ALBERT

Description: A significant source of ozone in the troposphere is transport from the stratosphere. The stratospheric contribution has been estimated mainly using global models that attribute the transport process largely to the global scale Brewer-Dobson circulation and synoptic scale dynamics associated with upper tropospheric jet streams. We report observations from research aircraft that reveal additional transport of ozone-rich stratospheric air downward into the upper troposphere by a leading-line-trailing-stratiform (LLTS) mesoscale convective system (MCS) with convection overshooting the tropopause altitude. The fine-scale transport demonstrated by these observations poses a significant challenge to global models that currently do not resolve storm scale dynamics. Thus the upper tropospheric ozone budget simulated by global chemistry-climate models where large-scale dynamics and photochemical production from lightning-produced NO are the controlling factors may require modification.

Description: Humic-like substances (HULIS) are a complex group of relatively high molecular weight organic compounds which contribute considerably to the mass of organic carbon (OC) and influence the light-absorbing properties of aerosols. In this work, HULIS were investigated for the first time in the high-Arctic atmosphere, focusing on the chemical characterization and mass contribution of HULIS to the total suspended particle (TSP) mass using weekly aerosol samples collected at Station Nord, north east Greenland every 4 th week during 2010. Average HULIS-C concentration was 11 ng C m -3 during the darker months (November - April) and 4 ng C m -3 during the other months (May - October) with an annual mass concentration of 0.02 ± 0.01 µg m -3 . HULIS-C contributed to 3 - 16 % of WSOC whereas HULIS accounted for 0.7 - 4.1 % of TSP mass, with TSP typically below 1.0 µg m -3 . Concentrations of OC, water soluble organic carbon (WSOC), HULIS, selected HULIS functional groups (carboxylic acids, aromatic carboxylic acids and organosulfates) and levoglucosan overlapped with the typical Arctic haze pattern with elevated concentrations during winter - early spring. The aromatic carboxylic acid portion accounted for a larger share of total carboxylic acid of HULIS during the darker months (7%) compared to the brighter months (3%). The more abundant aromatic carboxylic acid functional groups and the moderate correlation between HULIS and levoglucosan concentrations during the darker months both indicate that biomass burning aerosols and thereby emissions of aromatic compounds could contribute to HULIS in the Arctic, especially during late winter. During the brighter months, relatively higher average molecular weight (AMW) of HULIS was observed.

Description: In California, emission control strategies have been implemented to reduce air pollutants. Here we estimate the changes in nitrogen oxides (NO x  = NO + NO 2 ) emissions in 2005-2010 using a state-of-the-art four-dimensional variational (4D-Var) approach. We separately and jointly assimilate surface NO 2 concentrations and tropospheric NO 2 columns observed by Ozone Monitoring Instrument (OMI) into the regional-scale STEM chemical transport model on a 12 × 12 km 2 horizontal resolution grid in May 2010. The assimilation generates grid-scale top-down emission estimates, and the updated chemistry fields are evaluated with independent aircraft measurements during the NOAA CalNex field experiment. The emission estimates constrained only by NO 2 columns, only by surface NO 2 , and by both indicate statewide reductions of 26%, 29%, 30% from ~0.3 Tg N/year in the base year of 2005, respectively. The spatial distributions of the emission changes differ in these cases, which can be attributed to many factors including the differences in the observation sampling strategies and their uncertainties, as well as those in the sensitivities of column and surface NO 2 with respect to NO x emissions. The updates in California's NO x emissions reduced the mean error in modeled surface ozone in the western US, even though the uncertainties in some urban areas increased due to their NO x -saturated chemical regime. The statewide reductions in NO x emissions indicated from our observationally-constrained emission estimates are also reflected in several independently-developed inventories: ~30% in the California Air Resources Board (CARB) bottom-up inventory, ~4% in the 2008 National Emission Inventory, and ~20% in the annual-mean top-down estimates by Lamsal et al. using the global GEOS-Chem model and OMI NO 2 columns. Despite the grid-scale differences among all top-down and bottom-up inventories, they all indicate stronger emission reductions in the urban regions. This study shows the potential of using space/ground-based monitoring data and advanced data assimilation approach to timely and independently update NO x emission estimates on a monthly scale and at a fine grid resolution. The well-evaluated results here suggest that these approaches can be applied more broadly.

