Suchergebnisse

A hydroxypolyamide (HPA) manufactured from 2,2-bis(3-amino-4-hydroxy phenyl)-hexafluoropropane (APAF) diamine and 5-terbutyl-m-terphenyl-4,4-dicarboxylic acid chloride (tBT-pCl), and a copolyimide produced by stochiometric copolymerization of APAF and 4,4-(hexafluoroiso-propylidene) diamine (6FpDA), using the same diacid chloride, were obtained and used as polymeric matrixes in mixed matrix membranes (MMMs) loaded with 20% (w/w) of two porous polymer networks (triptycene-isatin, PPN-1, and triptycene-trifluoroacetophenone, PPN-2). These MMMs, and also the thermally rearranged membranes (TR-MMMs) that underwent a thermal treatment process to convert the o-hydroxypolyamide moieties to polybenzoxazole ones, were characterized, and their gas separation properties evaluated for H, N, O, CH, and CO. Both TR process and the addition of PPN increased permeability with minor decreases in selectivity for all gases tested. Excellent results were obtained, in terms of the permeability versus selectivity compromise, for H/CH and H/N separations with membranes approaching the 2008 Robeson's trade-off line. The best gas separation properties were obtained when PPN-2 was used. Finally, gas permeation was characterized in terms of chain intersegmental distance and fraction of free volume of the membrane along with the kinetic diameters of the permeated gases. The intersegmental distance increased after TR and/or the addition of PPN-2. Permeability followed an exponential dependence with free volume and a quadratic function of the kinetic diameter of the gas. ; This work was supported by the Spanish Government (AEI) through projects PID2019- 109403RB-C21 and PID2019-109403RB-C22 and by the Regional Government of Castilla y León and the EU-FEDER program (CLU2017-09, UIC082, VA088G19, and PhD grant of Cenit Soto). Cenit Soto thanks the University of Valladolid for mobility grant UVa-2019

Formaldehyde (CHO) is a tracer of the photochemical activity of the atmosphere. Linked to air quality, CHO is an ozone (O) precursor and serves as a proxy for natural and anthropogenic reactive organic emissions. As a product of the photooxidation of methane (CH) and other hydrocarbons (e.g., isoprene), CHO represents an important source of radicals in the remote free troposphere. This work aims at improving the characterization of this part of the troposphere where data are scarce. In particular, this study assesses the presence of CHO at two high-altitude remote sites: El Teide (TEI, 3570 m a.s.l., Tenerife, Canary Islands, Spain) and Pic du Midi (PDM, 2877 m a.s.l., French Pyrenees). Through ground-based remote sensing measurements performed during two field campaigns in July (TEI) and September (PDM) 2013, this study presents the vertical distribution of CHO at both locations. Results at PDM show that CHO mixing ratios follow a decreasing vertical profile with a mean maximum of 0.5 ± 0.2 nmol mol (i.e., ppbv) at the instruments' altitude. At TEI, observations indicate an uplifted layer of CHO with a mean maximum of 1.3 ± 0.3 nmol mol at 3.8 km a.s.l. (i.e., 300 m above the instrument's altitude). At both remote sites, the observed CHO levels are higher than expected for background methane oxidation (a threefold increase in the case of TEI). Air mass back trajectory analysis links CHO observations with abundant natural (e.g. forests) and/or anthropogenic isoprene emissions from the region nearby PDM, while the high CHO levels detected at TEI indicate in-plume formation of CHO resulting from its precursors emitted from west-African and Canadian fires. Finally, as a key trace gas for O and HO chemistries, we estimate the upper limit of bromine monoxide (BrO) in the free troposphere at TEI and PDM to be 0.8 and 1.5 pmol mol (i.e., pptv) respectively. ; The TEI campaign was funded through the AMISOC project (Atmospheric MInor Species relevant to the Ozone Chemistry, Spanish National RCD Funding Agency, CGL2011-24891). The PDM campaign was funded by the European Research Council Executive Agency under the European Union's Horizon 2020 Research and innovation program (ERC-2010-STG 258537) to JES. LGM would like to the MINECO support under grant VHODCA (CTM2017–83199P). The authors would like to thank the assistance of the personal working at the Izaña and at the Pic du Midi observatories. The authors acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and READY website (http://www.ready.noaa.gov) used in this publication. Also, we acknowledge the use of the aerosol product (AOD) from AERONET (http://aeronet.gsfc.nasa.gov/.) and the fire counts imagery from LANCE FIRMS operated by NASA's Earth Science Data and Information System (ESDIS) with funding provided by NASA Headquarters. The UV aerosol index visualization used in this work was produced with the Giovanni online data system, developed and maintained by the NASA GES DISC. We also acknowledge the OMI mission scientists and associated NASA personnel for the production of the UV aerosol index data used in this study (Bhartia P. K. 2012, OMTO3d-OMI/Aura TOMS-Like Ozone, Aerosol Index, Cloud Radiance Fraction L3 1 day 1° x 1° V3).

