Search

The terrestrial ecosystems of North America have been identified as a sink of atmospheric CO though there is no consensus on the magnitude. However, the emissions of non-CO greenhouse gases (CH and NO) may offset or even overturn the climate cooling effect induced by the CO sink. Using a coupled biogeochemical model, in this study, we have estimated the combined global warming potentials (GWP) of CO, CH and NO fluxes in North American terrestrial ecosystems and quantified the relative contributions of environmental factors to the GWP changes during 1979-2010. The uncertainty range for contemporary global warming potential has been quantified by synthesizing the existing estimates from inventory, forward modeling, and inverse modeling approaches. Our 'best estimate' of net GWP for CO, CH and NO fluxes was −0.50 ± 0.27 Pg CO eq/year (1 Pg = 10 g) in North American terrestrial ecosystems during 2001-2010. The emissions of CH and NO from terrestrial ecosystems had offset about two thirds (73 %±14 %) of the land CO sink in the North American continent, showing large differences across the three countries, with offset ratios of 57 % ± 8 % in US, 83 % ± 17 % in Canada and 329 % ± 119 % in Mexico. Climate change and elevated tropospheric ozone concentration have contributed the most to GWP increase, while elevated atmospheric CO concentration have contributed the most to GWP reduction. Extreme drought events over certain periods could result in a positive GWP. By integrating the existing estimates, we have found a wide range of uncertainty for the combined GWP. From both climate change science and policy perspectives, it is necessary to integrate ground and satellite observations with models for a more accurate accounting of these three greenhouse gases in North America. [ABSTRACT FROM AUTHOR]

Organic polymer solar materials are shown to exhibit better solubility in mixed solvents than in pure ones, which affects the performance of their solar cells. In this article, poly[ N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole) (PCDTBT) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) are used as active layer materials in solar cells. To optimize the performance of these active materials, the ratio of chloroform (CF) to chlorobenzene used as solvents to dissolve PCDTBT, and PCBM is varied, which is shown to affect power conversion efficiency (PCE). The solar cell that shows the best performance with a PCE as high as 6.82 % is produced using a volume ratio of CF to chlorobenzene of 1:1. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems in the southern United States (SUS) have experienced a complex set of changes in climate, atmospheric CO concentration, tropospheric ozone (O), nitrogen (N) deposition, and land-use and land-cover change (LULCC) during the past century. Although each of these factors has received attention for its alterations on ecosystem carbon (C) dynamics, their combined effects and relative contributions are still not well understood. By using the Dynamic Land Ecosystem Model (DLEM) in combination with spatially explicit, long -term historical data series on multiple environmental factors, we examined the century-scale responses of ecosystem C storage and flux to multiple environmental changes in the SUS. The results indicated that multiple environmental changes shifted SUS ecosystems from a C source of 1.20 ± 0.56 Pg (1 Pg = 10 g) during the period 1895 to 1950, to a C sink of 2.00 ± 0.94 Pg during the period 1951 to 2007. Over the entire period spanning 1895-2007, SUS ecosystems were a net C sink of 0.80 ± 0.38 Pg. The C sink was primarily due to an increase in the vegetation C pool, whereas the soil C pool decreased during the study period. The spatiotemporal changes of C storage were caused by changes in multiple environmental factors. Among the five factors examined (climate, LULCC, N deposition, atmospheric CO, and tropospheric O), elevated atmospheric CO concentration was the largest contributor to C sequestration, followed by N deposition. LULCC, climate, and tropospheric O concentration contributed to C losses during the study period. The SUS ecosystem C sink was largely the result of interactive effects among multiple environmental factors, particularly atmospheric N input and atmospheric CO [ABSTRACT FROM AUTHOR]