Description: Recent findings in several organ systems show that cytoneme-mediated signaling transports signaling proteins along cellular extensions and targets cell-to-cell exchanges to synaptic contacts. This mechanism of paracrine signaling may be a general one that is used by many (or all) cell types in many (or all) organs. We briefly review these findings in this perspective. We also describe the properties of several signaling systems that have previously been interpreted to support a passive diffusion mechanism of signaling protein dispersion, but can now be understood in the context of the cytoneme mechanism. Also watch the Video Abstract . The importance of paracrine signaling for animal development has been recognized for almost 100 years, but the discovery that epithelial cells transport signaling proteins over long distances with filopodia that make direct contact with target cells is recent. In this perspective we review the new findings and explore some of their many implications.

Description: The Lancang/Mekong River Basin is presently undergoing a period of rapid hydropower development. In its natural undeveloped state, the river transports about 160 million metric tons of sediment per year, maintaining the geomorphologic features of the basin, sustaining habitats, and transporting the nutrients that support ecosystem productivity. Despite the importance of sediment in the river, currently little attention is being paid to reservoir sediment trapping. This study is devoted to assessing the potential for managing sediment and its impact on energy production in the Se San, Sre Pok and Se Kong tributaries of the Mekong River. These tributaries drain a set of adjacent watersheds that are important with respect to biodiversity and ecological productivity, and serve as a significant source of flow and sediment to the mainstream Mekong River. A daily sediment transport model is used to assess tradeoffs among energy production and sediment and flow regime alteration in multiple reservoir systems. This study finds that eventually about 40%-80% of the annual suspended sediment load may be trapped in reservoirs. Clearly, these reservoirs will affect the rivers' sediment regimes. However, even after 100 years of simulated sedimentation, reservoir storage capacities and hydropower production at most reservoir sites are not significantly reduced. This suggests that the strongest motivation for implementing measures to reduce trapped sediment is their impact not on hydropower production but on fish migration and survival and on sediment dependent ecosystems such as the Vietnam Delta and Cambodia's Tonle Sap Lake.

Description: The U.S. Department of Energy has mandated the production of 16 billion gallons (60.6 billion liters) of renewable biofuel from cellulosic feedstocks by 2022. The perennial grass, Miscanthus x giganteus , is a potential candidate for cellulosic biofuel production because of high productivity with minimal inputs. This study determined the effect of three different spring fertilizer treatments (0, 60, and 120 kg N ha −1 yr −1 as urea) on biomass production, soil organic matter (SOM), and inorganic N leaching in Illinois, Kentucky, Nebraska, New Jersey, and Virginia, along with N 2 O and CO 2 emissions at the IL site. There were no significant yield responses to fertilizer treatments, except at the IL site in 2012 (yields in 2012, year 4, varied from 10 to 23.7 Mg ha −1 across all sites). Potentially mineralizable N increased across all fertilizer treatments and sites in the 0 – 10 cm soil depth. An increase in permanganate oxidizable carbon (POX-C, labile C) in surface soils occurred at the IL and NJ sites, which were regularly tilled before planting. Decreases in POX-C were observed in the 0 – 10 cm soil depth at the KY and NE sites where highly managed turfgrass was grown prior to planting. Growing M . x giganteus altered SOM composition in only four years of production by increasing the amount of potentially mineralizable N at every site, regardless of fertilization amount. Nitrogen applications increased N leaching and N 2 O emission without increasing biomass production. This suggests that for the initial period (4 yr) of M . x giganteus production, N application has a detrimental environmental impact without any yield benefits and thus should not be recommended. Further research is needed to define a time when N application to M . x giganteus results in increased biomass production. This article is protected by copyright. All rights reserved.

