J. P. Burrows

SCIAMACHY: Mission Objectives and Measurement Modes

Abstract SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) is a spectrometer designed to measure sunlight transmitted, reflected, and scattered by the earth’s atmosphere or surface in the ultraviolet, visible, and near-infrared wavelength region (240–2380 nm) at moderate spectral resolution (0.2–1.5 nm, λ/Δλ ≈ 1000–10 000). SCIAMACHY will measure the earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere observed in occultation. The extraterrestrial solar irradiance and lunar radiance will be determined from observations of the sun and the moon above the atmosphere. The absorption, reflection, and scattering behavior of the atmosphere and the earth’s surface is determined from comparison of earthshine radiance and solar irradiance. Inversion of the ratio of earthshine radiance and solar irradiance yields information about the amounts and distribution of important atmospheric constituents and the spectral reflecta...

The Global Ozone Monitoring Experiment (GOME): Mission Concept and First Scientific Results

The Global Ozone Monitoring Experiment (GOME) is a new instrument aboard the European Space Agencys (ESA) Second European Remote Sensing Satellite(ERS-2), which was launched in April 1995. The main scientific objective of the GOME mission is to determine the global distribution of ozone and several other trace gases, which play an important role in the ozone chemistry of the earths stratosphere and troposphere. GOME measures the sunlight scattered from the earths atmosphere and/or reflected by the surface in nadir viewing mode in the spectral region 240-790 nm at a moderate spectral resolution of between 0.2 and 0.4 nm. Using the maximum 960-km across-track swath width, the spatial resolution of a GOME ground pixel is 40 3 320 km2 for the majority of the orbit and global coverage is achieved in three days after 43 orbits. Operational data products of GOME as generated by DLR-DFD, the German Data Processing and Archiving Facility (D-PAF) for GOME, comprise absolute radiometrically calibrated earthshine radiance and solar irradiance spectra (level 1 products) and global distributions of total column amounts of ozone and NO 2 (level 2 products), which are derived using the DOAS approach (Differential Optical Absorption Spectroscopy). (Under certain conditions and some restrictions, the operational data products are publically available from the European Space Agency via the ERS Helpdesk.) In addition to the operational data products, GOME has delivered important information about other minor trace gases such as OClO, volcanic SO2 ,H 2CO from biomass burning, and tropospheric BrO. Using an iterative optimal estimation retrieval scheme, ozone vertical profiles can be derived from the inversion of the UV/VIS spectra. This paper reports on the GOME instrument, its operation mode, and the retrieval techniques, the latter with particular emphasis on DOAS (total column retrieval) and advanced optimal estimation (ozone profile retrieval). Observation of ozone depletion in the recent polar spring seasons in both hemispheres are presented. OClO observed by GOME under twilight conditions provides valuable information on the chlorine activation inside the polar vortex, which is believed to be responsible for the rapid catalytic destruction of ozone. Episodes of enhanced BrO in the Arctic, most likely contained in the marine boundary layer, were observed in early and late spring. Excess tropospheric nitrogen dioxide and ozone have been observed during the recent Indonesian fire in fall 1997. Formaldehyde could also clearly be identified by GOME and is known to be a by-product resulting from biomass burning.

Increase in tropospheric nitrogen dioxide over China observed from space.

Emissions from fossil fuel combustion and biomass burning reduce local air quality and affect global tropospheric chemistry. Nitrogen oxides are emitted by all combustion processes and play a key part in the photochemically induced catalytic production of ozone, which results in summer smog and has increased levels of tropospheric ozone globally. Release of nitrogen oxide also results in nitric acid deposition, and—at least locally—increases radiative forcing effects due to the absorption of downward propagating visible light. Nitrogen oxide concentrations in many industrialized countries are expected to decrease, but rapid economic development has the potential to increase significantly the emissions of nitrogen oxides in parts of Asia. Here we present the tropospheric column amounts of nitrogen dioxide retrieved from two satellite instruments GOME and SCIAMACHY over the years 1996–2004. We find substantial reductions in nitrogen dioxide concentrations over some areas of Europe and the USA, but a highly significant increase of about 50 per cent—with an accelerating trend in annual growth rate—over the industrial areas of China, more than recent bottom-up inventories suggest.

