Particle Formation and Growth From Ozonolysis of α-pinene

Observations of particle nucleation and growth during ozonolysis of α-pinene were carried out in Calspan\u27s 600 m3 environmental chamber utilizing relatively low concentrations of α-pinene (15 ppb) and ozone (100 ppb). Model simulations with a comprehensive sectional aerosol model which incorporated the relevant gas-phase chemistry show that the observed evolution of the size distribution could be simulated within the accuracy of the experiment by assuming only one condensable product produced with a molar yield of 5% to 6% and a saturation vapor pressure (SVP) of about 0.01 ppb or less. While only one component was required to simulate the data, more than one product may have been involved, in which case the one component must be viewed as a surrogate having an effective SVP of 0.01 ppb or less. Adding trace amounts of SO2greatly increased the nucleation rate while having negligible effect on the overall aerosol yield. We are unable to explain the observed nucleation in the α-pinene/ozone system in terms of classical nucleation theory. The nucleation rate and, more importantly, the slope of the nucleation rate versus the vapor pressure of the nucleating species would suggest that the nucleation rate in the α-pinene/ozone system may be limited by the initial nucleation steps (i.e., dimer, trimer, or adduct formation)

Sulfur Dioxide Uptake and Oxidation in Sea-Salt Aerosol

Measurements of SO2 and O3 uptake by sea-salt and NaCl aerosol were made in a 600 m3environmental chamber by measuring the rate of SO2 and O3 depletion during nebulization of seawater and NaCl solutions. The experiments were carried out with starting relative humidity between 80% and 92%, with SO2 concentrations between 35 and 60 ppb, and ozone concentrations between O and 110 ppb. For NaCl, no SO2 or O3uptake was observed. For sea-salt aerosol, uptake in the range of 0.21 and 1.2 millimoles of S per liter of (nebulized) seawater was observed. Surprisingly, no O3 uptake was observed even though the residence time of the aerosol in the chamber was long compared to the time required for the predicted S(IV)-O3 reaction to occur. Several S(IV) oxidation schemes are considered to explain these observations. The Cl-catalyzed aerobic mechanism as formulated by Zhang and Millero [1991] from empirical data best explains our observations. The Cl-catalyzed S(IV) reaction decreases rapidly with decreasing pH, making it important only at pH\u3e∼5.5. This rapid decrease with pH explains why SO2uptake was not observed in the NaCl aerosol and observed at a level approaching the sea-salt alkalinity in the case of sea-salt aerosol

In-cloud oxidation of SO2 by O3 and H2O2: Cloud Chamber Measurements and Modeling of Particle Growth

Controlled cloud chamber experiments were conducted to measure particle growth resulting from the oxidation of SO2 by O3 and H2O2 in cloud droplets formed on sulfuric acid seed aerosol. Clouds were formed in a 590 m3 environmental chamber with total liquid water contents ranging from 0.3–0.6 g m−3 and reactant gas concentrations \u3c10 ppbv for SO2 and H2O2 and \u3c70 ppbv for O3. Aerosol growth was measured by comparison of differential mobility analyzer size distributions before and after each 3–4 min cloud cycle. Predictions of aerosol growth were then made with a full microphysical cloud model used to simulate each individual experimental cloud cycle. Model results of the H2O2 oxidation experiments best fit the experimental data using the third-order rate constant of Maass et al. [1999] (k = 9.1 × 107 M−2 s−1), with relative aerosol growth agreeing within 3% of measured values, while the rate of Hoffmann and Colvert [1985] produced agreement within 4–9%, and the rate of Martin and Damschen [1981] only within 13–18%. Simulation results of aerosol growth during the O3 oxidation experiments were 60–80% less than the measured values, confirming previous results [Hoppel et al., 1994b]. Experimental results and analyses presented here show that the SO2 - O3 rate constants would have to be more than 5 times larger than currently accepted values to explain the measured growth. However, unmeasured NH3 contamination present in trace amounts (\u3c0.2 ppb) could explain the disagreement, but this is speculative and the source of this discrepancy is still unknown

Experimental and Modeling Studies of Secondary Organic Aerosol Formation and Some Applications to the Marine Boundary Layer

A series of controlled experiments were carried out in the Calspan Corporation\u27s 600 m3environmental chamber to study some secondary organic aerosol formation processes. Three precursor-ozone systems were studied: cyclopentene-ozone, cyclohexene-ozone, and α-pineneozone. Additionally, SO2 was added to the initial gas mixture in several instances and was likely present at trace levels in the ostensibly organic-only experiments. It was found that all three systems readily formed new submicron aerosols at very low reactant levels. The chemical composition of formed aerosols was consistent with some previous studies, but the yields of organic products were found to be lower in the Calspan experiments. A three-step procedure is proposed to explain the observed particle nucleation behavior: HO · production → H2SO4 formation → H2SO4-H2O (perhaps together with NH3) homogeneous nucleation. It is also proposed that some soluble organic products would partition into the newly formed H2SO4-H2O nuclei, enhance water condensation, and quickly grow these nuclei into a larger size range. While the observations in the two cycloolefin-ozone systems could be well explained by these proposed mechanisms, the exact nature of the nucleation process in the α-pinene-ozone system remains rather opaque and could be the result of nucleation involving certain organics. The results from three simple modeling studies further support these proposals. Their applicability to the marine boundary layer (MBL) is also discussed in some detail. Particularly, such a particle nucleation and growth process could play an important role in secondary aerosol formation and, quite likely, CCN formation as well in certain MBL regions

