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A numerical model including gas phase HOx, NOx, and SOx chemistry; H2SO4-soot adsorption; binary H2SO4-H20 nucleation; aerosol coagulation; and vapor condensation is used to investigate aerosol formation and growth in near-field aircraft plumes. The plume flow field is treated using the JANNAF standard plume flow field code, SPF-II. Model results are presented for a Mach 2.4 high-speed civil transport at 18 km altitude and 85øN latitude and a subsonic Boeing 707 at 12.2 km, 47øN. The results, based on hydroxyl radical driven oxidation kinetics, indicate that 1-2% of the emitted SO2 is converted to H2SO 4 in the near-field exhaust (1-2 s) and that for typical exhaust SO2 emission indices (=1 g kg-fuel) the plume is supersaturated with respect to both the pure liquid acid and H2SO4/H20 solutions. Classical nucleation theory predicts high levels of small (0.3-0.6 nm radius) H2SO4/H20 embryos. Coagulation and gas-to-particle conversion are followed to provide estimates for the number density of activated soot particles capable of serving as condensation nuclei for contrail formation. Results are presented illustrating the dependence of water condensation on the number density and size distribution of activated exhaust soot nuclei. IntroductionAircraft aerosol emissions in heavily traversed air traffic corridors may provide a major atmospheric perturbation. Concern over the potential effects on radiative properties and ambient ozone distributions has resulted in a number of airborne measurements in aircraft wakes aimed at quantifying the levels of gas phase HO:• (OH, HO2, H20:), NO:• (NO, NO:), and SOx (SO, SO2, SO3, HSO3, H2SO4) species, as well as exhaust aerosols [Ho]•nann and Rosen, 1978; Baurngardner et al., 1991; Arnold et al., 1992; Fahey et al., 1995a, b; Busen and Schumann, 1995]. These measurements have been supplemented by numerical calculations using plume models to track the homogeneous and heterogeneous plume chemistry from the exit plane through the near-field plume and wake-vortex interaction regime [Hoshizaki et al., 1975; Miake-Lye et al., 1993; Kdircher, 1994; Anderson et al., 1996] and atmospheric models to estimate the potential effect on atmospheric chemistry [Weisenstein et al., 1991, 1996; Bekki and Pyle, 1992, 1993; Rodriguez et al., 1994; Xue et al., 1994]. These atmospheric models indicate significant potential atmospheric effects depending to some extent on the gas phase and heterogeneous chemical kinetics in the exhaust plume. The recent twodimensional modeling study of Weisenstein et al. [1996], for example, predicts an increase in the stratospheric aerosol surface area by a factor of 2 due to sulfuric acid nucleation in supersonic high-speed civil transport (HSCT) plumes if 10% of the emitted SO2 is converted to H2SO 4 shortly after emission. In this paper, a numerical model is used to study the kinetic processes governing the formation and growth of aerosols in aircraft plumes. Results are presented for a Mach 2.4 HSCT at effects have been the focus of extensive research. In this regard...

The structures of poly(p-phenylenebenzobisthiazole) (PBZT) and poly(p-phenylenebenzobisoxazole) (PBO) fibers have been investigated by fiber diffraction techniques. d-spacings were obtained from equatorial and meridional scans recorded on a four-circle diffractometer. Intensity data were derived from x-ray rotation patterns taken on Weissenberg and vacuum cylindrical cameras. Unit cells were found to be monoclinic and non-primitive, each containing two chains per cell of dimensions a = 11.79(2), b = 3.539(5), c = 12.514(9) A, γ = 94.0(2)o for PBZT; and = 11.20(1), b = 3.540(2), c = 12.050(3) Å, γ = 101.3(1) for PBO. The fiber axes correspond to c. The conformational torsion angle between the bisthiazole and phenylene units and the orientation of chains within the unit cells were obtained from a ‘linked-atom least-squares’ (LALS)refinement procedure. A packing model is proposed for each polymer in which two independent molecular chains are displaced longitudinally by discrete rather than random increments. Primitive unit cells (Z = 1), besides requiring perfect axial registry of molecular chains, suffer from the occurrence of short intermolecular contacts and are rejected from further consideration.

The full multicomponent population dynamic equation is developed for systems with coagulation and solved using the split composition distribution method. A full discussion of the origins of this method and its advantages over conventional methods is followed by a complete and rigorous explanation of its numerical implementation. The Wiener expansion is introduced as a method for representing compositional variation in a number density distribution that is solved by orthogonal collocation on finite elements. Results are obtained by numerical integration using fifth-order Runge-Kutta and favorably compared to analytical results.

X-ray crystallographic and ab initio molecular orbital analyses are presented for three model compounds of methyl-substituted poly(p-phenylenebenzobisthiazole), PBZT, where monomethyl and dimethyl substitutents are located on the phenylene moiety. The barrier to phenylene rotation, a factor considered to be important for an understanding of the mechanical, electronic, and nonlinear optical properties of PBZT and related rigid-rod heterocyclic polymers, is calculated for each compound. Ortho substitution with a monomethyl group substantially lowers the rotational barrier and profoundly changes the shape of the rotational potential, whereas meta substitution has only a negligible effect. Discrepancies between experimental and theoretical phenyl torsion angles are attributed to crystal packing forces. Ab initio results differ quantitatively from semiempirical molecular orbital findings. Good agreement is observed between crystallographic and computed bond lengths and angles.