scholarly journals Improved slant column density retrieval of nitrogen dioxide and formaldehyde for OMI and GOME-2A from QA4ECV: intercomparison, uncertainty characterisation, and trends

2018 ◽  
Vol 11 (7) ◽  
pp. 4033-4058 ◽  
Author(s):  
Marina Zara ◽  
K. Folkert Boersma ◽  
Isabelle De Smedt ◽  
Andreas Richter ◽  
Enno Peters ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Column Density ◽  
Trend Detection ◽  
Optical Absorption Spectroscopy ◽  
Statistical Uncertainty ◽  
Random Component ◽  
Climate Variables ◽  
Total Uncertainty ◽  
Uncertainty Estimates ◽  
Calculation Step

Abstract. Nitrogen dioxide (NO2) and formaldehyde (HCHO) column data from satellite instruments are used for air quality and climate studies. Both NO2 and HCHO have been identified as precursors to the ozone (O3) and aerosol essential climate variables, and it is essential to quantify and characterise their uncertainties. Here we present an intercomparison of NO2 and HCHO slant column density (SCD) retrievals from four different research groups (BIRA-IASB, IUP Bremen, and KNMI as part of the Quality Assurance for Essential Climate Variables (QA4ECV) project consortium, and NASA) and from the OMI and GOME-2A instruments. Our evaluation is motivated by recent improvements in differential optical absorption spectroscopy (DOAS) fitting techniques and by the desire to provide a fully traceable uncertainty budget for the climate data record generated within QA4ECV. The improved NO2 and HCHO SCD values are in close agreement but with substantial differences in the reported uncertainties between groups and instruments. To check the DOAS uncertainties, we use an independent estimate based on the spatial variability of the SCDs within a remote region. For NO2, we find the smallest uncertainties from the new QA4ECV retrieval (0.8  ×  1015 molec. cm−2 for both instruments over their mission lifetimes). Relative to earlier approaches, the QA4ECV NO2 retrieval shows better agreement between DOAS and statistical uncertainty estimates, suggesting that the improved QA4ECV NO2 retrieval has reduced but not altogether eliminated systematic errors in the fitting approach. For HCHO, we reach similar conclusions (QA4ECV uncertainties of 8–12  ×  1015 molec. cm−2), but the closeness between the DOAS and statistical uncertainty estimates suggests that HCHO uncertainties are indeed dominated by random noise from the satellite's level 1 data. We find that SCD uncertainties are smallest for high top-of-atmosphere reflectance levels with high measurement signal-to-noise ratios. From 2005 to 2015, OMI NO2 SCD uncertainties increase by 1–2 % year−1, which is related to detector degradation and stripes, but OMI HCHO SCD uncertainties are remarkably stable (increase  <  1 % year−1) and this is related to the use of Earth radiance reference spectra which reduces stripes. For GOME-2A, NO2 and HCHO SCD uncertainties increased by 7–9 and 11–15 % year−1 respectively up until September 2009, when heating of the instrument markedly reduced further throughput loss, stabilising the degradation of SCD uncertainty to  <  3 % year−1 for 2009–2015. Our work suggests that the NO2 SCD uncertainty largely consists of a random component ( ∼  65 % of the total uncertainty) as a result of the propagation of measurement noise but also of a substantial systematic component ( ∼  35 % of the total uncertainty) mainly from stripe effects. Averaging over multiple pixels in space and/or time can significantly reduce the SCD uncertainties. This suggests that trend detection in OMI, GOME-2 NO2, and HCHO time series is not limited by the spectral fitting but rather by the adequacy of assumptions on the atmospheric state in the later air mass factor (AMF) calculation step.

scholarly journals Improved slant column density retrieval of nitrogen dioxide and formaldehyde for OMI and GOME-2A from QA4ECV: intercomparison, uncertainty characterization, and trends

2018 ◽  
Author(s):  
Marina Zara ◽  
K. Folkert Boersma ◽  
Isabelle De Smedt ◽  
Andreas Richter ◽  
Enno Peters ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Column Density ◽  
Random Noise ◽  
Uncertainty Budget ◽  
Optical Absorption Spectroscopy ◽  
Statistical Uncertainty ◽  
Climate Variables ◽  
Climate Data ◽  
Uncertainty Estimates ◽  
Climate Data Record

