Simulations of isoprene: Ozone reactions for a general circulation/chemical transport model

A parameterized reaction mechanism has been created to examine the interactions between isoprene and other tropospheric gas-phase chemicals. Tests of the parameterization have shown that its results match those of a more complex reaction set to a high degree of accuracy. Comparisons between test runs have shown that the presence of isoprene at the start of a six day interval can enhance later ozone concentrations by as much as twenty-nine percent. The test cases used no input fluxes beyond the initial time, implying that a single input of a biogenic hydrocarbon to an airmass can alter its ozone chemistry over a time scale on the order of a week

Development of a simple unified volatility-based scheme (SUVS) for secondary organic aerosol formation using genetic algorithms

A new method is proposed to simplify complex atmospheric chemistry reaction schemes, while preserving SOA formation properties, using genetic algorithms. The method is first applied in this study to the gas-phase α-pinene oxidation scheme. The simple unified volatility-based scheme (SUVS) reflects the multi-generation evolution of chemical species from a near-explicit master chemical mechanism (MCM) and, at the same time, uses the volatility-basis set speciation for condensable products. The SUVS also unifies reactions between SOA precursors with different oxidants under different atmospheric conditions. A total of 412 unknown parameters (product yields of parameterized products, reaction rates, etc.) from the SUVS are estimated by using genetic algorithms operating on the detailed mechanism. The number of organic species was reduced from 310 in the detailed mechanism to 31 in the SUVS. Output species profiles, obtained from the original subset of the MCM reaction scheme for α-pinene oxidation, are reproduced with maximum fractional error at 0.10 for scenarios under a wide range of ambient HC/NO<sub>x</sub> conditions. Ultimately, the same SUVS with updated parameters could be used to describe the SOA formation from different precursors

Young children's explorations of average through informal inferential reasoning

This study situates children's early notions of average within an inquiry classroom to investigate the rich inferential reasoning that young children drew on to make sense of the questions: Is there a typical height for a student in year 3? If so, what is it? Based on their deliberations over several lessons, students' ideas about average and typicality evolved as meaning reasonable, contrary to atypical, most common (value or interval), middle, normative, and representative of the population. The case study reported here documents a new direction for the development of children's conceptions of average in a classroom designed to elicit their informal inferential reasoning about data

Prediction of pure water stress corrosion cracking (PWSCC) in nickel base alloys using crack growth rate models

The Ford/Andresen slip dissolution SCC model, originally developed for stainless steel components in BWR environments, has been applied to Alloy 600 and Alloy X-750 tested in deaerated pure water chemistry. A method is described whereby the crack growth rates measured in compact tension specimens can be used to estimate crack growth in a component. Good agreement was found between model prediction and measured SCC in X-750 threaded fasteners over a wide range of temperatures, stresses, and material condition. Most data support the basic assumption of this model that cracks initiate early in life. The evidence supporting a particular SCC mechanism is mixed. Electrochemical repassivation data and estimates of oxide fracture strain indicate that the slip dissolution model can account for the observed crack growth rates, provided primary rather than secondary creep rates are used. However, approximately 100 cross-sectional TEM foils of SCC cracks including crack tips reveal no evidence of enhanced plasticity or unique dislocation patterns at the crack tip or along the crack to support a classic slip dissolution mechanism. No voids, hydrides, or microcracks are found in the vicinity of the crack tips creating doubt about classic hydrogen related mechanisms. The bulk oxide films exhibit a surface oxide which is often different than the oxides found within a crack. Although bulk chromium concentration affects the rate of SCC, analytical data indicates the mechanism does not result from chromium depletion at the grain boundaries. The overall findings support a corrosion/dissolution mechanism but not one necessarily related to slip at the crack tip

Mass tracking for chemical analysis: the causes of ozone formation in southern Ontario during BAQS-Met 2007

A three-level nested regional air pollution model has been used to study the processes leading to high ozone concentrations in the southern Great Lakes region of North America. The highest resolution simulations show that complex interactions between the lake-breeze circulation and the synoptic flow lead to significant enhancements in the photochemical production and transport of ozone at the local scale. Mass tracking of individual model processes show that Lakes Erie and St. Clair frequently act as photochemical ozone production regions, with average mid-day production rates of up to 3 ppbv per hour. Enhanced ozone levels are evident over these two lakes in 23-day-average surface ozone fields. Analysis of other model fields and aircraft measurements suggests that vertical circulation enhances ozone levels at altitudes up to 1500 m over Lake St. Clair, whereas subsidence enhances ozone over Lake Erie in a shallow layer only 250 m deep. Mass tracking of model transport shows that lake-breeze surface convergence zones combined with the synoptic flow can then carry ozone and its precursors hundreds of kilometers from these source areas, in narrow, elongated features. Comparison with surface mesonet ozone observations confirm the presence, magnitude, and timing of these features, which can create local ozone enhancements on the order of 30 ppbv above the regional ozone levels. Sensitivity analyses of model-predicted ozone and HO<sub>x</sub> concentrations show that most of the region is VOC-limited, and that the secondary oxidation pathways of aromatic hydrocarbons have a key role in setting the region's ozone and HO<sub>x</sub> levels