Numerical prediction of aerosol particle properties has become an important activity at many research and operational weather centers. This development is due to growing interest from a diverse set of stakeholders, such as air quality regulatory bodies, aviation and military authorities, solar energy plant managers, climate services providers, and health professionals. Owing to the complexity of atmospheric aerosol processes and their sensitivity to the underlying meteorological conditions, the prediction of aerosol particle concentrations and properties in the numerical weather prediction (NWP) framework faces a number of challenges. The modeling of numerous aerosol-related parameters increases computational expense. Errors in aerosol prediction concern all processes involved in the aerosol life cycle including (a) errors on the source terms (for both anthropogenic and natural emissions), (b) errors directly dependent on the meteorology (e.g., mixing, transport, scavenging by precipitation), and (c) errors related to aerosol chemistry (e.g., nucleation, gas–aerosol partitioning, chemical transformation and growth, hygroscopicity). Finally, there are fundamental uncertainties and significant processing overhead in the diverse observations used for verification and assimilation within these systems. Indeed, a significant component of aerosol forecast development consists in streamlining aerosol-related observations and reducing the most important errors through model development and data assimilation. Aerosol particle observations from satellite- and ground-based platforms have been crucial to guide model development of the recent years and have been made more readily available for model evaluation and assimilation. However, for the sustainability of the aerosol particle prediction activities around the globe, it is crucial that quality aerosol observations continue to be made available from different platforms (space, near surface, and aircraft) and freely shared. This paper reviews current requirements for ...

Numerical prediction of aerosol particle properties has become an important activity at many research and operational weather centres due to growing interest from a diverse set of stakeholders, such as air quality regulatory bodies, aviation and military authorities, solar energy plant managers, providers of climate services, and health professionals. The prediction of aerosol particle 5 properties in Numerical Weather prediction (NWP) models faces a number of challenges owing to the complexity of atmospheric aerosol processes and their sensitivity to the underlying meteorological conditions. Errors in aerosol prediction concern all processes involved in the aerosol life cycle. These include errors on the source terms (for both anthropogenic and natural emissions), errors directly dependent on the meteorology (e.g., mixing, transport, scavenging by precipitation), as well 10 as errors related to aerosol chemistry (e.g., nucleation, gas-aerosol partitioning, chemical transformation and growth, hygroscopicity). The main goal of current research on aerosol forecast consists in prioritizing these errors and trying to reduce the most important ones through model development and data assimilation. Aerosol particle observations from satellite and ground-based platforms have been crucial to guide model development of the recent years, and have been made more readily 15 available for model evaluation and assimilation. However, for the sustainability of the aerosol particle prediction activities around the globe, it is crucial that quality aerosol observations continue to be made available from different platforms (space, near-surface, and aircraft) and freely shared. This white paper reviews current requirements for aerosol observations in the context of the operational activities carried out at various global and regional centres. Some of the requirements are equally applicable to aerosol-climate research. However, the focus here is on the global operational prediction of aerosol properties such as mass concentrations ...