were compared, including relative error, repeatability and detection limit. As a result, the band from 314 to 332 nm was most suitable for the retrieval of HCHO. With these methods, high measurement precision of 1.9% was obtained and the detection limit of HCHO is less than 1.5 ppb. In addition, high linear relativity 0.9999 is achieved by measuring five different concentrations of HCHO with this system.

A Scanning Multi-Axis Differential Optical Absorption SpectroscopySystem for Measurement of Tropospheric NO2 in Beijing

A scanning multi-axis differential optical absorption spectroscopy(DOAS) system is developed for monitoring tropospheric NO2abundance. Measurements at different viewing angles near the horizoncan be performed sequentially with one telescope collecting scatteredsunlight reflected by a moving mirror. Tropospheric NO2 diurnalvariations can be derived from slant column densities (SCDs) ofdifferent elevation angles. The result from a field campaign in Beijingin summer of 2005 reveals potential possibility for the monitoring oftropospheric NO2 by multi-axis DOAS technique.

Measurements of nighttime nitrate radical concentrations in the atmosphere by long-path differential optical absorption spectroscopy

The long-path differential optical absorption spectroscopy (LP-DOAS) technique was developed to measure nighttime atmospheric nitrate radical (NO3) concentrations. An optimized retrieval method, resulting in a small residual structure and low detection limits, was developed to retrieve NO3. The time series of the NO3 concentration were collected from 17 to 24 March, 2006, where a nighttime average value of 15.8 ppt was observed. The interfering factors and errors are also discussed. These results indicate that the DOAS technique provides an essential tool for the quantification of NO3 concentration and in the study of its effects upon nighttime chemistry.

The uncertainties of satellite DOAS total ozone retrieval for a cloudy sky

This paper aimed to the study of the influence of the uncertainties of satellite Differential Optical Absorption Spectroscopy (DOAS) total ozone retrieval scheme due to unconstrained parameters of the plane-parallel scattering cloud model. The work is based on the exact radiative transfer calculations for a realistic atmospheric model described in the paper. In particular, the accuracy of the DOAS technique based on hyperspectral measurements in the ozone absorption band 315–340 nm is investigated. The general weighting functions approach to the calculation of the error of total ozone introduced in the paper can be used for studies of errors in the retrieved concentration of other trace gases (e.g., NO 2, SO 2, etc.) as well. It was found that the uncertainties in the cloud geometrical and optical characteristics can produce absolute errors in the retrieved total ozone column of up to 6%. This calls for the introduction of accurate cloud retrieval algorithms in ozone satellite retrieval schemes.

Concurrent multiaxis differential optical absorption spectroscopy system for the measurement of tropospheric nitrogen dioxide

The development of a new concurrent multiaxis (CMAX) sky viewing spectrometer to monitor rapidly changing urban concentrations of nitrogen dioxide is detailed. The CMAX differential optical absorption spectroscopy (DOAS) technique involves simultaneous spectral imaging of the zenith and off-axis measurements of spatially resolved scattered sunlight. Trace-gas amounts are retrieved from the measured spectra using the established DOAS technique. The potential of the CMAX DOAS technique to derive information on rapidly changing concentrations and the spatial distribution of NO2 in an urban environment is demonstrated. Three example data sets are presented from measurements during 2004 of tropospheric NO2 over Leicester, UK (52.62 degrees N, 1.12 degrees W). The data demonstrate the current capabilities and future potential of the CMAX DOAS method in terms of the ability to measure real-time spatially disaggregated urban NO2.

Measurements of NO2, SO2, O3, Benzene and Toluene Using Differential Optical Absorption Spectroscopy (DOAS) in Shanghai, China

NO2, SO2, O3, benzene, and toluene were measured in Taopu industry park of Shanghai during the period June to August 2003 by differential optical absorption spectroscopy (DOAS) technique. The daily average concentrations of SO2, NO2, and O3 ranged from 5.7 ppb to 40 ppb, 22 ppb to 123 ppb, and 10.6 ppb to 23 ppb respectively. SO2 and NO2 concentrations were found to depend on wind direction. The diurnal variation of NO2 concentrations had two peaks due to traffic emission. Our DOAS measurements of NO2, SO2 and O3 were compared with the conventional measurement instruments (API automatic monitoring instrument). The concept of a percent difference (PD) and linear regression methods were employed to study the difference between DOAS and API instruments. The correlation analysis between PD values and meteorological parameters and analysis of abnormal higher absolute PD values indicated that the lower visibility induced the bad compatibility between the two systems. The results showed that both systems exhibited strong compatibility with good correlation, therefore the DOAS system is able to provide reliable information on distribution patterns of major air pollutants. Average benzene and toluene concentrations were 1.4 and 8.0 ppb respectively.

