scholarly journals Multiple wavelength retrieval of tropospheric aerosol optical properties from MAXDOAS measurements in Beijing

2010 ◽  
Vol 3 (1) ◽  
pp. 111-145 ◽  
Author(s):  
K. Clémer ◽  
M. Van Roozendael ◽  
C. Fayt ◽  
F. Hendrick ◽  
C. Hermans ◽  
...  
Keyword(s):  
Real Time ◽  
Optimal Estimation ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
Vertical Profiles ◽  
Atmospheric Conditions ◽  
Multiple Wavelength ◽  
Tropospheric Aerosol ◽  
Wide Range ◽  
On Line

Abstract. We report on the retrieval of aerosol extinction profiles at four wavelengths from ground-based multi-axis differential absorption spectroscopy (MAXDOAS) measurements performed in Beijing (N 39°58'37" E 116°22'51"), China. Measurements were made over a 10-month time period (June 2008 to April 2009) using a newly developed MAXDOAS instrument. A retrieval algorithm, based on an on-line implementation of the radiative transfer code LIDORT and the optimal estimation technique, has been designed to provide near real time information on aerosol extinction vertical profiles. The algorithm was applied to O4 measurements at four wavelengths (360, 477, 577, and 630 nm). The total aerosol optical depths (AODs) calculated from the retrieved profiles exhibit higher values in spring and summer and lower values in autumn and winter. Comparison of the retrieved total AODs with values from a co-located CIMEL sunphotometer revealed a good correlation. The best results are obtained for the UV region with a correlation coefficient (R) of 0.91 and a slope of the linear regression fit of 1.1. At the longest wavelength, R drops down to 0.67 and the slope increases to 1.5. The results indicate that good quality O4 slant column measurements are essential for the success of the retrievals. It is demonstrated that the algorithm is capable of reliably retrieving aerosol extinction profiles for a wide range of atmospheric conditions (total AODs at 360 nm ranging from about 0.1 to 3). The results open up new perspectives for the extension of the algorithm for the near real time retrieval of trace gas vertical profiles.

scholarly journals Multiple wavelength retrieval of tropospheric aerosol optical properties from MAXDOAS measurements in Beijing

2010 ◽  
Vol 3 (4) ◽  
pp. 863-878 ◽  
Author(s):  
K. Clémer ◽  
M. Van Roozendael ◽  
C. Fayt ◽  
F. Hendrick ◽  
C. Hermans ◽  
...  
Keyword(s):  
Real Time ◽  
Optimal Estimation ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
Vertical Profiles ◽  
Atmospheric Conditions ◽  
Multiple Wavelength ◽  
Tropospheric Aerosol ◽  
Wide Range ◽  
On Line

Abstract. We report on the retrieval of aerosol extinction profiles at four wavelengths from ground-based multi-axis differential absorption spectroscopy (MAXDOAS) measurements performed in Beijing, China. Measurements were made over a 10-month time period (June 2008 to April 2009) using a newly developed MAXDOAS instrument. A retrieval algorithm, based on an on-line implementation of the radiative transfer code LIDORT and the optimal estimation technique, has been designed to provide near real time information on aerosol extinction vertical profiles. The algorithm was applied to O4 measurements at four wavelengths (360, 477, 577, and 630 nm). The total aerosol optical depths (AODs) calculated from the retrieved profiles exhibit higher values in spring and summer and lower values in autumn and winter. Comparison of the retrieved total AODs with values from a co-located CIMEL sunphotometer revealed a good correlation. The best results are obtained for the UV region with a correlation coefficient (R) of 0.91 and a slope of the linear regression fit of 1.1. At the longest wavelength, R drops down to 0.67 and the slope increases to 1.5. The results confirm that good quality O4 slant column measurements are essential for the success of the retrievals. A method is presented to determine a correction factor to account for systematic errors. It is demonstrated that the algorithm is capable of reliably retrieving aerosol extinction profiles for a wide range of atmospheric conditions (total AODs at 360 nm ranging from about 0.1 to 3). The results open up new perspectives for the extension of the algorithm for the near real time retrieval of trace gas vertical profiles.

