Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment version 3 data retrievals

Version 3 of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space Shuttle missions (in 1985, 1992, 1993, and 1994), profiles from more than 350 occultations were retrieved from the upper troposphere to the lower mesosphere. Previous results were unreliable for tropospheric retrievals, but with a new global-fitting algorithm profiles are reliably returned down to altitudes as low as 6.5 km (clouds permitting) and include notably improved retrievals of H2 O, CO, and other species. Results for stratospheric water are more consistent across the ATMOS spectral filters and do not indicate a net consumption of H2 in the upper stratosphere. A new sulfuric-acid aerosol product is described. An overview of ATMOS Version 3 processing is presented with a discussion of estimated uncertainties. Differences between these Version 3 and previously reported Version 2 ATMOS results are discussed. Retrievals are available at http: /atmos.jpl.nasa.gov /atmos

Retrieval of NO2 Column Amounts from Ground-Based Hyperspectral Imaging Sensor Measurements

Total column amounts of NO2 (TCN) were estimated from ground-based hyperspectral imaging sensor (HIS) measurements in a polluted urban area (Seoul, Korea) by applying the radiance ratio fitting method with five wavelength pairs from 400 to 460 nm. We quantified the uncertainty of the retrieved TCN based on several factors. The estimated TCN uncertainty was up to 0.09 Dobson unit (DU), equivalent to 2.687 ?? 1020 molecules m???2) given a 1?? error for the observation geometries, including the solar zenith angle, viewing zenith angle, and relative azimuth angle. About 0.1 DU (6.8%) was estimated for an aerosol optical depth (AOD) uncertainty of 0.01. In addition, the uncertainty due to the NO2 vertical profile was 14% to 22%. Compared with the co-located Pandora spectrophotometer measurements, the HIS captured the temporal variation of the TCN during the intensive observation period. The correlation between the TCN from the HIS and Pandora also showed good agreement, with a slight positive bias (bias: 0.6 DU, root mean square error: 0.7 DU)

On satellite observations of atmospheric composition and their interpretation

Since more than 30 years satellites contribute significantly to our understanding of the composition of the atmosphere by performing global observations of atmospheric constituents from space. A recent addition to the series of Earth observing instruments is the Ozone Monitoring Instrument (OMI) that since October 2004 performs daily global measurements at high spatial resolution. The work presented in thesis focuses on spaceborne observations of NO2 and tropospheric aerosols, and the interpretation of the behavior of these constituents. NO2 plays an important role in the chemistry of the atmosphere due to its involvement in the catalytic destruction of ozone in the stratosphere, and by being a precursor of tropospheric ozone, linking NO2 to air quality and climate change. Aerosols also play an important role in chemistry and climate. For the DOAS-based retrieval of NO2 from OMI measurement data an accurate characterization of the OMI spectral slitfunction is essential. The spectral slitfunction was characterized with a novel method where the slitfunction for each wavelength and viewing angle was sampled by the spectrally narrow diffraction orders of an echelle grating, with wavelength increments 10 times smaller than the spectral resolution of OMI. The resulting parameterization of the spectral slitfunction is used in the retrieval of NO2 and other DOAS-based products from OMI. Tropospheric NO2 columns are retrieved from OMI measurements on an operational basis by the Dutch OMI NO2 (DOMINO) system. The DOMINO algorithm assimilates NO2 slant column in the TM4 chemistry transport model to estimate the stratospheric NO2 column. DOMINO data are available as a near-real time (within 3-4 hours after measurement) and as a consistent reprocessed offline dataset of collection 3, version 1.0.2. Based on the findings of validation studies involving DOMINO data, improvements to the DOMINO algorithm regarding surface albedo and a priori profile shape are identified . An extensive validation study shows that OMI stratospheric NO2 columns are consistent within 13% with ground-based observations from the SAOZ and NDACC network. The DOMINO product performs superior to the parallel existing Standard Product by capturing the dynamic variability of NO2 in the stratosphere, such as the daytime increase of stratospheric NO2 and the day-to-day variations in the NO2 field associated with the collapse of the Arctic Polar vortex. Analysis of the 5+ year OMI data record shows that OMI observes variations in stratospheric NO2 on a seasonal and multi-annual scale, e.g., the quasi biennial oscillation (QBO) and trends. The NO2 QBO signal exhibits a distinct interhemispheric asymmetry over the tropics, and is stronger over the Southern Hemisphere. There is good agreement between the Lauder data record and collocated OMI stratospheric NO2 observations, both showing a small increase of approximately +0.5% per decade for the timespan of the OMI mission (2004-2010). Observations from OMI and the spaceborne lidar CALIOP were used to characterize the around the world transport of an aerosol plume that was released by the intense Australian forest fires of December 2006. The plume crossed the Pacific in 5 days and completed the circumnavigation of the globe in 12 days. Estimates of the plume’s altitude from the OMI cloud retrieval algorithm indicate that the plume was injected into the tropopause region by pyro-convection, triggered by the combination of a passing cold front and the latent heat of the fires. The high altitude of the plume was confirmed by CALIOP that detected the plume at 11-15 km altitude as it passed over South America. Radiative transfer calculations indicate that the underestimation of the OMI plume height in comparison with CALIOP in a later stage of the plume’s transport is caused by photons scattered from lower-lying clouds that outshine the diluted plume. Simulations with TM4 agree best with OMI and CALIOP observations of the plume’s transport when a passive tracer is released at approximately 10 km altitude, to mimic the effect of pyro-convective lofting which is not simulated by the model