Abstract. Nitrogen dioxide (NO2) and formaldehyde (HCHO) column data from satellite instruments are used for air quality and climate studies. Both NO2 and HCHO have been identified as precursors to the ozone and aerosol Essential Climate Variables, and it is essential to quantify and characterize their uncertainties. Here we present an intercomparison of NO2 and HCHO slant column density (SCD) retrievals from 4 different research groups (BIRA-IASB, IUP, and KNMI as part of the Quality Assurance for Essential Climate Variables (QA4ECV) project consortium, and NASA) and from the OMI and GOME-2A instruments. Our evaluation is motivated by recent improvements in Differential Optical Absorption Spectroscopy (DOAS) fitting techniques, and by the desire to provide a fully traceable uncertainty budget for climate data record generated within QA4ECV. The improved NO2 and HCHO SCD values are in close agreement, but with substantial differences in the reported uncertainties between groups and instruments. As a check of the DOAS uncertainties, we use an independent estimate based on the spatial variability of the SCDs within a remote region. For NO2, we find the smallest uncertainties from the new QA4ECV retrieval (0.8 × 1015 molec. cm−2 for both instruments over their mission lifetimes). Relative to earlier approaches, the QA4ECV NO2 retrieval shows better agreement between DOAS and statistical uncertainty estimates, suggesting that the improved QA4ECV NO2 retrieval has reduced but not altogether eliminated systematic errors in the fitting approach. For HCHO, we reach similar conclusions (QA4ECV uncertainties of 8–12 × 1015 molec. cm−2 ), but the closure between the DOAS and statistical uncertainty estimates suggests that HCHO uncertainties are indeed dominated by random noise from the satellite’s level-1 data. We find that SCD uncertainties are smallest for high top-of-atmosphere reflectance levels. From 2005 to 2015, OMI NO2 SCD uncertainties increase by 1–2 %/yr related to detector degradation and stripes, but OMI HCHO SCD uncertainties are remarkably stable (increase

scholarly journals Long-Term Variation in the Tropospheric Nitrogen Dioxide Vertical Column Density over Korea and Japan from the MAX-DOAS Network, 2007–2017

2021 ◽  
Vol 13 (10) ◽  
pp. 1937
Author(s):  
Yongjoo Choi ◽  
Yugo Kanaya ◽  
Hisahiro Takashima ◽  
Hitoshi Irie ◽  
Kihong Park ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Column Density ◽  
Optical Absorption Spectroscopy ◽  
Industrial Complex ◽  
Vertical Column ◽  
Source Regions ◽  
Potential Source ◽  
Vertical Column Density ◽  
Good Agreement

We investigated long-term observations of the tropospheric nitrogen dioxide vertical column density (NO2 TropVCD) from the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) network in Russia and ASia (MADRAS) from 2007 to 2017 at urban (Yokosuka and Gwangju) and remote (Fukue and Cape Hedo) sites in East Asia. The monthly mean in the NO2 TropVCD from MAX-DOAS measured at ~13:30 local time, which is the Ozone Monitoring Instrument (OMI) overpass time, shows good agreement with OMI data during summer, but differences between the two datasets increase in winter. The Theil-Sen slope of the long-term trend indicate a relatively rapid and gradual reduction in NO2 at Yokosuka and two remote sites (Fukue and Cape Hedo), respectively, regardless of the season except for fall at Fukue, but significant changes in NO2 are not observed at Gwangju, Korea. In contrast, OMI satellite data reveal an increase in the NO2 TropVCD at all sites except for Yokosuka, where a decreasing trend common to MAX-DOAS is found, suggesting that the results from satellites need to be cautiously used for investigating long-term trends in less polluted or remote areas. Using backward trajectories, potential source regions are identified for the two urban sites. The spatial distribution from OMI data shows good agreement with the potential source regions at Yokosuka. The potential source regions in Gwangju are identified as the National Industrial Complex in Yeosu and Gwangyang, while the transport route is not clearly visible with OMI data because of their low sensitivity in less polluted areas. The proposed approach is suitable for identifying potential source areas that might not be recognized by satellite observations.

scholarly journals Detection of pollution transport events southeast of Mexico City using ground-based visible spectroscopy measurements of nitrogen dioxide

2009 ◽  
Vol 9 (1) ◽  
pp. 4769-4804 ◽  
Author(s):  
M. L. Melamed ◽  
R. Basaldud ◽  
R. Steinbrecher ◽  
S. Emeis ◽  
L. G. Ruíz-Suárez ◽  
...  
Keyword(s):  
Nitrogen Dioxide ◽  
Mexico City ◽  
Column Density ◽  
Mixing Layer ◽  
Optical Absorption Spectroscopy ◽  
Pollution Transport ◽  
Visible Spectroscopy ◽  
Density Measurements ◽  
Research Site ◽  
Depth Analysis

Abstract. This work presents ground based differential optical absorption spectroscopy (DOAS) measurements of nitrogen dioxide (NO2) during the MILAGRO field campaign in March 2006 at the Tenango del Aire research site located to the southeast of Mexico City. The DOAS NO2 column density measurements are used in conjunction with ceilometer, meteorological and surface nitrogen oxides (NOx) and total reactive nitrogen (NOy) measurements to show a more comprehensive view of air pollution results when a research site has both surface and remote sensing instruments. An in depth analysis of 13 March 2006 demonstrates how DOAS NO2, surface NO2 and ceilometer data can be used to determine the extent of mixing of the pollution layer. In addition, we show the effectiveness of how DOAS measurements can be used to observe pollution sources that may reside above the mixing layer, such as the presence of lightning produced NO2 as seen on 28 March 2006.

