Showing papers by "Ulrich Platt published in 2012"

Retrieval of the optical depth and vertical distribution of particulate scatterers in the atmosphere using O 2 A- and B-band SCIAMACHY observations over Kanpur: a case study

Abstract: . Due to the well-defined vertical profile of O2 in the atmosphere, the strong A-band (757–774 nm) has long been used to estimate vertical distributions of aerosol/cloud from space. We extend this approach to include part of the O2 B-band (684–688 nm) as well. SCIAMACHY onboard ENVISAT is the first instrument to provide spectral data at moderate resolution (0.2–1.5 nm) in the UV/VIS/NIR including both the O2 A- and B-bands. Using SCIAMACHY specifications, we make combined use of these bands in an optimal estimation algorithm. Theoretical studies show that our algorithm is applicable both over bright and dark surfaces for the retrieval of a lognormal approximation of the vertical profile of particulate matter, in addition to its optical thickness. Synthetic studies and information content analyses prove that such a combined use provides additional information on the vertical distribution of atmospheric scatterers, attributable to differences in the absorption strengths of the two bands and their underlying surface albedos. Due to the high computational cost of the retrieval, we restrict application to real data to a case study over Kanpur through the year 2003. Comparison with AERONET data shows a commonly observed seasonal pattern of haziness, manifesting a correlation coefficient of r = 0.92 for non-monsoon monthly mean AOTs. The retrieved particulate optical thickness is found to be anti-correlated with the relative contrast of the Lambertian equivalent reflectivity (LER) at 682 nm and 755 nm by a coefficient of 0.788, confirming the hypothesis made in Sanghavi et al. (2010). Our case study demonstrates a stable physics-based retrieval of particulate matter using only SCIAMACHY data. The feasibility of our approach is enhanced by the information provided by measurements around the O2 B-band in addition to the A-band. Nonetheless, operational application to SCIAMACHY data remains challenged by radiometric uncertainties, yielding simultaneous retrieval of particle microphysical parameters impracticable and leading to over-reliance on climatological data. Addressing these issues in future instruments similar to SCIAMACHY, coupled with computational resources and speed-up of the current line-by-line radiative transfer calculations, can allow our approach to be extended to the global scale, particularly as it is not limited to dark surfaces.

Tropospheric BrO column densities in the Arctic derived from satellite: retrieval and comparison to ground-based measurements

Abstract: . During polar spring, halogen radicals like bromine monoxide (BrO) play an important role in the chemistry of tropospheric ozone destruction. Satellite measurements of the BrO distribution have become a particularly useful tool to investigate this probably natural phenomenon, but the separation of stratospheric and tropospheric partial columns of BrO is challenging. In this study, an algorithm was developed to retrieve tropospheric vertical column densities of BrO from data of high-resolution spectroscopic satellite instruments such as the second Global Ozone Monitoring Experiment (GOME-2). Unlike recently published approaches, the presented algorithm is capable of separating the fraction of BrO in the activated troposphere from the total BrO column solely based on remotely measured properties. The presented algorithm furthermore allows to estimate a realistic measurement error of the tropospheric BrO column. The sensitivity of each satellite pixel to BrO in the boundary layer is quantified using the measured UV radiance and the column density of the oxygen collision complex O4. A comparison of the sensitivities with CALIPSO LIDAR observations demonstrates that clouds shielding near-surface trace-gas columns can be reliably detected even over ice and snow. Retrieved tropospheric BrO columns are then compared to ground-based BrO measurements from two Arctic field campaigns in the Amundsen Gulf and at Barrow in 2008 and 2009, respectively. Our algorithm was found to be capable of retrieving enhanced near-surface BrO during both campaigns in good agreement with ground-based data. Some differences between ground-based and satellite measurements observed at Barrow can be explained by both elevated and shallow surface layers of BrO. The observations strongly suggest that surface release processes are the dominating source of BrO and that boundary layer meteorology influences the vertical distribution.

