CAPS: 2002 Publications

[1] The oxidation mechanisms of isoprene and butadiene initiated by OH in the presence of NO have been explored under wall-less flowing conditions, with products observed a few seconds after reaction by infrared spectroscopy. Since only similar to1% of alkene is reacted, any secondary chemistry is negligible. The use of reaction modulation spectroscopy permits the accurate measurement of a percent change in high alkene concentration and of 10(13) molecules/cm(3) concentrations for products. Measured carbonyl species agree with previous studies, while alkyl nitrate yields are consistent with upper values reported in the literature. NO sensitivity studies performed exclude the possibility of competing chemistry. Isoprene is not observed to form 3-methyl furan, indicating that this is not a prompt oxidation product. However, butadiene does form furan. In an auxiliary experiment, peroxy radicals in the second stage of butadiene oxidation are fully converted to peroxynitrates. Average cross sections for integrated peroxynitrate bands are determined from this experiment. C1 SUNY Albany, Atmospher Sci Res Ctr, Albany, NY 12205 USA. Harvard Univ, Dept Chem & Biol Chem, Cambridge, MA 02138 USA.

We present results of recent experiments on the pressure broadening of pure rotational transitions of (H2O)-O-16 water in the 400-600 cm(-1) range by nitrogen and oxygen. The average broadening coefficient is about 0.056 cm(-1)/atm for N-2 and about 0.029 cm(-1)/atm for O-2, however, as expected, the broadening coefficient varies as a strong function of transition. In general, the broadening decreases with increasing J and K-a, with a stronger dependence on K-a than on J. On average, air broadening coefficients obtained from the coefficients presented here are about 10% lower than those found in HITRAN '96, although, as detailed below, the differences are a function of quantum number. (C) 2002 Elsevier Science Ltd. All rights reserved. C1 Univ Maryland Baltimore Cty, Joint Ctr Earth Syst Technol, Baltimore, MD 21250 USA. Harvard Univ, Dept Chem & Biochem, Cambridge, MA 02138 USA. NASA, Goddard Space Flight Ctr, Extraterr Phys Lab, Greenbelt, MD 20771 USA.

[1] The organic fraction of ambient aerosols is a complex mixture of hundreds of organic compounds varying in chemical structure and physical properties. The cloud condensation nuclei (CCN) activities of single-component organic particles were experimentally investigated. Activation diameters were determined using a Tandem Differential Mobility Analyzer and a thermal diffusion Cloud Condensation Nucleus Counter. Studies were performed at supersaturations of 0.3 and 1% with dry particle diameters ranging between 0.02 and 0.2 mum. The focus was on both hygroscopic secondary organics and hydrophobic primary organics. Laboratory experiments were performed with sodium chloride, ammonium sulfate, glutaric acid, adipic acid, pinonic acid, glutamic acid, leucine, cholesterol, pinic acid, norpinic acid, hexadecane, hexadecanol, myristic acid, palmitic acid, and stearic acid. The results were compared with the classical Kohler theory and a theory that accounts for the limited solubility of many organics. It was discovered that organic species with bulk solubilities in water less than 0.01 g cm(-3) can be a good source of CCN in the atmosphere if their contact angles with water are zero. Experiments confirmed that Kohler theory works well in predicting activation of soluble inorganic species and organics that are wettable by water, while an extension of the theory appears necessary to account for the low-solubility organic species that are not wettable by water. C1 Carnegie Mellon Univ, Dept Chem Engn & Engn & Publ Policy, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.

A size-resolved equilibrium model, SELIQUID, is presented and used to simulate the size-composition distribution of semi-volatile inorganic aerosol in an urban environment. The model uses the efflorescence branch of aerosol behavior to predict the equilibrium partitioning of the aerosol components between the gas phase and a size-resolved aerosol population over the entire RH domain. Predictions of SELIQUID are compared against size-resolved composition measurements at different locations during the Southern California Air Quality Study. Based on the modeling results, the size distribution of sub-micrometer nitrate and ammonium can be determined by thermodynamic equilibrium when the RH > 60%. In cases where the RH < 60%, the assumption that all aerosol particles are metastable liquid solutions may introduce unacceptable errors. On the other hand, the equilibrium assumption, in some cases at least, introduces errors in the calculation of the coarse (particles with diameter <1 mum or so) nitrate and ammonium that increase with particle size. Finally, the inclusion of crustal species is important in modeling the size distribution of coarse inorganic aerosols when the concentration of these species is high. The effect of these crustal species can be complex and counterintuitive. (C) 2002 Published by Elsevier Science Ltd. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. Univ Nacl Autonoma Mexico, Fac Quim, Mexico City, DF, Mexico. Stanford Univ, Dept Civil & Environm Engn, Stanford, CA 94305 USA.