First trimester myomectomy as an alternative to termination of pregnancy in a woman with a symptomatic uterine leiomyoma: a case report

<p>Abstract</p> <p>Introduction</p> <p>Performing a myomectomy during pregnancy is extremely rare due to the risk of pregnancy loss, hemorrhage and hysterectomy. Favorable outcomes have been demonstrated with select second trimester gravid myomectomies. Literature documenting first trimester surgical management of myomas during pregnancy is scant. Patients with symptomatic myomas failing conservative management in the first trimester may be counseled to abort the pregnancy and then undergo myomectomy. Reports focusing on myomectomy in the first trimester are needed to permit more thorough options counseling for patients failing conservative management in the first trimester.</p> <p>Case presentation</p> <p>A 30-year-old Caucasian primagravid (G1P0) was referred for termination of her pregnancy at 10 weeks due to a 14 cm myoma causing severe pain, constipation and urine retention. Her referring physician planned an interval myomectomy following the abortion. Instead, our patient underwent myomectomy at 11 weeks. Two leiomyomas were successfully removed; she delivered a healthy infant at term.</p> <p>Conclusion</p> <p>Patients in the first trimester should not be counseled that termination followed by myomectomy is the best option for symptomatic myomas, failing conservative treatment. Management should be individualized after taking into account the patient's symptoms, gestational age and the location of the myomas in relation to the placenta. Any field providing women's health services will be impacted by the ability to offer more thorough options counseling for women with refractory myomas in the first trimester.</p

The effect of meteorological and chemical factors on the agreement between observations and predictions of fine aerosol composition in southwestern Ontario during BAQS-Met

The Border Air Quality and Meteorology Study (BAQS-Met) was an intensive, collaborative field campaign during the summer of 2007 that investigated the effects of transboundary pollution, local pollution, and local meteorology on air quality in southwestern Ontario. This analysis focuses on the measurements of the inorganic constituents of particulate matter with diameter of less than 1 μm (PM&lt;sub&gt;1&lt;/sub&gt;), with a specific emphasis on nitrate. We evaluate the ability of AURAMS, Environment Canada's chemical transport model, to represent regional air pollution in SW Ontario by comparing modelled aerosol inorganic chemical composition with measurements from Aerosol Mass Spectrometers (AMS) onboard the National Research Council (NRC) of Canada Twin Otter aircraft and at a ground site in Harrow, ON. The agreement between modelled and measured &lt;i&gt;p&lt;/i&gt;NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;&amp;minus;&lt;/sup&gt; at the ground site (observed mean (M&lt;sub&gt;obs&lt;/sub&gt;) = 0.50 μg m&lt;sup&gt;−3&lt;/sup&gt;; modelled mean (M&lt;sub&gt;mod&lt;/sub&gt;) = 0.58 μg m&lt;sup&gt;−3&lt;/sup&gt;; root mean square error (RSME) = 1.27 μg m&lt;sup&gt;−3&lt;/sup&gt;) was better than aloft (M&lt;sub&gt;obs&lt;/sub&gt; = 0.32 μg m&lt;sup&gt;−3&lt;/sup&gt;; M&lt;sub&gt;mod&lt;/sub&gt; = 0.09 μg m&lt;sup&gt;−3&lt;/sup&gt;; RSME = 0.48 μg m&lt;sup&gt;−3&lt;/sup&gt;). Possible reasons for discrepancies include errors in (i) emission inventories, (ii) atmospheric chemistry, (iii) predicted meteorological parameters, or (iv) gas/particle thermodynamics in the model framework. Using the inorganic thermodynamics model, ISORROPIA, in an offline mode, we find that the assumption of thermodynamic equilibrium is consistent with observations of gas and particle composition at Harrow. We develop a framework to assess the sensitivity of PM&lt;sub&gt;1&lt;/sub&gt; nitrate to meteorological and chemical parameters and find that errors in both the predictions of relative humidity and free ammonia (FA ≡ NH&lt;sub&gt;3&lt;/sub&gt;&lt;sub&gt;(g)&lt;/sub&gt; + &lt;i&gt;p&lt;/i&gt;NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; − 2 · &lt;i&gt;p&lt;/i&gt;SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt;) are responsible for the poor agreement between modelled and measured values