The Nitrate Radical: Physics, Chemistry and the Atmosphere

Abstract This review surveys the present state of knowledge of the nitrate (NO 3 radical. Laboratory data on the physics and chemistry of the radical and atmospheric determination of the concentrations of the radical are both considered. One aim of the review is to highlight the relationship between the laboratory and the atmospheric studies. Although the emphasis of the review is on gas-phase processes, relevant studies conducted in condensed phases are mentioned because of their potential importance in the interpretation of cloud and aerosol chemistry. The spectroscopy, structure, and photochemistry of the radical are examined. Here, the object is to establich the spectroscopic basis for detection of the radical and measurement of its concentration in the laboratory and in the atmosphere. Infrared, visible, and paramagnetic resonance spectra are considered. An important quantity discussed is the absorption cross section in the visible region, which is required for quantitative measurements. Interpretation of the spectroscopic features requires an understanding of the geometrical and electronic structure of the radical in its ground and excited states; there is still some controversy about the groundstate geometry, but the most recent experimental evidence 9eg from laser induced fluorescence) and theoretical calculations suggest that the radical has D 3h symmetry. Photodissociation of the radical is important in the atmosphere, and the product channels, quantum yields, and dissociation dynamics are discussed. A short examination of the thermodynamics (heat and entropy of formation) of the radical is presented. The main exposition of laboratory studies of the chemistry of the nitrate radical is preceded by a consideration of the techniques used for kinetic and mechanistic studies. Methods for the generation and detection of the radical and the kinetic tools employed are all presented. The exact nature of the technique used in individual studies has some relevance to the way in which data must be analysed, and to the type of mechanistic information that can be extracted. Continuous and stopped flow, flash photolysis and pulse radiolysis, molecular modulation, and static reactor techniques can all provide absolute kinetic data, while relative rate measurements have been a further rich source of information. The treatment of the chemical reactions of the nitrate radical is formally divided into the interactions with non-radical inorganic (deemed to include NO and NO 2 ) and organic species, and with atoms and free radicals. In general, the reactions with open-shell species are much more rapid than those with closed-shell reactants. With the closed-shell partners, addition reactions are faster than abstraction reactions. An attempt is made to consider critically the published data on most reactions of importance, and to tabulate rate constants and temperature dependences where possible. However, it is not the objective of this review to provide recommendations for rate parameters. Evidence for the products of the reactions is sought, and for the branching ratios into the various channels where more than one exists. One theme of this part of the review is the elucidation of correlations of reactivity with structure and with the reactions of other radical species such as OH. The review turns next to a consideration of the role of NO 3 in the atmosphere, of its atmospheric sources and sinks, and of field measurements of concentrations of the radical. Long-path visible-absorption spectroscopy and matrix-isolation ESR have both been used successfully in field measurements in the troposphere as well as the stratosphere. Balloon-borne instruments and ground-based remote sensing have been used to obtain stratospheric concentrations. Two of the most important implications of the measurements are that the stratospheric profiles are consistent with accepted chemistry (and, in particular, do not require the postulation of an unidentified scavenging mechanism that had, at one stage, been proposed), and that the highly variable night-time tropospheric concentrations imply that NO 3 is a reactive tropospheric constituent. The inter-relation between laboratory studies and atmospheric observations, and the problems in extrapolating laboratory data to atmospheric conditions, are both explored. Initiation of night-time chemical transformations by NO 3 and the possible production of OH are considered. The available information is then brought together to see how far NO 3 is a sensitive indicator of the state of the atmosphere, and some speculations are presented about the involvement of NO 3 (or N 2 O 5 ) in damage to trees and plants. The final section of the review suggests some issues that remain unresolved concerning the NO 3 radical which is directly or indirectly relevant to a better knowledge of the part played by the radical in the atmosphere. Amongst the requirements noted are improved data for the heat of formation of the radical, its absorption cross section in the visible region (and, especially, the temperature dependence of the cross section), and the details of its photochemistry. There is also still a need for a definitive determination of the equilibrium constant and its temperature dependence for the association with NO 2 and the reverse dissociation of N 2 O 5 . A series of chemical reactions deserves further investigation, especially with regard to elucidation of product channels, and overall oxidation mechanisms also need to be defined better. Future atmospheric studies that are desirable include study of basic NO 3 chemistry in the field to understand the influence of humidity on the conversion (probably on surfaces) of N 2 O 5 to HNO 3 , and thus on NO 3 concentrations. In addition, a study of the chemistry of NO 3 in the presence of volatile organic compounds and at elevated concentrations of the oxides of nitrogen should help in the understanding of, for example, polluted marine coasts, forests, and urban areas.

SCIAMACHY—scanning imaging absorption spectrometer for atmospheric chartography

Abstract SCIAMACHY will perform global measurements of atmospheric trace gases in order to retrieve their global total column amounts as well as their stratospheric and tropospheric profiles. Aerosol abundances will be derived from observations of wavelength-dependent light scattering characteristics. Furthermore, the instrument will yield physical parameters of clouds, stratospheric temperature and pressure profiles; the latter being derived from Sun occultation measurements. SCIAMACHY observes the backscattered radiance over the wavelength range 240–2380 nm. Differential optical absorption spectrometry (DOAS) and back scattered u.v. (BUY) retrieval techniques are selected for the inversion of radiance. Ground scenes are scanned by a two-mirror scanning mechanism of high positioning accuracy. The instrument electronics, including subsystem controller and data electronics, mechanisms and thermal control electronics, allow SCIAMACHY to be operated autonomously. The instrument will be flown on the polar platform of the first European Polar Orbit Earth Observation Mission (POEM-1), now known as ENVISAT. It has been developed by the following industrial team: Dornier (prime-contractor, thermal control, instrument control); OHB (data electronics); SRON (detector modules and analogue electronics); TPD (optical unit).

