D. P. Edwards

National Research Center (CO, USA), Boulder, Colorado, United States

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Publications (123)224.55 Total impact

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    ABSTRACT: This review paper provides a framework for the application of the Observing System Simulation Experiment (OSSE) methodology to satellite observations of atmospheric constituents relevant for air quality. The OSSEs are experiments used to determine the potential benefit of future observing systems using an existing monitoring or forecasting system and by this can help to define optimal characteristics of future instruments. To this end observations from future instruments are simulated from a model representing the realistic state of the atmosphere and an instrument simulator. The added value of the new observations is evaluated through assimilation into another model or model version and comparison with the simulated true state and a control run.
    Atmospheric Environment 05/2015; 115. DOI:10.1016/j.atmosenv.2015.05.032 · 3.06 Impact Factor
  • 01/2015; 8(4):4095-4135. DOI:10.5194/amtd-8-4095-2015
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    ABSTRACT: The Measurements of Pollution in the Troposphere (MOPITT) Version 6 (V6) product for carbon monoxide (CO) incorporates several enhancements which will benefit many users of MOPITT data. V6 algorithm improvements are described in detail, and V6 validation results are presented. First, a geolocation bias related to the orientation of the MOPITT instrument relative to the TERRA platform was characterized and eliminated. Second, the variable a priori for CO concentrations for V6 is based on simulations performed with the chemical transport model Community Atmosphere Model with Chemistry (CAM-chem) for the years 2000–2009 instead of the model-derived climatology for 1997–2004 used for V5. Third, meteorological fields required for V6 retrieval processing are extracted from the MERRA (Modern-Era Retrospective Analysis For Research And Applications) reanalysis. Finally, a significant latitude-dependent retrieval bias in the upper troposphere in Version 5 products has been substantially reduced.
    Atmospheric Measurement Techniques 11/2014; 7(11):3623-3632. DOI:10.5194/amt-7-3623-2014 · 3.21 Impact Factor
  • 01/2014; 7(7):7013-7051. DOI:10.5194/amtd-7-7013-2014
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    ABSTRACT: We apply the Tropospheric Emission Spectrometer (TES) ozone retrieval algorithm to Infrared Atmospheric Sounding Instrument (IASI) radiances and characterise the uncertainties and information content of the retrieved ozone profiles. This study focuses on mid-latitudes for the year 2008. We validate our results by comparing the IASI ozone profiles to ozone sondes. In the sonde comparisons, we find a positive bias in the IASI ozone profiles in the UTLS region of up to 14% on average. For the described cases, the degrees of freedom for signal are on average 3.2, 0.3, 0.8, and 0.9 for the columns 0 km-top of atmosphere, (0-6) km, (0-11) km, and (8-16) km, respectively. We find that our biases with respect to sondes and our degrees of freedom for signal for ozone are comparable to previously published results from other IASI ozone algorithms. In addition to evaluating biases, we validate the retrieval errors by comparing predicted errors to the sample covariance matrix of the IASI observations themselves. For the predicted vs. empirical error comparison, we find that these errors are consistent and that the measurement noise and the interference of temperature and water vapour on the retrieval together mostly explain the empirically derived random errors. In general, the precision of the IASI ozone profiles is better than 20%.
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    ABSTRACT: [1] Validation results are reported for the MOPITT (Measurements of Pollution in the Troposphere) “Version 5” (V5) product for tropospheric carbon monoxide (CO) and are compared to results for the “Version 4” product. The V5 retrieval algorithm introduces (1) a method for reducing retrieval bias drift associated with long-term instrumental degradation, (2) a more exact representation of the effects of random errors in the radiances and, for the first time, (3) the use of MOPITT's near-infrared (NIR) radiances to complement the thermal-infrared (TIR) radiances. Exploiting TIR and NIR radiances together facilitates retrievals of CO in the lowermost troposphere. V5 retrieval products based (1) solely on TIR measurements, (2) solely on NIR measurements and (3) on both TIR and NIR measurements are separately validated and analyzed. Actual retrieved CO profiles and total columns are compared with equivalent retrievals based on in situ measurements from (1) routine NOAA aircraft sampling mainly over North America and (2) the “HIAPER Pole to Pole Observations” (HIPPO) field campaign. Particular attention is focused on the long-term stability and geographical uniformity of the retrieval errors. Results for the retrieved total column clearly indicate reduced temporal bias drift in the V5 products compared to the V4 product, and do not exhibit a positive bias in the Southern Hemisphere, which is evident in the V4 product.