Retrieval And Monitoring of Atmospheric Trace Gas Concentrations in Nadir and Limb Geometry Using the Space-Borne Sciamachy Instrument

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) onboard the European Envisat spacecraft performs continuous spectral observations of reflected, scattered and transmitted sunlight in various observation geometries. A unique feature of SCIAMACHY is the capability of probing the atmosphere in three different observation geometries:The nadir, limb, and occultation measurement modes. In nadir mode, column densities of trace gases are retrieved with a spatial resolution of typically 30 x 60 km using the Differential Optical Absorption Spectroscopy (DOAS) technique (Platt and Perner, 1983). Alternating with the nadir measurement, vertical profiles of absorber concentration in the stratosphere are derived in limb and occultation. In this paper we present an overview over some applications of SCIAMACHY data in space-based monitoring of atmospheric pollution. The DOAS algorithms for the retrieval of total column amounts from nadir spectra are briefly described and case studies of pollution events are presented. We also illustrate the technique used to derive stratospheric concentration profiles from limb observations and show comparisons with other remote sensing systems. Special emphasis will be given to techniques, which take advantage of SCIAMACHY's different viewing geometries. In particular, we will discuss the potential and limits of strategies to infer tropospheric abundances of O3 and NO2.

Total ozone from the ozone monitoring instrument (OMI) using the DOAS technique

This paper describes the algorithm for deriving the total column ozone from spectral radiances and irradiances measured by the Ozone Monitoring Instrument (OMI) on the Earth Observing System Aura satellite. The algorithm is based on the differential optical absorption spectroscopy technique. The main characteristics of the algorithm as well as an error analysis are described. The algorithm has been successfully applied to the first available OMI data. First comparisons with ground-based instruments are very encouraging and clearly show the potential of the method.

Seasonal Evolution of Levels of Gaseous Pollutants in an Urban Area (Ciudad Real) in Central-Southern Spain: A Doas Study

Long term continuous monitoring measurements of urban atmospheric concentrations of O3, NO2, NO, and SO2 were performed for the first time in Ciudad Real, a city in central-southern Spain. The measurements were carried out using the differential optical absorption spectroscopy (DOAS) technique, with a commercial system (OPSIS, Lund-Sweden), covering the summer and winter seasons (from 21st July 2000 to 23rd March 2001). Mean levels of O3, NO2 and SO2 monitored during this period were: 27 μg m−3, 50 μg m−3 and 7 μg m−3 respectively. The highest hourly averaged value of O3 (160 μg m−3) was measured during the summer period, while NO2 was enhanced in wintertime (highest values 90 μg m−3). In the coldest period, when central heating installations were operating, SO2 showed maximum levels of 20 μg m−3. The daily, weekly and seasonal analysis of the data shows that photochemical air pollution dominates in this urban atmosphere and is strongly influenced by levels of motor traffic and domestic heating system emissions. These measurements were compared with other studies in Spain and Europe. Also, the long path averaged DOAS measurements were compared with in situ observations made in Ciudad Real, from 23rd August 2000 to 25th September 2000, using a mobile air pollution control station. All gas concentrations reported in this paper are below the WHO guidelines and the different thresholds introduced by the European Environmental Legislation.

An indoor test campaign of the tomography long path differential optical absorption spectroscopy technique

In this study we validate the two-dimensional long path DOAS tomography measurement technique by means of an indoor experiment with well-known concentration distributions. The experiment was conducted over an area of 10 m x 15 m using one and two cylindrical polycarbonate containers of diameter 2 m, respectively, filled with NO2. The setup was realized with three of the multibeam instruments recently developed by Pundt and Mettendorf (Appl. Opt., 2005, in press), which allow the simultaneous measurement along at least four light paths each. The configuration consisted of twelve simultaneous light beams, 39 horizontal light paths in total, and 18 different cylinder positions inside the field. It was found that for the discretization and inversion technique shown here reconstructions of the concentration distributions from experimental data agree well with simulated reconstructions. In order to draw conclusions for atmospheric applications, numerical studies including instrumental errors were carried out. It was found that with the presented measurement setup it is possible to measure and reconstruct one or two NO2 plumes of 600 m diameter and average concentrations above 4.2 ppbv each, on a scale of 13.5 km2. Theoretical investigations show that it should be possible to localize and quantify 600 m diameter plumes of SO2 > 1.5 ppbv, H2CO > 6.3 ppbv, HONO > 3.2 ppbv, and ozone > 46.2 ppbv. Larger plumes can be measured with higher precision.

