The technique of single-particle mass spectrometry has been coupled to a reaction flow tube to measure the uptake coefficient, γ, of ozone (O 3 ) by oleic acid (9-octadecenoic acid) aerosol particles. The reaction was followed by monitoring the decrease of oleic acid in the size-selected particles as a function of O 3 exposure. The reactive uptake coefficient is found to depend on the size of the particle, with γ meas ranging from (7.3 ( 1.5) × 10 -3 to (0.99 ( 0.09) × 10 -3 for particles ranging in radius from 680 nm to 2.45 µm. It is suggested that the decrease in γ meas with increasing particle size results from the reaction being limited by the diffusion of oleic acid within the particle, and based on our measurements we estimate the value of γ to be (5.8-9.8) × 10 -3 for particles that are not limited by oleic acid diffusion. A reaction model that includes simultaneous diffusion and reaction of both O 3 and oleic acid is developed and used to fit the observed rates of reaction. Solutions obtained from this model indicate that oleic acid must diffuse within the particle more slowly than is predicted by the measured oleic acid self-diffusion constant. 1 It is proposed that this oleic acid-diffusionlimited uptake is attributable to the ozonolysis reaction products. Furthermore, these experiments demonstrate that it is not always possible to describe heterogeneous uptake by a model that decouples all relevant processes, including reaction and diffusion. Finally, the possible implications that these findings have for the role of particle morphology in the reaction of gas-phase species with atmospheric aerosols are discussed.

Frequency-dependent optical constants have been determined from the Fourier transform infrared spectra of laboratory-generated liquid sulfuric acid/water aerosols over a range of temperatures and compositions that are relevant to the upper troposphere and lower stratosphere of Earth. The compositions of the particles were determined in situ using a tunable diode laser to monitor equilibrium water vapor pressures. The infrared complex refractive indices of sulfuric acid are shown to be strongly dependent on temperature and composition, because of changes in the equilibrium between sulfate and bisulfate ions. Results from this study also have implications in understanding the temperature dependence of intermolecular interactions within ionic solutions. The database presented here is the most extensive yet available for the liquid solutions of sulfuric acid.

Ambient high‐volume (hi‐vol) air samples were collected between 15 March and 30 May 2002, at Cheeka Peak Observatory (CPO), located on the tip of the Olympic Peninsula, Washington State. This sampling campaign was in conjunction with the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) campaign and the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere 2 (PHOEBA2) experiment. The anthropogenic semivolatile organic compounds (SOCs) measured during this time period included polycyclic aromatic hydrocarbons (PAHs) and various U.S. current‐use and historical‐use pesticides. The total PAH concentration ranged from 0.480 to 4.49 ng/m3, which is comparable to other remote sites throughout the globe. Ten pesticides (hexachlorobenzene, dacthal, chlorothalonil, heptachlor, trans‐nonachlor, cis‐nonachlor, endosulfan I, triallate, trifluralin, and mirex) were also measured, and their concentrations (0.104–57.0 pg/m3) were comparable to other remote sites and less than agricultural areas. Gas‐phase/particle‐phase partitioning was explored, with significant correlation to temperature found with endosulfan I and retene and the possible relationship at CPO of low TSP concentration and the concentration of nonexchangeable compounds in the particle phase. Principal component analysis, as well as a t‐test, showed that there were elevated concentrations of anthropogenic SOCs measured during possible transpacific events on 15–16 March, 27–28 March, and 22–23 April 2002 that were identified using the GEOS‐CHEM model. The potential sources of these compounds at CPO were determined using diagnostic ratios of their concentrations, back trajectories calculated using Hybrid Single‐Particle Lagrangian Integrated Trajectory (HYSPLIT4), local meteorological conditions, and U.S. pesticide use data. Additional data are needed to confirm the sources of anthropogenic SOCs at CPO during regional and transpacific atmospheric transport events.

Hydrogen peroxide concentrations obtained by a commonly used stripping coil method were compared with data obtained by the method of collection and analysis of atmospheric condensate. Good agreement was achieved between gas-phase hydrogen peroxide concentrations obtained by each method over the concentration range from 0.1 to 1.8 ppb; the average deviation between the analytical results and the mean of those results was 10%. The deviations between concentrations obtained by each method were random, suggesting no systematic differences. Because of this analytical agreement and the versatility of the condensate collection technique, this method was employed in several field applications. Gas-phase hydrogen peroxide concentrations were determined from condensate samples collected during the summers of 1994 and 1995 in and near Wilmington, NC. Concentrations were not statistically different (t-test, p < 0.05) in samples collected at the Wilmington reference site relative to a nearby salt marsh. Gas-phase hydrogen peroxide concentrations were lower at an automobile traffic-impacted site relative to this reference site. Midday net production rates at sea over the Gulf Stream and Sargasso Sea (110 + 55 ppt/h) were one-quarter of those on land (440 + 230 ppt/h) during comparable times, in agreement with prior stripping coil results.

Studies of the interaction between a pulsed CO2 laser and micrometer-sized aqueous and organic particles by use of light-scattering methods and step-scan Fourier-transform infrared (FTIR) spectroscopy are reported. Visible two-color extinction experiments indicate primary particle shattering, accompanied by a high fraction of vaporization, followed by secondary particle evaporation. The extent of the latter depends on the pulse intensity and particle composition. Angle-resolved light-scattering investigations provide insight into the aerosol size distribution and temperature following the pulsed heating event. The time dependence of the vapor plume, monitored with step-scan FTIR spectroscopy, confirms that a large fraction of the initial particle is quickly evaporated during the shattering event, followed by secondary fragment evaporation and thermal expansion.

A new approach is reported for determining the composition of multicomponent organic aerosols using FT-IR spectroscopy. In this study, laboratory-generated aerosol particles are thermally evaporated and the resulting vapor is immediately analyzed using FT-IR spectroscopy. The composition of the aerosol is determined by fitting the vapor spectrum to a linear combination of reference spectra of the individual components. Application of the method to the detection of polycyclic aromatic hydrocarbons, changes in aerosol composition, and analysis of diesel fuel is demonstrated.