    06/2013; 118(12). DOI:10.1002/jgrd.50272
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    ABSTRACT: Practical implementations of chemical OSSEs (Observing System Simulation Experiments) usually rely on approximations of the pseudo-observations by means of a prior parametrization of the averaging kernels, which describe the sensitivity of the observing systems to the target atmospheric species. This is intended to avoid the need for use of a computationally expensive pseudo-observations simulator that relies on full radiative transfer calculations. Here we present an investigation on how no, or limited, scene dependent averaging kernels parametrizations may misrepresent the sensitivity of an observing system, and thus possibly lead to inaccurate results of OSSEs. We carried out the full radiative transfer calculation for a three-days period over Europe, to produce reference pseudo-observations of lower tropospheric ozone, as they would be observed by a concept geostationary observing system called MAGEAQ (Monitoring the Atmosphere from Geostationary orbit for European Air Quality). The selected spatiotemporal interval is characterized by a peculiar ozone pollution event. We then compared our reference with approximated pseudo-observations, following existing simulation exercises made for both the MAGEAQ and GEOstationary Coastal and Air Pollution Events (GEO-CAPE) missions. We found that approximated averaging kernels may fail to replicate the variability of the full radiative transfer calculations. Then, we compared the full radiative transfer and the approximated pseudo-observations during a pollution event. We found that the approximations substantially overestimate the capability of the MAGEAQ to follow the spatiotemporal variations of the lower tropospheric ozone in selected areas. We conclude that such approximations may lead to false conclusions if used in an OSSE. Thus, we recommend to use comprehensive scene-dependent approximations of the averaging kernels, in cases where the full radiative transfer is computationally too costly for the OSSE being investigated.
    Atmospheric Measurement Techniques 03/2013; 6(2):2413-2448. DOI:10.5194/amtd-6-2413-2013 · 3.21 Impact Factor
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    ABSTRACT: A current obstacle to the Observation System Simulation Experiments (OSSEs) used to quantify the potential performance of future atmospheric composition remote sensing systems is a computationally efficient method to define the scene-dependent vertical sensitivity of measurements as expressed by the retrieval averaging kernels (AKs). We present a method for the efficient prediction of AKs for multispectral retrievals of carbon monoxide (CO) and ozone (O3) based on actual retrievals from MOPITT on EOS-Terra and TES and OMI on EOS-Aura, respectively. This employs a multiple regression approach for deriving scene-dependent AKs using predictors based on state parameters such as the thermal contrast between the surface and lower atmospheric layers, trace gas volume mixing ratios (VMR), solar zenith angle, water vapor amount, etc. We first compute the singular vector decomposition (SVD) for individual cloud-free AKs and retain the 1st three ranked singular vectors in order to fit the most significant, orthogonal components of the AK in the subsequent multiple regression on a training set of retrieval cases. The resulting fit coefficients are applied to the predictors from a different test set of retrievals cased to reconstruct predicted AKs, which can then be evaluated against the true test set retrieval AKs. By comparing the VMR profile adjustment resulting from the use of the predicted vs. true AKs, we quantify the CO and O3 VMR profile errors associated with the use of the predicted AKs compared to the true AKs that might be obtained from a computationally expensive full retrieval calculation as part of an OSSE. Similarly, we estimate the errors in CO and O3 VMRs from using a single regional average AK to represent all retrievals, which has been a common approximation in chemical OSSEs performed to-date. For both CO and O3 in the lower troposphere, we find a significant reduction in error when using the predicted AKs as compared to a single average AK. This study examined data from the continental United States (CONUS) for 2006, but the approach could be applied to other regions and times.
