Indirect long-term global radiative cooling from NOx emissions

Anthropogenic emissions of short‐lived, chemically reactive gases, such as NO x and CO, are known to influence climate by altering the chemistry of the global troposphere and thereby the abundance of the greenhouse gases O3, CH4 and the HFCs. This study uses the characteristics of the natural modes of the tropospheric chemical system to decompose the greenhouse effect of NO x and CO emissions into (i) short‐lived modes involving predominantly tropospheric O3 and (ii) the long‐lived mode involving a global coupled CH4‐CO‐O3 perturbation. Combining these two classes of greenhouse perturbations—large, short‐lived, regional O3 increases and smaller, long‐lived, global decreases in CH4 and O3—we find that most types of anthropogenic NO x emissions lead to a negative radiative forcing and an overall cooling of the earth

Giant viscosity enhancement in a spin-polarized Fermi liquid

The viscosity is measured for a Fermi liquid, a dilute $^3$He-$^4$He mixture, under extremely high magnetic field/temperature conditions ($B \leq 14.8$ T, $T \geq 1.5$ mK). The spin splitting energy $\mu B$ is substantially greater than the Fermi energy $k_B T_F$; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for $T \ll T_F$. Using a novel composite vibrating-wire viscometer an enhancement of the viscosity is observed by a factor of more than 500 over its low-field value. Good agreement is found between the measured viscosity and theoretical predictions based upon a $t$-matrix formalism.Comment: 4 pages, 4 figure

Seasonal cycles of ozone and oxidized nitrogen species in northeast Asia - 2:A model analysis of the roles of chemistry and transport

[1] The dominant factors controlling the seasonal variations of ozone (O-3) and three major oxidized nitrogen species, peroxyacetyl nitrate (PAN), nitrogen oxides (NOx), and nitric acid (HNO3), in northeast Asia are investigated by using a three-dimensional global chemical transport model to analyze surface observations made at Rishiri Island, a remote island in northern Japan. The model was evaluated by comparing with observed seasonal variations, and with the relationships between O-3, CO, and PAN. We show that the model reproduces the chemical environment at Rishiri Island reasonably well, and that the seasonal cycles of O-3, CO, NOy species, and VOCs are well predicted. The impact of local emissions on some of these constituents is significant, but is not the dominant factor affecting the seasonal cycles. The seasonal roles of chemistry and transport in controlling O-3 and PAN are revealed by examining production/ destruction and import/ export/deposition fluxes in the boundary layer over the Rishiri region. For O-3, transport plays a key role throughout the year, and the regional photochemical contribution is at most 10% in summer. For PAN, in contrast, transport dominates in winter, while in-situ chemistry contributes as much as 75% in summer. It is suggested that the relative contribution of transport and in-situ chemistry is significantly different for O-3 and PAN, but that the wintertime dominance of transport due to the long chemical lifetimes of these species is sufficient to drive the seasonal cycles of springtime maximum and summertime minimum characteristic of remote sites

A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

International audienceA new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL

Observation of strong electron dephasing in disordered Cu93_{93}Ge4_4Au3_3 thin films

We report the observation of strong electron dephasing in a series of disordered Cu$_{93}$Ge$_4$Au$_3$ thin films. A very short electron dephasing time possessing very weak temperature dependence around 6 K, followed by an upturn with further decrease in temperature below 4 K, is found. The upturn is progressively more pronounced in more disordered samples. Moreover, a ln$T$ dependent, but high-magnetic-field-insensitive, resistance rise persisting from above 10 K down to 30 mK is observed in the films. These results suggest a nonmagnetic dephasing process which is stronger than any known mechanism and may originate from the coupling of conduction electrons to dynamic defects.Comment: to appear in Phys. Rev. Let

Chemical transport model ozone simulations for spring 2001 over the western Pacific:comparisons with TRACE-P lidar, ozonesondes, and Total Ozone Mapping Spectrometer columns

Two closely related chemical transport models (CTMs) employing the same high-resolution meteorological data (similar to180 km x similar to180 km x similar to600 m) from the European Centre for Medium-Range Weather Forecasts are used to simulate the ozone total column and tropospheric distribution over the western Pacific region that was explored by the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) measurement campaign in February-April 2001. We make extensive comparisons with ozone measurements from the lidar instrument on the NASA DC-8, with ozonesondes taken during the period around the Pacific Rim, and with TOMS total column ozone. These demonstrate that within the uncertainties of the meteorological data and the constraints of model resolution, the two CTMs (FRSGC/UCI and Oslo CTM2) can simulate the observed tropospheric ozone and do particularly well when realistic stratospheric ozone photochemistry is included. The greatest differences between the models and observations occur in the polluted boundary layer, where problems related to the simplified chemical mechanism and inadequate horizontal resolution are likely to have caused the net overestimation of about 10 ppb mole fraction. In the upper troposphere, the large variability driven by stratospheric intrusions makes agreement very sensitive to the timing of meteorological features

Performance of MAX-DOAS measurements of aerosols at Tsukuba, Japan: a comparison with lidar and sky radiometer measurements

International audienceGround-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed at Tsukuba, Japan (36.1° N, 140.1° E), in November?December 2006. The measured spectra of scattered sunlight are analyzed by DOAS and optimal estimation methods to retrieve the aerosol optical depth (?) and the vertical profile of the aerosol extinction coefficient (?) at 476 nm in the lower troposphere. We characterize these retrieved quantities through comparisons with coincident lidar and sky radiometer measurements. The retrieved ? values for layers of 0?1 and 1?2 km agree with lidar data to within 30% and 60%, respectively, for most cases, including partly cloudy conditions. Results similar to ? at 0?1 km are obtained for the retrieved ? values, demonstrating that MAX-DOAS provides the new, unique aerosol dataset in the lower troposphere