The organic carbon (OC)/elemental carbon (EC) tracer method is applied to the Pittsburgh, PA, area to estimate the contribution of secondary organic aerosol (SOA) to the monthly average concentration of organic particulate matter (PM) during 1995. An emissions inventory is constructed for the primary emissions of OC and EC in the area of interest. The ratio of primary emissions of OC to those of EC ranges between 2.4 in the winter months and 1.0 in the summer months. A mass balance model and ambient measurements were used to assess the accuracy of the emissions inventory. It is estimated to be accurate to within 50%. The results from this analysis show a strong monthly dependence of the SOA contribution to the total organic PM concentration, varying from near zero during winter months to as much as 50% of the total OC concentration in the summer. C1 Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA.

A dilution sampler has been designed and manufactured to simulate the effects of dilution processes on particulate matter emissions from coal-fired power plants and other combustion systems. The sampler allows independent control of the dilution ratio and residence time. Experiments were performed to examine the effects of these parameters on the particulate emissions of a pilot-scale pulverized coal combustor burning a low sulfur bituminous coal. Measurements included the particle size distribution in the range from 0.003 to 20 mum and the PM2.5 mass emission rate. The residence time and dilution ratio do not influence the particle mass emission rate, but have a significant effect on the size distribution and the total number of particles emitted. Increasing the residence time dramatically decreases the total particle number concentration, and shifts the particle mass to larger sizes. Increasing the dilution ratio increases the concentration of ultrafine particles. The effects of residence time can be explained quantitatively by the coagulation of the emitted particles; however, the effects of dilution ratio are more complex because the dilution ratio influences both the coagulation rate and gas-to-particle conversion. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Chem Engn, Pittsburgh, PA 15213 USA.

Cofiring biomass with coal is a promising short-term option for reducing the net CO2 emissions from existing coal-fired power plants. This paper examines the effects of cofiring biomass and coal on ash deposition under conditions representative of those found in the superheater region of pulverized-coal boilers. Experiments were conducted with blends of eight different fuels-three types of bituminous coal, sub-bituminous coal, two types of straw, switchgrass, and wood. For each fuel, reference tests of unblended fuel establish a baseline against which to compare the results from the cofiring tests. The deposition rates for the cofire blends are between the measured deposition rates of the unblended fuels. Therefore, blending straw with coal reduces the high deposition rates observed while firing unblended straw, and cofiring coal with wood results in slightly lower deposition rates than those that occur while firing unblended coal. The primary interaction between the biomass and coal during cofiring is the reaction of the sulfur from the coal with the alkali species from the biomass. This sulfation reduces the stickiness of the deposit, which substantially reduces the deposition rate of the coal-straw blends in comparison to expectations based on the performance of the unblended fuels. Sulfation also reduces the chlorine content of the deposits, potentially reducing the corrosion potential of the deposits. A scaling parameter is proposed to estimate the deposit chlorine content on the basis of the properties of the cofire blend; the ratio of fuel-S to available alkali must be in excess of 5 times the S-to-alkali stoichiometric ratio to eliminate chlorine from the deposit. The results demonstrate that cofiring can mitigate some of the fouling difficulties associated with combustion of high-fouling biofuels. C1 Sandia Natl Labs, Combust Res Facil, Livermore, CA 94550 USA.

[1] To better represent the indirect effect of aerosols on climate, a size-resolved simulation of aerosol microphysics, size distributions, number and mass concentrations has been incorporated into the GISS general circulation model (GCM). The TwO-Moment Aerosol Sectional (TOMAS) microphysics model used here conserves aerosol number as well as mass. It has high size resolution, 30 bins between 0.01 and 10 mum diameter. As a first application, a size-resolved simulation of sulfate has been performed. The model reproduces important features of the atmospheric aerosol such as number concentrations that increase with altitude and land-sea contrasts in aerosol number concentrations and size distributions. Comparisons with observations show that simulated size distributions are realistic and condensation nuclei (CN) concentrations agree with observations within about 25%. Predicted cloud condensation nuclei (CCN) concentrations are also in reasonable agreement with observations, although there are locations for which agreement would be improved by including other aerosol components such as sea salt and carbonaceous aerosols. Sensitivity scenarios show that uncertainties in nucleation and primary emissions from fossil fuels can have significant effects on predictions of CN and CCN concentrations. C1 Carnegie Mellon Univ, Dept Civil & Environm Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Dept Engn & Publ Policy, Pittsburgh, PA 15213 USA. CALTECH, Dept Chem Engn, Pasadena, CA 91125 USA.