    03/2013; 6(2):2751-2791. DOI:10.5194/amtd-6-2751-2013
  • Atmospheric Measurement Techniques 01/2013; 6(7):1633-1646. DOI:10.5194/amt-6-1633-2013 · 3.21 Impact Factor
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    ABSTRACT: Atmospheric carbon monoxide (CO) distributions are controlled by anthropogenic emissions, biomass burning, transport and oxidation by reaction with the hydroxyl radical (OH). Quantifying trends in CO is therefore important for understanding changes related to all of these contributions. Here we present a comprehensive record of satellite observations from 2000 through 2011 of total column CO using the available measurements from nadir-viewing thermal infrared instruments: MOPITT, AIRS, TES and IASI. We examine trends for CO in the Northern and Southern Hemispheres along with regional trends for Eastern China, Eastern USA, Europe and India. We find that all the satellite observations are consistent with a modest decreasing trend ∼-1% yr-1 in total column CO over the Northern Hemisphere for this time period and a less significant, but still decreasing trend in the Southern Hemisphere. Although decreasing trends in the United States and Europe have been observed from surface CO measurements, we also find a decrease in CO over E. China that, to our knowledge, has not been reported previously. Some of the interannual variability in the observations can be explained by global fire emissions, but the overall decrease needs further study to understand the implications for changes in anthropogenic emissions.
    Atmospheric Chemistry and Physics 01/2013; 13(2-2):837-850. DOI:10.5194/acp-13-837-2013 · 4.88 Impact Factor
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    ABSTRACT: The new Version 5 MOPITT (Measurements of Pollution in the Troposphere) product for carbon monoxide (CO) is the first satellite product to exploit simultaneous near-infrared and thermal-infrared observations to enhance retrieval sensitivity in the lower troposphere. This feature is important to air quality analyses and studies of CO sources. However, because of the influence of both thermal contrast and geophysical noise, the retrieval characteristics for this new multispectral product are highly variable. New V5 products for surface-level CO concentrations have been evaluated over the contiguous United States using both in situ vertical profiles and NOAA ground-based "Tall Tower" measurements. Validation results based on the in situ profiles indicate that retrieval biases are on the order of a few percent. However, direct comparisons with the Tall Tower measurements demonstrate that smoothing error, which depends on both the retrieval averaging kernels and CO variability in the lower troposphere, exhibits significant geographical and seasonal variability.
    Journal of Geophysical Research Atmospheres 07/2012; 117(D13):13306-. DOI:10.1029/2012JD017553 · 3.44 Impact Factor
  • ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2012; DOI:10.5194/acp-12-1067-2012 · 5.30 Impact Factor
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    ABSTRACT: The new MOPITT Version 5 product is the first satellite product for carbon monoxide (CO) to exploit multispectral observations. Together, near-infrared (NIR) and thermal-infrared (TIR) observations permit the retrieval of CO concentrations in the lower troposphere, near the actual sources. However, while this feature is potentially valuable for applications including chemical weather forecasting and inverse modeling, the retrieval characteristics of the new multispectral product (e.g., the retrieval averaging kernels) are highly variable. The underlying causes of this variability include thermal contrast and geophysical noise. Validating the new V5 product is challenging for several reasons. Compared to the TIR-only MOPITT product, random retrieval errors in the multispectral product are substantially larger. To compensate, stronger temporal and spatial averaging may be necessary. However, the temporal and spatial variability of CO in the planetary boundary layer (PBL) are much greater than in the free troposphere. Consequently, in-situ CO measurements made in the PBL may be poorly correlated with CO concentrations averaged over areas representative of MOPITT pixels (~ 22 km). Errors from this effect are only compounded as multiple MOPITT pixels are averaged together, particularly if there are significant regional sources. Previous MOPITT validation efforts have relied mainly on in-situ profiles measured from aircraft. While these are valuable, we are also exploring new sources of validation data. For example, we have begun comparing MOPITT retrieval results with CO in-situ measurements from the NOAA 'Tall Tower' network. Instruments on these towers measure CO concentrations at high temporal frequency and at multiple fixed altitudes within the PBL.