Stratospheric nitrogen dioxide in the Antarctic

Several UV–visible spectrometers have been developed at the ISAC‐CNR Institute. Differential Optical Absorption Spectroscopy (DOAS) methodology is applied to their measurements to monitor the amounts of stratospheric trace gases: mainly ozone (O3) and nitrogen dioxide (NO2) which is involved in the ozone cycle. Observations of the scattered zenith‐sky light were performed with one of these instruments installed at the Terra Nova Bay station (TNB), Antarctica. GASCOD (Gas Analyzer Spectrometer Correlating Optical Differences) is described briefly and a method for data analysis and validation of the results introduced. Some aspects of the DOAS technique are presented: the algorithm allowing the best spectral alignment between spectra obtained with GASCOD and a high‐resolution wavelength calibrated spectrum, is explained. Simple considerations allow for calculation of the NO2 concentration in the background spectrum used in DOAS analysis. For the period of activity of the GASCOD at TNB (1996–2003), the results of NO2 vertical column density (VCD) at twilight show a maximum in the summer and a minimum in the winter. Three years of measurements (2001–2003) are analysed in terms of stratospheric temperature and potential vorticity to obtain information about stratospheric warming that occurred in 2002 over Antarctica. The correlation between NO2 atmospheric content and stratospheric temperature is highlighted. The diurnal variations of NO2, which are controlled by photochemistry, show an unusual behaviour at high latitudes. Analysis of the a.m./p.m. ratios—the sunrise NO2 VC (a.m.) over the sunset VC (p.m.)—during different seasons and at various Solar Zenith Angles (SZA) is presented and discussed.

Ground-based zenith sky abundances and in situ gas cross sections for ozone and nitrogen dioxide with the Earth Observing System Aura Ozone Monitoring Instrument

High-accuracy spectral-slit-function calibration measurements, in situ ambient absorption gas cell measurements for ozone and nitrogen dioxide, and ground-based zenith sky measurements with the Earth Observing System Aura Ozone Monitoring Instrument (OMI) flight instrument are reported and the results discussed. For use of high-spectral-resolution gas absorption cross sections from the literature in trace gas retrieval algorithms, accurate determination of the instrument's spectral slit function is essential. Ground-based measurements of the zenith sky provide a geophysical determination of atmospheric trace gas abundances. When compared with other measurements, they can be used to verify the performance of the OMI flight instrument. We show that the approach of using published high-resolution absolute absorption cross sections convolved with accurately calibrated spectral slit functions for OMI compares well with in situ gas absorption cell measurements made with the flight instrument and that use of these convolved cross sections works well for reduction of zenith sky data taken with the OMI flight instrument for ozone and nitrogen dioxide that are retrieved from measured spectra of the zenith sky with the differential optical absorption spectroscopy technique, the same method to be used for the generation of in-flight data products. Finally, it is demonstrated that the spectral stability and signal-to-noise ratio performance of the OMI flight instrument, as determined from preflight component and full instrument tests, are sufficient to meet OMI mission objectives.

Ground‐based measurements of ozone and NO2 during MANTRA 1998 using a Zenith‐sky spectrometer

A portable ground‐based instrument has been constructed for the automated measurement of vertical column abundances of a number of gases pertinent to stratospheric ozone chemistry. The instrumentation is described in this paper and results are presented from the first set of field measurements, made during the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) 1998 field campaign at Vanscoy, Saskatchewan, Canada. Zenith‐sky spectra in the near ultraviolet and visible wavelength regions were recorded for a period of seven days, prior to and following the launch of the MANTRA balloon on 24 August 1998. The spectra were then analysed using the differential optical absorption spectroscopy (DOAS) technique in conjunction with a radiative transfer model to determine vertical column amounts of ozone and NO2. Ozone measurements compared favourably with concurrent observations by ozonesondes, a Brewer spectrophotometer, and satellite instruments. Vertical NO2 columns were in broad agreement with those determined by the Global Ozone Monitoring Experiment (GOME) satellite instrument.