scholarly journals Retrieval and evaluation of tropospheric-aerosol extinction profiles using multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements over Athens, Greece

2021 ◽  
Vol 14 (1) ◽  
pp. 749-767
Author(s):  
Myrto Gratsea ◽  
Tim Bösch ◽  
Panagiotis Kokkalis ◽  
Andreas Richter ◽  
Mihalis Vrekoussis ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Absorption Spectroscopy ◽  
Optimal Estimation ◽  
Differential Optical Absorption Spectroscopy ◽  
Optical Absorption Spectroscopy ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
The Sun ◽  
Tropospheric Aerosol ◽  
Vertical Distributions

Abstract. In this study, we report on the retrieval of aerosol extinction profiles from ground-based scattered sunlight multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, carried out at Athens, Greece. It is the first time that aerosol profiles are retrieved from MAX-DOAS measurements in Athens. The reported aerosol vertical distributions at 477 nm are derived from the oxygen dimer (O4) differential-slant-column-density observations at different elevation angles by applying the BRemen Optimal estimation REtrieval for Aerosol and trace gaseS (BOREAS) retrieval algorithm. Four case studies have been selected for validation purposes; the retrieved aerosol profiles and the corresponding aerosol optical depths (AODs) from the MAX-DOAS are compared with lidar extinction profiles and with sun-photometric measurements (Aerosol Robotic Network, AERONET, observations), respectively. Despite the different approach of each method regarding the retrieval of the aerosol information, the comparison with the lidar measurements at 532 nm reveals a very good agreement in terms of vertical distribution, with r>0.90 in all cases. The AODs from the MAX-DOAS and the sun photometer (the latter at 500 nm) show a satisfactory correlation (with 0.45 < r < 0.7 in three out of the four cases). The comparison indicates that the MAX-DOAS systematically underestimates the AOD in the cases of large particles (small Ångström exponent) and for measurements at small relative azimuthal angles between the viewing direction and the sun. Better agreement is achieved in the morning, at large relative azimuthal angles. Overall, the aerosol profiles retrieved from MAX-DOAS measurements are of good quality; thus, new perspectives are opened up for assessing urban aerosol pollution on a long-term basis in Athens from continuous and uninterrupted MAX-DOAS measurements.

scholarly journals The Iowa Atmospheric Observatory: Revealing the Unique Boundary Layer Characteristics of a Wind Farm

2019 ◽  
Vol 23 (2) ◽  
pp. 1-27 ◽  
Author(s):  
Eugene S. Takle ◽  
Daniel A. Rajewski ◽  
Samantha L. Purdy
Keyword(s):  
Boundary Layer ◽  
Wind Farm ◽  
Agricultural Landscape ◽  
Potential Temperature ◽  
Wind Farms ◽  
Vertical Profiles ◽  
Atmospheric Conditions ◽  
Wide Range ◽  
Water Vapor Mixing Ratio ◽  
Utility Scale

Abstract The Iowa Atmospheric Observatory was established to better understand the unique microclimate characteristics of a wind farm. The facility consists of a pair of 120-m towers identically instrumented to observe basic landscape–atmosphere interactions in a highly managed agricultural landscape. The towers, one within and one outside of a utility-scale low-density-array wind farm, are equipped to measure vertical profiles of temperature, wind, moisture, and pressure and can host specialized sensors for a wide range of environmental conditions. Tower measurements during the 2016 growing season demonstrate the ability to distinguish microclimate differences created by single or multiple turbines from natural conditions over homogeneous agricultural fields. Microclimate differences between the two towers are reported as contrasts in normalized wind speed, normalized turbulence intensity, potential temperature, and water vapor mixing ratio. Differences are analyzed according to conditions of no wind farm influence (i.e., no wake) versus wind farm influence (i.e., waked flow) with distance downwind from a single wind turbine or a large group of turbines. Differences are also determined for more specific atmospheric conditions according to thermal stratification. Results demonstrate agreement with most, but not all, currently available numerical flow-field simulations of large wind farm arrays and of individual turbines. In particular, the well-documented higher nighttime surface temperature in wind farms is examined in vertical profiles that confirm this effect to be a “suppression of cooling” rather than a warming process. A summary is provided of how the wind farm boundary layer differs from the natural boundary layer derived from concurrent measurements over the summer of 2016.