Tropospheric NO2 from GOME measurements

Measurements from the Global Ozone Monitoring Experiment (GOMB) have been analysed for tropospheric NO, using the Differential Optical Absorption method. The retrieval technique is described and a detailed error analysis is given. A case study of tropospheric NO, above Africa in fall 1997 is presented, showing the influence of both biomass burning and lightning. Comparison of clear and cloudy pixels reveals, that substantial amounts of NO, am present in the free troposphere over the African continent and in the outflow regions over the Southern Atlantic and the Indian Ocean. This has important implications for the formation of the tropospheric ozone maxima observed in these areas.

GOME observations of tropospheric BrO in northern hemispheric spring and summer 1997

Measurements from the Global Ozone Monitoring Experiment GOME have been analysed for tropospheric BrO in the northern hemispheric spring and summer 1997. Tropospheric excess columns have been determined by subtracting measurements from a longitude range which is assumed to represent background conditions. From February until the end of May enhanced tropospheric BrO columns are observed over the Hudson Bay area and parts of the Canadian Arctic. This large and persistent event has not been reported before and can only be explained by a large local source of bromine. In addition, from March to May other smaller and shorter tropospheric BrO events are detectable along the coast lines of the Arctic Sea and over the polar ice. They correspond to the ground-based observations of enhanced tropospheric BrO reported from several stations in the high Arctic.

Simultaneous global observations of glyoxal and formaldehyde from space

[1] The first global simultaneous observations of glyoxal (CHOCHO) and formaldehyde (HCHO) columns retrieved from measurements by the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) satellite instrument are presented and compared to model calculations. The global pattern of the distribution of CHOCHO is similar to that of HCHO. High values are observed over areas with large biogenic isoprene emissions (Central Africa, parts of South America, and Indonesia). Also regions with biomass burning and anthropogenic pollution exhibit elevated levels of CHOCHO. The ratio of the columns of CHOCHO to HCHO is generally of the order of 0.05 in regions having biogenic emissions, which is in reasonable agreement with the current understanding of the oxidation of hydrocarbons emitted by the biosphere. However and in contrast to our model, high values of both HCHO and CHOCHO are also observed over areas of the tropical oceans. This is tentatively attributed to outflow from the continents and local oceanic biogenic sources of the precursors of HCHO and CHOCHO. Citation: Wittrock, F., A. Richter, H. Oetjen, J. P. Burrows, M. Kanakidou, S. Myriokefalitakis, R. Volkamer, S. Beirle, U. Platt, and T. Wagner (2006), Simultaneous global observations of glyoxal and formaldehyde from space, Geophys. Res. Lett., 33, L16804, doi:10.1029/2006GL026310.

Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry

[1] Frost flowers grow on newly-formed sea ice from a saturated water vapour layer. They provide a large effective surface area and a reservoir of sea salt ions in the liquid phase with triple the ion concentration of sea water. Recently, frost flowers have been recognised as the dominant source of sea salt aerosol in the Antarctic, and it has been speculated that they could be involved in processes causing severe tropospheric ozone depletion events during the polar sunrise. These events can be explained by heterogeneous autocatalytic reactions taking place on salt-laden ice surfaces which exponentially increase the reactive gas phase bromine (‘‘bromine explosion’’). We analyzed tropospheric bromine monoxide (BrO) and the sea ice coverage both measured from satellite sensors. Our model based interpretation shows that young ice regions potentially covered with frost flowers seem to be the source of bromine found in bromine explosion events. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 1640 Global Change: Remote sensing; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 3360 Meteorology and Atmospheric Dynamics: Remote sensing. Citation: Kaleschke, L., et al. (2004), Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry, Geophys. Res. Lett., 31, L16114, doi:10.1029/ 2004GL020655.

Absorption cross-sections of NO2 in the UV and visible region (200 – 700 nm) at 298 K

Abstract The absorption cross-sections of NO 2 have been measured in the wavelength range 200 – 700 nm at 298 K with a spectral resolution of 0.04 nm. The data were acquired digitally, allowing post-processing such as integration in different wavelength intervals. The cross-sections are averaged over 1 nm intervals and over the atmospheric wavelength intervals used in solar photolysis calculations.