Variations in Atmospheric CO2CO_2 Mixing Ratios across a Boston, MA Urban to Rural Gradient

Urban areas are directly or indirectly responsible for the majority of anthropogenic $CO_2$ emissions. In this study, we characterize observed atmospheric $CO_2$ mixing ratios and estimated $CO_2$ fluxes at three sites across an urban-to-rural gradient in Boston, MA, USA. $CO_2$ is a well-mixed greenhouse gas, but we found significant differences across this gradient in how, where, and when it was exchanged. Total anthropogenic emissions were estimated from an emissions inventory and ranged from $1.5 to 37.3 mg·C·ha^{-1}·yr^{-1}$ between rural Harvard Forest and urban Boston. Despite this large increase in anthropogenic emissions, the mean annual difference in atmospheric $CO_2$ between sites was approximately 5% $(20.6 \pm 0.4 ppm)$. The influence of vegetation was also visible across the gradient. Green-up occurred near day of year 126, 136, and 141 in Boston, Worcester and Harvard Forest, respectively, highlighting differences in growing season length. In Boston, gross primary production—estimated by scaling productivity by canopy cover—was ~75% lower than at Harvard Forest, yet still constituted a significant local flux of $3.8 mg·C·ha^{-1}·yr^{-1}$. In order to reduce greenhouse gas emissions, we must improve our understanding of the space-time variations and underlying drivers of urban carbon fluxes.Engineering and Applied Science

Soil surface temperatures reveal moderation of the urban heat island effect by trees and shrubs

Urban areas are major contributors to air pollution and climate change, causing impacts on human health that are amplified by the microclimatological effects of buildings and grey infrastructure through the urban heat island (UHI) effect. Urban greenspaces may be important in reducing surface temperature extremes, but their effects have not been investigated at a city-wide scale. Across a midsized UK city we buried temperature loggers at the surface of greenspace soils at 100 sites, stratified by proximity to city centre, vegetation cover and land-use. Mean daily soil surface temperature over 11 months increased by 0.6 °C over the 5 km from the city outskirts to the centre. Trees and shrubs in non-domestic greenspace reduced mean maximum daily soil surface temperatures in the summer by 5.7 °C compared to herbaceous vegetation, but tended to maintain slightly higher temperatures in winter. Trees in domestic gardens, which tend to be smaller, were less effective at reducing summer soil surface temperatures. Our findings reveal that the UHI effects soil temperatures at a city-wide scale, and that in their moderating urban soil surface temperature extremes, trees and shrubs may help to reduce the adverse impacts of urbanization on microclimate, soil processes and human health

Structure and morphology of segmented polyurethanes: 2. Influence of reactant incompatibility

By following the copolymerization of a model polyurethane system, HTP B D /2,6 (or 2.4 )-TD I /B DO, byoptical microscopy, it was found that initial reactant incompatibility was the key factor in determining thefinal morphology of bulk sample. Based on this finding and the esults from the previous paper, modelsare proposed to describe the morphology during polymerization of this particular polyurethane systemfor several hard segment compositions where both macro-phase separation and micro-phase separationof reactants can occur during polymerization. The copolymerization of one seemingly compatiblesystem, PPO-EO/MDl/BDO, which has been previously studied and commercially produced, was alsofollowed by optical microscopy. In the size range which can be detected with an optical microscopeusing conventional optics, no heterogeneities were observable at the beginning of this reaction butphase separation was evident later in the reaction and can be xplained by the presence of micro-phaseseparation of reactants. Globule and spherulite formation and the presence of multiple T(g)\u27s and T(m)\u27sobserved by previous workers can be explained by the two levels of heterogenities present duringpolymerization

Using Block Copolymer Self-Assembly to Imprint the Crystallization of Polymer Dendrites

We utilize the self-assembly of cylinder-forming block copolymer (BCP) films to create templates for dendritic polymercrystallization patterns. This templating was achieved by simply spin-casting thin films from a solution containing both the BCP [polystyrene-block-poly(ethylene oxide) (PS-b-PEO)] and a homopolymer (polyethylene oxide) under controlled vapor atmosphere conditions, without the need for any additional processing (e.g. solvent or thermal annealing). The BCP first organized into a hexagonal array of vertically oriented PEO cylinders that served to template dendritic PEOhomopolymer crystals on the surface of the BCP pattern. No surface defects such as dewetting holes or macroscopically phase-separated domains were observed on top of the BCP film. We find that the PEOdendrites crystallized on this BCP template exhibit a periodic height undulation pattern on their surface. The undulation pattern directly reflects the hexagonal pattern symmetry and associated height undulations of the BCP underneath these crystals. The formation of this hierarchically organized polymercrystallization morphology illustrates how one self-assembly can be used as a template to control the organization of another self-assembly process—a fabrication strategy of potentially great significance in the programming of complex structures using self-assembly

Article Variations in Atmospheric CO2 Mixing Ratios across a Boston, MA Urban to Rural Gradient

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