Emissions from motor vehicles are a significant source of fine particulate matter (PM) and gaseous pollutants in urban environments. Few studies have characterized both gaseous and PM emissions from individual in-use vehicles under real-world driving conditions. Here we describe chase vehicle studies in which Received 27 February 2003; accepted 29 March 2004. This work was supported in part by the New York State Energy Research and Development Authority (NYSERDA), contract # 4918ERT-ERES99; the US Environmental Protection Agency (EPA), cooperative agreement # R828060010; and New York State Department of Environmental Conservation (NYS DEC), contract # C004210. Although the research described in this article has been funded in part by US EPA, it has not been subjected to the Agency's required peer and policy review and therefore does not necessary reflect the views of the Agency, and no official endorsement should be inferred. The authors thank the MTA for their cooperation, including Chris Bush for providing bus fleet information and Dana Lowell for help in organizing the logistics of the Fall 2000 campaign, the NYS DEC for providing drivers during the chase experiments, and Queens College for logistical support during the Summer 2001 campaign. The TILDAS scientists on-board the mobile laboratory, particularly Joanne Shorter and Mark Zahniser, are acknowledged for their assistance throughout the two phases of this study. Thanks also go to Jay Slowik and Leah Williams for help with laboratory soot experiments, Tim Onasch for assistance with the development of data analysis programs, and Paul Ziemann for useful discussions about organic mass spectral analysis. P. J. Silva thanks the Camille and Henry Dreyfus Foundation for Support. D. A. Ghertner thanks Robert Harriss for providing funding for his involvement in this project.Address correspondence to Manjula R. Canagaratna, Center for Aerosol and Cloud Chemistry and Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., 45 Manning Road, Billerica, MA 01821, USA. E-mail: mrcana@aerodyne.com on-road emissions from individual vehicles were measured in real time within seconds of their emission. This work uses an Aerodyne aerosol mass spectrometer (AMS) to provide size-resolved and chemically resolved characterization of the nonrefractory portion of the emitted PM; refractory materials such as elemental carbon (EC) were not measured in this study. The AMS, together with other gas-phase and particle instrumentation, was deployed on the Aerodyne Research Inc. (ARI) mobile laboratory, which was used to "chase" the target vehicles. Tailpipe emission indices of the targeted vehicles were obtained by referencing the measured nonrefractory particulate mass loading to the instantaneous CO 2 measured simultaneously in the plume. During these studies, nonrefractory PM 1.0 (NRPM 1 ) emission indices for a representative fraction of the New York City Metropolitan Transit Authority (MTA) bus fleet were determined. Diesel bus emissions ranged from 0.10 g NRPM 1...

[1] The reaction kinetics of submicron oleic (9-octadecanoic (Z)-) acid aerosols with ozone was studied using a novel aerosol mass spectrometric technique. In the apparatus a flow of size-selected aerosols is introduced into a flow reactor where the particles are exposed to a known density of ozone for a controlled period of time. The aerosol flow is then directed into an aerosol mass spectrometer for particle size and composition analyses. Data from these studies were used to: (a) quantitatively model the size-dependent kinetics process, (b) determine the aerosol size change due to uptake of ozone, (c) assess reaction stoichiometry, and (d) obtain qualitative information about the volatility of the reaction products. The reactive uptake probability for ozone on oleic acid particles obtained from modeling is 1.6 (± 0.2) Â 10 À3 with an upper limit for the reactodiffusive length of $10 nm. Atmospheric implications of the results are discussed.

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[1] A simple formalism is presented to model chemical interactions between aerosols and reactive trace gases over a wide range of conditions. The model takes into account gas phase diffusion, mass accommodation, bulk phase chemical reactions, surface reactions and particle phase reactant diffusion from the aerosol interior toward the surface. While previous models have focused on the heterogeneous uptake of trace gases by atmospheric droplets and particles, this model focuses on the reactive transformation of condensed phase species. In limiting cases, the model leads to simple analytical expressions for the condensed phase species depletion as a function of aerosol/gas interaction time.

