Spaceborne detection of localized carbon dioxide sources Schwandner, Florian M.; Gunson, Michael R.; Miller, Charles E. ...
Science (American Association for the Advancement of Science),
10/2017, Volume:
358, Issue:
6360
Journal Article
Peer reviewed
Spaceborne measurements by NASA's Orbiting Carbon Observatory-2 (OCO-2) at the kilometer scale reveal distinct structures of atmospheric carbon dioxide (CO
) caused by known anthropogenic and natural ...point sources. OCO-2 transects across the Los Angeles megacity (USA) show that anthropogenic CO
enhancements peak over the urban core and decrease through suburban areas to rural background values more than ~100 kilometers away, varying seasonally from ~4.4 to 6.1 parts per million. A transect passing directly downwind of the persistent isolated natural CO
plume from Yasur volcano (Vanuatu) shows a narrow filament of enhanced CO
values (~3.4 parts per million), consistent with a CO
point source emitting 41.6 kilotons per day. These examples highlight the potential of the OCO-2 sensor, with its unprecedented resolution and sensitivity, to detect localized natural and anthropogenic CO
sources.
Interest in stratospheric aerosol and its role in climate have increased over the last decade due to the observed increase in stratospheric aerosol since 2000 and the potential for changes in the ...sulfur cycle induced by climate change. This review provides an overview about the advances in stratospheric aerosol research since the last comprehensive assessment of stratospheric aerosol was published in 2006. A crucial development since 2006 is the substantial improvement in the agreement between in situ and space-based inferences of stratospheric aerosol properties during volcanically quiescent periods. Furthermore, new measurement systems and techniques, both in situ and space based, have been developed for measuring physical aerosol properties with greater accuracy and for characterizing aerosol composition. However, these changes induce challenges to constructing a long-term stratospheric aerosol climatology. Currently, changes in stratospheric aerosol levels less than 20% cannot be confidently quantified. The volcanic signals tend to mask any nonvolcanically driven change, making them difficult to understand. While the role of carbonyl sulfide as a substantial and relatively constant source of stratospheric sulfur has been confirmed by new observations and model simulations, large uncertainties remain with respect to the contribution from anthropogenic sulfur dioxide emissions. New evidence has been provided that stratospheric aerosol can also contain small amounts of nonsulfatematter such as black carbon and organics. Chemistry-climate models have substantially increased in quantity and sophistication. In many models the implementation of stratospheric aerosol processes is coupled to radiation and/or stratospheric chemistry modules to account for relevant feedback processes.
Severe smog episodes over China in January 2013 received worldwide attention. This air pollution was distinguished by heavy loadings of fine particulate matter and SO2. To characterize these ...episodes, we employed the Ozone Mapping and Profiler Suite, Nadir Mapper (OMPS NM), an ultraviolet (UV) spectrometer flying on the Suomi National Polar‐orbiting Partnership (SNPP) spacecraft since October 2011. We developed an advanced algorithm to quantify SO2 in the lower troposphere and achieved high‐quality retrievals from OMPS NM, which are characterized by high precision, ∼0.2 Dobson Units (DU; 1 DU = 2.69×1016molecules/cm2) for instantaneous field of view SO2 data and low biases (within ±0.2 DU). Here we report SO2retrievals and UV aerosol index data for these pollution events. The SO2 columns and the areas covered by high pollutant concentrations are quantified; the results reveal for the first time the full extent (an area of ∼106km2 containing up to 60 kt of SO2) of these episodes.