scholarly journals Recommendations for HCHO and SO2 Retrieval Settings from MAX-DOAS Observations under Different Meteorological Conditions

2021 ◽  
Vol 13 (12) ◽  
pp. 2244
Author(s):  
Zeeshan Javed ◽  
Aimon Tanvir ◽  
Muhammad Bilal ◽  
Wenjing Su ◽  
Congzi Xia ◽  
...  
Keyword(s):  
Column Density ◽  
Trace Gases ◽  
Meteorological Conditions ◽  
Optical Absorption Spectroscopy ◽  
Chemical Production ◽  
Vertical Column ◽  
Phase Oxidation ◽  
Fog Days ◽  
Rms Errors ◽  
Optimal Settings

Recently, the occurrence of fog and haze over China has increased. The retrieval of trace gases from the multi-axis differential optical absorption spectroscopy (MAX-DOAS) is challenging under these conditions. In this study, various reported retrieval settings for formaldehyde (HCHO) and sulfur dioxide (SO2) are compared to evaluate the performance of these settings under different meteorological conditions (clear day, haze, and fog). The dataset from 1st December 2019 to 31st March 2020 over Nanjing, China, is used in this study. The results indicated that for HCHO, the optimal settings were in the 324.5–359 nm wavelength window with a polynomial order of five. At these settings, the fitting and root mean squared (RMS) errors for column density were considerably improved for haze and fog conditions, and the differential slant column densities (DSCDs) showed more accurate values compared to the DSCDs between 336.5 and 359 nm. For SO2, the optimal settings for retrieval were found to be at 307–328 nm with a polynomial order of five. Here, root mean square (RMS) and fitting errors were significantly lower under all conditions. The observed HCHO and SO2 vertical column densities were significantly lower on fog days compared to clear days, reflecting a decreased chemical production of HCHO and aqueous phase oxidation of SO2 in fog droplets.

scholarly journals Calculating uncertainty for the RICE ice core continuous flow analysis water isotope record

2018 ◽  
Vol 11 (8) ◽  
pp. 4725-4736 ◽  
Author(s):  
Elizabeth D. Keller ◽  
W. Troy Baisden ◽  
Nancy A. N. Bertler ◽  
B. Daniel Emanuelsson ◽  
Silvia Canessa ◽  
...  
Keyword(s):  
High Resolution ◽  
Continuous Flow ◽  
Ice Core ◽  
Flow Analysis ◽  
Calibration Error ◽  
Data Set ◽  
Total Uncertainty ◽  
Continuous Flow Analysis ◽  
Uncertainty Estimates ◽  
Water Isotope

Abstract. We describe a systematic approach to the calibration and uncertainty estimation of a high-resolution continuous flow analysis (CFA) water isotope (δ2H, δ18O) record from the Roosevelt Island Climate Evolution (RICE) Antarctic ice core. Our method establishes robust uncertainty estimates for CFA δ2H and δ18O measurements, comparable to those reported for discrete sample δ2H and δ18O analysis. Data were calibrated using a time-weighted two-point linear calibration with two standards measured both before and after continuously melting 3 or 4 m of ice core. The error at each data point was calculated as the quadrature sum of three factors: Allan variance error, scatter over our averaging interval (error of the variance) and calibration error (error of the mean). Final mean total uncertainty for the entire record is δ2H=0.74 ‰ and δ18O=0.21 ‰. Uncertainties vary through the data set and were exacerbated by a range of factors, which typically could not be isolated due to the requirements of the multi-instrument CFA campaign. These factors likely occurred in combination and included ice quality, ice breaks, upstream equipment failure, contamination with drill fluid and leaks or valve degradation. We demonstrate that our methodology for documenting uncertainty was effective across periods of uneven system performance and delivered a significant achievement in the precision of high-resolution CFA water isotope measurements.

scholarly journals Uncertainty information in climate data records from Earth observation

2017 ◽  
Author(s):  
Christopher J. Merchant ◽  
Frank Paul ◽  
Thomas Popp ◽  
Michael Ablain ◽  
Sophie Bontemps ◽  
...  
Keyword(s):  
Weather Prediction ◽  
Earth Observation ◽  
Satellite Measurement ◽  
Climate Modelling ◽  
Climate Data ◽  
Total Uncertainty ◽  
Sources Of Uncertainty ◽  
Uncertainty Estimates ◽  
Wide Range ◽  
Uncertainty Information