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    ABSTRACT: The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission is required to be able to measure ozone with two degrees of freedom for signal (DFS) in the troposphere, and to provide sensitivity in the lowest 2 km (lowermost troposphere, LMT). We explore the feasibility of using multispectral measurements from the ultraviolet (UV) to the thermal infrared (TIR) to improve LMT ozone retrievals compared to conventional retrievals employing only the UV or the TIR. Simulations spanning a range of ozone mixing ratios indicate that the combination of UV, visible and TIR significantly improves the total column DFS as well as the LMT DFS. We will present results both for clear sky scenarios and those containing realistic cloud and aerosol loadings.
  • A. Boynard, G. Pfister, D. P. Edwards
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    ABSTRACT: As a tracer of pollution and a precursor of tropospheric ozone, carbon monoxide (CO) is a key species for studying air quality. This pollutant is highly variable and the integration of observations and modelling can provide a better insight into, for example, pollution episode development and pollution transport on regional to global scales. In this work, we analyse CO concentrations simulated by the WRF chem regional model over the U.S. during the summer 2008 in order to characterize its geographical and temporal variations at the surface, in the lowermost troposphere and in the free troposphere. The model is evaluated by comparisons with surface measurements available from several EPA ground-based stations over the U.S. and satellite observations from Terra/MOPITT. CO tracers for different emission sources are also used to differentiate the variability due to dynamics, photochemistry and emissions and to assess the CO budget. Finally, we compare the representation of surface and planetary boundary layer CO concentration variability that would be captured by representative satellite sensor observations using the different CO spectral bands. These comprise thermal infrared measurements sensitive primarily to the free troposphere concentration, near-infrared measurements sensitive to the total column and combined multispectral measurements that would provide sensitivity to the lowermost troposphere concentration.
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    ABSTRACT: Carbon monoxide (CO) is an important trace gas for understanding air quality and atmospheric composition. It is a good tracer of pollution plumes and atmospheric dynamics. In this talk we describe the analysis of global and regional CO distributions as seen by both the MOPITT/Terra and IASI/MetOp missions, from mid-2007 up to now. Long term trends for IASI and MOPITT (version 3, 4 and 5) CO total columns over specific areas are presented, and show excellent agreement. CO distributions over polluted and clean regions are compared. Preliminary results of a study comparing the surface CO level for the two sounders over different cities will be presented, using MOPITT version 5 products that include the NIR and show a better sensitivity near the ground. Finally, this talk will also illustrate how the data processed at ULB-LATMOS are currently assimilated in the MACC project in near-real time in order to generate the CO pollution forecasts over Europe. Surface CO obtained after assimilation show better agreement with ground-based station measurements.
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    ABSTRACT: In this paper, we analyze tropospheric O3 together with HNO3 during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) program, combining observations and model results. Aircraft observations from the NASA ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and NOAA ARCPAC (Aerosol, Radiation and Cloud Processes affecting Arctic Climate) campaigns during spring and summer of 2008 are used together with the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) to assist in the interpretation of the observations in terms of the source attribution and transport of O3 and HNO3 into the Arctic. The MOZART-4 simulations reproduce the aircraft observations generally well (within 15 %), but some discrepancies in the model are identified and discussed. The observed correlation of O3 with HNO3 is exploited to evaluate the MOZART-4 model performance for different air mass types (fresh plumes, free troposphere and stratospheric-contaminated air masses). Based on model simulations of O3 and HNO3 tagged by source type and region, we find that the anthropogenic pollution from the Northern Hemisphere is the dominant source of O3 and HNO3 in the Arctic at pressure greater than 400 hPa, and that the stratospheric influence is the principal contribution at pressures less 400 hPa. During the summer, intense Russian fire emissions contribute some amount to the tropospheric columns of both gases over the American sector of the Arctic. North American fire emissions (California and Canada) also show an important impact on tropospheric ozone in the Arctic boundary layer. Additional analysis of tropospheric O3 measurements from ground-based FTIR and from the IASI satellite sounder made at the Eureka (Canada) and Thule (Greenland) polar sites during POLARCAT has been performed using the tagged contributions. It demonstrates the capability of these instruments for observing pollution at Northern high latitudes. Differences between contributions from the sources to the tropospheric columns as measured by FTIR and IASI are discussed in terms of vertical sensitivity associated with these instruments. The first analysis of O3 tropospheric columns observed by the IASI satellite instrument over the Arctic is also provided. Despite its limited vertical sensitivity in the lowermost atmospheric layers, we demonstrate that IASI is capable of detecting low-altitude pollution transported into the Arctic with some limitations.