scholarly journals Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

2010 ◽  
Vol 10 (9) ◽  
pp. 4295-4317 ◽  
Author(s):  
D. Wurl ◽  
R. G. Grainger ◽  
A. J. McDonald ◽  
T. Deshler
Keyword(s):  
Surface Area ◽  
Lower Stratosphere ◽  
Optimal Estimation ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
Size Distributions ◽  
Extinction Data ◽  
Aerosol Properties ◽  
Area And Volume

Abstract. Stratospheric aerosol particles under non-volcanic conditions are typically smaller than 0.1 μm. Due to fundamental limitations of the scattering theory in the Rayleigh limit, these tiny particles are hard to measure by satellite instruments. As a consequence, current estimates of global aerosol properties retrieved from spectral aerosol extinction measurements tend to be strongly biased. Aerosol surface area densities, for instance, are observed to be about 40% smaller than those derived from correlative in situ measurements (Deshler et al., 2003). An accurate knowledge of the global distribution of aerosol properties is, however, essential to better understand and quantify the role they play in atmospheric chemistry, dynamics, radiation and climate. To address this need a new retrieval algorithm was developed, which employs a nonlinear Optimal Estimation (OE) method to iteratively solve for the monomodal size distribution parameters which are statistically most consistent with both the satellite-measured multi-wavelength aerosol extinction data and a priori information. By thus combining spectral extinction measurements (at visible to near infrared wavelengths) with prior knowledge of aerosol properties at background level, even the smallest particles are taken into account which are practically invisible to optical remote sensing instruments. The performance of the OE retrieval algorithm was assessed based on synthetic spectral extinction data generated from both monomodal and small-mode-dominant bimodal sulphuric acid aerosol size distributions. For monomodal background aerosol, the new algorithm was shown to fairly accurately retrieve the particle sizes and associated integrated properties (surface area and volume densities), even in the presence of large extinction uncertainty. The associated retrieved uncertainties are a good estimate of the true errors. In the case of bimodal background aerosol, where the retrieved (monomodal) size distributions naturally differ from the correct bimodal values, the associated surface area (A) and volume densities (V) are, nevertheless, fairly accurately retrieved, except at values larger than 1.0 μm2 cm−3 (A) and 0.05 μm3 cm−3 (V), where they tend to underestimate the true bimodal values. Due to the limited information content in the SAGE II spectral extinction measurements this kind of forward model error cannot be avoided here. Nevertheless, the retrieved uncertainties are a good estimate of the true errors in the retrieved integrated properties, except where the surface area density exceeds the 1.0 μm2 cm−3 threshold. When applied to near-global SAGE II satellite extinction measured in 1999 the retrieved OE surface area and volume densities are observed to be larger by, respectively, 20–50% and 10–40% compared to those estimates obtained by the SAGE~II operational retrieval algorithm. An examination of the OE algorithm biases with in situ data indicates that the new OE aerosol property estimates tend to be more realistic than previous estimates obtained from remotely sensed data through other retrieval techniques. Based on the results of this study we therefore suggest that the new Optimal Estimation retrieval algorithm is able to contribute to an advancement in aerosol research by considerably improving current estimates of aerosol properties in the lower stratosphere under low aerosol loading conditions.

scholarly journals AerGOM, an improved algorithm for stratospheric aerosol extinction retrieval from GOMOS observations – Part 2: Intercomparisons

2016 ◽  
Vol 9 (9) ◽  
pp. 4701-4718 ◽  
Author(s):  
Charles Étienne Robert ◽  
Christine Bingen ◽  
Filip Vanhellemont ◽  
Nina Mateshvili ◽  
Emmanuel Dekemper ◽  
...  
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Stratospheric Aerosol ◽  
Cirrus Clouds ◽  
Apparent Temperature ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
Extinction Coefficients ◽  
Wide Range