DETERMINATION OF THE A10 DISSOCIATION ENERGY BY A LASER FLUORESCENCE STUDY OF THE A1+O2A1 + O_{2} REACTION

${^{1}}$ Studied previously with an unselected effusive A1 beam [P. J. Dagdigian, H. W. Cruse, and R. N. Zare, J. Chem. Phys. 62, 1824 (1975)]. ${^{2}}L$. Pasternack and P. J. Dagdigian, Rev. Sci. Instrum., March 1977 issue. Acknowledgment is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, and to the National Science Foundation for support of this research.Author Institution: Department of Chemistry, The Johns Hopkins UniversityThe reaction of velocity selected A1 atoms with $O_{2}$ has been studied by laser-induced $fluorescence^{1}$ so that individual A10 internal states could be observed. Velocity-selection is achieved by a recently developed time-of-flight (TOF) $technique^{2}$ utilizing pulsed laser excitation. Spectra of the A10 B-X system have been taken at several A1 velocities, and the intensities of the $\Delta\nu = + 1$ band heads as a function of A1 velocity have also been measured. Using two different methods of analysis, we have arrived at a value of $D_{0}{^\circ (A10)} = 123 \pm 1$ kcal/mole. One method employs the excitation spectra to find the maximum internal energy of A10 formed, while in the other, the translational energy threshold for formation of v = 2 A10 is determined. The present value agrees well with previous determinations by other methods; moreover, the present experiment considerably narrows the permissible range of values for $D_{0}{^\circ (A10)}$

APPLICATION OF SATURATION SPECTROSCOPE FOR MEASUREMENT OF Na AND MgO CONCENTRATIONS IN ACETYLENE FLAMES

Louise Pasternak has been an NRC/NRL Resident Research Associate.Author Institution: Naval Research LaboratoryAbsolute atomic Na and MgO concentrations in an acetylene air flame are determined using laser-induced fluorescence saturation spectroscopy. The combustor is a slot burner using salt solutions aspirated into premixed acetylene and air to create a stable, homogeneous, atmospheric pressure flame. Independent atomic and molecular absorption measurements are made for Na and the MgO $(X^{1}\Sigma^{+})$ state which are in agreement with the saturation spectroscopy concentration determinations. We will report laser-induced fluorescence spectra of MgO $(B^{1}\Sigma^{+} - X^{1}\Sigma^{+})$ and $(B^{1}\Sigma^{+} - A^{1}\Pi)$ transitions. From the relative intensities of these spectra it is apparent that a significant inversion exists between MgO A and X states in the flame

Treatment Preferences in Young Adults with Moderate to Severe Psoriasis: A Qualitative Study from the Nordic Countries

Introduction The purpose of this study is to explore treatment preferences and identify patient characteristics in young bio-naive adults with moderate to severe psoriasis in the Nordic countries (Norway, Finland, Sweden, and Denmark). Methods Patients were 18–45 years old and bio-naive but referred for biologic treatment of moderate to severe psoriasis. Patients were included at eight Nordic dermatology clinics. Patients with significant comorbidity or psoriatic arthritis were excluded. The Psoriasis Area and Severity Index (PASI) and Dermatology Life Quality Index (DLQI) were assessed along with basic patient information. A semistructured interview guide was used in individual qualitative interviews, asking patients about their treatment preferences and reasons, disease journey, and disease management. The interviews were analyzed using thematic content analysis. Twenty-four patients sufficed to reach saturation in this qualitative study. Results The patient sample characteristics represented a qualitative variation in age, sex, symptoms, duration of disease, and country. We included a total of 12 male and 12 female patients. The mean age was 34 years (range 18–45 years), the mean age at diagnosis was 20 years (range 6–34 years), the mean ± standard deviation (SD) time since diagnosis was 13 ± 8 years, PASI was 9.5 ± 4.7, and DLQI was 15.2 ± 6.4. Interviews suggested that both the burden of disease as well as the burden of treatment influenced patient preferences regarding treatment attributes, hence getting alleviation from symptoms did not alone influence patient preferences. Time, effort, and inconvenience related to psoriasis treatments also influenced patient preferences. Conclusions This first in-depth, qualitative study in young bio-naive adults with psoriasis suggests that patient preferences are focusing not only on symptom relief but also on alleviating the burden of psoriasis treatment. Understanding the reasons for patient preferences and the perspectives of young adults is needed to guide individual shared decision-making in psoriasis management.publishedVersio