Key Points
Reveal for the first time the full extent of synoptic scale pollution episodesDemonstrate monitoring global atmospheric environments with SNPP/OMPSHighlight that coal combustion contributes to air pollution today in China
Satellite measurements of volcanic sulfur dioxide (SO₂) emissions can provide critical information for aviation hazard mitigation, particularly when ash detection techniques fail. Recent developments ...in space-based SO₂ monitoring are discussed, focusing on daily, global ultraviolet (UV) measurements by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. OMI's high sensitivity to SO₂ permits long-range tracking of volcanic clouds in the upper troposphere and lower stratosphere (UTLS) and accurate mapping of their perimeters to facilitate avoidance. Examples from 2006 to 2007 include eruptions of Soufriere Hills (Montserrat), Rabaul (Papua New Guinea), Nyamuragira (DR Congo), and Jebel at Tair (Yemen). A tendency for some volcanic clouds to occupy the jet stream suggests an increased threat to aircraft that exploit this phenomenon. Synergy between NASA A-Train sensors such as OMI and the Atmospheric Infrared Sounder (AIRS) on the Aqua satellite can provide critical information on volcanic cloud altitude. OMI and AIRS SO₂ data products are being produced in near real-time for distribution to Volcanic Ash Advisory Centers (VAACs) via a NOAA website. Operational issues arising from these improved SO₂ measurements include the reliability of SO₂ as proxy for co-erupted ash, the duration of VAAC advisories for long-lived volcanic clouds, and the potential effects of elevated concentrations of SO₂ and sulfate aerosol in ash-poor clouds on aircraft and avionics (including cumulative effects after multiple inadvertent transits through dilute clouds). Further research is required in these areas. Aviation community assistance is sought through continued reporting of sulfurous odors or other indications of diffuse volcanic cloud encounters, in order to validate the satellite retrievals.
The Dutch-Finnish Ozone Monitoring Instrument (OMI) launched on the NASA Aura satellite in July 2004 offers unprecedented spatial resolution, coupled with contiguous daily global coverage, for ...space-based UV measurements of sulfur dioxide (SO2). We present a first validation of the OMI SO2 data with in situ aircraft measurements in NE China in April 2005. The study demonstrates that OMI can distinguish between background SO2 conditions and heavy pollution on a daily basis. The noise (expressed as the standard deviation,sigma) is approximately 1.5 DU (Dobson units; 1 DU = 2.69 10 (exp 16) molecules/cm (exp 2)) for instantaneous field of view boundary layer (PBL) SO2 data. Temporal and spatial averaging can reduce the noise to sigma approximetly 0.3 DU over a remote region of the South Pacific; the long-term average over this remote location was within 0.1 DU of zero. Under polluted conditions collection 2 OMI data are higher than aircraft measurements by a factor of two. Improved calibrations of the radiance and irradiance data (collection 3) result in better agreement with aircraft measurements on polluted days. The air mass corrected collection 3 data still show positive bias and sensitivity to UV absorbing aerosols. The difference between the in situ data and the OMI SO2 measurements within 30 km of the aircraft profiles was about 1 DU, equivalent to approximately 5 ppb from 0 to 3000 m altitude. Quantifying the SO2 and aerosol profiles and spectral dependence of aerosol absorption between 310 and 330 nm are critical for an accurate estimate of SO2 from satellite UV measurements.
We present a new algorithm based on the iterative spectral fitting technique for direct retrieval of nitrogen dioxide (NO2) vertical columns from hyperspectral satellite measurements, and a new ...spatial technique for separating the stratospheric and tropospheric contributions to the total NO2 vertical columns. This direct vertical column fitting (DVCF) algorithm allows more complete treatment of underlying algorithm physics compared to the differential optical absorption spectroscopy technique and enables more accurate accounting for the effects of spectral and altitude variations in NO2 measurement sensitivities. This DVCF algorithm and the stratosphere‐troposphere separation scheme are applied to ultraviolet measurements from the Nadir Mapper of the Ozone Mapping and Profiler Suite (OMPS) on the Suomi National Polar‐orbiting Partnership spacecraft. The first results demonstrate the potential of OMPS for sensitive global monitoring of tropospheric NO2. Comparisons show good agreement with Aura Ozone Monitoring Instrument (OMI) tropospheric NO2 data and that OMPS data have sufficient quality to continue and extend OMI NO2 data records.
