Direct observation of changing NO_x lifetime in North American cities

NO_x lifetime relates nonlinearly to its own concentration; therefore, by observing how NO_x lifetime changes with changes in its concentration, inferences can be made about the dominant chemistry occurring in an urban plume. We used satellite observations of NO₂ from a new high-resolution product to show that NOx lifetime in approximately 30 North American cities has changed between 2005 and 2014 in a manner consistent with our understanding of NO_x chemistry

Trends in Elasticity and Electronic Structure of Transition-Metal Nitrides and Carbides from First Principles

The elastic properties of the $B_1$-structured transition-metal nitrides and their carbide counterparts are studied using the {\it ab initio\} density functional perturbation theory. The linear response results of elastic constants are in excellent agreement with those obtained from numerical derivative methods, and are also consistent with measured data. We find the following trends: (1) Bulk moduli $B$ and tetragonal shear moduli $G^{\prime}=(C_{11}-C_{12})/2$, increase and lattice constants $a_{0}$ decrease rightward or downward on the Periodic Table for the metal component or if C is replaced by N; (2) The inequality $B > G^{\prime} > G > 0$ holds for $G=C_{44}$; (3) $G$ depends strongly on the number of valence electrons per unit cell ($Z_{V}$). From the fitted curve of $G$ as a function of $Z_{V}$, we can predict that MoN is unstable in $B_{1}$ structure, and transition-metal carbonitrides ($e.g.$ ZrC$_{x}$N$_{1-x}$) and di-transition-metal carbides ($e.g.$ Hf$_{x}$Ta$_{1-x}$C) have maximum $G$ at $Z_{V} \approx 8.3$.Comment: 4 pages, 2 figures, submitted to PRL. 2 typos in ref. 15 were correcte

Airborne Instruments for the In Situ Detection of ClONO2, NO2, ClO, and BrO in the Stratosphere

Design and construction of an in situ sensor for the detection of stratospheric ClONO2, ClO, BrO, and NO2, was conceived as a two-year program. The experiment has two novel components: a resistive silicon thermal dissociation heater used to fragment ClONO2 into ClO and NO2 and a laser-induced fluorescence sensor for N02. These two new components are integrated into an experiment that uses technology developed in our labs for the ER-2 ClO and ER-2 HO(X) instruments. During the first year we reconstructed our laboratory prototypes for ClONO2 and NO2 detection and made substantial improvements in the calibration apparatus. Results from these laboratory experiments have been used to refine the design of the flight instrument. During this year we began the design of all of the long-lead items required to produce a flight instrument: including the design and fabrication of the air flow system used to direct stratospheric air to our halogen sensors, design and prototyping of an aircraft-compatible thermal dissociation heater, and development and test of a new high powered laser system. Finally, we have designed and released for fabrication several subsystems

The Berkeley High Resolution Tropospheric NO_2 product

We describe upgrades to the Berkeley High Resolution (BEHR) NO2 satellite retrieval product. BEHR v3.0B builds on the NASA version 3 standard Ozone Monitoring Instrument (OMI) tropospheric NO_2 product to provide a high spatial resolution product for a domain covering the continental United States and lower Canada that is consistent with daily variations in the 12km a priori NO_2 profiles. Other improvements to the BEHR v3.0 product include surface reflectance and elevation, and factors affecting the NO_2 a priori profiles such as lightning and anthropogenic emissions.- We describe the retrieval algorithm in detail and evaluate the impact of changes to the algorithm between v2.1C and v3.0B on the retrieved NO_2 vertical column densities (VCDs). Not surprisingly, we find that, on average, the changes to the a priori NO_2 profiles and the update to the new NASA slant column densities have the greatest impact on the retrieved VCDs. More significantly, we find that using daily a priori profiles results in greater average VCDs than using monthly profiles in regions and times with significant lightning activity. The BEHR product is available as four subproducts on the University of California DASH repository, using monthly a priori profiles at native OMI pixel resolution (https://doi.org/10.6078/D1N086) and regridded to 0.05° × 0.05° (https://doi.org/10.6078/D1RQ3G) and using daily a priori profiles at native OMI (https://doi.org/10.6078/D1WH41) and regridded (https://doi.org/10.6078/D12D5X) resolutions. The subproducts using monthly profiles are currently available from January 2005 to July 2017, and will be expanded to more recent years. The subproducts using daily profiles are currently available for years 2005–2010 and 2012–2014; 2011 and 2015 on will be added as the necessary input data are simulated for those years

Lightning NO₂ simulation over the contiguous US and its effects on satellite NO₂ retrievals

Lightning is an important NO_x source representing ∼10 % of the global source of odd N and a much larger percentage in the upper troposphere. The poor understanding of spatial and temporal patterns of lightning contributes to a large uncertainty in understanding upper tropospheric chemistry. We implement a lightning parameterization using the product of convective available potential energy (CAPE) and convective precipitation rate (PR) coupled with the Kain–Fritsch convective scheme (KF/CAPE-PR) into the Weather Research and Forecasting-Chemistry (WRF-Chem) model. Compared to the cloud-top height (CTH) lightning parameterization combined with the Grell 3-D convective scheme (G3/CTH), we show that the switch of convective scheme improves the correlation of lightning flash density in the southeastern US from 0.30 to 0.67 when comparing against the Earth Networks Total Lightning Network; the switch of lightning parameterization contributes to the improvement of the correlation from 0.48 to 0.62 elsewhere in the US. The simulated NO₂ profiles using the KF/CAPE-PR parameterization exhibit better agreement with aircraft observations in the middle and upper troposphere. Using a lightning NO_x production rate of 500 mol NO flash−1, the a priori NO₂ profile generated by the simulation with the KF/CAPE-PR parameterization reduces the air mass factor for NO₂ retrievals by 16 % on average in the southeastern US in the late spring and early summer compared to simulations using the G3/CTH parameterization. This causes an average change in NO₂ vertical column density 4 times higher than the average uncertainty

A Probe of New Physics in Top Quark Pair Production at e−e+e^-e^+ Colliders

We describe how to probe new physics through examination of the form factors describing the Ztt couplings via the scattering process e^-e^+->t+tbar. We focus on experimental methods on how the top quark momentum can be determined and show how this can be applied to select polarized samples of $t\bar{t}$ pairs through the angular correlations in the final state leptons. We also study the dependence on the energy and luminosity of an \ee\ collider to probe a CP violating asymmetry at the $10^{-2}$ level.}Comment: 24 pages in TeXsis (figures available upon request) (revised July 1993