    Atmospheric Chemistry and Physics 08/2011; 11(8):23707-23760. DOI:10.5194/acpd-11-23707-2011 · 4.88 Impact Factor
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    ABSTRACT: Air pollution is of concern in many parts of California and is impacted by both local emissions and also by pollution inflow from the Pacific. In this study, we use the regional chemical transport model WRF-Chem V3.2 to examine the CO budget over California. We include model CO tracers for different emission sources in the model, which allow estimating the relative importance of local sources versus pollution inflow on the distribution of CO at the surface and in the free troposphere. The focus of our study is on the 15 June–15 July 2008 time period, which coincides with the aircraft deployment of the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission over California. Model simulations are evaluated using these aircraft observations as well as satellite retrievals and surface observations of CO. Evaluation results show that the model overall predicts the observed CO fields well, but points towards an underestimate of CO from the fires in Northern California, which had a strong influence during the study period, and towards a slight overestimate of CO from pollution inflow and local anthropogenic sources. The analysis of the CO budget over California reveals that inflow of CO explains on average 53 ± 21% of surface CO during the study period, compared to 22 ± 18% for local anthropogenic sources and 18 ± 22% for fires. In the free troposphere, the average CO contributions are estimated as 78 ± 16% for CO inflow, 6 ± 4% for CO from local anthropogenic sources and 11 ± 13% for CO from fires.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 08/2011; 11(15). DOI:10.5194/acpd-11-3627-2011 · 5.30 Impact Factor
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    ABSTRACT: This paper describes the capabilities of a nadir thermal infrared (TIR) sensor proposed for deployment onboard a geostationary platform to monitor ozone (O3) and carbon monoxide (CO) for air quality (AQ) purposes. To assess the capabilities of this sensor we perform idealized retrieval studies considering typical atmospheric profiles of O3 and CO over Europe with different instrument configuration (signal to noise ratio, SNR, and spectral sampling interval, SSI) using the KOPRA forward model and the KOPRA-fit retrieval scheme. We then select a configuration, referred to as GEO-TIR, optimized for providing information in the lowermost troposphere (LmT; 0-3 km in height). For the GEO-TIR configuration we obtain ~1.5 degrees of freedom for O3 and ~2 for CO at altitudes between 0 and 15 km. The error budget of GEO-TIR, calculated using the principal contributions to the error (namely, temperature, measurement error, smoothing error) shows that information in the LmT can be achieved by GEO-TIR. We also retrieve analogous profiles from another geostationary infrared instrument with SNR and SSI similar to the Meteosat Third Generation Infrared Sounder (MTG-IRS) which is dedicated to numerical weather prediction, referred to as GEO-TIR2. We quantify the added value of GEO-TIR over GEO-TIR2 for a realistic atmosphere, simulated using the chemistry transport model MOCAGE (MOdèle de Chimie Atmospherique à Grande Echelle). Results show that GEO-TIR is able to capture well the spatial and temporal variability in the LmT for both O3 and CO. These results also provide evidence of the significant added value in the LmT of GEO-TIR compared to GEO-TIR2 by showing GEO-TIR is closer to MOCAGE than GEO-TIR2 for various statistical parameters (correlation, bias, standard deviation).
    Atmospheric Measurement Techniques 01/2011; 4:297-317. DOI:10.5194/amt-4-297-2011 · 3.21 Impact Factor

Publication Stats

4k Citations
224.55 Total Impact Points

Institutions

  • 2002–2013
    • National Research Center (CO, USA)
      Boulder, Colorado, United States
  • 1997–2012
    • National Center for Atmospheric Research
      • Division of Atmospheric Chemistry
      Boulder, Colorado, United States
  • 2004–2006
    • University of Maryland, Baltimore County
      • Department of Physics
      Baltimore, Maryland, United States