85 research outputs found
Improvements to the OMI O<sub>2</sub>-O<sub>2</sub> operational cloud algorithm and comparisons with ground-based radar-lidar observations
No full textThe OMI (Ozone Monitoring Instrument on board NASA's Earth Observing System (EOS) Aura satellite) OMCLDO2 cloud product supports trace gas retrievals of for example ozone and nitrogen dioxide. The OMCLDO2 algorithm derives the effective cloud fraction and effective cloud pressure using a DOAS (differential optical absorption spectroscopy) fit of the O2-O2 absorption feature around 477m. A new version of the OMI OMCLDO2 cloud product is presented that contains several improvements, of which the introduction of a temperature correction on the O2-O2 slant columns and the updated look-up tables have the largest impact. Whereas the differences in the effective cloud fraction are on average limited to 0.01, the differences of the effective cloud pressure can be up to 200hPa, especially at cloud fractions below 0.3. As expected, the temperature correction depends on latitude and season. The updated look-up tables have a systematic effect on the cloud pressure at low cloud fractions. The improvements at low cloud fractions are very important for the retrieval of trace gases in the lower troposphere, for example for nitrogen dioxide and formaldehyde. The cloud pressure retrievals of the improved algorithm are compared with ground-based radar-lidar observations for three sites at mid-latitudes. For low clouds that have a limited vertical extent the comparison yields good agreement. For higher clouds, which are vertically extensive and often contain several layers, the satellite retrievals give a lower cloud height. For high clouds, mixed results are obtained.</p
Sources of Formaldehyde in U.S. Oil and Gas Production Regions
No full textAuthors: Barbara Dix, Meng Li, Esther Roosenbrand, Colby Francoeur, Steven S. Brown, Jessica B. Gilman, Thomas F. Hanisco, Frank Keutsch, Abigail Koss, Brian M. Lerner, Jeff Peischl, James M. Roberts, Thomas B. Ryerson, Jason M. St. Clair, Patrick R. Veres, Carsten Warneke, Robert J. Wild, Glenn M. Wolfe, Bin Yuan, J. Pepijn Veefkind, Pieternel F. Levelt, Brian C. McDonald, and Joost de GouwWe analyzed observational and model data to study the sources of formaldehyde over oil and gas production regions and to investigate how these observations may be used to constrain oil and gas volatile organic compound (VOC) emissions. The analysis of aircraft and satellite data consistently found that formaldehyde over oil and gas production regions during spring and summer is mostly formed by the photooxidation of precursor VOCs. Formaldehyde columns over the Permian Basin, one of the largest oil- and gas-producing regions in the United States, are correlated with the production locations. Formaldehyde simulations by the atmospheric chemistry and transport model WRF-Chem, which included oil and gas NOx and VOC emissions from the fuel-based oil and gas inventory, were in very good agreement with TROPOMI satellite measurements. Sensitivity studies illustrated that VOCs released from oil and gas activities are important precursors to formaldehyde, but other sources of VOCs contribute as well and that the formation of secondary formaldehyde is highly sensitive to NOₓ. We also investigated the ability of the chemical mechanism used in WRF-Chem to represent formaldehyde formation from oil and gas hydrocarbons by comparing against the Master Chemical Mechanism. Further, our work provides estimates of primary formaldehyde emissions from oil and gas production activities, with per basin averages ranging from 0.07 to 2.2 kg h⁻¹ in 2018. A separate estimate for natural gas flaring found that flaring emissions could contribute 5 to 12% to the total primary formaldehyde emissions for the Permian Basin in 2018.This work was financially supported by the NASA ACMAP program under award number 80NSSC19K0979. We acknowledge funding from the Rocky Mountain Institute and Blue Sky Resources. We are grateful to Enverus for providing access to the DrillingInfo database. We thank NOAA’s High Performance Computing Program and NASA’s Tropospheric Composition Program. We thank GEO-CAPE for supporting the formaldehyde measurements during SONGNEX. This research was funded in part by the National Science Foundation under cooperative agreement no. AGS-1755088 and in part by NOAA cooperative agreement NA17OAR4320101. KNMI contributions were funded by The Netherlands Space Office (NSO) under the TROPOMI Science Contract. This work contains modified Copernicus Sentinel 5 Precursor data 2018–2020.https://pubs.acs.org/doi/full/10.1021/acsearthspacechem.3c0020
Minimizing aerosol effects on the OMI tropospheric NO<sub>2</sub> retrieval - An improved use of the 477nm O<sub>2</sub>-O<sub>2</sub> band and an estimation of the aerosol correction uncertainty
