Validation of the TROPOspheric Monitoring Instrument (TROPOMI) surface UV radiation product

The TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P) satellite was launched on 13 October 2017 to provide the atmospheric composition for atmosphere and climate research. The S5P is a Sun-synchronous polar-orbiting satellite providing global daily coverage. The TROPOMI swath is 2600 km wide, and the ground resolution for most data products is 7:23:5 km2 (5:63:5 km2 since 6 August 2019) at nadir. The Finnish Meteorological Institute (FMI) is responsible for the development of the TROPOMI UV algorithm and the processing of the TROPOMI surface ultraviolet (UV) radiation product which includes 36 UV parameters in total. Ground-based data from 25 sites located in arctic, subarctic, temperate, equatorial and Antarctic areas were used for validation of the TROPOMI overpass irradiance at 305, 310, 324 and 380 nm, overpass erythemally weighted dose rate/UV index, and erythemally weighted daily dose for the period from 1 January 2018 to 31 August 2019. The validation results showed that for most sites 60 % 80% of TROPOMI data was within 20% of ground-based data for snow-free surface conditions. The median relative differences to ground-based measurements of TROPOMI snow-free surface daily doses were within 10% and 5% at two-Thirds and at half of the sites, respectively. At several sites more than 90% of cloud-free TROPOMI data was within 20% of groundbased measurements. Generally median relative differences between TROPOMI data and ground-based measurements were a little biased towards negative values (i.e. satellite data ground-based measurement), but at high latitudes where non-homogeneous topography and albedo or snow conditions occurred, the negative bias was exceptionally high: from 30% to 65 %. Positive biases of 10 % 15% were also found for mountainous sites due to challenging topography. The TROPOMI surface UV radiation product includes quality flags to detect increased uncertainties in the data due to heterogeneous surface albedo and rough terrain, which can be used to filter the data retrieved under challenging conditions

Pinning down electron correlations in RaF via spectroscopy of excited states

We report the spectroscopy of 11 electronic states in the radioactive molecule radium monofluoride (RaF). The observed excitation energies are compared with state-of-the-art relativistic Fock-space coupled cluster (FS-RCC) calculations, which achieve an agreement of >99.71% (within ~8 meV) for all states. High-order electron correlation and quantum electrodynamics corrections are found to be important at all energies. Establishing the accuracy of calculations is an important step towards high-precision studies of these molecules, which are proposed for sensitive searches of physics beyond the Standard Model.Comment: Submitted for publicatio

Models for molecular motions within polymer chains. Part 1. A solid-state NMR study of hexane-1,6-diyl bis(p-nitrobenzoate)

Solid-state NMR experiments on hexane-1,6-diyl bis(p-nitrobenzoate) and its 1,1,6,6- and 2,2,5,5-deuteriated derivatives present a coherent view of the molecular dynamics of the central alkyl chain. The techniques used include C-13 CP/MAS spectra, H-2 quadrupole echo spectra, associated with measurements of C-13 T-1 rho relaxation times, H-2 and C-13 T-1 relaxation times and quadrupole echo reduction factors. Molecular dynamics in the central chain are dominated by librational motions at the CH2 groups that can best be approximated by a six-site conical model. The activation energies for these librations are ca. 35 kJ mol(-1). gauche-trans flips in the chain can be ruled out as the origin of the effects observed.</p

Structure and dynamics of methyl groups in the deuterated microporous organic-inorganic hybrid, aluminium methylphosphonate-b

Neutron powder diffraction at 4.6 K and H-2 NMR spectroscopy over the range 100-400 K have been used to examine the structure and rotational dynamics of CD3 groups pointing into the unidimensional channels of the beta-polymorph of the hybrid organic/inorganic microporous solid aluminium methylphosphonate, Al-2(CD3PO3)(3), The methyl groups rotate rapidly at all temperatures studied in the NMR experiments, with a correlation time in the fast limit of similar to 2 x 10(-13) s and with an activation energy of similar to 10 kT mol(-1). Extrapolation to 4.6 K indicates that the groups will be stationary and this is confirmed by the neutron diffraction experiment, where the lowest-energy configurations of the methylphosphonate groups are all found to have the methyl deuterons staggered with respect to the phosphonate oxygens. (C) 1999 Elsevier Science B.V. All rights reserved.</p

Structure and dynamics of methyl groups in the deuterated microporous organic-inorganic hybrid, aluminium methylphosphonate-b

Neutron powder diffraction at 4.6 K and H-2 NMR spectroscopy over the range 100-400 K have been used to examine the structure and rotational dynamics of CD3 groups pointing into the unidimensional channels of the beta-polymorph of the hybrid organic/inorganic microporous solid aluminium methylphosphonate, Al-2(CD3PO3)(3), The methyl groups rotate rapidly at all temperatures studied in the NMR experiments, with a correlation time in the fast limit of similar to 2 x 10(-13) s and with an activation energy of similar to 10 kT mol(-1). Extrapolation to 4.6 K indicates that the groups will be stationary and this is confirmed by the neutron diffraction experiment, where the lowest-energy configurations of the methylphosphonate groups are all found to have the methyl deuterons staggered with respect to the phosphonate oxygens. (C) 1999 Elsevier Science B.V. All rights reserved.</p

A new approach to correct for absorbing aerosols in OMI UV

Several validation studies of surface UV irradiance based on the Ozone Monitoring Instrument (OMI) satellite data have shown a high correlation with ground-based measurements but a positive bias in many locations. The main part of the bias can be attributed to the boundary layer aerosol absorption that is not accounted for in the current satellite UV algorithms. To correct for this shortfall, a post-correction procedure was applied, based on global climatological fields of aerosol absorption optical depth. These fields were obtained by using global aerosol optical depth and aerosol single scattering albedo data assembled by combining global aerosol model data and ground-based aerosol measurements from AERONET. The resulting improvements in the satellite-based surface UV irradiance were evaluated by comparing satellite and ground-based spectral irradiances at various European UV monitoring sites. The results generally showed a significantly reduced bias by 5-20%, a lower variability, and an unchanged, high correlation coefficient. Citation: Arola, A., et al. (2009), A new approach to correct for absorbing aerosols in OMI UV, Geophys. Res. Lett., 36, L22805, doi:10.1029/2009GL041137