Measurements of trace gas distributions using Long-path DOAS-Tomography during the motorway campaign BAB II: experimental setup and results for NO2

Abstract The Tomographic Differential Optical Absorption Spectroscopy (Tom-DOAS) technique and results from a first application are presented. This novel technique serves to measure 2–3-dimensional concentration fields of different trace gases (e.g. NO 2 , SO 2 , ozone) in the planetary boundary layer on a small scale (100–10 000 m) by the use of multiple light paths. Ways to use telescopes, lamps, retroreflector arrays and spectrometers for the simultaneous measurement of many light-paths are proposed. The results from a first Long-path Tom-DOAS experiment next to a German motorway, which was part of the BAB II campaign April/May 2001 [Edition of the Institut fur Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe/Universitat Karlsruhe, pp. 45, 2001), are presented. From the measurements along 16 different light paths vertical profiles on both sides of the motorway as well as a two-dimensional map of the NO 2 vehicle emission plume are derived. The concentration distributions agree qualitatively with model simulations of an earlier campaign.

Recent applications of Differential Optical Absorption Spectroscopy: Halogen chemistry in the lower troposphere

This chapter provides a comprehensive review of the atmospheric chemistry of halogens in the lower troposphere, including a discussion of the important ways in which halogens affect this region of the atmosphere. It then describes the recent progress made in observing these species by the Differential Optical Absorption Spectroscopy (DOAS) technique. A brief description of the technique and its capabilities is also provided.

Derivation of polarization from Odin/OSIRIS limb spectra

A new technique for deriving the degree of linear polarization from limb‐scattered sunlight radiance measurements is presented and applied to Odin/OSIRIS. In this technique, the measured OSIRIS grating efficiency spectrum is fit to OSIRIS limb spectra using the differential optical absorption spectroscopy technique and the resultant fitting constant is shown to represent the difference in linear polarization between two tangent heights. The validity of this technique is confirmed using simulations from a vector limb radiative transfer model. OSIRIS scans of the difference in linear polarization from October 2003 are shown to be very sensitive to stratospheric and upper tropospheric aerosols, including background sulphates, clouds, and polar stratospheric clouds.

Observations of carbon disulfide by differential optical absorption spectroscopy in Shanghai

Carbon disulfide, CS2, is an important sulfur‐containing species in the global environment. Its oxidation to SO2 and COS are basic atmospheric chemical processes in the sulfur cycle. The typical measurement methods for CS2 are gas chromatography with flame photometric detection (GC‐FPD) and gas chromatography ‐ mass spectrometry (GC‐MS). This paper presents CS2 and SO2 long‐term measurements made by the long path Differential Optical Absorption Spectroscopy (DOAS) technique in the winter of 2001 to 2002 in the urban area of Shanghai, China. We found a good correlation between SO2 and CS2 with average [SO2]/[CS2] ≈ 2.1. Combined with an analysis of pollution sources near the measurement site, our measurements indicate that CS2 came mainly from a coal burning furnace close to the measurement site.

Field measurements of water vapor continuum absorption in the visible and near‐infrared

We carried out a spectroscopic field experiment designed to measure water vapor continuum absorption in the visible and near‐infrared spectral regions. Atmospheric spectra at ∼1 nm resolution were recorded using direct sunlight at high solar zenith angles during sunrise. Simultaneously radiosonde soundings and a network of geodetic Global Positioning System (GPS) receivers were deployed to constrain the water vapor amount along the absorption path. The solar spectra were analyzed using the Differential Optical Absorption Spectroscopy technique, while the GPS and radiosonde observations were used as input data to a line‐by‐line radiative transfer model to compute theoretical differential absorption spectra. The difference between the measurements and the simulated spectra provides information regarding the additional absorption owing to the H2O continuum. The data are compared to predictions of the widely used Clough‐Kneizys‐Davies continuum model as well as with theoretically derived spectra of water dimer. The results show that continuum absorption contributes significantly to solar absorption even in highly saturated H2O bands. The comparisons provide the needed observations to improve future continuum parameterizations.