Halogenation processes of secondary organic aerosol and implications on halogen release mechanisms

Abstract: Reactive halogen species (RHS), such as X·, X2 and HOX containing X = chlorine and/or bromine, are released by various sources like photo-activated sea-salt aerosol or from salt pans, and salt lakes Despite many studies of RHS reactions, the potential of RHS reacting with secondary organic aerosol (SOA) and organic aerosol derived from biomass-burning (BBOA) has been neglected Such reactions can constitute sources of gaseous organohalogen compounds or halogenated organic matter in the tropospheric boundary layer and can influence physicochemical properties of atmospheric aerosols Model SOA from α-pinene, catechol, and guaiacol was used to study heterogeneous interactions with RHS Particles were exposed to molecular chlorine and bromine in an aerosol smog-chamber in the presence of UV/VIS irradiation and to RHS, released from simulated natural halogen sources like salt pans Subsequently, the aerosol was characterized in detail using a variety of physicochemical and spectroscopic methods Fundamental features were correlated with heterogeneous halogenation, which results in new functional groups (FTIR spectroscopy), changes UV/VIS absorption, chemical composition (ultrahigh resolution mass spectroscopy (ICR-FT/MS)), or aerosol size distribution However, the halogen release mechanisms were also found to be affected by the presence of organic aerosol Those interaction processes, changing chemical and physical properties of the aerosol are likely to influence eg the ability of the aerosol to act as cloud condensation nuclei, its potential to adsorb other gases with low-volatility, or its contribution to radiative forcing and ultimately the Earth's radiation balance

Observations of bromine explosions in smog chamber experiments above a model salt pan

Abstract: Reactive halogen species (RHS), such as Cl, Br, or BrO, can have significant influence on chemical processes in the troposphere, including the destruction of ozone, change in the chemical balance of OH and HO2, and increased deposition of toxic compounds (like mercury), with potential consequences for the global climate. Previous studies have shown that salt lakes can provide a significant source for gaseous RHS. Environmental conditions, such as salt composition, relative humidity (RH), pH, and temperature (T), might have a strong influence on reactive bromine levels. In our laboratory experiments, NaCl salt containing 0.33% NaBr by weight was exposed to simulated sunlight in a Teflon smog chamber under various conditions of RH and ozone concentrations. BrO levels were observed by a differential optical absorption spectrometer in combination with a multireflection cell (White cell). The concentrations of OH and Cl radicals were quantified by the radical clock method. We present the first direct observation of BrO from the “bromine explosion” (autocatalytic release of reactive bromine from salt surfaces—key to ozone destruction) in the laboratory above a simulated salt pan. The maximum BrO mixing ratio of 6419 ± 71 ppt at 60% RH was observed to be one order of magnitude higher than at 37% RH and 2% RH. The release of RHS from the salt pan is possibly controlled by the thickness of the quasi-liquid layer, covering the reactive surface of the halide crystals, as the layer thickness strongly depends on RH. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 312–326, 2012

Radiation and Optics in the Atmosphere

Abstract: This chapter describes the fundamentals of radiation transport in general and in the Earthʼs atmosphere. The role of atmospheric aerosol and clouds are discussed and the connections between radiation and climate are described. Finally, natural optical phenomena of the atmosphere are discussed.

Retrieval interval mapping, a tool to optimize the spectral retrieval range in differential optical absorption spectroscopy

Abstract: Introduction Conclusions References

Erneuerbare Energie für Europa

Abstract: Soll Europas Elektrizitatsversorgung von konventioneller auf hundert Prozent erneuerbare Energie umgestellt werden, dann muss diese Energie hauptsachlich aus Sonne und Wind kommen. Damit wachst der schwankende Anteil in der Netzeinspeisung. Ein schrittweiser Umbau des europaischen Netzes und Kraftwerkparks auf hundert Prozent regenerativen Strom bis 2050 hatte deshalb zwei Konsequenzen. Zum einen muss die Uberkapazitat an vorhandener Kraftwerksleistung im Verhaltnis zur im Jahresmittel nachgefragten Leistung im Netz vom heutigen Faktor 1,8 auf 3,4 ansteigen. Zum anderen erfordert das Ausgleichen der Schwankungen “Regelenergie”. Diese muss entweder aus regelbaren konventionellen Kraftwerken oder aus Energiespeichern kommen. Letzte Variante ware voll regenerativ. Sie wurde aber einen Ausbau der Speicherkapazitat von heute 2,5 TWh auf 122 TWh oder 3,8 % des Jahresenergiebedarfs bei zwei Ladezyklen pro Jahr erfordern. Durch das Installieren zusatzlicher Erzeugerleistung kann dieser Speicherbedarf deutlich reduziert werden.