The uptake of gas-phase ammonia by aqueous surfaces was measured as a function of temperature, gas liquid interaction time, and pH in the range 0-13. Uptake measurements at low pH yielded values of the mass accommodation coefficient (R) as a function of temperature. The mass accommodation coefficient increases as the temperature decreases, from 0.08 at 290 K to 0.35 at 260 K. Time dependence of the uptake yielded values for the Henry's law constant. Uptake measurements at high pH indicate that an ammonia surface complex is formed at the interface. Codeposition studies in which an aqueous surface, initially at pH ) 4, was simultaneously exposed to both gas-phase ammonia and SO 2 were also performed. In such a codeposition experiment, the species entering the liquid neutralize each other and as a result the uptake of each species is enhanced. Modeling calculations indicate that the uptake of each species is in accord with bulk liquid-phase kinetics. IntroductionAmmonia in the atmosphere originates primarily from ground sources including decaying organic matter and chemical fertilizers. Significant amounts of NH 3 (0.1-100 ppbv) are found in both clean and polluted atmospheres as well as in cloud and fog droplets. 1 Since ammonia is the only soluble base found in the atmosphere in significant quantities, it plays a principal role in neutralizing acidic aerosols (H 2 SO 4 , HNO 3 , and HCl) converting them to new nonvolatile or semivolatile components; (NH 4 ) 2 SO 4 , NH 4 HSO 4 , NH 4 NO 3 , NH 4 Cl. 2 The process of neutralization influences the aqueous oxidation rates of S(IV) species. A recent study by Meng et al. 3 found that atmospheric ammonia is an important precursor for aerosol formation in the Los Angeles area.Gas-phase reactions involving NH 3 are slow. 4 Tropospheric lifetime for reaction with OH radical for example, is typically about 3 months, and tropospheric photolysis is negligible. 5 Therefore, uptake by aerosols and liquid droplets is the principal tropospheric sink for gaseous ammonia and heterogeneous interactions of NH 3 are of significant interest to atmospheric chemists.The uptake of gas phase ammonia by water has been previously studied in a limited range of acidities by Ponche et al. 6 at 17°C, and Bongartz et al. 7 at 25°C. We have completed a series of NH 3 -liquid water and the NH 3 -sulfuric acid uptake measurements in two independent studies using separate droplet train apparatuses. The water studies were done as a function of pH (0-13) and temperature in the range 20°C to -10°C. The sulfuric acid studies were done in the range 10 to 70 wt % H 2 -SO 4 and as a function of temperature in the range 20°C to -25°C. The time dependence of the uptake was measured by varying the gas-liquid interaction time from 2 to 15 ms. Uptake measurements yielded values of the mass accommodation coefficient (R) and provided information about interactions of

We report a confined proton transportation in the CeO 2 /CeO 2−δ core−shell structure to build up proton shuttles, leading to a super proton conductivity of 0.16 S cm −1 for the electrolyte and advanced fuel cell performance, 697 mW cm −2 at 520 °C. The semiconductor nature of the CeO 2 (i-type) core and the CeO 2−δ (n-type) shell reveals a unique proton transport mechanism based on the charged layers formed at the interface of the CeO 2−δ /CeO 2 heterostructure. Two key factors of this structure confine proton transport to the particle surface. The first is the high concentration of oxygen vacancies in the surface layer, which benefits proton conduction. The second is a depletion region created by the core−shell interface that allows proton migration only on the surface layer rather than into the bulk CeO 2 . The constrained surface region of the CeO 2−δ builds up continuous proton shuttles. This work presents a new methodology and understanding for proton transport in general oxides and a new generation proton ceramic fuel cells.

Abstract. The heterogeneous reactions C1ONO 2 + H20 • HOC1 + HNO3 (1), C1ONO2 + HC1 • C12 + HNO3 (2), and HOC1 + HC1 • C12 + H20 (3)on stratospheric aerosols convert C1ONO2 and HC1 to photo-labile species, producing reactive C1 and C10 which are responsible for catalyzing ozone destruction in the lower stratosphere. The extent of the resulting ozone loss mirrors the steep negative temperature dependence of these reactions, which strongly depend on the solubility of C1ONO2, HC1, and HOC1, and on the activity of H20. Predicting the effect of these heterogeneous processes throughout the stratosphere requires detailed modeling of liquid phase solubility, diffusion, and reaction kinetics. A series of recent experiments from a number of laboratories have refined measurements of liquid diffusion coefficients, HC1 and HOC1 solubilities, and the reactivity of C1ONO 2 + H20, C1ONO2 + HC1 and HC1 + HOC1 on liquid films, droplets, and aerosols. On the basis of those measurements we present a phenomenological uptake model in which parameterizations of C1ONO2, HC1, and HOC1 heterogeneous kinetics appropriate for stratospheric H2SO4/H20 aerosols are addressed. In this model we suggest that under high acid concentration conditions both HOC1 and C1ONO2 are protonated before they react with HC1. Data for all three reactions in concentrated H2SO 4 solution indicate an acid-catalyzed reaction channel, which had previously been inferred for C1ONO2 hydrolysis. This updated parameterization is most significant at relatively high temperatures above 205 K which produce H2SO 4 aerosols of >60 acid wt%, where the acid-catalyzed reaction channels dominate. The comparisons between our new formulation and other recent formulations are presented. Since most stratospheric aerosols are primarily sulfuric acid, detailed knowledge of the processes governing these heterogeneous reactions over the stratospherically relevant acid concentration ranges of--•40 to 80 wt% H2SO 4 is required to understand stratospheric ozone chemistry. These reaction probabilities are strongly dependent on the temperature and water vapor partial pressure, which in turn determine the H2SO4/H20 condensed phase concentration ratio and solubility of C1ONO2, HOC1, and HC1. A number of research groups using complementary experimental techniques have measured these reaction probabilities on sulfuric acid solutions and aero-

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