Abstract. AerGOM is a retrieval algorithm developed for the GOMOS instrument onboard Envisat as an alternative to the operational retrieval (IPF). AerGOM enhances the quality of the stratospheric aerosol extinction retrieval due to the extension of the spectral range used, refines the aerosol spectral parameterization, the simultaneous inversion of all atmospheric species as well as an improvement of the Rayleigh scattering correction. The retrieval algorithm allows for a good characterization of the stratospheric aerosol extinction for a wide range of wavelengths.In this work, we present the results of stratospheric aerosol extinction comparisons between AerGOM and various spaceborne instruments (SAGE II, SAGE III, POAM III, ACE-MAESTRO and OSIRIS) for different wavelengths. The aerosol extinction intercomparisons for λ < 700 nm and above 20 km show agreements with SAGE II version 7 and SAGE III version 4.0 within ±15 % and ±45 %, respectively. There is a strong positive bias below 20 km at λ < 700 nm, which suggests that cirrus clouds at these altitudes have a large impact on the extinction values. Comparisons performed with GOMOS IPF v6.01 alongside AerGOM show that at short wavelengths and altitudes below 20 km, IPF retrievals are more accurate when evaluated against SAGE II and SAGE III but are much less precise than AerGOM. A modified aerosol spectral parameterization can improve AerGOM in this spectral and altitude range and leads to results that have an accuracy similar to IPF retrievals. Comparisons of AerGOM aerosol extinction coefficients with OSIRIS and SAGE III measurements at wavelengths larger than 700 nm show a very large negative bias at altitudes above 25 km. Therefore, the use of AerGOM aerosol extinction data is not recommended for λ > 700 nm.Due to the unique observational technique of GOMOS, some of the results appear to be dependent on the star occultation parameters such as star apparent temperature and magnitude, solar zenith angle and latitude of observation. A systematic analysis is carried out to identify biases in the dataset, using the various spaceborne instruments as references. The quality of the aerosol retrieval is mainly influenced by the star magnitude, as well as star temperature to a lesser degree. To ensure good-quality profiles, we suggest to select occultations performed with star magnitude M < 2.5 and star temperature T > 6 × 103 K. Stray-light contamination is negligible for extinction coefficients below 700 nm using occultations performed with a solar zenith angle  > 110° but becomes important at larger wavelengths. Comparison of AerGOM results in the tropics shows an enhanced bias below 20 km that seem to confirm cirrus clouds as its cause. There are also differences between mid-latitude and tropical observations that cannot yet be explained, with a bias difference of up to 25 %.This bias characterization is extremely important for data users and might prove valuable for the production of unbiased long-term merged dataset.

scholarly journals Global stratospheric aerosol extinction profile retrievals from SCIAMACHY limb-scatter observations

2012 ◽  
Vol 5 (4) ◽  
pp. 5993-6035 ◽  
Author(s):  
F. Ernst ◽  
C. von Savigny ◽  
A. Rozanov ◽  
V. Rozanov ◽  
K.-U. Eichmann ◽  
...  
Keyword(s):  
Surface Albedo ◽  
Optimal Estimation ◽  
Stratospheric Aerosol ◽  
Visible Spectral Range ◽  
Radiative Transfer Model ◽  
Retrieval Algorithm ◽  
Transfer Model ◽  
Aerosol Extinction ◽  
Index Approach ◽  
The Impact

Abstract. Stratospheric aerosol extinction profiles are retrieved from SCIAMACHY/Envisat limb-scatter observations in the visible spectral range. The retrieval algorithm is based on a colour-index approach using the normalized limb-radiance profiles at 470 nm and 750 nm wavelength. The optimal estimation approach in combination with the radiative transfer model SCIATRAN is employed for the retrievals. This study presents a detailed description of the retrieval algorithm, and a sensitivity analysis investigating the impact of the most important parameters that affect the aerosol extinction profile retrieval accuracy. It is found that the parameter with the largest impact is surface albedo, particularly for SCIAMACHY observations in the Southern Hemisphere where the error in stratospheric aerosol extinction can be up to 50% if the surface albedo is not well known. The effect of errors in the assumed ozone and neutral density profiles on the aerosol profile retrievals is with generally less than 6% relatively small. The aerosol extinction profiles retrieved from SCIAMACHY are compared with co-located SAGE II solar occultation measurements of stratospheric aerosol extinction during the period 2003–2005. The mean aerosol extinction profiles averaged over all co-locations agree to within 20% between 15 and 35 km altitude. However, larger differences are observed at specific latitudes.