No full textGlobal mapping of satellite tropospheric NO2 vertical column density (VCD), a key gas in air quality monitoring, requires accurate retrievals over complex urban and industrialized areas and under any atmospheric conditions. The high abundance of aerosol particles in regions dominated by anthropogenic fossil fuel combustion, e.g. megacities, and/or biomass-burning episodes, affects the space-borne spectral measurement. Minimizing the tropospheric NO2 VCD biases caused by aerosol scattering and absorption effects is one of the main retrieval challenges from air quality satellite instruments. In this study, the reference Ozone Monitoring Instrument (OMI) DOMINO-v2 product was reprocessed over cloud-free scenes, by applying new aerosol correction parameters retrieved from the 477 nm O2-O2 band, over eastern China and South America for 2 years (2006 2007). These new parameters are based on two different and separate algorithms developed during the last 2 years in view of an improved use of the OMI 477 nm O2-O2 band: 1. the updated OMCLDO2 algorithm, which derives improved effective cloud parameters, 2. the aerosol neural network (NN), which retrieves explicit aerosol parameters by assuming a more physical aerosol model. The OMI aerosol NN is a step ahead of OMCLDO2 because it primarily estimates an explicit aerosol layer height (ALH), and secondly an aerosol optical thickness τ for cloud-free observations. Overall, it was found that all the considered aerosol correction parameters reduce the biases identified in DOMINO-v2 over scenes in China with high aerosol abundance dominated by fine scattering and weakly absorbing particles, e.g. from [-20% V -40%] to [0% V 20%] in summertime. The use of the retrieved OMI aerosol parameters leads in general to a more explicit aerosol correction and higher tropospheric NO2 VCD values, in the range of [0% V 40%], than from the implicit correction with the updated OMCLDO2. This number overall represents an estimation of the aerosol correction strategy uncertainty nowadays for tropospheric NO2 VCD retrieval from space-borne visible measurements. The explicit aerosol correction theoretically includes a more realistic consideration of aerosol multiple scattering and absorption effects, especially over scenes dominated by strongly absorbing particles, where the correction based on OMCLDO2 seems to remain insufficient. However, the use of ALH and τ from the OMI NN aerosol algorithm is not a straightforward operation and future studies are required to identify the optimal methodology. For that purpose, several elements are recommended in this paper. Overall, we demonstrate the possibility of applying a more explicit aerosol correction by considering aerosol parameters directly derived from the 477 nm O2-O2 spectral band, measured by the same satellite instrument. Such an approach can, in theory, easily be transposed to the new-generation of space-borne instruments (e.g. TROPOMI on board Sentinel- 5 Precursor), enabling a fast reprocessing of tropospheric NO2 data over cloud-free scenes (cloudy pixels need to be filtered out), as well as for other trace gas retrievals (e.g. SO2, HCHO).Atmospheric Remote Sensin
Spatial distribution analysis of the OMI aerosol layer height: a pixel-by-pixel comparison to CALIOP observations
No full textAbstract. A global picture of atmospheric aerosol vertical distribution with a high temporal resolution is of key importance not only for
climate, cloud formation, and air quality research studies but also for correcting scattered radiation induced by aerosols in
absorbing trace gas retrievals from passive satellite sensors. Aerosol layer height (ALH) was retrieved from the OMI 477 nm
O2−O2 band and its spatial pattern evaluated over selected cloud-free scenes. Such retrievals benefit from a synergy with
MODIS data to provide complementary information on aerosols and cloudy pixels. We used a neural network approach previously trained
and developed. Comparison with CALIOP aerosol level 2 products over urban and industrial pollution in eastern China shows consistent
spatial patterns with an uncertainty in the range of 462–648 m. In addition, we show the possibility to determine the height
of thick aerosol layers released by intensive biomass burning events in South America and Russia from OMI visible
measurements. A Saharan dust outbreak over sea is finally discussed. Complementary detailed analyses show that the assumed aerosol
properties in the forward modelling are the key factors affecting the accuracy of the results, together with potential cloud
residuals in the observation pixels. Furthermore, we demonstrate that the physical meaning of the retrieved ALH scalar corresponds to
the weighted average of the vertical aerosol extinction profile. These encouraging findings strongly suggest the potential of the OMI
ALH product, and in more general the use of the 477 nm O2−O2 band from present and future similar satellite
sensors, for climate studies as well as for future aerosol correction in air quality trace gas retrievals.