From photon paths to pollution plumes: better radiative transfer calculations to monitor NOx emissions with OMI and TROPOMI

Nitrogen oxides (NOx = NO + NO2) play an important role in atmospheric chemistry, therefore affecting air quality and Earth's radiative forcing, which impact public health, ecosystems and climate. Remote sensing from satellites in the ultraviolet and visible (UV-Vis) spectral range results in measurements of tropospheric NO2 column densities with high spatial and temporal resolution that allow, among many applications, to monitor NO2 concentrations and to estimate NOx emissions. NO2 satellite retrievals have improved extensively in the last decade, together with the increased need of having traceable characterization of the uncertainties associated with the NO2 satellite measurements. The spatial resolution of the satellite instruments is improving such that the observed NO2 pollution can now be traced back to emissions from individual cities, power plants, and transportation sectors. However, the uncertainty of satellite NO2 retrievals is still considerable and mainly related to the adequacy of the assumptions made on the state of the atmosphere. In this thesis we have improved the critical assumptions and our understanding in the radiative transfer modelling for NO2 satellite measurements, and we use the new TROPOMI NO2 measurements to quantify daily NOx emissions from a single urban hot spot. The work presented in this thesis contributes to the satellite remote sensing community (1) because of the improvement of the satellite retrieval and the knowledge of its main uncertainty sources (Chapter 2, 3 and 4), and (2) because of the application of TROPOMI NO2 measurements for the first time to infer daily NOx emissions at urban scales (Chapter 5). </p

Information content of ozone retrieval algorithms

The algorithms are characterized that were used for production processing by the major suppliers of ozone data to show quantitatively: how the retrieved profile is related to the actual profile (This characterizes the altitude range and vertical resolution of the data); the nature of systematic errors in the retrieved profiles, including their vertical structure and relation to uncertain instrumental parameters; how trends in the real ozone are reflected in trends in the retrieved ozone profile; and how trends in other quantities (both instrumental and atmospheric) might appear as trends in the ozone profile. No serious deficiencies were found in the algorithms used in generating the major available ozone data sets. As the measurements are all indirect in someway, and the retrieved profiles have different characteristics, data from different instruments are not directly comparable

CEOS Intercalibration of Ground-Based Spectrometers and Lidars: Contract Change Notice 2012-2013: Final Report

This document is the final report of the Intercalibration of ground-based spectrometers and Lidars - Extension 2012-2013. It summarizes the activities performed in the period from November 2012 until December 2013 and the main results obtained

Air mass factor formulation for spectroscopic measurements from satellites: Application to formaldehyde retrievals from the Global Ozone Monitoring Experiment

Abstract. We present a new formulation for the air mass factor (AMF) to convert slant column measurements of optically thin atmospheric species from space into total vertical columns. Because of atmospheric scattering, the AMF depends on the vertical distribution of the species. We formulate the AMF as the integral of the relative vertical distribution (shape factor) of the species over the depth of the atmosphere, weighted by altitudedependent coefficients (scattering weights) computed independently from a radiative transfer model. The scattering weights are readily tabulated, and one can then obtain the AMF for any observation scene by using shape factors from a three dimensional (3-D) atmospheric chemistry model for the period of observation. This approach subsequently allows objective evaluation of the 3-D model with the observed vertical columns, since the shape factor and the vertical column in the model represent two independent pieces of information. We demonstrate the AMF method by using slant column measurements of formaldehyde at 346 nm from the Global Ozone Monitoring Experiment satellite instrument over North America during July 1996. Shape factors are computed with the Global Earth Observing System CHEMistry (GEOS-CHEM) global 3-D model and are checked for consistency with the few available aircraft measurements. Scattering weights increase by an order of magnitude from the surface to the upper troposphere. The AMFs are typically 20-40 % less over continents than over the oceans and are approximately half the values calculated in the absence of scattering. Model-induced errors in the AMF are estimated to be • 10%. The GEOS-CHEM model captures 50 % and 60 % of the variances in the observed slant and vertical columns, respectively. Comparison of the simulated and observed vertical columns allows assessment of model bias. 1