Abstract. Climate data records (CDRs) derived from Earth observation (EO) should include rigorous uncertainty information, to support application of the data in policy, climate modelling and numerical weather prediction reanalysis. Uncertainty, error and quality are distinct concepts, and CDR products should follow international norms for presenting quantified uncertainty. Ideally, uncertainty should be quantified per datum in a CDR, and the uncertainty estimates should be able to discriminate more and less certain data with confidence. In this case, flags for data quality should not duplicate uncertainty information, but instead describe complementary information (such as the confidence held in the uncertainty estimate provided, or indicators of conditions violating retrieval assumptions). Errors have many sources and some are correlated across a wide range of time and space scales. Error effects that contribute negligibly to the total uncertainty in a single satellite measurement can be the dominant sources of uncertainty in a CDR on large space and long time scales that are highly relevant for some climate applications. For this reason, identifying and characterizing the relevant sources of uncertainty for CDRs is particularly challenging. Characterisation of uncertainty caused by a given error effect involves assessing the magnitude of the effect, the shape of the error distribution, and the propagation of the uncertainty to the geophysical variable in the CDR accounting for its error correlation properties. Uncertainty estimates can and should be validated as part of CDR validation, where possible. These principles are quite general, but the form of uncertainty information appropriate to different essential climate variables (ECVs) is highly variable, as confirmed by a quick review of the different approaches to uncertainty taken across different ECVs in the European Space Agency’s Climate Change Initiative. User requirements for uncertainty information can conflict with each other, and again a variety of solutions and compromises are possible. The concept of an ensemble CDR as a simple means of communicating rigorous uncertainty information to users is discussed. Our review concludes by providing eight recommendations for good practice in providing and communicating uncertainty in EO-based climate data records.

scholarly journals Intercomparison of NO<sub>2</sub>, O<sub>4</sub>, O<sub>3</sub> and HCHO slant column measurements by MAX-DOAS and zenith-sky UV–visible spectrometers during CINDI-2

2020 ◽  
Vol 13 (5) ◽  
pp. 2169-2208 ◽  
Author(s):  
Karin Kreher ◽  
Michel Van Roozendael ◽  
Francois Hendrick ◽  
Arnoud Apituley ◽  
Ermioni Dimitropoulou ◽  
...  
Keyword(s):  
Regression Analysis ◽  
Nitrogen Dioxide ◽  
European Space Agency ◽  
Visible Region ◽  
Atmospheric Pollutants ◽  
Optical Absorption Spectroscopy ◽  
Data Sets ◽  
Systematic Bias ◽  
Measurement Protocol ◽  
Data Products

Abstract. In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17 d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97∘ N, 4.93∘ E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation. The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions. The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.

scholarly journals HCl and ClO in activated Arctic air; first retrieved vertical profiles from TELIS submillimetre limb spectra

2012 ◽  
Vol 5 (2) ◽  
pp. 487-500 ◽  
Author(s):  
A. de Lange ◽  
M. Birk ◽  
G. de Lange ◽  
F. Friedl-Vallon ◽  
O. Kiselev ◽  
...  
Keyword(s):  
Michelson Interferometer ◽  
The Arctic ◽  
Optical Absorption Spectroscopy ◽  
Altitude Range ◽  
Balloon Flight ◽  
Total Uncertainty ◽  
Atmospheric Sounding ◽  
Systematic Effects ◽  
Equilibrium Profile ◽  
Peak Value

Abstract. The first profile retrieval results of the Terahertz and submillimeter Limb Sounder (TELIS) balloon instrument are presented. The spectra are recorded during a 13-h balloon flight on 24 January 2010 from Kiruna, Sweden. The TELIS instrument was mounted on the MIPAS-B2 gondola and shared this platform with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and the mini-Differential Optical Absorption Spectroscopy (mini-DOAS) instruments. The flight took place within the Arctic vortex at an altitude of ≈34 km in chlorine activated air, and both active (ClO) and inactive chlorine (HCl) were measured over an altitude range of respectively ≈16–32 km and ≈10–32 km. In this altitude range, the increase of ClO concentration levels during sunrise has been recorded with a temporal resolution of one minute. During the daytime equilibrium, a maximum ClO level of 2.1 ± 0.3 ppbv has been observed at an altitude of 23.5 km. This equilibrium profile is validated against the ClO profile by the satellite instrument Microwave Limb Sounder (MLS) aboard EOS Aura. HCl profiles have been determined from two different isotopes – H35Cl and H37Cl – and are also validated against MLS. The precision of all profiles is well below 0.01 ppbv and the overall accuracy is therefore governed by systematic effects. The total uncertainty of these effects is estimated to be maximal 0.3 ppbv for ClO around its peak value at 23.5 km during the daytime equilibrium, and for HCl it ranges from 0.05 to 0.4 ppbv, depending on altitude. In both cases the main uncertainty stems from a largely unknown non-linear response in the detector.

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