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Spatial distribution analysis of the OMI aerosol layer height: a pixel-by-pixel comparison to CALIOP observations
No full textAbstract. A global picture of atmospheric aerosol vertical distribution with a high temporal resolution is of key importance not only for climate, cloud formation and air quality research studies, but also for correcting aerosol radiation effect in absorbing trace gas retrievals from passive satellite sensors. Aerosol layer height (ALH) was retrieved from the OMI 477 nm O2−O2 band and its spatial pattern evaluated over selected cloud-free scenes. Such retrievals benefit from a synergy with MODIS data to provide complementary information on aerosols and cloudy pixels. We used a neural network approach previously trained and developed. Comparison with CALIOP aerosol level 2 products over urban and industrial pollution in east China shows consistent spatial patterns with an uncertainty in the range of 462–648 m. In addition, we show the possibility to determine the height of thick aerosol layers released by intensive biomass burning events in South-America and Russia, and of a Saharan dust outbreak over sea from OMI visible measurements. Complementary detailed analyses show that the assumed aerosol properties in the modeling are the key factors affecting the accuracy of the results, together with potential cloud residuals in the observation pixels. Furthermore, we demonstrate that the physical meaning of the retrieved ALH scalar corresponds to the weighted average of the vertical aerosol extinction profile. These encouraging findings strongly suggest the potential of the OMI ALH product, and in more general the use of the 477 nm O2−O2 band from present and future similar satellite sensors, for climate studies as well as for future aerosol correction in air quality trace gas retrievals.
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XUV-LASER SPECTROSCOPY ON THE C'4 SIGMA-U+, UPSILON=0 AND C3 1-PI-U, UPSILON=0 RYDBERG STATES OF N2
No full textThe c
XUV-LASER SPECTROSCOPY ON CO - ISOTOPE-SELECTIVE PREDISSOCIATION RATES
No full textThe K (4p-sigma) (1)SIGMA+, upsilon = 0 and W (3s-sigma) 1II, upsilon = 2 states in (CO)-C-12-O-16 and (CO)-C-13-O-16 have been studied in high resolution with extreme ultraviolet laser radiation in the wavelength range 94 - 97 nm. Accurate spectroscopic constants for both isotopes and states have been derived from absolute rotational line positions. From linewidths of individual rotational transitions predissociation rates for (CO)-C-12-O-16 and (CO)-C-13-O-16 in the W 1II upsilon = 2 state have been deduced: k(p) (CO)-C-12 = 1.15 (15) x 10(11) s-1 and k(p) (CO)-C-13 = 0.58 (13) x 10(11) s-1. The rate of photodissociation of K (1)SIGMA+, upsilon = 0 was found to be smaller: k(p) = 2.6 (1.3) x 10(10) s-1 for both isotopes
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