Description: To meet U.S. renewable fuel mandates, perennial grasses have been identified as important potential feedstocks for processing into biofuels. Triploid Miscanthus × giganteus , a sterile, rhizomatous grass, has proven to be a high-yielding biomass crop over the past few decades in the European Union and, more recently, in the U.S. However, high establishment costs from rhizomes are a limitation to more widespread plantings without government subsidies. A recently developed tetraploid cultivar of M . × giganteus producing viable seeds (seeded miscanthus) shows promise in producing high yields with reduced establishment costs. Field experiments were conducted in Urbana, Illinois from 2011 to 2013 to optimize seeded miscanthus establishment by comparing seeding rates (10, 20 and 40 seeds m −2 ) and planting methods (drilling seeds at 38 and 76 cm row spacing versus hydroseeding with and without pre-moistened seeds) under irrigated and rainfed conditions. Drought conditions in 2011 and 2012 coincided with stand establishment failure under rainfed conditions, suggesting that seeded miscanthus may not establish well in water-stressed environments. In irrigated plots, hydroseeding without pre-moistening was significantly better than hydroseeding with pre-moistening, drilling at 38 cm and drilling at 76 cm with respect to plant number (18, 54 and 59% higher, respectively), plant frequency (13, 30 and 40% better, respectively), and the rate of canopy closure (18, 33 and 43% faster, respectively) when averaged across seeding rates. However, differences in second-year biomass yields among treatments were less pronounced, as plant size partially compensated for plant density. Both hydroseeding and drilling at rates of 20 or 40 seeds m −2 appear to be viable planting options for establishing seeded miscanthus provided sufficient soil moisture, but additional strategies are required for this new biomass production system under rain-fed conditions. This article is protected by copyright. All rights reserved.

Description: Concerns about invasions by novel bioenergy feedstocks are valid, given the parallels between the traits of energy crops and those of many common invasive plants. As the bioenergy industry is poised to introduce nonnative bioenergy crops to large acreages in the United States under state and federal mandates, it is important to consider these concerns – and not simply in an academic sense. Instead, the prevention of invasions should be codified in statutes and regulations pertaining to bioenergy production on both the state and federal level. Unfortunately, this is not occurring regularly or consistently at this time. The few existing regulations that do consider invasiveness in bioenergy systems suffer from vague terminology that could have major economic, environmental, and legal consequences. Here, we discuss existing regulatory challenges and provide solutions to address invasion potential of bioenergy crops. We provide model definitions and provisions to be included in revised or new state and federal regulations, including an invasion risk assessment process, a permit and bond system for high-risk crops, and a risk mitigation provision for all novel crops. Our proposal provides a consistent and transparent system that will allow the industry to move forward with minimal risk of invasion by novel feedstocks.

Description: We present in situ observations of convectively injected water vapor in the lower stratosphere from instruments aboard two aircraft operated during the Deep Convective Clouds and Chemistry (DC3) experiment. Water vapor mixing ratios in the injected air are observed to be 60-225 ppmv at altitudes 1-2 km above the tropopause (350-370 K potential temperature), well above observed background mixing ratios of 5-10 ppmv in the lower stratosphere. Radar observations of the responsible convective systems show deep overshooting at altitudes up to 4 km above the lapse-rate tropopause and above the flight ceilings of the aircraft. Backward trajectories from the in situ observations show that convectively injected water vapor is observed from three distinct types of systems: isolated convection, a convective line, and a leading line - trailing stratiform mesoscale convective system. Significant transport of additional tropospheric or boundary layer trace gases is observed only for the leading-line trailing stratiform case. In addition, all observations of convective injection are found to occur within large-scale double tropopause events from poleward Rossby wave breaking. Based on this relationship, we present a hypothesis on the role of the large-scale lower stratosphere during convective overshooting. In particular, the reduced lower stratosphere stability associated with double tropopause environments may facilitate deeper levels of overshooting and convective injection.