Understanding the molecular geometry at interfaces is not only of importance for optimizing contact properties but also sets the basis in energy alignment in multilayer samples. Here we present a ...method to determine the tilt angle of molecular compounds by a combination of the orbital imaging technique with photoemission matrix element calculations. By simulating different tilt angles of isolated molecules and comparing the resulting photoemission intensity distribution with momentum maps measured on molecular multilayers, one is able to determine the molecules' tilt angles for each separate layer independently from one another.
Analysis of in situ airborne measurements from the CalNex 2010 field experiment (Research at the Nexus of Air Quality and Climate Change) show that ozone in the boundary layer over Southern ...California was increased by downward mixing of air from the free troposphere (FT). The chemical composition, origin, and transport of air upwind and over Los Angeles, California, were studied using measurements of carbon monoxide (CO), ozone, reactive nitrogen species, and meteorological parameters from the National Oceanic and Atmospheric Administration WP‐3D aircraft on 18 research flights in California in May and June 2010. On six flights, multiple vertical profiles from 0.2–3.5 km above ground level were conducted throughout the Los Angeles (LA) basin and over the Pacific Ocean. Gas phase compounds measured in 32 vertical profiles are used to characterize air masses in the FT over the LA basin, with the aim of determining the source of increased ozone observed above the planetary boundary layer (PBL). Four primary air mass influences were observed regularly in the FT between approximately 1 and 3.5 km altitude: upper tropospheric air, long‐range transport of emissions, aged regional emissions, and marine air. The first three air mass types accounted for 89% of the FT observations. Ozone averaged 71 ppbv in air influenced by the upper troposphere, 69 ppbv in air containing emissions transported long distances, and 65 ppbv in air with aged regional emissions. Correlations between ozone and CO, and ozone and nitric acid, demonstrate entrainment of ozone from the FT into the LA PBL. Downward transport of ozone‐rich air from the FT into the PBL contributes to the ozone burden at the surface in this region and makes compliance with air quality standards challenging.
Key Points
Air mass chemical composition over Los Angeles Basin measured from aircraft
Upper tropospheric influence increased ozone in the lower free troposphere
Downward mixing of ozone‐rich air increased ozone in California
•The adsorption behaviour of tetracyanoquinodimethane (TCNQ) on copper and silver surfaces has been studied.•The molecules form an incommensurable superstructure on the Cu(001) surface.•Two distinct ...phases with different packing density are established on the Ag(001).•Coadsorption of Mn leads to the formation of a long-range ordered mixed metal–organic superstructure.•The TCNQ LUMO receives charge transfer from the substrate.
Copper and silver surfaces can be used as model systems to study structure formation and interfacial bonding upon adsorption of organic molecules. We have investigated the geometric and electronic structure of ordered monolayers of TCNQ on Cu(001) and Ag(001) and of TCNQ+Mn on Ag(001) surfaces by LEED and photoelectron momentum microscopy. While TCNQ forms an incommensurable superstructure on Cu(001), two coverage-dependant, commensurable superstructures are established on Ag(001). Subsequent adsorption of Mn on top of TCNQ/Ag(001) results in the formation of a long-range ordered mixed metal–organic superstructure, which is also commensurable with the Ag(001) substrate. The photoelectron spectroscopy (PES) data shows a filling of the TCNQ LUMO by charge transfer from the substrate for all investigated interfaces and the coadsorption of Mn leads to an energy shift of the TCNQ HOMO and LUMO of 230meV with respect to TCNQ/Ag(001). The characteristic angle-dependent intensity pattern of the TCNQ LUMO in PES was utilized to investigate the azimuthal orientation of the molecules in the respective unit cells. The angle-resolved PES data was further analyzed to identify lateral band dispersion effects in the adsorbate layers, but no significant dispersion was observed.