Key Points
First one‐step vertical NO2 column retrieval from a new direct fitting algorithm
A new spatial technique for reliable stratosphere‐troposphere NO2 separation
Demonstration of sensitive global tropospheric NO2 measurements from SNPP OMPS
We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it ...has been possible to reconstruct the nature and evolution of the eruption through analysis of regional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodigious quantity of SO
2
emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic significance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shallow, NW–SE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response mitigated the human costs of the eruption.
To improve global measurements of atmospheric sulfur dioxide (SO2), we have developed a new technique, called the linear fit (LF) algorithm, which uses the radiance measurements from the Ozone ...Monitoring Instrument (OMI) at a few discrete ultraviolet wavelengths to derive SO2, ozone, and effective reflectivity simultaneously. We have also developed a sliding median residual correction method for removing both the along‐ and cross‐track biases from the retrieval results. The achieved internal consistencies among the LF‐retrieved geophysical parameters clearly demonstrate the success of this technique. Comparison with the results from the Band Residual Difference technique has also illustrated the drastic improvements of this new technique at high SO2 loading conditions. We have constructed an error equation and derived the averaging kernel to characterize the LF retrieval and understand its limitations. Detailed error analysis has focused on the impacts of the SO2 column amounts and their vertical distributions on the retrieval results. The LF algorithm is robust and fast; therefore it is suitable for near real‐time application in aviation hazards and volcanic eruption warnings. Very large SO2 loadings (>100 DU) require an off‐line iterative solution of the LF equations to reduce the retrieval errors. Both the LF and sliding median techniques are very general so that they can be applied to measurements from other backscattered ultraviolet instruments, including the series of Total Ozone Mapping Spectrometer (TOMS) missions, thereby offering the capability to update the TOMS long‐term record to maintain consistency with its OMI extension.
Clouds play an important role in the oxidation of sulfur dioxide to sulfate, since aqueous phase sulfur dioxide oxidation is typically much faster than oxidation in the gas phase. Important aqueous ...phase oxidants include hydrogen peroxide, ozone and oxygen (catalyzed by trace metals). Because quantities of emitted sulfur dioxide in China are so large, however, it is possible that they exceed the capacity of regional clouds for sulfate production, leading to enhanced long-range transport of emitted SO2 and its oxidation product, sulfate. In order to assess the ability of regional clouds to support aqueous sulfur oxidation, four field campaigns were conducted in 2007 and 2008 at Mt. Tai in eastern China. Single and 2-stage Caltech Active Strand Cloudwater Collectors were used to collect bulk and drop size-resolved cloudwater samples, respectively. Key species that determine aqueous phase sulfur oxidation were analyzed, including cloudwater pH, S(IV), H2O2, Fe, and Mn. Gas phase SO2, O3, and H2O2 were also measured continuously during the campaigns. A wide range of cloud pH values was observed, from 2.6 to 7.6; 60% of cloud samples had a pH between 3 and 5. H2O2 was found to be an important sulfur oxidant, especially at cloudwater pH lower than 5. H2O2 was the most important oxidant in 68% of the cloud sampling periods. High concentrations of residual H2O2 were observed in many periods, especially in summer, implying a substantial capacity for additional sulfur oxidation. O3 was an important oxidant when cloudwater pH was higher than approximately 5–5.3, and was the most important oxidant in 20% of the studied periods. Aqueous sulfur oxidation by O2 (catalyzed by Fe and Mn) was found to be the fastest sulfate production pathway in 12% of the cases. Observed chemical heterogeneity among cloud drop populations was found to enhance rates of S(IV) oxidation by ozone and enhance or slow metal-catalyzed S(IV) autooxidation rates in some periods. These effects were found to be only of minor importance for the total S(IV) oxidation rate, however, as H2O2 was the dominant S(IV) oxidant during most periods.
► Aqueous phase sulfur chemistry is examined in clouds in east China. ► Spring and summer clouds were sampled and analyzed in 2007 and 2008. ► H2O2 was the dominant S(IV) oxidant. ► Ozone and oxygen (catalyzed by trace metals) were important oxidants in high pH clouds. ► Many summer clouds contained residual H2O2 suggesting additional capacity for aqueous sulfur oxidation.
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