The exchange of mass and energy is a turbulent process that often occurs in coherent periods of time and in discrete regions of space. Prior to the development of volume imaging lidars, the study of coherent structures in the atmosphere was limited, for the most part, to time-series analysis of point-instrument data. This paper describes the use of the Los Alamos National Laboratories scanning Raman lidar to observe both temporal and spatial coherent structures, such as plume and ramp-like features, that developed over a Green Ash orchard. Most of the ramp structures identified from lidar data were between 20 and 30 m in size and had transit lifetimes of between 20 and 30 s. The validity of these results was confirmed by comparison with previously collected point-instrument data. An analysis of the multi-dimensional lidar images was also able to relate discrete spatial features, such as plumes to ramp patterns, found at the base of plumes in both the temporal and spatial domains. A further finding supports the concept that ramp development is a function of shear-scale and roughness length. The lidar represents a new tool to gain a deeper understanding of the mechanisms underlying the turbulent exchange process.

Over the last two decades, Mexico City, like many large industrial and populous urban areas, has developed a serious air pollution problem, especially during the winter months when there are frequent temperature inversions and weak winds. The deterioration in air quality is the result of several factors. The basin within which Mexico City lies is Mexico`s center of political, administrative and economic activity, generating 34% of the cross domestic product and 42% of the industrial revenue, and supporting a population which is rapidly approaching the 20 minion mark. The basin is surrounded by mountains on three sides which inhibit rapid dispersal of pollutants. Emissions from the transportation fleet (more than 3 million vehicles) are one of the primary pollution sources, and are mostly uncontrolled. Catalytic converters are just now being introduced into the fleet. The Mexico City Air Quality Research Initiative is an international collaborative project between the Los Alamos National Laboratory and the Mexican Petroleum Institute dedicated to the investigation of the air quality problem in Mexico City. The main objective of the project is to identify and assess the cost and benefits of major options being proposed to improve the air quality.

Line profiles of 10 Ar I lines emitted from an ICP (T = 6800 K) are carefully evaluated with the Los Alamos Fourier Transform Spectrometer. In contrast to a previous paper, which reported measurements of 6p-4s, 5p-4s, and 4p-4s transitions (all 4s ground state), this Note deals with shifts for the transitions with 4p ground states. The shifts in line positions are on the order of 1 cm−1. These shifts are accompanied by line profiles which have large contributions of pressure broadening. Previous work on a-parameters of elements in the analytical zone are on the order of 0.3–0.6 [1]. This note reports a-parameters as great as 39.03. Our HCL emission source could not be used as a standard because it lacked the excitation energy needed to adequately populate the higher energy levels. This results in a poor SNR for these lines. Argon I data reported by Li and Humphery [4] have been used for the unshifted values.

A lidar system based on ultraviolet (UV) laser induced fluorescence (LIF) has been developed for the remote detection of atmospherically dispersed biological particles, such as the vegetative cells of bacillus thuringiensis (BT) and bacillus globiggi (BG) released from an aerosol generator. The main goal of this work is to investigate the research issues associated with the long range detection and identification of these biological materials using fluorescence lidar. In particular, we are interested in extending the detection range of a solar-blind 248-nm lidar system demonstrated (with a range of 1-km or so) in previous field experiments1. To ensure favorable atmospheric light transmission characteristics in longer range detection, we are using excitation laser wavelengths > 290-nm (i.e. at wavelengths above that of ozone absorption).

Vacuum ultraviolet (VUV) light radiation was used to produce electronically excited KrF excimers (in D-, B- and C-states) by the photolysis of KrF2 and F2/Kr mixtures at various excitation wavelengths. The excited KrF photoproduct quantum yield was measured over the excitation wavelength range of 120 to 200 nm, and a quantum efficiency of 0.11 was estimated at the peak absorption wavelength of 159 nm for KrF2. The collision-free fluorescence lifetime of the B-X transition near 248 nm was determined to be 9.5 ± 0.6 ns when the KrF2 was excited with the 159 nm light. Near gas kinetic rate constants were measured for the quenching of KrF B-X emission by KrF2 and CO2. Using the threshold wavelength needed for the production of excited KrF photofragments, an upper bound for the bond dissociation energy of KrF2 was determined to be 1.03 ± 0.05 eV.

Shifts in spectral line positions of argon, iron, barium, calcium and strontium are addressed in this preliminary study of the effect of pressure, and electron density on wavenumber position in the 27.12 MHz inductively coupled plasma (ICP). We report line shifts for three sets of data in an argon ICP. The first set of data shows the effect of power (1.1, 1.5, 1.9 kW) on shifts of argon (21 lines) and iron (28 lines) lines in the ultraviolet and visible. The second set of data gives shifts of 25 Ar lines in the near infrared (i.r.) and far visible at 1.1 kW. The third set of data concerns prominent ion lines of calcium, barium and strontium. Commercial hollow cathode lamps (HCL) were used to obtain unshifted line positions. The Los Alamos Fourier Transform Spectrometer was used to obtain the data.

Ten self-contained 27.12-MHz Inductively Coupled Plasmas (ICP) are generated in a static torch. The torch offers spectroscopists a closed-system, low-pressure (0.1-100 Torr), variable-power (currently up to 1 kW) plasma. Doppler temperatures (Na D) measured are approximately 5 times those of electrodeless discharge lamps (EDLs) or Hollow Cathode Lamps (HCLs) operating under normal conditions. This torch has improved noise considerations, compared with those for the flowing ICP traditionally used.

The Fourier-transform spectra (0.015-cm−1 resolution) of the nonresonant 405.8-, 368.4-, and 364.0-nm lines and the resonant 283.3-nm line from a lead hollow-cathode lamp are reported. The splittings for the various isotopic and nuclear hyperfine transitions for all four lines are found to be consistent with previous measurements and assignments. At the recommended lamp operating current of 4 mA, all peak shapes within all four lines studied were satisfactorily fitted with Gaussian functions corresponding to the same Doppler temperature of 750 ± 30 K, indicating no significant self-absorption of the 283.3-nm resonant line. At a much-elevated lamp current the peaks for the nonresonant lines are increased in intensity and slightly broadened, whereas the peaks for the resonant line have approximately the same intensity as at 4 mA but are no longer Gaussian shaped.

Previous studies of line widths and shapes of spectral lines emitted from the inductively coupled plasmas (ICP) have concentrated on plasmas sustained in pure argon [1]. For the present study, we used the Los Alamos Fourier transform spectrometer to estimate line widths and line shapes of Fe I lines emitted from helium and argon-nitrogen ICP discharges. The effect of gas composition and plasma operating conditions on widths and shapes of the spectral lines were examined. Line widths and line shapes of Fe lines were compared with those of argon and helium for Ar ICP and He ICP discharges. Results were used to calculate Doppler temperatures and electron number densities of the cited plasmas.