Oxidation of isoprene through reaction with NO3 radicals is a significant sink for isoprene that persists after dark. The main products of the reaction are multifunctional nitrates. These nitrates ...constitute a significant NOx sink in the nocturnal boundary layer and they likely play an important role in formation of secondary organic aerosol. Products of the isoprene+NO3 reaction will, in many locations, be abundant enough to affect nighttime radical chemistry and to persist into daytime where they may represent a source of NOx. Product formation in the isoprene + NO3 reaction was studied in a smog chamber at Purdue University. Isoprene nitrates and other hydrocarbon products were observed using Proton Transfer Reaction-Mass Spectrometry (PTR-MS) and reactive nitrogen products were observed using Thermal Dissociation–Laser Induced Fluorescence (TD-LIF). The organic nitrate yield is found to be 65±12% of which the majority was nitrooxy carbonyls and the combined yield of methacrolein and methyl vinyl ketone (MACR+MVK) is found to be ∼10%. PTR-MS measurements of nitrooxy carbonyls and TD-LIF measurements of total organic nitrates agreed well. The PTR-MS also observed a series of minor oxidation products which were tentatively identified and their yields quantified These other oxidation products are used as additional constraints on the reaction mechanism.
Ethanol made from corn now constitutes approximately 10% of the fuel used in gasoline vehicles in the U.S. The ethanol is produced in over 200 fuel ethanol refineries across the nation. We report ...airborne measurements downwind from Decatur, Illinois, where the third largest fuel ethanol refinery in the U.S. is located. Estimated emissions are compared with the total point source emissions in Decatur according to the 2011 National Emissions Inventory (NEI‐2011), in which the fuel ethanol refinery represents 68.0% of sulfur dioxide (SO2), 50.5% of nitrogen oxides (NOx = NO + NO2), 67.2% of volatile organic compounds (VOCs), and 95.9% of ethanol emissions. Emissions of SO2 and NOx from Decatur agreed with NEI‐2011, but emissions of several VOCs were underestimated by factors of 5 (total VOCs) to 30 (ethanol). By combining the NEI‐2011 with fuel ethanol production numbers from the Renewable Fuels Association, we calculate emission intensities, defined as the emissions per ethanol mass produced. Emission intensities of SO2 and NOx are higher for plants that use coal as an energy source, including the refinery in Decatur. By comparing with fuel‐based emission factors, we find that fuel ethanol refineries have lower NOx, similar VOC, and higher SO2 emissions than from the use of this fuel in vehicles. The VOC emissions from refining could be higher than from vehicles, if the underestimated emissions in NEI‐2011 downwind from Decatur extend to other fuel ethanol refineries. Finally, chemical transformations of the emissions from Decatur were observed, including formation of new particles, nitric acid, peroxyacyl nitrates, aldehydes, ozone, and sulfate aerosol.
Key Points
Emissions from the third largest fuel ethanol refinery in the U.S. were measured
Emissions of NOx and SO2 agreed with the NEI‐2011 emission inventory
Emissions of VOCs were underestimated by the NEI‐2011 inventory
Deposition fluxes of terpenes over grassland Bamberger, I.; Hörtnagl, L.; Ruuskanen, T. M. ...
Journal of Geophysical Research,
27 July 2011, Letnik:
116, Številka:
D14
Journal Article
Recenzirano
Odprti dostop
Eddy covariance flux measurements were carried out for two subsequent vegetation periods above a temperate mountain grassland in an alpine valley using a proton‐transfer‐reaction‐mass spectrometer ...(PTR‐MS) and a PTR time‐of‐flight‐mass spectrometer (PTR‐TOF). In 2008 and during the first half of the vegetation period 2009 the volume mixing ratios (VMRs) for the sum of monoterpenes (MTs) were typically well below 1 ppbv and neither MT emission nor deposition was observed. After a hailstorm in July 2009 an order of magnitude higher amount of terpenes was transported to the site from nearby coniferous forests causing elevated VMRs. As a consequence, deposition fluxes of terpenes to the grassland, which continued over a time period of several weeks without significant reemission, were observed. For days without precipitation the deposition occurred at velocities close to the aerodynamic limit. In addition to monoterpene uptake, deposition fluxes of the sum of sesquiterpenes (SQTs) and the sum of oxygenated terpenes (OTs) were detected. Considering an entire growing season for the grassland (i.e., 1 April to 1 November 2009), the cumulative carbon deposition of monoterpenes reached 276 mg C m−2. This is comparable to the net carbon emission of methanol (329 mg C m−2), which is the dominant nonmethane volatile organic compound (VOC) emitted from this site, during the same time period. It is suggested that deposition of monoterpenes to terrestrial ecosystems could play a more significant role in the reactive carbon budget than previously assumed.
