Sensitivity analysis of differential absorption lidar measurements in the mid-infrared region.

The availability of new laser sources that are tunable in the IR spectral region opens new perspectives for differential absorption lidar (DIAL) measurements. A region of particular interest is located in the near IR, where some of the atmospheric pollutants have absorption lines that permit monitoring of emissions from industrial plants and in urban areas. In DIAL measurements, the absorption lines for the species to be measured must be carefully chosen to prevent interference from other molecules, to minimize the dependence of the absorption cross section on temperature, and to optimize the measurements with respect to the optical depth. We analyze the influence of these factors and discuss a set of criteria for selecting the best pairs of wavelengths (lambda(on) and lambda(off)) to be used in DIAL measurements of several molecular species (HCl, CO, CO(2), NO(2), CH(4), H(2)O, and O(2)). Moreover, a sensitivity study has been carried out for selected lines in three different regimes: clean air, urban polluted air, and emission from an incinerator stack.

Aerosol observations by lidar in the nocturnal boundary layer.

Aerosol observations by lidar in the nocturnal boundary layer (NBL) were performed in Potenza, Southern Italy, from 20 January to 20 February 1997. Measurements during nine winter nights were considered, covering a variety of boundary-layer conditions. The vertical profiles of the aerosol backscattering coefficient at 355 and 723.37 nm were determined through a Klett-modified iterative procedure, assuming the extinction-to-backscattering ratio within the NBL has a constant value. Aerosol average size characteristics were retrieved from almost simultaneous profiles of the aerosol backscattering coefficient at 355 and 723.37 nm, the measurements being consistent with an accumulation mode radius not exceeding 0.4 microm. Similar results in terms of aerosol sizes were obtained from measurements of the extinction-to-backscattering ratio profile at 355 nm performed on six nights during the measurement campaign. Backscattering profiles at 723.37 nm were also converted into profiles of aerosol liquid water content.

Isolation of vitamin B 12 transport mutants of Escherichia coli.

Escherichia coli KBT001, a methionine-vitamin B(12) auxotroph, was found to require a minimum of 20 molecules of vitamin B(12) (CN-B(12)) per cell for aerobic growth in the absence of methionine. After mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine and penicillin selection, two kinds of B(12) transport mutant were isolated from this strain. Mutants of class I, such as KBT069, were defective in the initial rapid binding of CN-B(12) to the cell and were unable to grow in the absence of methionine even with CN-B(12) concentrations as high as 100 ng/ml. The class II mutants possessed intact initial phases of CN-B(12) uptake but were defective in the secondary energy-dependent phase. These strains were also unable to convert the CN-B(12) taken up into other cobalamins. In the absence of methionine, some of these strains (e.g., KBT103) were able to grow on media containing 1 ng of CN-B(12)/ml, whereas others (e.g., KBT041) were unable to grow with any of the CN-B(12) concentrations used. Osmotic shock treatment did not affect the initial rate of uptake of CN-B(12) but gave a substantial decrease in the secondary rate. Trace amounts of B(12)-binding macromolecules were released from the cells by the osmotic shock, but only from strains such as KBT001 and KBT041 which possessed an active initial phase of CN-B(12) uptake. These results are interpreted as being consistent with the view that the initial CN-B(12) binding site which functions in this transport system is probably bound to the cell membrane.

Transport of vitamin B 12 in Escherichia coli.

The uptake of (60)Co-labeled cyanocobalamin (vitamin B(12)) by cells of Escherichia coli K-12lambda was shown to consist of an initial rapid phase (complete in <1 min), followed by a slower secondary phase. Methods enabling the measurement of (60)Co-B(12) uptake after incubation times of 1 to 2 sec were used in studies on the initial rate of B(12) uptake. This initial process showed saturation kinetics, with a V(max) of 56 molecules per sec per cell and a K(m) of 5 nm, and was essentially independent of cellular energy metabolism. No inhibition was obtained with cyanide, fluoride, arsenite, or 2, 4-dinitrophenol, and an energy of activation of 3.8 kcal/mole for this initial phase of uptake was calculated from its response to temperature changes between 15 and 35 C. The inhibition by HgCl(2) (50% at 0.1 mm) but not by 1 mmN-ethylmaleimide or 1 mmp-chloromercuribenzoate was consistent with a role for a relatively inaccessible sulfhydryl residue at the initial B(12) binding site. The secondary phase of B(12) uptake was clearly dependent on the energy metabolism of the cell, and, from its response to temperature, an energy of activation of about 17 kcal/mole was calculated. Cyanide (10 mm), arsenite (10 mm), and 2, 4-dinitrophenol (0.1 mm) gave at least 70% inhibition of the rate of the secondary phase. The formation of other cobalamins, such as 5'-deoxyadenosyl cobalamin, was not an obligate part of B(12) transport. The cells were also able to take up (60)Co-labeled cobinamide cyanide.