Long Term Experience of the Real Time Fouling Deposits Thickness Measurements for On-Line Sootblowing Optimization

2015 ◽  
Author(s):  
B. Chudnovsky ◽  
N. Menn
Keyword(s):  
Renewable Energy ◽  
Power Plant ◽  
Real Time ◽  
Operation Conditions ◽  
Wide Range ◽  
On Line ◽  
Cycle Efficiency ◽  
The Impact ◽  
Long Term Experience

Over the past years there has been a dramatic increase in the regulatory requirements for low emissions. Renewable energy targets and CO2 emissions markets drive the transition to a cleaner and renewable energy production system. In addition to increasing the overall plant cycle efficiency, there two principal means of the reduction of the CO2 from coal fired power plants: by coal and biomass co-firing and by the capture and long term storage of the CO2 emitted from power plant. Carbon dioxide capture and storage will involve substantial capital investment, accompanied by a significant power plant cycle efficiency penalty, and is not currently available on a fully commercial basis. Co-firing biomass, in comparison with other renewable sources, is the main contributor to technologies meeting the world’s renewable energy target. However, the impact of biomass co-firing on boilers performance and integrity has been modest. Operational problems associated with the deposition and retention of ash materials can and do occur on all the major gas-side components of combustion and boilers. The process occurs over a wide range of flue gas and surface temperatures, and dependent both on the characteristics of the ash and on the design and operation conditions of the furnace and boiler. Development and validation of the predictive models have been hindered significantly by the practical difficulties in the obtaining reliable data from the boilers operated with coal and biomass. Although specialized on–line deposition monitoring and sootblowing control systems are commercially available, but they are based on a very simple estimates of the fouling factors, which results in crude and not reliable approach to optimization of sootblowers operation. In the present paper an alternative approach and a new technique based on electro-optical sensor are demonstrated. The long term experience with the system attached to the furnace wall and capable to move the compact sensor in and out of the furnace, allowing to measure simultaneously deposits thickness and reflectivity, is described in details. Results of our study show that dynamics of both parameters on the operated power unit can be registered simultaneously in real time and then interpreted separately. Experiments have been carried out with different coal types at 575MW unit equipped with CE tangential boiler and 550 Mw equipped with B&W boiler with opposite fired burners. The measurements were performed in different locations of the furnace. It was shown that dynamics of thickness and reflectivity variation just after the wall cleaning activation are quite different. Situations have been registered where changes of reflectivity have a significant impact on heat transfer, comparable and sometimes even greater than that of growing fouling thickness. Technique and device exploited in this study appears to be a very useful tool for sootblowing optimization and, as a result, for improvement of boiler efficiency and reduction of water wall erosion and corrosion in both pulverized coal and co-firing boilers.

scholarly journals AerGOM, an improved algorithm for stratospheric aerosol retrieval from GOMOS observations. Part 2: Intercomparisons

2016 ◽  
Author(s):  
Charles Étienne Robert ◽  
Christine Bingen ◽  
Filip Vanhellemont ◽  
Nina Mateshvili ◽  
Emmanuel Dekemper ◽  
...  
Keyword(s):  
Rayleigh Scattering ◽  
Stratospheric Aerosol ◽  
Apparent Temperature ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
Systematic Analysis ◽  
Simultaneous Inversion ◽  
Atmospheric Species ◽  
Observational Technique ◽  
Wide Range