The relevance of aerosol in the retrieval of tropospheric NO2 from satellite - a study of model data applicability

Nitrogen dioxide (NO2) is a key pollutant in the troposphere, being one of the main precursors of tropospheric ozone, and source of nitric acid, as well as contributing to global climate change. Tropospheric NO2 vertical columns can be determined from satellite observations, although some uncertainties are still associated with the retrieval process. The conversion from measured slant columns to vertical columns is accomplished with airmass factors (AMF) that are determined by radiative transfer (RT) models. While the measurement (instrumental) conditions are well assessed, improvement is still needed regarding the a priori information of atmospheric characteristics required for the estimation of AMFs (e.g., vertical distribution of the gas, aerosol loading and clouds). This thesis presents a sensitivity study focused on the impact of aerosol on the tropospheric NO2 AMF. Optical properties, size distribution, and vertical distribution of the aerosol were varied within several scenarios. Overall, the results show a tendency for two main opposite effects. On the one hand, enhancement of the measurement sensitivity occurs by means of multiple scattering, when aerosol is mixed with the trace gas. On the other hand, a shielding effect by an aerosol layer located above the NO2 is also verified. The identified pivotal factors for the AMF calculations were the relative vertical distribution of aerosol and NO2, the aerosol optical depth and the single scattering albedo, as well as the surface reflectance. A case study was developed, focusing on the impact on the NO2 measurements of volcanic ash emitted from Eyjafjallajökull during the spring of 2010. Aerosol and NO2 data from the EURAD chemical transport model (CTM) were used to design scenarios for the RT calculations. A small variation of AMFs was found, revealing that, in the days and region analysed, the satellite observations of NO2 were not significantly affected by the mentioned eruption. Nonetheless, it was verified that the conclusions of the study are dependent on the accuracy of the CTM data, and on the approach employed to account for (and determine) aerosol optical properties. Such findings highlight the potential challenges that can be faced in the future if model data are used in satellite retrievals. In addition, a model evaluation performed within the GEMS project is described, where global stratospheric and tropospheric NO2 columns predicted by two chemical transport models MOZART and TM5 are compared with SCIAMACHY observations. The evaluation exercise allowed for the identification of flaws in the model systems, showing problems with the prediction of high levels of pollution in some regions (e.g., East-Asia), and with the simulation of NO2 concentrations during biomass burning events

The relevance of aerosol in the retrieval of tropospheric NO2 from satellite - a study of model data applicability

Nitrogen dioxide (NO2) is a key pollutant in the troposphere, being one of the main precursors of tropospheric ozone, and source of nitric acid, as well as contributing to global climate change. Tropospheric NO2 vertical columns can be determined from satellite observations, although some uncertainties are still associated with the retrieval process. The conversion from measured slant columns to vertical columns is accomplished with airmass factors (AMF) that are determined by radiative transfer (RT) models. While the measurement (instrumental) conditions are well assessed, improvement is still needed regarding the a priori information of atmospheric characteristics required for the estimation of AMFs (e.g., vertical distribution of the gas, aerosol loading and clouds). This thesis presents a sensitivity study focused on the impact of aerosol on the tropospheric NO2 AMF. Optical properties, size distribution, and vertical distribution of the aerosol were varied within several scenarios. Overall, the results show a tendency for two main opposite effects. On the one hand, enhancement of the measurement sensitivity occurs by means of multiple scattering, when aerosol is mixed with the trace gas. On the other hand, a shielding effect by an aerosol layer located above the NO2 is also verified. The identified pivotal factors for the AMF calculations were the relative vertical distribution of aerosol and NO2, the aerosol optical depth and the single scattering albedo, as well as the surface reflectance. A case study was developed, focusing on the impact on the NO2 measurements of volcanic ash emitted from Eyjafjallajökull during the spring of 2010. Aerosol and NO2 data from the EURAD chemical transport model (CTM) were used to design scenarios for the RT calculations. A small variation of AMFs was found, revealing that, in the days and region analysed, the satellite observations of NO2 were not significantly affected by the mentioned eruption. Nonetheless, it was verified that the conclusions of the study are dependent on the accuracy of the CTM data, and on the approach employed to account for (and determine) aerosol optical properties. Such findings highlight the potential challenges that can be faced in the future if model data are used in satellite retrievals. In addition, a model evaluation performed within the GEMS project is described, where global stratospheric and tropospheric NO2 columns predicted by two chemical transport models MOZART and TM5 are compared with SCIAMACHY observations. The evaluation exercise allowed for the identification of flaws in the model systems, showing problems with the prediction of high levels of pollution in some regions (e.g., East-Asia), and with the simulation of NO2 concentrations during biomass burning events