The chemical properties of the particulate exhaust emissions from an in-use commercial aircraft engine were characterized in April 2004 as part of the Aircraft Particle Emissions Experiment. The test aircraft was the NASA DC-8 equipped with CFM56-2-C1 engines and the test matrix included 11 different engine throttle levels, three fuel compositions, and three sampling distances. The variations in particle emissions number, size, mass, and chemical composition were measured using a suite of instruments, including an aerosol mass spectrometer. The particle emissions were characterized by a trimodal size distribution. The largest mode was dominated by ambient accumulation mode particles mixed into the plume. The middle mode consisted of carbon soot with sulfate and organic coatings. The smallest mode was completely volatile and consisted of sulfate and organic components. The soot emission indices increased with power from 2-120 mg=kg fuel. The semivolatile components increased with distance and decreased with power from 33-5 mg=kg fuel. The sulfate emissions increased with distance and fuel sulfur content. The emissions under low power were dominated by organics, and the high-power conditions were dominated by soot. The CFM56 engine was less efficient at the low thrust levels typically used on the ground at an airport.

Changes in ion abundance from the plasma of an abnormal dc glow discharge, using a copper cathode, have been studied as a function of ͑a͒ gas residence time in the discharge and ͑b͒ the amount of H 2 added to the positive column, without disturbing the discharge. The ArϩH 2 spectra show a severe, but selective, quenching of the ionization. All major ions are quenched except for Cu ϩ , which increases in abundance. It is shown that this cannot be explained by either ion-molecule reactions or the fast recombination suggested previously ͓R. F. G. Meulenbroeks et al., Phys. Rev. E 49, 4397 ͑1994͔͒ for such mixtures. The kinetic behavior is consistent with the heavy involvement of stepwise ionization processes in which high excited metastable states of neutral Ar are precursors for most ions observed in the spectrum. It is proposed that these states are rapidly quenched by H 2 down to the Ar(4s) levels, preventing ionization of most species in the discharge, but significantly boosting the Penning ionization of Cu atoms sputtered from the cathode.

Ions created from the fast-flowing positive column plasma of a glow discharge were monitored using a high voltage magnetic sector mass spectrometer. Since the field gradient and sheath potentials created by the plasma inside the source opposed cation transfer, it is inferred that the ions detected were the field-ionized Rydberg species. This is supported by the mass spectral changes which occurred when a negative bias was applied to the sampling aperture and by the contrasting behavior when attached to a quadrupole analyzer. Reaction with H2 (titrated into the flowing plasma) quenched not only the ionization of discharge gas Rydberg atoms but also the passage of electric current through the plasma, without significant changes to the field and sheath potentials. Few "free" ions were present and the lifetimes of the Rydberg atoms detected were much longer than seen in lower pressure experiments, indicating additional stabilization in the plasma environment. The observations support the model of the flowing plasma, given previously [R. S. Mason, P. D. Miller, and I. P. Mortimer, Phys. Rev. E 55, 7462 (1997)] as mainly a neutral Rydberg atom gas, rather than a conventional ion-electron plasma.

An ion source is described for use in low power glow discharge mass spectrometry, using fast flowing argon as the discharge gas, and attached to a quadrupole analyser. The flow carries the plasma downstream onto an ion exit sampling cone which can be variably biased relative to the anode, enabling the physical and chemical properties of the plasma to be studied independently of the main ionisation region, the cathode fall. The parts of the plasma studied were characterised by fixed probe potential measurements. Cone bias effects are consistent with a plasma which contains large quantities of high n Rydberg atoms of both the discharge gas and the sputtered cathode. The ionisable atom flux passing through the sampling aperture was measured directly, giving densities inside the plasma of 10 10 -10 11 cm 23 . The densities of lower n Rydbergs are expected to be very much higher. H 2 is shown to quench these states and promote excitation of the cathode atoms to their Rydberg states. Field-ionisation or Auger deexcitation of the Rydberg gas inside the cell gives a high intensity cathode ion beam, which is relatively uncontaminated by the higher ionisation potential species, such as are formed from the discharge gas.

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Oxidative stress produces a variety of radicals in DNA, including pyrimidine nucleobase radicals. The nitrogencentered DNA radical 2′-deoxycytidin-N4-yl radical (dC•) plays a role in DNA damage mediated by one electron oxidants, such as HOCl and ionizing radiation. However, the reactivity of dC• is not well understood. To reduce this knowledge gap, we photochemically generated dC• from a nitrophenyl oxime nucleoside and within chemically synthesized oligonucleotides from the same precursor. dC• formation is confirmed by transient UV-absorption spectroscopy in laser flash photolysis (LFP) experiments. LFP and duplex DNA cleavage experiments indicate that dC• oxidizes dG. Transient formation of the dG radical cation (dG +• ) is observed in LFP experiments. Oxidation of the opposing dG in DNA resultsin hole transfer when the opposing dG is part of a dGGG sequence. The sequence dependence is attributed to a competition between rapid proton transfer from dG +• to the opposing dC anion formed and hole transfer. Enhanced hole transfer when less acidic O6-methyl-2′-deoxyguanosine is opposite dC• supports this proposal. dC• produces tandem lesions in sequences containing thymidine at the 5′-position by abstracting a hydrogen atom from the thymine methyl group. The corresponding thymidine peroxyl radical completes tandem lesion formation by reacting with the 5′-adjacent nucleotide. As dC• is reduced to dC, its role in the process is traceless and is only detectable because of the ability to independently generate it from a stable precursor. These experiments reveal that dC• oxidizes neighboring nucleotides, resulting in deleterious tandem lesions and hole transfer in appropriate sequences.

DNA polymerase θ (Pol θ) is a multifunctional enzyme. It is nonessential in normal cells, but its upregulation in cancer cells correlates with cellular resistance to oxidative damage and poor prognosis. Pol θ possesses polymerase activity and poorly characterized lyase activity. We examined the Pol θ lyase activity on various abasic sites and determined that the enzyme is inactivated upon attempted removal of the oxidized abasic site commonly associated with C4'-oxidation (pC4-AP). Covalent modification of Pol θ by the DNA lesion enabled determination of the primary nucleophile (Lys) responsible for Schiff base formation in the lyase reaction. Unlike some other base excision repair polymerases, Pol θ uses a single active site for polymerase and lyase activity. Mutation of Lys significantly reduces both enzyme activities but not DNA binding. Demonstration that Lys is required for polymerase and lyase activities indicates that this residue is an Achilles heel for Pol θ and suggests a path forward for designing inhibitors of this attractive anticancer target.