Abstract. AerGOM is a retrieval algorithm developed for the GOMOS instrument onboard Envisat as an alternative to the operational retrieval (IPF). AerGOM enhances the quality of the stratospheric aerosol extinction retrieval due to the extension of the spectral range used, a refinement of the aerosol spectral parameterisation, the simultaneous inversion of all atmospheric species as well as an improvement of the Rayleigh scattering correction. The retrieval algorithm allows for a good characterisation of the stratospheric aerosol extinction for a wide range of wavelengths. In this work, we present the results of stratospheric aerosol extinction comparisons between AerGOM and various spaceborne instruments (SAGE II, SAGE III, POAM III, ACE-MAESTRO and OSIRIS) for different wavelengths. Due to the unique observational technique of GOMOS, some of the results appear to be dependent on the star occultation parameters such as star apparent temperature and magnitude, solar zenith angle, latitude and obliquity. A systematic analysis is carried out to identify biases in the dataset, using the various spaceborne instruments as references. This bias characterization is extremely important for data users and might prove valuable for the production of unbiased long-term merged dataset.

scholarly journals Parameterization retrieval of trace gas volume mixing ratios from airborne MAX-DOAS

2016 ◽  
Author(s):  
Barbara Dix ◽  
Theodore K. Koenig ◽  
Rainer Volkamer
Keyword(s):  
Column Density ◽  
Elevation Angle ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Aerosol Extinction ◽  
Reference Spectrum ◽  
Atmospheric Conditions ◽  
Tropical Ocean ◽  
Mixing Ratios ◽  
Wide Range

Abstract. We present a parameterization retrieval of volume mixing ratios (VMR) from differential slant column density (dSCD) measurements by airborne multi-axis differential optical absorption spectroscopy (AMAX-DOAS). The method makes use of the fact that horizontally recorded limb spectra (elevation angle 0°) are strongly sensitive to the atmospheric layer at instrument altitude. These limb spectra are analysed using reference spectra that largely cancel out column contributions from above and below the instrument, so that the resulting limb dSCDs, i.e., the column integrated concentration with respect to a reference spectrum, are almost exclusively sensitive to the atmospheric layers around instrument altitude. The conversion of limb dSCDs into VMRs is then realized by calculating box-air mass factors (Box-AMFs) for a Rayleigh atmosphere and applying a scaling factor constrained by O4 dSCDs to account for aerosol extinction. An iterative VMR retrieval scheme corrects for trace gas profile shape effects. Benefits of this method are 1) a fast conversion that only requires the computation of Box-AMFs in a Rayleigh atmosphere; 2) neither local aerosol extinction nor the slant column density in the DOAS reference (SCDref) need to be known; and 3) VMRs can be retrieved for every measurement point along a flight track, in contrast to profile inversion techniques. Sensitivity studies are performed for bromine monoxide (BrO), iodine monoxide (IO) and nitrogen dioxide (NO2), using 1) simulated dSCD data for different trace gas and aerosol profiles; and 2) field measurements from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) field experiment. For simulated data in a Rayleigh atmosphere, the agreement between the VMR from the parameterization method (VMRpara) and the true VMR (VMRtrue) is excellent for all trace gases. Offsets, slopes and R2 values for the linear fit of VMRpara over VMRtrue are as follows: BrO: (0.008 ± 0.001) pptv, 0.988 ± 0.001, 0.987; IO: (−0.0066 ± 0.0001) pptv, 1.0021 ± 0.0003, 0.9979; NO2: (−0.17 ± 0.03) pptv, 1.0036 ± 0.0001, 0.9997. The agreement for atmospheres with aerosol shows comparable R2 values to the Rayleigh case, but slopes deviate a bit more from one: BrO: (0.093 ± 0.002) pptv, 0.933 ± 0.002, 0.907; IO: (0.0021 ± 0.0004) pptv, 0.887 ± 0.001, 0.973; NO2: (8.5 ± 0.1) pptv, 0.8302 ± 0.0006, 0.9923. VMRpara from field data are further compared with optimal estimation retrievals (VMROE). Least orthogonal distance fit of the data give the following equations: BrOpara = (0.1 ± 0.2) pptv + (0.95 ± 0.14) x BrOOE; IOpara = (0.01 ± 0.02) pptv + (1.00 ± 0.12) x IOOE; NO2para = (1.7 ± 8.0) pptv + (0.90 ± 0.51) x NO2OE. Overall, we conclude that the parameterization retrieval is accurate with an uncertainty of 20 % for IO, 30 % for BrO and NO2, but not better than 0.05 pptv IO, 0.5 pptv BrO, and 10 pptv NO2. The retrieval is applicable over a wide range of atmospheric conditions and measurement geometries, and not limited to the interpretation of vertical profile measurements in the remote troposphere.

