Quantitative structures of the fully hydrated fluid phases of dimyristoylphosphatidylcholine (DMPC) and dilauroylphosphatidylcholine (DLPC) were obtained at 30 degrees C. Data for the relative form factors F(q(z)) for DMPC were obtained using a combination of four methods. 1), Volumetric data provided F(0). 2), Diffuse x-ray scattering from oriented stacks of bilayers provided relative form factors |F(q(z))| for high q(z), 0.22 < q(z) < 0.8 A(-1). 3), X-ray scattering from extruded unilamellar vesicles with diameter 600 A provided |F(q(z))| for low q(z), 0.1 < q(z) < 0.3 A(-1). 4), Previous measurements using a liquid crystallographic x-ray method provided |F(2 pi h/D)| for h = 1 and 2 for a range of nearly fully hydrated D-spacings. The data from method 4 overlap and validate the new unilamellar vesicles data for DMPC, so method 4 is not required for DLPC or future studies. We used hybrid electron density models to obtain structural results from these form factors. Comparison of the model electron density profiles with that of gel phase DMPC provides areas per lipid A, 60.6 +/- 0.5 A(2) for DMPC and 63.2 +/- 0.5 A(2) for DLPC. Constraints on the model provided by volume measurements and component volumes obtained from simulations put the electron density profiles rho(z) and the corresponding form factors F(q(z)) on absolute scales. Various thicknesses, such as the hydrophobic thickness and the steric thickness, are obtained and compared to literature values.

Arrays of bilayers of the lipid dimyristoylphosphatidylcholine ͑DMPC͒ exhibit anomalous swelling as the temperature decreases from T = 27°C toward the main phase transition at T M = 24°C, within the fluid L ␣ thermodynamic phase. Analysis of diffuse x-ray scattering data from oriented stacks of biological lipid bilayers now makes it possible to obtain the bending modulus K C and the bulk compressibility modulus B separately. We report results that show that the measured bending modulus K C for DMPC decreases by almost a factor of 2 between T = 27°C and the transition temperature at T M = 24°C, which is the same temperature range where the anomalous swelling occurs. We also report Monte Carlo simulations that show that the anomalous swelling can be fully accounted for by the measured decrease in K C with no changes in the van der Waals or hydration forces.

A simple statistical method is described for identifying the likely importance of local sources of PM2.5 in a region on days when the National Ambient Air Quality Standard is exceeded. The method requires only PM2.5 mass concentration and wind direction data, and makes use of the EPA database on PM2.5 emissions in the local region of interest. The method has been illustrated using data from the Pittsburgh Air Quality Study, and suggests that local sources can be very important in affecting PM2.5 exceedances. The results have implications for many of the urban areas in the eastern United States downwind of large sources in the Midwest, and shows that simple statistical tests can be of value in identifying regions where further testing with sophisticated air quality dispersion models and source-receptor models is warranted.

BackgroundBraddock, Pennsylvania is home to the Edgar Thomson Steel Works (ETSW), one of the few remaining active steel mills in the Pittsburgh region. An economically distressed area, Braddock exceeds average annual (>15 μg/m3) and daily (>35 μg/m3) National Ambient Air Quality Standards (NAAQS) for particulate matter (PM2.5).MethodsA mobile air monitoring study was designed and implemented in morning and afternoon hours in the summer and winter (2010–2011) to explore the within-neighborhood spatial and temporal (within-day and between-day) variability in PM2.5 and PM10.ResultsBoth pollutants displayed spatial variation between stops, and substantial temporal variation within and across study days. For summer morning sampling runs, site-specific mean PM2.5 ranged from 30.0 (SD = 3.3) to 55.1 (SD = 13.0) μg/m3. Mean PM10 ranged from 30.4 (SD = 2.5) to 69.7 (SD = 51.2) μg/m3, respectively. During summer months, afternoon concentrations were significantly lower than morning for both PM2.5 and PM10, potentially owing to morning subsidence inversions. Winter concentrations were lower than summer, on average, and showed lesser diurnal variation. Temperature, wind speed, and wind direction predicted significant variability in PM2.5 and PM10 in multiple linear regression models.ConclusionsData reveals significant morning versus afternoon variability and spatial variability in both PM2.5 and PM10 concentrations within Braddock. Information obtained on peak concentration periods, and the combined effects of industry, traffic, and elevation in this region informed the design of a larger stationary monitoring network.

Using data from the Pittsburgh Air Quality Study, we find that temperature, relative humidity, their squared terms, and their interactions explain much of the variation in airborne concentrations of PM 2.5 in the city. Factors that do not appreciably influence the concentrations over a full year include wind direction, inverse mixing height, UV radiation, SO 2 , O 3 , and season of the year. Comparison with similar studies of PM 2.5 in other cities suggests that the relative importance of different factors can vary greatly. Temperature and relative humidity are important factors in both Pittsburgh and New York City, and synoptic scale meteorology influencing these two sites can explain much of the pattern in PM 2.5 concentrations which peak in the summer. However, PM 2.5 levels in other cities have different seasonal patterns and are affected by a number of other factors, and thus the results presented here cannot be generalized to other locations without additional study.

No abstract