Key Points
First deposition fluxes of terpenes to grass
Deposition flux of monoterpenes
Deposition flux of sesquiterpenes
Volatile organic compound (VOC) emission rates during the growth and simulated harvest phases were determined for switchgrass (Panicum virgatum) using laboratory chamber measurements. Switchgrass is ...a candidate for use in second-generation (cellulosic) biofuel production and the acreage dedicated to its growth in the USA has already increased during the past decade. We estimate that the yearly emissions from switchgrass plantations, including both the growth and harvest phases will be on the order of 3 kg C ha−1 methanol, 1 kg C ha−1 acetaldehyde, 1 kg C ha−1 acetone, 0.9 kg C ha−1 monoterpenes, 0.5 kg C ha−1 isoprene + another compound, most likely 1-penten-3-ol, 0.2 kg C ha−1 hexenals, and 0.1 kg C ha−1 hexenols. These emission rates are much lower than those expected from Eucalyptus or poplar plantations, which are other potential biofuel crops and have significantly higher VOC emissions, suggesting that the choice of species in the production of biofuels could have serious implications for regional air quality.
Grasslands comprise natural tropical savannah over managed temperate fields to tundra and cover one quarter of the Earth's land surface. Plant growth, maintenance and decay result in volatile organic ...compound (VOCs) emissions to the atmosphere. Furthermore, biogenic VOCs (BVOCs) are emitted as a consequence of various environmental stresses including cutting and drying during harvesting. Fluxes of BVOCs were measured with a proton-transfer-reaction-mass-spectrometer (PTR-MS) over temperate mountain grassland in Stubai Valley (Tyrol, Austria) over one growing season (2008). VOC fluxes were calculated from the disjunct PTR-MS data using the virtual disjunct eddy covariance method and the gap filling method. Methanol fluxes obtained with the two independent flux calculation methods were highly correlated (
= 0.95×-0.12,
= 0.92). Methanol showed strong daytime emissions throughout the growing season - with maximal values of 9.7 nmol m
s
, methanol fluxes from the growing grassland were considerably higher at the beginning of the growing season in June compared to those measured during October (2.5 nmol m
s
). Methanol was the only component that exhibited consistent fluxes during the entire growing periods of the grass. The cutting and drying of the grass increased the emissions of methanol to up to 78.4 nmol m
s
. In addition, emissions of acetaldehyde (up to 11.0 nmol m
s
), and hexenal (leaf aldehyde, up to 8.6 nmol m
s
) were detected during/after harvesting.
Thymic stromal lymphopoietin (TSLP) potently induces deregulation of Th2 responses, a hallmark feature of allergic inflammatory diseases such as asthma, atopic dermatitis, and allergic rhinitis. ...However, direct downstream in vivo mediators in the TSLP-induced atopic immune cascade have not been identified. In our current study, we have shown that OX40 ligand (OX40L) is a critical in vivo mediator of TSLP-mediated Th2 responses. Treating mice with OX40L-blocking antibodies substantially inhibited immune responses induced by TSLP in the lung and skin, including Th2 inflammatory cell infiltration, cytokine secretion, and IgE production. OX40L-blocking antibodies also inhibited antigen-driven Th2 inflammation in mouse and nonhuman primate models of asthma. This treatment resulted in both blockade of the OX40-OX40L receptor-ligand interaction and depletion of OX40L-positive cells. The use of a blocking, OX40L-specific mAb thus presents a promising strategy for the treatment of allergic diseases associated with pathologic Th2 immune responses.
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