scholarly journals Parameterization retrieval of trace gas volume mixing ratios from Airborne MAX-DOAS

2016 ◽  
Vol 9 (11) ◽  
pp. 5655-5675 ◽  
Author(s):  
Barbara Dix ◽  
Theodore K. Koenig ◽  
Rainer Volkamer
Keyword(s):  
Column Density ◽  
Elevation Angle ◽  
Trace Gas ◽  
Optical Absorption Spectroscopy ◽  
Aerosol Extinction ◽  
Reference Spectrum ◽  
Atmospheric Conditions ◽  
Tropical Ocean ◽  
Mixing Ratios ◽  
Wide Range

Abstract. We present a parameterization retrieval of volume mixing ratios (VMRs) from differential slant column density (dSCD) measurements by Airborne Multi-AXis Differential Optical Absorption Spectroscopy (AMAX-DOAS). The method makes use of the fact that horizontally recorded limb spectra (elevation angle 0°) are strongly sensitive to the atmospheric layer at instrument altitude. These limb spectra are analyzed using reference spectra that largely cancel out column contributions from above and below the instrument, so that the resulting limb dSCDs, i.e., the column integrated concentration with respect to a reference spectrum, are almost exclusively sensitive to the atmospheric layers around instrument altitude. The conversion of limb dSCDs into VMRs is then realized by calculating box air mass factors (Box-AMFs) for a Rayleigh atmosphere and applying a scaling factor constrained by O4 dSCDs to account for aerosol extinction. An iterative VMR retrieval scheme corrects for trace gas profile shape effects. Benefits of this method are (1) a fast conversion that only requires the computation of Box-AMFs in a Rayleigh atmosphere; (2) neither local aerosol extinction nor the slant column density in the DOAS reference (SCDref) needs to be known; and (3) VMRs can be retrieved for every measurement point along a flight track, thus increasing statistics and adding flexibility to capture concentration gradients. Sensitivity studies are performed for bromine monoxide (BrO), iodine monoxide (IO) and nitrogen dioxide (NO2), using (1) simulated dSCD data for different trace gas and aerosol profiles and (2) field measurements from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) field experiment. For simulated data in a Rayleigh atmosphere, the agreement between the VMR from the parameterization method (VMRpara) and the true VMR (VMRtrue) is excellent for all trace gases. Offsets, slopes and R2 values for the linear fit of VMRpara over VMRtrue are, respectively (0.008 ± 0.001) pptv, 0.988 ± 0.001, 0.987 for BrO; (−0.0066 ± 0.0001) pptv, 1.0021 ± 0.0003, 0.9979 for IO; (−0.17 ± 0.03) pptv, 1.0036 ± 0.0001, 0.9997 for NO2. The agreement for atmospheres with aerosol shows comparable R2 values to the Rayleigh case, but slopes deviate a bit more from one: (0.093 ± 0.002) pptv, 0.933 ± 0.002, 0.907 for BrO; (0.0021 ± 0.0004) pptv, 0.887 ± 0.001, 0.973 for IO; (8.5 ± 0.1) pptv, 0.8302 ± 0.0006, 0.9923 for NO2. VMRpara from field data are further compared with optimal estimation retrievals (VMROE). Least orthogonal distance fit of the data give the following equations: BrOpara =  (0.1 ± 0.2) pptv + (0.95 ± 0.14)  ×  BrOOE; IOpara =  (0.01 ± 0.02) pptv + (1.00 ± 0.12)  ×  IOOE; NO2para  =  (3.9 ± 2.5) pptv + (0.87 ± 0.15)  ×  NO2OE. Overall, we conclude that the parameterization retrieval is accurate with an uncertainty of 20 % for IO, 30 % for BrO and NO2, but not better than 0.05 pptv IO, 0.5 pptv BrO and 10 pptv NO2. The retrieval is applicable over a wide range of atmospheric conditions and measurement geometries and not limited to the interpretation of vertical profile measurements in the remote troposphere.

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